Science of Synthesis Knowledge Updates 2012 Vol. 3 E-Book

• Herausgeber: Thieme
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 1125

Veröffentlichungsjahr: 2014

Beschreibung

Science of Synthesis is a reference work for preparative methods in synthetic chemistry. Its product-based classification system enables chemists to easily find solutions to their synthetic problems.

Key Features:

• Critical selection of reliable synthetic methods, saving the researcher the time required to find procedures in the primary literature.
• Expertise provided by leading chemists.
• Detailed experimental procedures.
• The information is highly organized in a logical format to allow easy access to the relevant information.

The Science of Synthesis Editorial Board, together with the volume editors and authors, is constantly reviewing the whole field of synthetic organic chemistry as presented in Science of Synthesis and evaluating significant developments in synthetic methodology. Four annual volumes updating content across all categories ensure that you always have access to state-of-the-art synthetic methodology.

Leseprobe

Science of Synthesis

Science of Synthesis is the authoritative and comprehensive reference work for the entire field of organic and organometallic synthesis.

Science of Synthesis presents the important synthetic methods for all classes of compounds and includes:

Methods critically evaluated by leading scientists

Background information and detailed experimental procedures

Schemes and tables which illustrate the reaction scope

Preface

As the pace and breadth of research intensifies, organic synthesis is playing an increasingly central role in the discovery process within all imaginable areas of science: from pharmaceuticals, agrochemicals, and materials science to areas of biology and physics, the most impactful investigations are becoming more and more molecular. As an enabling science, synthetic organic chemistry is uniquely poised to provide access to compounds with exciting and valuable new properties. Organic molecules of extreme complexity can, given expert knowledge, be prepared with exquisite efficiency and selectivity, allowing virtually any phenomenon to be probed at levels never before imagined. With ready access to materials of remarkable structural diversity, critical studies can be conducted that reveal the intimate workings of chemical, biological, or physical processes with stunning detail.

The sheer variety of chemical structural space required for these investigations and the design elements necessary to assemble molecular targets of increasing intricacy place extraordinary demands on the individual synthetic methods used. They must be robust and provide reliably high yields on both small and large scales, have broad applicability, and exhibit high selectivity. Increasingly, synthetic approaches to organic molecules must take into account environmental sustainability. Thus, atom economy and the overall environmental impact of the transformations are taking on increased importance.

The need to provide a dependable source of information on evaluated synthetic methods in organic chemistry embracing these characteristics was first acknowledged over 100 years ago, when the highly regarded reference source Houben–Weyl Methoden der Organischen Chemie was first introduced. Recognizing the necessity to provide a modernized, comprehensive, and critical assessment of synthetic organic chemistry, in 2000 Thieme launched Science of Synthesis, Houben–Weyl Methods of Molecular Transformations. This effort, assembled by almost 1000 leading experts from both industry and academia, provides a balanced and critical analysis of the entire literature from the early 1800s until the year of publication. The accompanying online version of Science of Synthesis provides text, structure, substructure, and reaction searching capabilities by a powerful, yet easy-to-use, intuitive interface.

From 2010 onward, Science of Synthesis is being updated quarterly with high-quality content via Science of Synthesis Knowledge Updates. The goal of the Science of Synthesis Knowledge Updates is to provide a continuous review of the field of synthetic organic chemistry, with an eye toward evaluating and analyzing significant new developments in synthetic methods. A list of stringent criteria for inclusion of each synthetic transformation ensures that only the best and most reliable synthetic methods are incorporated. These efforts guarantee that Science of Synthesis will continue to be the most up-to-date electronic database available for the documentation of validated synthetic methods.

Also from 2010, Science of Synthesis includes the Science of Synthesis Reference Library, comprising volumes covering special topics of organic chemistry in a modular fashion, with six main classifications: (1) Classical, (2) Advances, (3) Transformations, (4) Applications, (5) Structures, and (6) Techniques. Titles will include Stereoselective Synthesis, Water in Organic Synthesis, and Asymmetric Organocatalysis, among others. With expertevaluated content focusing on subjects of particular current interest, the Science of Synthesis Reference Library complements the Science of Synthesis Knowledge Updates, to make Science of Synthesis the complete information source for the modern synthetic chemist.

The overarching goal of the Science of Synthesis Editorial Board is to make the suite of Science of Synthesis resources the first and foremost focal point for critically evaluated information on chemical transformations for those individuals involved in the design and construction of organic molecules.

Throughout the years, the chemical community has benefited tremendously from the outstanding contribution of hundreds of highly dedicated expert authors who have devoted their energies and intellectual capital to these projects. We thank all of these individuals for the heroic efforts they have made throughout the entire publication process to make Science of Synthesis a reference work of the highest integrity and quality.

The Editorial Board

July 2010

E. M. Carreira (Zurich, Switzerland)

C. P. Decicco (Princeton, USA)

A. Fuerstner (Muelheim, Germany)

G. A. Molander (Philadelphia, USA)

P. J. Reider (Princeton, USA)

E. Schaumann (Clausthal-Zellerfeld, Germany)

M. Shibasaki (Tokyo, Japan)

E. J. Thomas (Manchester, UK)

B. M. Trost (Stanford, USA)

Abstracts

1.4.5 Organometallic Complexes of Cobalt

M. Amatore, C. Aubert, M. Malacria, and M. Petit

This chapter is an update of the first report on organometallic cobalt complexes in Science of Synthesis, Section 1.4.1.4.1.4.1.4. It summarizes the more recent and most relevant advances concerning the synthesis and use of various cobalt complexes. During the decade 2000– 2010, two major developments were made concerning cobalt complexes. The first involves the extensive use of cobalt–η5-dienyl complexes. The second major advance is the use of more-convenient and easy-to-handle complexes based on cobalt(II) or -(III) salts.

Keywords: cobalt complexes · cobalt catalysis · cocyclization · cyclic compounds · [m + n + 2] cycloadditions · [m + 2] cycloadditions · cross-coupling reactions · C—H bond activation · ring expansion · ring formation · ring opening

3.6.14 Organometallic Complexes of Gold (Update 1)

M. J. Campbell and F. D. Toste

This chapter is a comprehensive review of asymmetric transformations catalyzed by gold salts published between 2005 and 2011. It focuses primarily on gold(I)-catalyzed reactions using enantiomerically enriched chiral phosphines, phosphoramidites, phosphites, and N-heterocyclic carbene ligands.

Keywords: gold · catalysis · asymmetric · cycloisomerization · cyclopropanation · aldol · hydroalkoxylation · hydroamination · hydrogenation · cycloaddition · alkyne · allene · phosphine · phosphoramidite · N-heterocyclic carbene

3.6.15 Organometallic Complexes of Gold (Update 2)

T. de Haro, D. Garayalde, and C. Nevado

The strong relativistic effects governing the coordination chemistry of gold have triggered the development of a large number of transformation that take advantage of the interaction of gold(I) and gold(III) complexes with alkenes. In this account, we have aimed to summarize the most relevant reactivity modes stemming from these interactions in homogeneous catalysis.

Keywords: alkene · gold · activation · addition

6.1.3.8 Diborane(4) Compounds

G. E. Ferris, S. N. Mlynarski, and J. P. Morken

This chapter is an update to the earlier Science of Synthesis contribution describing reactions involving bis(pinacolato)diboron. It focuses primarily on enantioselective catalytic transformations covered in the literature over the period 2005-2011.

Keywords: alkenes · alkynes · allylic compounds · boron compounds · borylation · conjugate addition · cyclization · dienes · dihydroxylation · enones · hydroboration · ring opening · stereoselective synthesis · transition metals

6.1.35.20 Allylboranes Yu. N. Bubnov and G. D. Kolomnikova

This chapter is an update to the earlier Science of Synthesis contribution describing methods for the synthesis of allylboranes and their application in organic synthesis. Libraries of chiral allylic boranes and boronates have been obtained and numerous natural substances and their analogues have been prepared with the use of compounds of this type.

Keywords: allylboranes · allylboronates · allylboration · hydroboration · diboration · silaboration · homologation · metathesis · cross coupling · asymmetric synthesis

16.15.5 Quinoxalines

D. O. Tymoshenko

This chapter is an update to the earlier Science of Synthesis contribution describing methods for the synthesis of quinoxalines and related compounds such as quinoxaline N-oxides and quinoxaline 1,4-dioxides. Classical routes to 2,3-substituted quinoxalines involve the intermolecular cyclization of benzene-1,2-diamines with keto aldehydes or 1,2-diketones. More recent developments with different approaches, including C—C bondformation methods, are also surveyed.

Keywords: quinoxalines · quinoxalin-2-ones · quinoxaline-2,3-diones · 2-chloroquinoxalines · benzene-1,2-diamine cyclization · annulation · amination · Suzuki coupling

21.16 Synthesis of Scalemic Amides by Kinetic Resolution

D. Seidel

This chapter provides an overview of non-enzymatic methods for the kinetic resolution of racemic amines. Covered are approaches based on chiral small-molecule reagents and catalysts. The scope is limited to kinetic resolutions of amines and desymmetrizations of diamines that proceed via amine acylation.

Keywords: kinetic resolution · desymmetrization · amines · diamines · acylation · asymmetric catalysis

27.16.3 Azines

A. Nodzewska and R. Łaźny

This update covers the literature published from the year 2001 up to 2011; the preparation and application of 1,4-disubstituted, trisubstituted, and tetrasubstituted azines is described.

Keywords: allenic compounds · azines · carbonyl compounds · diazo compounds · hydrazines · hydrazones · intramolecular reactions · nitrogen heterocycles · semicarbazones · Ugi reaction

27.17.5 Hydrazones

R. Łaźny and A. Nodzewska

This chapter is an update to the earlier Science of Synthesis contribution describing methods for the synthesis of N-unsubstituted, N-monosubstituted, N,N-disubstituted, and Nsulfonylated hydrazones and their applications in organic synthesis. It focuses on the literature published in the period 2000–2011.

Keywords: alkenes · alkylation · allenes · arylation · cycloaddition · diazo compounds · hydrazines · hydrazones · nitrogen heterocycles · organometallic reagents · polymers · radical reaction

27.18.3 Hydrazonium Compounds

A. Nodzewska and R. Łaźny

This update covers the literature on hydrazonium compounds published from the year 2000 up to 2011, during which time only the preparation and application of 1,1,1-trialkyl-2-alkylidenehydrazinium compounds has been described.

Keywords: azirines · hydrazones · hydrazonium compounds · hydrazinium salts · hydrolysis · 1H-pyrroles

Science of Synthesis Knowledge Updates 2012/3

Preface

Abstracts

Table of Contents

1.4.5 Organometallic Complexes of Cobalt (Update 2012)

M. Amatore, C. Aubert, M. Malacria, and M. Petit

3.6.14 Organometallic Complexes of Gold (Update 1, 2012)

M. J. Campbell and F. D. Toste

3.6.15 Organometallic Complexes of Gold (Update 2, 2012)

T. de Haro, D. Garayalde, and C. Nevado

6.1.3.8 Diborane(4) Compounds (Update 2012)

G. E. Ferris, S. N. Mlynarski, and J. P. Morken

6.1.35.20 Allylboranes (Update 2012)

Yu. N. Bubnov and G. D. Kolomnikova

16.15.5 Quinoxalines (Update 2012)

D. O. Tymoshenko

21.16 Synthesis of Scalemic Amides by Kinetic Resolution

D. Seidel

27.16.3 Azines (Update 2012)

A. Nodzewska and R. Łaźny

27.17.5 Hydrazones (Update 2012)

R. Łaźny and A. Nodzewska

27.18.3 Hydrazonium Compounds (Update 2012)

A. Nodzewska and R. Łaźny

Author Index

Abbreviations

Table of Contents

Volume 1: Compounds with Transition Metal—Carbon π-Bonds and Compounds of Groups 10–8 (Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, Os)

1.4 Product Class 4: Organometallic Complexes of Cobalt

1.4.5 Organometallic Complexes of Cobalt

M. Amatore, C. Aubert, M. Malacria, and M. Petit

1.4.5 Organometallic Complexes of Cobalt

1.4.5.1 Cobalt–η5-Dienyl Complexes

1.4.5.1.1 Synthesis of Cobalt–η5-Dienyl Complexes

1.4.5.1.1.1 Method 1: Synthesis of Chiral Dicarbonyl(η5-cyclopentadienyl)cobalt(I) and (η5-Cyclopentadienyl)(η4-diene)cobalt(I) Complexes

1.4.5.1.1.1.1 Variation 1: Synthesis of Chiral Dicarbonyl(η5-cyclopentadienyl)cobalt(I) Complexes by Oxidative Addition

1.4.5.1.1.1.2 Variation 2: Synthesis of Chiral (η5-Cyclopentadienyl)(η4-diene)cobalt(I) Complexes by Substitution of Ligands

1.4.5.1.1.2 Method 2: Synthesis of (Alkene)carbonyl(η5-cyclopentadienyl)cobalt(I) Complexes via Displacement of One Carbonyl Moiety

1.4.5.1.1.3 Method 3: Synthesis of (η5-Cyclopentadienyl)(η4-diene)cobalt(I) Complexes via Substitution of Ligands

1.4.5.1.1.4 Method 4: Synthesis of (η5-Cyclopentadienyl)cobalt–N-Heterocyclic Carbene Complexes by Exchange of Ligands

1.4.5.1.1.4.1 Variation 1: Synthesis of Carbonyl(η5-cyclopentadienyl)cobalt–N-Hetero-cyclic Carbene Complexes

1.4.5.1.1.4.2 Variation 2: Synthesis of (η5-Cyclopentadienyl)(ethene)cobalt–N-Hetero-cyclic Carbene Complexes

1.4.5.1.1.4.3 Variation 3: Synthesis of (η5-Cyclopentadienyl)(triphenylphosphine)cobalt–N-Heterocyclic Carbene Complexes

1.4.5.1.1.5 Method 5: Synthesis of (η5-Cyclopentadienyl)(phosphine)cobalt(I)–Ligand Complexes

1.4.5.1.1.5.1 Variation 1: Synthesis of Carbonyl(η5-cyclopentadienyl)(triphenylphosphine)cobalt(I)

1.4.5.1.1.5.2 Variation 2: Synthesis of (η5-Cyclopentadienyl)(triphenylphosphine)cobalt(I)–Alkene Complexes

1.4.5.1.1.5.3 Variation 3: Synthesis of {[2-(Di-tert-butylphosphino)ethyl]cyclopentadienyl}(ethene)cobalt(I)

1.4.5.1.1.6 Method 6: Synthesis of (η5-Cyclopentadienyl)cobalt–Dinitrosoalkane Complexes

1.4.5.1.1.7 Method 7: Synthesis of (η5-Pentamethylcyclopentadienyl)cobalt–η3-Allyl Complexes by Exchange of Ligands

1.4.5.1.1.8 Method 8: Synthesis of (η5-Cyclopentadienyl)cobalt–η5-Pentadienyl Complexes by Exchange of Ligands

1.4.5.1.1.9 Method 9: Synthesis of (η5-Cyclopentadienyl)cobalt–Alkyne Complexes

1.4.5.1.1.10 Method 10: Synthesis of (η5-Cyclopentadienyl)cobaltacycles

1.4.5.1.1.10.1 Variation 1: Synthesis of (η5-Cyclopentadienyl)cobaltacyclobutenes

1.4.5.1.1.10.2 Variation 2: Synthesis of (η5-Cyclopentadienyl)cobaltasilacyclopentenes

1.4.5.1.2 Applications of Cobalt–η5-Dienyl Complexes in Organic Synthesis

1.4.5.1.2.1 Method 1: Inter- and Intramolecular [2 +2+2] Cyclizations

1.4.5.1.2.1.1 Variation 1: Inter- and Intramolecular [2 +2+2] Cyclizations of Triynes in Aromatic and Aqueous Solvents

1.4.5.1.2.1.2 Variation 2: Intermolecular [2 +2+2] Cyclizations of Diynes and Nitriles: Preparation of Pyridines

1.4.5.1.2.1.3 Variation 3: Intermolecular [2 +2+2] Cyclizations of Enediynes and Allenediynes

1.4.5.1.2.1.4 Variation 4: Inter- and Intramolecular [2 +2+2] Cyclizations of Diynes with Heteroatom-Substituted Multiple Bonds

1.4.5.1.2.2 Method 2: Other Cyclizations

1.4.5.1.2.2.1 Variation 1: [2 + 2] Cycloaddition

1.4.5.1.2.2.2 Variation 2: [3 + 2] Annulation

1.4.5.1.2.2.3 Variation 3: [3 +2+2] Cycloaddition

1.4.5.1.2.2.4 Variation 4: [5 + 2] Cycloaddition

1.4.5.1.2.3 Method 3: Miscellaneous Reactions

1.4.5.1.2.3.1 Variation 1: Cobalt-Mediated Ring Expansion

1.4.5.1.2.3.2 Variation 2: Linear Co-oligomerization of Alkynes with Alkenes

1.4.5.1.2.3.3 Variation 3: Hydroamination of Alkynes

1.4.5.1.2.3.4 Variation 4: Activation of sp3 C—H Bonds

1.4.5.1.2.3.5 Variation 5: Vinylic C—H Functionalization Reactions

1.4.5.2 Miscellaneous Cobalt Complexes

1.4.5.2.1 Synthesis of Miscellaneous Cobalt Complexes

1.4.5.2.1.1 Method 1: Synthesis of Methyltetrakis(trimethylphosphine)cobalt(I)

1.4.5.2.1.2 Method 2: Synthesis of Chlorotris(trimethylphosphine)cobalt(I)

1.4.5.2.1.3 Method 3: Synthesis of Dihalobis(phosphine)cobalt(II) Complexes

1.4.5.2.1.4 Method 4: Cobalt(II) or -(III) Salts as Precatalysts

1.4.5.2.1.5 Method 5: Preformed Cobalt(II) and Cobalt(III) Complexes

1.4.5.2.2 Applications of Miscellaneous Cobalt Complexes in Organic Synthesis

1.4.5.2.2.1 Method 1: Cobalt-Catalyzed Homocoupling Reactions

1.4.5.2.2.2 Method 2: C(sp2)—C(sp2) Cross-Coupling Reactions

1.4.5.2.2.2.1 Variation 1: Alkenylation

1.4.5.2.2.2.2 Variation 2: Biaryl Formation

1.4.5.2.2.3 Method 3: C(sp2)—C(sp3) Cross-Coupling Reactions

1.4.5.2.2.3.1 Variation 1: Alkylation of Alkenyl Halides

1.4.5.2.2.3.2 Variation 2: Alkenylation of Alkyl Halides

1.4.5.2.2.3.3 Variation 3: Alkylation of Aromatic Halides

1.4.5.2.2.3.4 Variation 4: Arylation of Alkyl Halides

1.4.5.2.2.3.5 Variation 5: Pseudodirect and Direct Arylation of Alkyl Halides

1.4.5.2.2.3.6 Variation 6: Allylation

1.4.5.2.2.4 Method 4: C(sp3)—C(sp3) Cross-Coupling Reactions

1.4.5.2.2.4.1 Variation 1: Allylation

1.4.5.2.2.4.2 Variation 2: Benzylation

1.4.5.2.2.4.3 Variation 3: Alkylation

1.4.5.2.2.5 Method 5: Alkynylation

1.4.5.2.2.5.1 Variation 1: Benzylation of Alkynes

1.4.5.2.2.5.2 Variation 2: Alkylation of Alkynes

1.4.5.2.2.5.3 Variation 3: Alkenylation of Alkynes

1.4.5.2.2.6 Method 6: Acylation

1.4.5.2.2.7 Method 7: Radical Reactions

1.4.5.2.2.8 Method 8: Cross Coupling of Unsaturated Compounds

1.4.5.2.2.8.1 Variation 1: Alkyne Functionalization

1.4.5.2.2.8.2 Variation 2: Cross Coupling of Alkynes with Enones

1.4.5.2.2.8.3 Variation 3: Cross-Coupling Reactions Involving Alkenes and Alkynes

1.4.5.2.2.9 Method 9: Michael-Type Conjugate Additions

1.4.5.2.2.10 Method 10: Formation of Carbon—Heteroatom Bonds

1.4.5.2.2.11 Method 11: Cross-Coupling Reactions with Carbonyl Compounds

1.4.5.2.2.11.1 Variation 1: Allylation

1.4.5.2.2.11.2 Variation 2: Formation of Hydroxy Amides and Esters

1.4.5.2.2.11.3 Variation 3: Arylation

1.4.5.2.2.12 Method 12: Multicomponent Reactions

1.4.5.2.2.13 Method 13: Preparation of Organometallic Derivatives

1.4.5.2.2.14 Method 14: Cyclization Reactions

1.4.5.2.2.15 Method 15: Cobalt-Catalyzed Cycloadditions

1.4.5.2.2.15.1 Variation 1: [2 + 2] Cycloadditions

1.4.5.2.2.15.2 Variation 2: [3 + 2] Cycloadditions

1.4.5.2.2.15.3 Variation 3: [4 + 2] Cycloadditions

1.4.5.2.2.15.4 Variation 4: Homo-Diels–Alder Reactions

1.4.5.2.2.15.5 Variation 5: [6 + 2] Cycloadditions

1.4.5.2.2.15.6 Variation 6: [2 +2+2] Cycloadditions

1.4.5.2.2.15.7 Variation 7: [4 +2+2] Cycloadditions

1.4.5.2.2.15.8 Variation 8: [6 + 4] Cycloadditions

1.4.5.2.2.15.9 Variation 9: Dipolar Cycloadditions with Nitrones

1.4.5.2.2.16 Method 16: Alkene Functionalizations

1.4.5.2.2.16.1 Variation 1: Cyclopropanation

1.4.5.2.2.16.2 Variation 2: Aziridination

1.4.5.2.2.16.3 Variation 3: Hydrovinylation of Alkenes

1.4.5.2.2.16.4 Variation 4: Miscellaneous Alkene Functionalizations

1.4.5.2.2.17 Method 17: C—H Activation

1.4.5.2.2.17.1 Variation 1: Cobalt-Catalyzed Assisted ortho-Functionalization

1.4.5.2.2.17.2 Variation 2: Cobalt-Catalyzed Direct Arylation

1.4.5.2.2.17.3 Variation 3: Cobalt-Catalyzed Transformation of Alkynyl C—H Bonds

1.4.5.2.2.17.4 Variation 4: Cobalt-Catalyzed C—H Amination

1.4.5.2.2.17.5 Variation 5: Formation of Organocobalt Complexes

1.4.5.2.2.18 Method 18: Cobalt-Catalyzed Ring-Expansion and Ring-Opening Reactions

1.4.5.2.2.18.1 Variation 1: Cobalt-Catalyzed Carboxylative and Carbonylative Ring Expansion/Opening

1.4.5.2.2.18.2 Variation 2: Cobalt-Catalyzed Ring-Opening Reactions

Volume 3: Compounds of Groups 12 and 11 (Zn, Cd, Hg, Cu, Ag, Au)

3.6 Product Class 6: Organometallic Complexes of Gold

3.6.14 Organometallic Complexes of Gold (Update 1)

M. J. Campbell and F. D. Toste

3.6.14 Organometallic Complexes of Gold (Update 1)

3.6.14.1 Asymmetric Gold-Catalyzed Transformations

3.6.14.1.1 Asymmetric Gold(I)-Catalyzed Transformations Proceeding via Initial Alkyne π-Activation

3.6.14.1.1.1 Cycloisomerization Reactions

3.6.14.1.1.1.1 Method 1: Cycloisomerizations of 1,6-Enynes

3.6.14.1.1.1.1.1 Variation 1: 5-exo-dig Cyclization

3.6.14.1.1.1.1.2 Variation 2: 6-endo-dig Cyclization

3.6.14.1.1.1.2 Method 2: Cycloisomerizations of 1,5-Enynes

3.6.14.1.1.1.3 Method 3: Cyclizations of 1,3-Enynes

3.6.14.1.1.1.4 Method 4: Cyclopropanations

3.6.14.1.1.1.4.1 Variation 1: Intermolecular Cyclopropanation

3.6.14.1.1.1.4.2 Variation 2: Intramolecular Cyclopropanation

3.6.14.1.1.1.5 Method 5: Analogous Cycloisomerizations Proceeding through Gold(I) Carbenoids

3.6.14.1.1.1.6 Method 6: Other Cycloisomerization Reactions of Propargyl Carboxylates

3.6.14.1.1.2 Desymmetrization Reactions

3.6.14.1.1.2.1 Method 1: Desymmetrization of Diynes

3.6.14.1.1.2.2 Method 2: Desymmetrization of Diols

3.6.14.1.2 Asymmetric Gold(I)-Catalyzed Transformations Proceeding via Initial Allene π-Activation

3.6.14.1.2.1 Cycloisomerization Reactions

3.6.14.1.2.1.1 Method 1: Hydroindolization

3.6.14.1.2.1.2 Method 2: Cycloisomerization of 1,6-Allenenes

3.6.14.1.2.1.3 Method 3: Formal [2 + 2]-Cycloaddition Reactions

3.6.14.1.2.1.4 Method 4: Formal [4 + 2]-Cycloaddition Reactions

3.6.14.1.2.1.5 Method 5: Ring Expansion of Allenylcyclopropanols

3.6.14.1.2.2 Addition Reactions

3.6.14.1.2.2.1 Method 1: Intramolecular Hydroalkoxylation and Hydroamination

3.6.14.1.2.2.2 Method 2: Intramolecular Hydroindolization

3.6.14.1.2.2.3 Method 3: Intermolecular Hydroamination

3.6.14.1.3 Asymmetric Reactions of Alkenes

3.6.14.1.3.1 Method 1: Hydrogenation

3.6.14.1.4 Miscellaneous Reactions

3.6.14.1.4.1 Method 1: Enantioselective Reactions by Lewis Acidic Heteroatom Coordination

3.6.14.1.4.1.1 Variation 1: Aldol Reaction

3.6.14.1.4.1.2 Variation 2: Cycloaddition of Münchnones with Electron-Deficient Alkenes

3.6.14.1.4.2 Method 2: Enantioselective Reactions of Alkynyl–Gold(I) Species

3.6.14.1.4.3 Method 3: Enantioselective Protonation of Silyl Enol Ethers

3.6.15 Organometallic Complexes of Gold (Update 2)

T. de Haro, D. Garayalde, and C. Nevado

3.6.15 Organometallic Complexes of Gold (Update 2)

3.6.15.1 Gold-Catalyzed Reactions of Alkenes

3.6.15.1.1 Functionalization of Alkenes

3.6.15.1.1.1 Hydrofunctionalization of Unactivated Alkenes

3.6.15.1.1.1.1 Method 1: Inter- and Intramolecular Hydroalkylation of Alkenes

3.6.15.1.1.1.2 Method 2: Inter- and Intramolecular Hydroarylation of Alkenes

3.6.15.1.1.1.2.1 Variation 1: Formation of Hexahydrodibenzo[b,d]furans

3.6.15.1.1.1.3 Method 3: Hydroalkoxylation of Alkenes

3.6.15.1.1.1.3.1 Variation 1: Formation of Allylic Ethers

3.6.15.1.1.1.3.2 Variation 2: Formation of Dihydrobenzofurans from Allyl Aryl Ethers

3.6.15.1.1.1.4 Method 4: Inter- and Intramolecular Hydroamination of Alkenes

3.6.15.1.1.1.4.1 Variation 1: Formation of Pyrrolidines through Domino Ring Opening/Ring Closing of Methylenecyclopropanes with Sulfonamides

3.6.15.1.1.1.4.2 Variation 2: Inter- and Intramolecular Hydroamination of Dienes

3.6.15.1.1.1.5 Method 5: Hydrothiolation of Alkenes

3.6.15.1.1.2 Michael-Type Addition to α,β-Unsaturated Carbonyl Compounds

3.6.15.1.1.2.1 Method 1: Addition of Indoles and 7-Azaindoles to α,β-Unsaturated Ketones

3.6.15.1.1.2.1.1 Variation 1: Formation of Alkylated Indoles from 2-Alkynylanilines

3.6.15.1.1.2.2 Method 2: Addition of Furans and Pyrroles to α,β-Unsaturated Ketones

3.6.15.1.1.2.2.1 Variation 1: Formation of Phenols from Furans and α,β-Unsaturated Alkynyl Ketones

3.6.15.1.1.2.3 Method 3: Addition of Electron-Rich Arenes to α,β-Unsaturated Carbonyl Compounds and Nitriles

3.6.15.1.1.2.4 Method 4: Addition of Carbamates and 4-Toluenesulfonamides to α,β-Unsaturated Ketones

3.6.15.1.1.3 Reactions of Allylic Acetates

3.6.15.1.1.3.1 Method 1: Rearrangement of Allylic Acetates

3.6.15.1.1.3.2 Method 2: Allyl–Allyl Coupling

3.6.15.1.1.3.3 Method 3: Cascade Intermolecular Allylic Substitution/Enyne Cycloisomerization

3.6.15.1.1.4 Intermolecular Cyclopropanation of Alkenes

3.6.15.1.1.4.1 Method 1: Cyclopropanation via Transfer Reaction from Diazo Compounds

3.6.15.1.1.4.2 Method 2: Cyclopropanation via In Situ Generated Gold Carbenes from Propargylic Acetates

3.6.15.1.1.4.2.1 Variation 1: Cyclopropanation via Retro-Buchner Reaction

3.6.15.1.1.5 Cycloaddition Reactions

3.6.15.1.1.5.1 Method 1: Intermolecular [3 + 2] Cycloaddition of Alkynyl Epoxides with Alkenes

3.6.15.1.1.5.1.1 Variation 1: Formation of Tricyclic Indoles from Azomethine Ylides

3.6.15.1.1.5.2 Method 2: Intermolecular [4 + 2] Cycloaddition of Enynes and Alkynes

3.6.15.1.1.5.2.1 Variation 1: Formation of Benzonorcaradienes by Intermolecular [4 + 3] Cycloaddition of Diynes and Alkenes

3.6.15.1.1.5.3 Method 3: Intermolecular [3 + 2] and [4 + 3] Cycloadditions of Propargyl Carboxylates and Alkenes or Dienes

3.6.15.1.1.5.4 Method 4: 1,3-Dipolar Cycloadditions

3.6.15.1.1.5.4.1 Variation 1: Enantioselective 1,3-Dipolar Cycloadditions of Münchnones

3.6.15.1.1.6 Oxidation of Alkenes

3.6.15.1.1.6.1 Method 1: Formation of Carbonyl Compounds

Volume 6: Boron Compounds

6.1 Product Class 1: Boron Compounds

6.1.3.8 Diborane(4) Compounds

G. E. Ferris, S. N. Mlynarski, and J. P. Morken

6.1.3.8 Diborane(4) Compounds

6.1.3.8.1 Applications of Diborane(4) Compounds in Organic Synthesis

6.1.3.8.1.1 Method 1: Diboration of Alkenes

6.1.3.8.1.1.1 Variation 1: Enantioselective Diboration of Terminal Alkenes

6.1.3.8.1.1.2 Variation 2: Metal-Free Diboration

6.1.3.8.1.2 Method 2: Enantioselective Diboration of Allenes

6.1.3.8.1.3 Method 3: Enantioselective Diboration of (E)-1,3-Dienes

6.1.3.8.1.4 Method 4: Advances in Alkyne Hydroboration and Diboration

6.1.3.8.1.4.1 Variation 1: N-Heterocyclic Carbene–Copper Catalyzed Dihydroboration of Terminal Alkynes

6.1.3.8.1.4.2 Variation 2: Borylative Cyclization of Enynes

6.1.3.8.1.4.3 Variation 3: Platinum-Catalyzed Diborylation of Arynes

6.1.3.8.1.4.4 Variation 4: Differentially Protected Diboron Reagents

6.1.3.8.1.5 Method 5: Allylic Substitution

6.1.3.8.1.5.1 Variation 1: Nickel-Catalyzed Borylative Ring Opening of Vinyl Epoxides and Aziridines

6.1.3.8.1.5.2 Variation 2: Reaction Using a Copper(I)–Bidentate Phosphine Complex

6.1.3.8.1.5.3 Variation 3: Reaction Using a Copper(II)–N-Heterocyclic Carbene Complex

6.1.3.8.1.5.4 Variation 4: Desymmetrization of meso-Diols

6.1.3.8.1.6 Method 6: Copper-Catalyzed Synthesis of Multisubstituted Allenylboronates

6.1.3.8.1.7 Method 7: Nickel-Catalyzed Borylative Ring Opening

6.1.3.8.1.7.1 Variation 1: Reaction of Vinylcyclopropanes

6.1.3.8.1.7.2 Variation 2: Reaction of Aryl Cyclopropyl Ketones

6.1.3.8.1.8 Method 8: Copper-Catalyzed Conjugate Addition of 2,2′-Bi-1,3,2-dioxaborolane to α,β-Unsaturated Carbonyl Compounds

6.1.3.8.1.8.1 Variation 1: Racemic Addition to Carbonyl Compounds

6.1.3.8.1.8.2 Variation 2: Enantioselective Addition to Carbonyl Compounds

6.1.3.8.1.8.3 Variation 3: Addition to Aldehydes and Imines

6.1.3.8.1.8.4 Variation 4: Metal-Free Addition to Carbonyl Compounds

6.1.3.8.1.8.5 Variation 5: Tertiary Boronic Esters by Addition to 3,3-Disubstituted Enones

6.1.3.8.1.8.6 Variation 6: Enantioselective Addition to 3-Boryl Enoates

6.1.3.8.1.9 Method 9: Synthesis of Cycloalkylboronates

6.1.3.8.1.9.1 Variation 1: Stereospecific Synthesis of Cyclobutylboronates

6.1.3.8.1.9.2 Variation 2: Enantioselective Synthesis of Cyclopropylboronates

6.1.35.20 Allylboranes Yu. N. Bubnov and G. D. Kolomnikova

6.1.35.20 Allylboranes

6.1.35.20.1 Synthesis of Allylboranes

6.1.35.20.1.1 Method 1: Synthesis by Transmetalation

6.1.35.20.1.2 Method 2: Synthesis by Hydroboration of 1,3-Dienes or Allenes

6.1.35.20.1.2.1 Variation 1: Catalyzed Hydroboration of 1,3-Dienes

6.1.35.20.1.2.2 Variation 2: Thermal Hydroboration

6.1.35.20.1.3 Method 3: Synthesis by Diboration or Silaboration of 1,3-Dienes, Allenes, or Vinylcyclopropanes

6.1.35.20.1.3.1 Variation 1: Diboration of 1,3-Dienes, Enones, or Allenes

6.1.35.20.1.3.2 Variation 2: Diboration of Vinylcyclopropanes, Vinyloxiranes, or Aziridines

6.1.35.20.1.3.3 Variation 3: Silaboration of 1,3-Dienes or Allenes

6.1.35.20.1.4 Method 4: Synthesis by [4 + 2] Cycloaddition

6.1.35.20.1.5 Method 5: Synthesis from Diborane(4) Derivatives and Allylic Alcohols, Acetates, or Carbonates

6.1.35.20.1.6 Method 6: Synthesis by 3,3-Sigmatropic Rearrangement

6.1.35.20.1.7 Method 7: Homologation of Alkenylboron Compounds

6.1.35.20.1.8 Method 8: Synthesis by Vinylation of (α-Haloalkyl)boron Derivatives

6.1.35.20.1.9 Method 9: Synthesis by Metathesis

6.1.35.20.1.10 Method 10: Synthesis by Miscellaneous Methods

6.1.35.20.2 Applications of Allylboranes in Organic Synthesis

6.1.35.20.2.1 Method 1: Synthesis of Homoallylic Alcohols, Amines, and Hydrazines via Allylboration of C=O and C=N Bonds

6.1.35.20.2.1.1 Variation 1: Allylboration of Aldehydes and Ketones

6.1.35.20.2.1.2 Variation 2: Allylboration of C=N Bonds

6.1.35.20.2.2 Method 2: Allylboration of N=N and CɛN Bonds

6.1.35.20.2.3 Method 3: Allylation by Cross-Coupling Reactions

6.1.35.20.2.4 Method 4: Allylboron–Acetylene Condensation

6.1.35.20.2.5 Method 5: Reductive trans-Diallylation of Aromatic N-Heterocycles

6.1.35.20.2.6 Method 6: Miscellaneous Methods

Volume 16: Six-Membered Hetarenes with Two Identical Heteroatoms

16.15 Product Class 15: Quinoxalines

16.15.5 Quinoxalines

D. O. Tymoshenko

16.15.5 Quinoxalines

16.15.5.1 Synthesis by Ring-Closure Reactions

16.15.5.1.1 By Annulation to an Arene

16.15.5.1.1.1 By Formation of Two N—C Bonds and One C—C Bond

16.15.5.1.1.1.1 Fragments N—Arene—N, C, and C

16.15.5.1.1.1.1.1 Method 1: From Benzene-1,2-diamine, Aldehydes, and Isocyanides

16.15.5.1.1.1.1.2 Method 2: From Benzene-1,2-diamine, Aldehydes, and Tosylmethyl Isocyanide

16.15.5.1.1.2 By Formation of Two N—C Bonds

16.15.5.1.1.2.1 Fragments N—Arene—N and C—C

16.15.5.1.1.2.1.1 Method 1: From Benzene-1,2-diamines and Glyoxal or Its Synthetic Equivalents

16.15.5.1.1.2.1.1.1 Variation 1: From Substituted Benzene-1,2-diamines and 1,4-Dioxane-2,3-diol

16.15.5.1.1.2.1.1.2 Variation 2: From Benzene-1,2-diamine and Hexahydro-[1,4]dioxino[2,3-b]-1,4-dioxin-2,3,6,7-tetraol

16.15.5.1.1.2.1.1.3 Variation 3: From Benzene-1,2-diamine and Disodium 1,2-Dihydroxyethane-1,2-disulfonate

16.15.5.1.1.2.1.1.4 Variation 4: From Benzene-1,2-diamine and N,N′-Dicyclohexylethane-1,2-diimine

16.15.5.1.1.2.1.2 Method 2: From Benzene-1,2-diamines and α-Oxoaldehydes or Their Synthetic Equivalents

16.15.5.1.1.2.1.2.1 Variation 1: From Benzene-1,2-diamine and α,α-Dihydroxy Ketones

16.15.5.1.1.2.1.2.2 Variation 2: From Benzene-1,2-diamine and α-Ketoaldehyde Oximes or Hydrazones

16.15.5.1.1.2.1.3 Method 3: From Benzene-1,2-diamines and 1,2-Diketones or Their Synthetic Equivalents

16.15.5.1.1.2.1.3.1 Variation 1: Synthesis of Quinoxalinium Salts from N-Substituted Benzene-1,2-diamines and Butane-2,3-dione

16.15.5.1.1.2.1.3.2 Variation 2: From Benzene-1,2-diamines and Alkynes under Oxidative Conditions

16.15.5.1.1.2.1.3.3 Variation 3: From Benzene-1,2-diamines and Diiminosuccinonitrile

16.15.5.1.1.1.1.4 Method 4: From Benzene-1,2-diamines and α-Oxo Acids or Their Derivatives (The Hinsberg Reaction)

16.15.5.1.1.1.1.5 Method 5: From Benzene-1,2-diamines and Oxalic Acid Derivatives

16.15.5.1.1.1.1.5.1 Variation 1: From Benzene-1,2-diamines and Alkyl Alkoxy(imino)acetates

16.15.5.1.1.2.1.6 Method 6: From Benzene-1,2-diamines and Dialkyl Acetylenedicarboxylates

16.15.5.1.1.2.1.7 Method 7: From Benzene-1,2-diamine and Aryl Methyl Ketones and Their Derivatives

16.15.5.1.1.2.1.7.1 Variation 1: Oxidative Cyclization of Benzene-1,2-diamine and Acetylpyridines

16.15.5.1.1.2.1.7.2 Variation 2: From Benzene-1,2-diamines and Hydroxymethyl Ketones

16.15.5.1.1.2.1.7.3 Variation 3: From Benzene-1,2-diamines and Halomethyl Ketones

16.15.5.1.1.2.1.7.4 Variation 4: From Benzene-1,2-diamines and Aminomethyl Ketones

16.15.5.1.1.2.1.8 Method 8: From Benzene-1,2-diamines and α-Diazo Ketones

16.15.5.1.1.2.2 Fragments N—C—C—N and C—C (Arene)

16.15.5.1.1.2.2.1 Method 1: From 1,2-Diamines and Benzo-1,4-quinones and -1,2-quinones

16.15.5.1.1.2.3 Fragments N—Arene and N—C—C

16.15.5.1.1.2.3.1 Method 1: Synthesis of Quinoxalinone N-Oxides from Anilines and 1,1,2-Trichloro-2-nitroethene

16.15.5.1.1.3 By Formation of One N—C and One C—C Bond

16.15.5.1.1.4 By Formation of One N—C Bond

16.15.5.1.1.4.1 Fragment N—Arene—N—C—C

16.15.5.1.1.4.1.1 Method 1: Intramolecular Reactions of C-Electrophiles with a 2-Aminophenyl Group

16.15.5.1.1.4.1.1.1 Variation 1: Intramolecular Reductive Cyclization of N-(2-Nitrophenyl)-2-oxopropanamide

16.15.5.1.1.4.1.1.2 Variation 2: From N-(2-Nitrophenyl)glycines by a Reductive Cyclization/Oxidation Sequence

16.15.5.1.1.4.1.1.3 Variation 3: Intramolecular Reductive Cyclization of 2-(2-Nitrophenylamino)-2-oxoacetates

16.15.5.1.1.4.1.2 Method 2: Quinoxalinone N-Oxides by Intramolecular C-Nucleophilic Attack on a 2-Nitrophenyl Group

16.15.5.1.1.4.2 Fragment Arene—N—C—C—N

16.15.5.1.1.4.2.1 Method 1: Intramolecular Cyclization of (Phenylimino)acetaldehyde

16.15.5.1.1.4.2.2 Method 2: Unsymmetrical 2,3-Substituted Quinoxalines from N-Aryl Nitroketene N,S-Acetals and Phosphoryl Chloride

16.15.5.1.2 By Annulation to the Heterocyclic Ring

16.15.5.1.2.1 By Formation of Two C—C Bonds

16.15.5.1.2.1.1 Fragments C—Hetarene—C and C—C

16.15.5.1.2.1.1.1 Method 1: Cycloaddition of 2,3-Bis(dibromomethyl)pyrazine to Dienophiles

16.15.5.2 Synthesis by Ring Transformation

16.15.5.2.1 By Ring Enlargement

16.15.5.2.1.1 Method 1: From Benzimidazoles and 1,2-Diketones

16.15.5.2.1.2 Method 2: Quinoxalines from Benzofurazans and 2-Aminoethanol

16.15.5.2.1.3 Method 3: Quinoxaline 1,4-Dioxides from Benzofurazan 1-Oxides and Enolizable Carbonyl Compounds

16.15.5.2.1.4 Method 4: From Benzene-1,2-diamines and 1H-Indole-2,3-diones (Isatins)

16.15.5.3 Synthesis by Ring Modification

16.15.5.3.1 Oxidative Ring Modifications

16.15.5.3.1.1 Method 1: Aromatization by Oxidation of 1,2,3,4-Tetrahydroquinoxalines

16.15.5.3.1.2 Method 2: Aromatization by Oxidation of 1,2-Dihydroquinoxaline Derivatives

16.15.5.3.1.3 Method 3: Quinoxaline N-Oxides by N-Oxidation of Quinoxalines

16.15.5.3.1.4 Method 4: Quinoxaline 1,4-Dioxides by N-Oxidation of Quinoxalines

16.15.5.3.1.4.1 Variation 1: Quinoxaline 1,4-Dioxides by N-Oxidation of Quinoxaline N-Oxides

16.15.5.3.1.5 Method 5: Quinoxaline-2,3-diones from Quinoxalin-2-ones by Oxidation

16.15.5.3.2 Reductive Ring Modifications

16.15.5.3.2.1 Method 1: Reduction of Quinoxalines to 1,2,3,4-Tetrahydroquinoxalines

16.15.5.3.2.2 Method 2: Reduction of Quinoxalin-2-ones to 3,4-Dihydroquinoxalin-2(1H)-ones

16.15.5.3.2.3 Method 3: Reduction of Quinoxaline N-Oxides to Quinoxalines

16.15.5.3.2.4 Method 4: Reduction of Quinoxaline 1,4-Dioxides to Quinoxalines

16.15.5.3.3 Addition of C-Nucleophiles

16.15.5.3.3.1 Method 1: Addition of Ketone Enols to Quinoxalin-2-ones

16.15.5.3.3.2 Method 2: Addition of Anions Derived from 1-Haloalkyl Sulfones

16.15.5.3.3.3 Method 3: Addition of Organometallics

16.15.5.3.3.4 Method 4: Addition of Potassium Phenylacetylide to Quinoxaline 1-Oxides

16.15.5.3.3.5 Method 5: Cycloaddition Reactions

16.15.5.3.4 Elimination Reactions

16.15.5.3.4.1 Method 1: Aromatization by Elimination from 1-Acyl-1,2-dihydroquinoxalines

16.15.5.4 Ring Functionalization by Substitution of Ring Hydrogens or N-Alkylation

16.15.5.4.1 Method 1: Hydrogen–Deuterium Exchange

16.15.5.4.2 Method 2: Alkylation

16.15.5.4.2.1 Variation 1: Radical C-Alkylation

16.15.5.4.2.2 Variation 2: C-Alkylation of Quinoxaline Anions

16.15.5.4.2.3 Variation 3: N-Alkylation of Quinoxalin-2-ones

16.15.5.4.2.4 Variation 4: Synthesis of Onium Salts

16.15.5.4.3 Method 3: Acylation

16.15.5.4.3.1 Variation 1: Free-Radical Acylation of Quinoxaline

16.15.5.4.3.2 Variation 2: Electrophilic Acylation of Quinoxaline Anions

16.15.5.4.4 Method 4: Cyanation

16.15.5.4.5 Method 5: Halogenation

16.15.5.4.6 Method 6: Chlorosulfonylation

16.15.5.4.7 Method 7: Nitration

16.15.5.4.8 Method 8: Amination

16.15.5.5 Synthesis by Substituent Transformation

16.15.5.5.1 Transformation of Carbon Functionalities

16.15.5.5.1.1 Method 1: Substitution with Hydrogen

16.15.5.5.1.2 Method 2: Rearrangements of Carbon Functionalities

16.15.5.5.1.2.1 Variation 1: Curtius Rearrangement

16.15.5.5.1.2.2 Variation 2: Hofmann Rearrangement

16.15.5.5.1.3 Method 3: Oxidation

16.15.5.5.1.4 Method 4: Halogenation

16.15.5.5.1.5 Method 5: Reductive Amination of Quinoxaline-2-carbaldehyde

16.15.5.5.1.6 Method 6: Amidation of Quinoxaline Carboxylic Acids and Their Derivatives

16.15.5.5.1.7 Method 7: Reactions with Electrophiles

16.15.5.5.1.7.1 Variation 1: 3-Substitution of 3-Methylquinoxalin-2(1H)-one

16.15.5.5.1.7.2 Variation 2: Knoevenagel Reaction

16.15.5.5.2 Transformation of Halogen Functionalities

16.15.5.5.2.1 Method 1: Dehalogenation

16.15.5.5.2.2 Method 2: Halogen Exchange

16.15.5.5.2.3 Method 3: Halogen–Metal Exchange

16.15.5.5.2.4 Method 4: Reaction with C-Nucleophiles

16.15.5.5.2.4.1 Variation 1: Cyanation

16.15.5.5.2.4.2 Variation 2: α-Hetarylation of Esters, Lactones, Amides, and Nitriles with 2-Chloroquinoxaline

16.15.5.5.2.4.3 Variation 3: Cross Coupling with Organolithiums

16.15.5.5.2.4.4 Variation 4: Cross Coupling with Grignard Reagents

16.15.5.5.2.4.5 Variation 5: Cross Coupling with Organozinc Compounds

16.15.5.5.2.4.6 Variation 6: Stille Cross Coupling

16.15.5.5.2.4.7 Variation 7: Cross Coupling with Organoboron Compounds

16.15.5.5.2.4.8 Variation 8: Heck Cross Coupling

16.15.5.5.2.4.9 Variation 9: Sonogashira Cross Coupling

16.15.5.5.2.5 Method 5: Reaction with N-Nucleophiles

16.15.5.5.2.6 Method 6: Reaction with O-Nucleophiles

16.15.5.5.2.7 Method 7: Reaction with S-Nucleophiles

16.15.5.5.3 Transformation of Nitrogen Functionalities

16.15.5.5.3.1 Method 1: Reduction of Nitro Groups

16.15.5.5.3.2 Method 2: Substitution with a Halogen via Diazotization

16.15.5.5.3.3 Method 3: N-Alkylation

16.15.5.5.3.4 Method 4: N-Acylation

16.15.5.5.4 Transformation of Oxygen Functionalities

16.15.5.5.4.1 Method 1: Haloquinoxalines from the Corresponding Oxo Derivatives

16.15.5.5.4.2 Method 2: Reaction with C-Nucleophiles

16.15.5.5.4.3 Method 3: Reactions with N-Nucleophiles

16.15.5.5.4.4 Method 4: Reaction with S-Nucleophiles

16.15.5.5.4.5 Method 5: O-Alkylation

16.15.5.5.4.6 Method 6: O-Demethylation

16.15.5.5.5 Transformation of Sulfur Functionalities

16.15.5.5.5.1 Method 1: Oxidation

16.15.5.5.5.2 Method 2: Reaction with C-Nucleophiles

16.15.5.5.5.3 Method 3: Reaction with N-Nucleophiles

16.15.5.5.5.4 Method 4: S-Alkylation

16.15.5.5.5.5 Method 5: C—S Bond Cleavage

Volume 21: Three Carbon—Heteroatom Bonds: Amides and Derivatives; Peptides; Lactams

21.16 Synthesis of Scalemic Amides by Kinetic Resolution

D. Seidel

21.16 Synthesis of Scalemic Amides by Kinetic Resolution

21.16.1 Method 1: Kinetic Resolution by Acylation with Stoichiometric Amounts of Chiral Acylating Reagents

21.16.2 Method 2: Kinetic Resolution with Catalytic Amounts of a Chiral Promoter

21.16.2.1 Variation 1: Kinetic Resolution of Amines with Attenuated Reactivities

21.16.2.2 Variation 2: Kinetic Resolution with Azlactone-Derived Acylating Reagents

21.16.2.3 Variation 3: Kinetic Resolution with Carboxylic Acid Anhydrides as Acylating Reagents

21.16.2.4 Variation 4: Kinetic Resolution with α′-Hydroxyenones as Acylating Reagents

21.16.2.5 Variation 5: Kinetic Resolution with Carboxylic Acids as Acylating Reagents

Volume 27: Heteroatom Analogues of Aldehydes and Ketones

27.16 Product Class 16: Azines

27.16.3 Azines

A. Nodzewska and R. Łaźny

27.16.3 Azines

27.16.3.1 Synthesis of Azines

27.16.3.1.1 1,4-Disubstituted Azines

27.16.3.1.1.1 Method 1: Reaction of Aldehydes with Hydrazine

27.16.3.1.1.2 Method 2: Reaction of Aldehyde Hydrazones with Aldehydes

27.16.3.1.1.3 Method 3: Hydrazone Oxidation

27.16.3.1.1.4 Method 4: Reaction of Aldehyde Hydrazones with Disulfur Compounds

27.16.3.1.1.5 Method 5: Reaction of Semicarbazones with Aldehydes

27.16.3.1.2 Trisubstituted Azines

27.16.3.1.2.1 Method 1: Reaction of Aldehyde Hydrazones with Ketones

27.16.3.1.2.2 Method 2: Reaction of Ketone Hydrazones with Aldehydes

27.16.3.1.3 Tetrasubstituted Azines

27.16.3.1.3.1 Method 1: Ketone Dimerization with Hydrazine

27.16.3.1.3.2 Method 2: Reaction of Hydrazones with Ketones

27.16.3.1.3.3 Method 3: Diazoalkane Dimerization

27.16.3.1.3.4 Method 4: Imine Oxidation

27.16.3.2 Applications of Azines in Organic Synthesis

27.16.3.2.1 Method 1: Oxidation and Reduction

27.16.3.2.2 Method 2: Addition Reactions

27.16.3.2.3 Method 3: Formation of Organometallic Complexes

27.16.3.2.4 Method 4: Intramolecular Cyclization Reactions

27.16.3.2.5 Method 5: Cycloaddition Reactions

27.16.3.2.6 Method 6: Hydrolytic Cleavage

27.16.3.2.7 Method 7: Ugi Reaction

27.17 Product Class 17: Hydrazones

27.17.5 Hydrazones

R. Łaźny and A. Nodzewska

27.17.5 Hydrazones

27.17.5.1 N-Unsubstituted Hydrazones

27.17.5.1.1 Synthesis of N-Unsubstituted Hydrazones

27.17.5.1.1.1 Method 1: Synthesis from Aldehydes and Ketones

27.17.5.1.1.1.1 Variation 1: From Oximes

27.17.5.1.1.2 Method 2: Synthesis from Diazo Compounds

27.17.5.1.1.3 Method 3: Synthesis from Unsaturated Hydrocarbons

27.17.5.1.1.3.1 Variation 1: From Terminal Alkynes

27.17.5.1.1.3.2 Variation 2: From Allenes

27.17.5.1.1.3.3 Variation 3: From Fluoroalkenes

27.17.5.1.2 Applications of N-Unsubstituted Hydrazones in Organic Synthesis

27.17.5.1.2.1 Method 1: Reductive Elimination of the Hydrazono Group

27.17.5.1.2.2 Method 2: Synthesis of Nitrogen Heterocycles

27.17.5.1.2.3 Method 3: Synthesis of Diazo Compounds by Oxidation

27.17.5.1.2.4 Method 4: Synthesis of Halogenated Alkenes

27.17.5.2 N-Monosubstituted Hydrazones

27.17.5.2.1 Synthesis of N-Monosubstituted Hydrazones

27.17.5.2.1.1 Method 1: Synthesis from Aldehydes and Ketones

27.17.5.2.1.1.1 Variation 1: Hydroformylation–Hydrazone Formation from Alkenes

27.17.5.2.1.1.2 Variation 2: Synthesis from Masked Carbonyl Groups

27.17.5.2.1.2 Method 2: Synthesis by Arylation of Benzophenone Hydrazone

27.17.5.2.1.3 Method 3: Synthesis from Activated Methylene Compounds

27.17.5.2.1.3.1 Variation 1: Reaction with Benzotriazoles

27.17.5.2.1.3.2 Variation 2: Reaction with Diazonium Salts

27.17.5.2.1.4 Method 4: Synthesis from Terminal Alkynes

27.17.5.2.1.5 Method 5: Synthesis from Diazo Esters

27.17.5.2.2 Applications of N-Monosubstituted Hydrazones in Organic Synthesis

27.17.5.2.2.1 Method 1: Synthesis of Nitrogen Heterocycles

27.17.5.2.2.1.1 Variation 1: Fischer Indole Synthesis from N-Arylhydrazones

27.17.5.2.2.2 Method 2: N-tert-Butylhydrazones as Acyl Anion Equivalents

27.17.5.2.2.3 Method 3: Synthesis of N,N-Disubstituted Hydrazones by Acylation

27.17.5.2.2.4 Method 4: Synthesis of Bicyclic Diazenium Salts

27.17.5.3 N,N-Disubstituted Hydrazones

27.17.5.3.1 Synthesis of N,N-Disubstituted Hydrazones

27.17.5.3.1.1 Method 1: Synthesis from Aldehydes and Ketones

27.17.5.3.1.1.1 Variation 1: Synthesis from Masked Aldehydes and Ketones

27.17.5.3.1.1.2 Variation 2: Solid-Supported Synthesis

27.17.5.3.1.2 Method 2: Synthesis from Unsaturated Hydrocarbons

27.17.5.3.1.3 Method 3: Synthesis from N-Monosubstituted Hydrazones

27.17.5.3.2 Applications of N,N-Disubstituted Hydrazones in Organic Synthesis

27.17.5.3.2.1 Method 1: Alkylation of Hydrazone Anions

27.17.5.3.2.1.1 Variation 1: Solid-Supported Synthesis

27.17.5.3.2.1.2 Variation 2: Alkylation of Cyclic Carbamates Derived from N-Acyl-N-alkylhydrazones

27.17.5.3.2.2 Method 2: Primary Amine Synthesis

27.17.5.3.2.2.1 Variation 1: Solid-Supported Synthesis

27.17.5.3.2.3 Method 3: Radical Reactions

27.17.5.3.2.3.1 Variation 1: Radical Cyclization

27.17.5.3.2.3.2 Variation 2: Radical Addition

27.17.5.3.2.4 Method 4: Cycloaddition Reactions

27.17.5.3.2.4.1 Variation 1: [4 + 2]-Cycloaddition Reactions

27.17.5.3.2.4.2 Variation 2: [2 + 2]-Cycloaddition Reactions

27.17.5.3.2.5 Method 5: Cleavage of N,N-Dialkylhydrazones

27.17.5.3.2.5.1 Variation 1: Solid-Phase Synthesis of Nitriles

27.17.5.4 N-Sulfonylated Hydrazones

27.17.5.4.1 Synthesis of N-Sulfonylated Hydrazones

27.17.5.4.1.1 Method 1: Synthesis from Aldehydes and Ketones

27.17.5.4.1.1.1 Variation 1: Synthesis from O,O-Acetals

27.17.5.4.1.2 Method 2: Synthesis from Nitriles

27.17.5.4.1.3 Method 3: N-Alkylation of N-Tosylhydrazones

27.17.5.4.2 Applications of N-Sulfonylated Hydrazones in Organic Synthesis

27.17.5.4.2.1 Method 1: Synthesis of Unsaturated Hydrocarbons

27.17.5.4.2.1.1 Variation 1: Synthesis of Alkenes

27.17.5.4.2.1.2 Variation 2: Synthesis of Allenes

27.17.5.4.2.1.3 Variation 3: Synthesis of Alkynes

27.17.5.4.2.2 Method 2: N-Sulfonylated Hydrazones in Reduction Reactions

27.17.5.4.2.2.1 Variation 1: Synthesis of Sulfides and Ethers

27.17.5.4.2.2.2 Variation 2: Synthesis of Sulfones

27.17.5.4.2.2.3 Variation 3: Synthesis of Arenes from Arylboronic Acids

27.17.5.4.2.3 Method 3: Synthesis of α-Alkylated and α,α-Dialkylated N-Tosylhydrazones

27.17.5.4.2.4 Method 4: Synthesis of Nitrogen Heterocycles

27.18 Product Class 18: Hydrazonium Compounds

27.18.3 Hydrazonium Compounds

A. Nodzewska and R. Łaźny

27.18.3 Hydrazonium Compounds

27.18.3.1 1,1,1-Trialkyl-2-alkylidenehydrazinium Compounds

27.18.3.1.1 Synthesis of 1,1,1-Trialkyl-2-alkylidenehydrazinium Compounds

27.18.3.1.1.1 Method 1: Alkylation of Hydrazone Compounds

27.18.3.1.2 Applications of 1,1,1-Trialkyl-2-alkylidenehydrazinium Compounds in Organic Synthesis

27.18.3.1.2.1 Method 1: Synthesis of Azirines

27.18.3.1.2.2 Method 2: Synthesis of Pyrroles

27.18.3.1.2.3 Method 3: Synthesis of Ketones

Author Index

Abbreviations

1.4.5 Organometallic Complexes of Cobalt (Update 2012)

M. Amatore, C. Aubert, M. Malacria, and M. Petit

General Introduction

The present chapter is an update of the first report on organometallic cobalt complexes in Science of Synthesis (see Section 1.4). It summarizes the more recent and most relevant advances concerning the use and the synthesis of important cobalt complexes. During the decade 2000–2010, two major developments were made concerning cobalt complexes:

The first involves the extensive use of cobalt–η5-dienyl complexes not only in the context of the synthesis of new complexes, but also in terms of powerful applications in a wide range of reactions. This can be related to the increase in the number of reviews in this area since the beginning of the new millennium.[1–9]

The second major development in the organometallic chemistry of cobalt complexes is the use of more-convenient and easy-to-handle complexes based on cobalt(II) or -(III) salts. From economic and environmental points of view, these complexes represent an interesting alternative to the well-known cyclopentadienylcobalt(I) [Co(Cp)L2] or octacarbonyldicobalt(0) [Co2(CO)8] catalysts. Although early applications of these complexes in organic synthesis have been reported, their use has been generalized only recently. Because of their low cost, low toxicity, and relatively high stability, these cobalt complexes have gained an increasingly important role in the field of cross-coupling reactions, cycloadditions, alkene functionalizations, C—H bond activations, and even the chemistry of strained rings.[5,10] The most commonly employed catalytic systems are combinations of cobalt(II) or -(III) salts with defined ligands, such as phosphines or amines, that can be prepared in a previous step or generated in situ under reductive conditions. Another class of complexes that have shown high efficiency is represented by cobalt(II) or -(III) complexes incorporating macrocyclic ligands such as porphyrins, salens, or cobaloximes. Finally, cobalt(I) species obtained from tetrakis(trimethylphosphine)cobalt(0) have been employed with success in the course of C—H bond activation processes for the generation of new cobalt complexes. This review provides an overview of contemporary methods that require the preparation and the use of these complexes.

1.4.5.1 Cobalt–η5-Dienyl Complexes

1.4.5.1.1 Synthesis of Cobalt–η5-Dienyl Complexes

1.4.5.1.1.1 Method 1: Synthesis of Chiral Dicarbonyl(η5-cyclopentadienyl)cobalt(I) and (η5-Cyclopentadienyl)(η4-diene)cobalt(I) Complexes

In the course of asymmetric reactions, cobalt-mediated [2 + 2 + 2] cycloaddition has been for a long time one of the most difficult challenges. Chiral cobalt–η5-dienyl complexes may be obtained by introducing an asymmetric cyclopentadienyl moiety as a permanent ligand. Two general procedures are reported; these differ in the nature of the labile ligand on the complex.[11,12]

1.4.5.1.1.1.1 Variation 1: Synthesis of Chiral Dicarbonyl(η5-cyclopentadienyl)cobalt(I) Complexes by Oxidative Addition

The reaction between octacarbonyldicobalt(0), a readily available starting material, and the freshly distilled chiral cyclopentadiene 1 in a refluxing chlorinated solvent in the absence of light gives the desired chiral cobalt(I) complex 2 in moderate to good yields (▶ Scheme 1).[11]

▶ Scheme 1 Synthesis of a Dicarbonyl(η5-cyclopentadienyl)cobalt(I) Complex from Octacarbonyldicobalt(0) and a Chiral Cyclopentadiene[11]

Dicarbonyl{η5-(3S,4S)-3,4-(isopropylidenedioxy)bicyclo[4.3.0]nona-6,8-dienyl}cobalt(I) (2); Typical Procedure:[11]

A soln of chiral cyclopentadiene 1 (0.58 g, 3.0 mmol) in CH2Cl2 (10 mL) and pent-1-ene (5 mL) was degassed by three freeze–pump–thaw cycles, added to Co2(CO)8 (0.85 g, 2.5 mmol) in a round-bottomed flask equipped with a reflux condenser, and the mixture was heated at reflux in the dark under N2 for 30 h. The solvent was removed under reduced pressure, and the oil was taken up in degassed pentane. The mixture was purified by chromatography [alumina (activity 3), degassed Et2O/pentane 1:4] under N2. A single red fraction was obtained, which crystallized upon removal of the solvent under reduced pressure to provide a red solid; yield: 0.39 g (43%); mp 72–73 °C; [α]D26 +70 (c 0.00095, 95% EtOH).

1.4.5.1.1.1.2 Variation 2: Synthesis of Chiral (η5-Cyclopentadienyl)(η4-diene)cobalt(I) Complexes by Substitution of Ligands

▶ Scheme 2 Synthesis of Chiral (η5-Cyclopentadienyl)(η4-diene)cobalt(I) Complexes[12,13]

(+)-(η4-Cycloocta-1,5-diene)(η5-1-neomenthylindenyl)cobalt(I) (3); Typical Procedure:[12]

A 2.5 M soln of BuLi in hexanes (2 mL, 5 mmol) was added in one portion to a soln of (–)-3-neomenthylindene (1.27 g, 5 mmol) in THF (15 mL) at –78 °C. The mixture was stirred for 5 min, the temperature was allowed to rise to 20 °C for 30 min, and stirring was continued for 2 h at rt. The soln of (1-neomenthylindenyl)lithium was again cooled to –78 °C, and CoCl(PPh3)3 (4.41 g, 5 mmol) was added. The stirred soln was allowed to warm to rt over 1 h and then stirred for an additional 1 h. Cycloocta-1,5-diene (0.92 mL, 7.5 mmol) was added to the dark red mixture, which was then heated to reflux for 0.5 h. The color soon changed to red-orange, and the soln was cooled and filtered through a thin pad of degassed silica gel (2 × 3 cm), eluting with THF. The solvent was removed under reduced pressure, and the oily residue was dried for 1 h under high vacuum and purified by column chromatography [degassed silica gel (1.5 × 30 cm)]. Elution with pentane allowed the separation of the main diastereomer as the first red-orange fraction, and the more slowly moving second minor fraction was set aside. The eluate was concentrated under reduced pressure to a volume of 5 mL. Cooling to –78 °C caused the precipitation of the complex 3 as a dark red crystalline compound, which was collected by filtration and dried under high vacuum; yield: 1.11 g (53%); mp 89 °C; [α]D20 +156 (c 0.06, toluene).

(η4-Cycloocta-1,5-diene){η5-(3S,4S)-3,4-(isopropylidenedioxy)bicyclo[4.3.0]nona-6,8-dienyl}cobalt(I) (4); Typical Procedure:[13]

A soln of cyclopentadiene 1 (1.44 g, 7.5 mmol) in THF (20 mL) was treated with a 10% suspension of LDA (0.8 g, 7.5 mmol) in hexanes. The mixture was stirred for 5 min, and a suspension of CoCl(PPh3)3 (6.35 g, 7.2 mmol) and cycloocta-1,5-diene (1.29 mL, 10.5 mmol) in toluene (40 mL) was added. After it had been stirred for 1 h at rt, the dark red mixture was heated to 80 °C for 1 h, resulting finally in a clear orange soln. The mixture was cooled and filtered through a short column of silica gel (1.5 cm × 3 cm) degassed by three argon– vacuum pump cycles, 1 h each. Volatiles were removed under reduced pressure, and the residue was dissolved in pentane (20 mL) and left overnight at 0 °C. Precipitated Ph3P was filtered off, and the soln was filtered through a column of degassed silica gel (1.5 cm × 20 cm), an orange band being eluted with pentane. The soln was concentrated to a volume of 10 mL and cooled to –78 °C to crystallize 4 as orange needles; yield: 1.82 g (68%); mp 102 °C; [α]D20 +5.5 (c 0.17, toluene).

1.4.5.1.1.2 Method 2: Synthesis of (Alkene)carbonyl(η5-cyclopentadienyl)cobalt(I) Complexes via Displacement of One Carbonyl Moiety

Among the commercially available cyclopentadienylcobalt catalysts, dicarbonyl(η5-cyclopentadienyl)cobalt(I) is probably the most widely used. Its activation usually requires heat and/or visible light. The use of (η4-cycloocta-1,5-diene)(η5-cyclopentadienyl)cobalt(I), which has been employed mostly for the preparation of pyridines, also requires high temperatures and/or light. Conversely, (η5-cyclopentadienyl)bis(ethene)cobalt(I), which is also employed frequently, is active at room temperature or lower temperatures. However, these very efficient catalysts are all very sensitive to air and require the use of distilled and thoroughly degassed solvents. The challenge of finding easy-to-handle air-stable cobalt catalysts has been addressed by the use of complexes of the type (alkene)carbonyl(η5-cyclopentadienyl)cobalt(I), e.g. 5 and 6 (▶ Schemes 3 and 4).[14,15] These complexes do not need degassed solvents but do, however, still need energetic activation to be reactive.

▶ Scheme 3 Synthesis of Carbonyl(η5-cyclopentadienyl)(η2-maleic anhydride)cobalt(I)[14]

▶ Scheme 4 Synthesis of Carbonyl(η5-cyclopentadienyl)(η2-maleic anhydride)cobalt(I) Complexes[15]

R

1

Yield (%)

Ref

Me

100

[

15

]

iBu

100

[

15

]

t

-Bu

65

[

15

]

1-adamantyl

74

[

15

]

Carbonyl(η5-cyclopentadienyl)(η2-maleic anhydride)cobalt(I) (5); Typical Procedure:[14]

A soln of Co(Cp)(CO)2 (0.48 mL, 3.4 mmol) and maleic anhydride (1.2 g, 12.2 mmol) in xylenes (20 mL) was heated at 140 °C for 3 h to precipitate brown solids. The precipitate, separated by filtration, was extracted with acetone (30 mL). The extract was concentrated under reduced pressure to give a red-brown solid. Recrystallization (acetone/hexanes) gave a mixture of 5A and 5B as a red-brown solid; yield: 0.61 g (73%).

A soln of dimethyl fumarate (216 mg, 1.5 mmol) in toluene (30 mL) and Co(Cp)(CO)2(210 μL, 1.5 mmol) was refluxed for 3 h under visible-light irradiation. The mixture was concentrated under reduced pressure and purified by chromatography (silica gel, petroleum ether/EtOAc 7:3) to give a red solid; yield: 0.439 g (100%); mp 154 °C.

1.4.5.1.1.3 Method 3: Synthesis of (η5-Cyclopentadienyl)(η4-diene)cobalt(I) Complexes via Substitution of Ligands

The balance between stability and activation energy is very important for the design of new highly reactive and stable complexes. As mentioned in ▶ Section 1.4.5.1.1.2, (η4-cycloocta-1,5-diene)(η5-cyclopentadienyl)cobalt(I) requires high temperatures and/or light to be activated, whereas (η5-cyclopentadienyl)bis(ethene)cobalt(I) is reactive at low temperature but very unstable. Recently it has been shown that the use of noncyclic diene ligands is enough to increase the stability of the new complexes while keeping the high reactivity. Use of cobalt(I)–bis(alkene) complex 7, synthesized by a modified Jonas protocol, allows the formation of the desired new complexes 8 by simple ligand exchange (▶ Scheme 5).[16,17]

▶ Scheme 5 Synthesis of (η5-Cyclopentadienyl)(η4-diene)cobalt(I) Complexes by Ligand Substitution[17]

(η5-Cyclopentadienyl)(η4-diene)cobalt(I) Complexes 8; General Procedure:[17]

CAUTION:

Metallic potassium on prolonged exposure to air forms a coating of potassium superoxide, which is explosive under certain conditions.

Cobaltocene (0.5 g, 2.6 mmol) and metallic K (0.109 g, 2.8 mmol) were dissolved in Et2O (10 mL) and stirred at –78 °C. Trimethyl(vinyl)silane (1.8 g, 18.2 mmol) was added dropwise via syringe, and the brown slurry was stirred at –78 °C for 5 d. After this time, the solvent was removed under reduced pressure and the residue was dissolved in pentane (10 mL) and filtered over a Schlenk frit. The resulting red soln was concentrated under reduced pressure to give complex 7; yield: 0.678 g (80%). To a stirred 0.2 M soln of bis(alkene)cobalt(I) complex 7 (1.0 mmol) in Et2O (5 mL) an excess of the appropriate diene (2.5 mmol) was added dropwise at –30 °C over 2 min. The resulting soln was stirred for a further 5 min and finally the solvent was removed under reduced pressure at –20 °C. The residue was dried under vacuum to give complex 8; yield: quant.

1.4.5.1.1.4 Method 4: Synthesis of (η5-Cyclopentadienyl)cobalt–N-Heterocyclic Carbene Complexes by Exchange of Ligands

Since their discovery by Fischer in 1964,[18] carbene complexes of almost all transition metals have been synthesized. Many complexes of these ligands show interesting chemical properties, but there are only scattered reports of cobalt–N-heterocyclic carbene complexes. Recently, access to more stable organic carbenes has led to the preparation of several new (η5-cyclopentadienyl)cobalt–N-heterocyclic carbene complexes.[19–22]

1.4.5.1.1.4.1 Variation 1: Synthesis of Carbonyl(η5-cyclopentadienyl)cobalt–N-Heterocyclic Carbene Complexes

Carbonyl(η5-cyclopentadienyl)cobalt–N-heterocyclic carbene complexes, e.g. 9 and 10, are obtained by addition of the desired carbene dimer (▶ Scheme 6)[19] or carbene (▶ Scheme 7)[20–22] to commercially available dicarbonyl(η5-cyclopentadienyl)cobalt(I) by simple ligand-substitution chemistry.

▶ Scheme 6 Synthesis of Carbonyl(η5-cyclopentadienyl)(1,3-dimethyl-4,5-dihydroimidazol-2-ylidene)cobalt(I) from a Carbene Dimer[19]

▶ Scheme 7 Synthesis of Carbonyl(η5-cyclopentadienyl)(1,3-dialkylimidazol-2-ylidene)cobalt(I) Complexes from a Carbene[20–22]

R

1

Solvent

Temp (°C)

Time (h)

Yield (%)

Ref

Mes

Et

2

O

20

20

71

[

20

]

2,6-iPr

2

C

6

H

3

toluene

50

16

72

[

21

]

iPr

toluene

35

48

30

[

22

]

A soln of Co(Cp)(CO)2 (1.7 g, 9.5 mmol) and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (3.4 g, 8.7 mmol) in toluene (50 mL) was stirred at 50 °C for 16 h. The solvent was removed under reduced pressure until 5 mL remained and then hexanes (50 mL) were added. The soln was cooled to –30 °C, producing the product as dark red crystals; yield: 3.38 g (72%).

1.4.5.1.1.4.2 Variation 2: Synthesis of (η5-Cyclopentadienyl)(ethene)cobalt–N-Heterocyclic Carbene Complexes

Using (η5-cyclopentadienyl)bis(ethene)cobalt(I) as starting material, (η5-cyclopentadienyl)(ethene)cobalt–N-heterocyclic carbene complexes, such as 11, are obtained (▶ Scheme 8).[20,23]

▶ Scheme 8 Synthesis of (η5-Cyclopentadienyl)(1,3-dimesitylimidazol-2-ylidene)-(ethene)cobalt(I)[20]

(η5-Cyclopentadienyl)(1,3-dimesitylimidazol-2-ylidene)(ethene)cobalt(I) (11); Typical Procedure:[20]

A Schlenk flask was loaded with Co(Cp)(H2C=CH2)2 (36 mg, 0.2 mmol), 1,3-dimesitylimidazol-2-ylidene (50 mg, 0.16 mmol), and a magnetic stirrer bar. Degassed Et2O (10 mL) was added and the reddish brown soln was stirred at rt for 15 min, followed by solvent removal under reduced pressure. The solid was washed with degassed pentane (1–2 mL), extracted with degassed Et2O (5 mL), and crystallized by cooling at –20 °C to give 11 as reddish brown crystals. The solid decomposed over 2–3 d at rt; yield: 30 mg (41%).

1.4.5.1.1.4.3 Variation 3: Synthesis of (η5-Cyclopentadienyl)(triphenylphosphine)cobalt–NHeterocyclic Carbene Complexes

Using (η5-cyclopentadienyl)bis(triphenylphosphine)cobalt(I) as starting material, (η5-cyclopentadienyl)(triphenylphosphine)cobalt–N-heterocyclic carbene complexes, such as 12, are obtained (▶ Scheme 9).[22]

▶ Scheme 9 Synthesis of (η5-Cyclopentadienyl)(1,3-diisopropylimidazol-2-ylidene)(triphenylphosphine)cobalt(I)[22]

(η5-Cyclopentadienyl)(1,3-diisopropylimidazol-2-ylidene)(triphenylphosphine)cobalt(I) (12); Typical Procedure:[22]

A degassed soln of Co(Cp)(PPh3)2 (1.17 g, 1.80 mmol) in toluene (40 mL) was added to a degassed soln of 1,3-diisopropylimidazol-2-ylidene (0.55 g, 3.61 mmol) in toluene (10 mL), and the mixture was stirred at rt for 20 h. The solvent was removed under reduced pressure and the residue was crystallized (toluene/hexanes 1:10) to give a dark blue powder; yield: 0.67 g (69%); mp 190.1–191.3 °C.

1.4.5.1.1.5 Method 5: Synthesis of (η5-Cyclopentadienyl)(phosphine)cobalt(I)–Ligand Complexes

As mentioned in ▶ Section 1.4.5.1.1.2, the commercially available catalyst dicarbonyl(η5-cyclopentadienyl)cobalt(I) needs high-energy activation to react. The use of a phosphine ligand is employed to obtain lower energy activation, and although the resulting complexes may be air sensitive, they are worthy of inclusion here.

1.4.5.1.1.5.1 Variation 1: Synthesis of Carbonyl(η5-cyclopentadienyl)(triphenylphosphine)cobalt(I)

Using dicarbonyl(η5-cyclopentadienyl)cobalt(I) as starting material, the triphenylphosphine complex 13 is obtained by refluxing in methylcyclohexane (▶ Scheme 10).[24]

▶ Scheme 10 Synthesis of Carbonyl(η5-cyclopentadienyl)(triphenylphosphine)cobalt(I)[24]

Carbonyl(η5-cyclopentadienyl)(triphenylphosphine)cobalt(I) (13); Typical Procedure:[24]

A degassed soln of Co(Cp)(CO)2 (7.0 g, 38.90 mmol) and Ph3P (12.5 g, 47.70 mmol) in methylcyclohexane (250 mL) was refluxed for 24 h. Red crystals were precipitated by cooling the soln to rt. After several hours, these were collected by filtration, washed with degassed Et2O (2 × 50 mL) and degassed pentane (50 mL), and then dried to give red-black crystals; yield: 12.88 g (80%); mp 140–143 °C.

1.4.5.1.1.5.2 Variation 2: Synthesis of (η5-Cyclopentadienyl)(triphenylphosphine)cobalt(I)–Alkene Complexes

Since activation energy is lower with phosphine as a ligand, (η5-cyclopentadienyl)(triphenylphosphine)cobalt(I)–alkene complexes, e.g. 14 and 15, have great potential in catalysis at low temperature (▶ Scheme 11).[14]

▶ Scheme 11 Synthesis of (η5-Cyclopentadienyl)(triphenylphosphine)cobalt(I)–η2-Alkene Complexes[14]

(η5-Cyclopentadienyl)(η2-dimethyl fumarate)(triphenylphosphine)cobalt(I) (14); Typical Procedure:[14]

To a soln of Co(Cp)(PPh3)2 (1.5 g, 2 mmol) in benzene (50 mL) (CAUTION:carcinogen) was added dimethyl fumarate (0.8 g, 5.6 mmol). The mixture was stirred at rt for 1 h. The red soln was concentrated under reduced pressure and the residue was subjected to column chromatography (alumina). From the red fraction eluted with benzene/EtOAc were obtained red-brown crystals, which were further recrystallized (benzene/EtOAc) to give 14 as red-brown crystals; yield: 0.94 g (89%).

1.4.5.1.1.5.3 Variation 3: Synthesis of {[2-(Di-tert-butylphosphino)ethyl]cyclopentadienyl}(ethene)cobalt(I)

A recent strategy allows the synthesis of cobalt complexes with two different donor ligands in very high yields. Indeed, starting from a cobalt(II) salt, the reaction with metalated [2-(di-tert-butylphosphino)ethyl]cyclopentadiene provides the cyclopentadienylcobalt(II) intermediate 16. This is reduced in the presence of ethene to give the desired cobalt(I) 17 complex in very good yield (▶ Scheme 12).[25]

▶ Scheme 12 Synthesis of {[2-(Di-tert-butylphosphino)ethyl]cyclopentadienyl}-(ethene)cobalt(I)[25]

{[2-(Di-tert-butylphosphino)ethyl]cyclopentadienyl}(ethene)cobalt(I) (17); Typical Procedure:[25]

CAUTION:

Mercury vapor is readily absorbed by inhalation and is neurotoxic.

To a Schlenk tube containing CoCl2 (1.95 g, 15.1 mmol) was added a cooled (–30 °C) soln of lithium [2-(di-tert-butylphosphino)ethyl]cyclopentadienide (7.35 g, 30.1 mmol) in THF (120 mL). The red suspension was stirred for 20 min, during which time the temperature was raised from –30 to 20 °C. The mixture was stirred at this temperature for a further 1 h before the THF was removed under reduced pressure. The residue was taken up in Et2O (2500 mL) and the soln was filtered through a P4 frit (under argon). The red-violet Et2O soln was cooled to –78 °C for crystallization, which afforded complex 16 as black-violet plates; yield: 3.8 g (73%); mp 192 °C (dec).

In a 1-L three-necked flask with a gas-inlet tube, a magnetic stirrer, and two gas inlets with taps, ethene was introduced into a soln of the above black-violet solid 16 (6.8 g, 20.5 mmol) in THF (400 mL) at –55 °C. After 10 min, 1% Na amalgam (301.5 g, 152 mmol Na) was pipetted into the cooled red-violet soln. The mixture was stirred for 1 h and warmed to 20 °C. The mud-brown mixture was filtered through a P4 frit, and the red filtrate was concentrated to 20 mL and cooled to –78 °C to afford 17 as red-black crystals; yield: 6.15 g (93%); mp 115 °C (dec).

1.4.5.1.1.6 Method 6: Synthesis of (η5-Cyclopentadienyl)cobalt–Dinitrosoalkane Complexes

▶ Scheme 13 Synthesis of (η5-Cyclopentadienyl)cobalt–Dinitrosoalkane Complexes[26,28]

R

1

R

2

R

3

R

4

R

5

Yield (%)

Ref

H

H

Me

H

Me

84

[

26

]

H

H

Me

Me

H

63

[

26

]

H

Me

Me

H

H

62

[

26

]

H

Me

Me

H

Me

84

[

26

]

H

Me

Me

Me

Me

79

[

26

]

H

Et

Me

Me

H

82

[

26

]

H

Me

Et

Me

H

86

[

26

]

H

H

Ph

H

Me

92

[

26

]

H

H

(CH

2

)

3

H

73

[

26

]

Me

H

H

89

[

28

]

Me

H

H

77

[

28

]

R

1

R

2

R

3

R

4

R

5

Yield (%)

Ref

Me

TMS

H

87

[

28

]

Me

H

H

44

[

28

]

Me

H

(CH

2

)

2

H

66

[

28

]

Me

H

(CH

2

)

3

H

92

[

28

]

Me

H

CH

2

OCH

2

H

72

[

28

]

Me

H

CH

2

NTsCH

2

H

19

[

28

]

Me

H

(CH

2

)

2

O

H

64

[

28

]

(η5-Cyclopentadienyl)cobalt–Dinitrosoalkane Complexes 19; General Procedure:[28]

An oven-dried Schlenk flask was charged with enough dry CH2Cl2 to prepare a 0.1–0.2 M soln of the dicarbonyl(η5-cyclopentadienyl)cobalt(I) complex. The solvent was deoxygenated by sparging it with N2 for 5 min, and then the dicarbonyl(η5-cyclopentadienyl)cobalt(I) complex (1.0 equiv) and the alkene (10 equiv) were added quickly in one portion. The dark red soln was cooled to 0 °C by immersing the flask in an ice–water bath and NO was bubbled slowly through the soln at a rate of approximately 1 bubble per second using a silicone oil bubbler. A dark brown solid gradually precipitated from the dark red-black soln as the reaction progressed. The reaction was closely monitored by TLC until no starting material was seen (generally about 30–40 min for reactions utilizing less than 1.0 g of the starting Co complex). The NO addition was stopped and N2 was bubbled through the mixture for 5 min to ensure that any traces of NO(g) were removed. The entire mixture was loaded onto a silica gel column packed with hexanes, and the column was eluted with hexanes until all the excess alkene and starting material had been removed (the alkene generally eluted first as a light yellow band and any excess starting material eluted as an orange band). The polarity of the mobile phase was then increased to hexanes/EtOAc (4:1) to elute the desired cobalt dinitrosoalkane complex 19; yield: 19–92%.

1.4.5.1.1.7 Method 7: Synthesis of (η5-Pentamethylcyclopentadienyl)cobalt–η3-Allyl Complexes by Exchange of Ligands

Neutral (η3-allyl)cobalt(III) trifluoromethanesulfonate complexes 20 and 21 are easily accessible from allyl alcohol or a diene in the presence of bis(ethene)(η5-pentamethylcyclopentadienyl)cobalt(I) in high yield (▶ Scheme 14).[29,30]

▶ Scheme 14 Synthesis of (η3-Allyl)(η5-Pentamethylcyclopentadienyl)cobalt(III) Trifluoromethanesulfonates[29]

R

1

Yield (%)

Ref

H

92

[

29

]

Me

89

[

29

]

(η3-Allyl)(η5-pentamethylcyclopentadienyl)cobalt(III) Trifluoromethanesulfonate (20); Typical Procedure:[29]

A Schlenk flask in a drybox was charged with Co(Cp*)(H2C=CH2)2 (527.4 mg, 2.107 mmol). Degassed Et2O (2 mL) was added and the flask was capped with a rubber septum and removed to a Schlenk line. The soln was cooled to –78 °C in a dry ice/acetone bath. Dry and degassed allyl alcohol (0.720 mL, 10.6 mmol) was added via microliter syringe and then 1.0 M TfOH in Et2O (2.0 mL, 2.0 mmol) was added carefully with a gastight syringe (the mixture immediately turned from orange to dark red). The mixture was stirred for 30 min at –78 °C and then allowed to warm to rt. After 3.5 h at rt, the solvent was removed under reduced pressure. In the drybox, the solid was rinsed with pentane on a glass frit and then taken up in benzene (CAUTION:carcinogen) and filtered through a plug of Celite. The benzene was removed by lyophilization to give a dark red powder. Crystals of 20 were obtained from toluene/pentane at –40 °C; yield: 643.3 mg (79%).

In a drybox, a soln of Co(Cp*)(H2C=CH2)2 (103.5 mg, 0.414 mmol) in hexanes (15 mL) was placed in a medium-walled glass vessel fitted with a vacuum stopcock. The reaction vessel was removed to a Schlenk line, the Teflon stopcock was replaced by a rubber septum under N2 flow, and buta-1,3-diene was bubbled through the soln for 20 min. The bomb was sealed and then heated to 65 °C for 5 h. The solvent was removed under reduced pressure, the residue was dissolved in pentane, and the soln was filtered through a plug of Celite in the drybox. Concentration gave a dark red solid, which was used without further purification. In the drybox, a soln of the previous solid (82.2 mg, 0.331 mmol) in Et2O (6 mL) was placed in a Schlenk flask capped with a rubber septum. The flask was removed to the Schlenk line and cooled to –78 °C before 1 M TfOH in Et2O (0.33 mL, 0.33 mmol) was added. The resulting mixture was allowed to warm to rt and then stirred overnight. The solvent was removed under reduced pressure and benzene (5 mL) (CAUTION:carcinogen) was added. After being stirred overnight at rt, the soln was filtered trough a plug of Celite in the drybox. Lyophilization gave a brown powder, which was recrystallized (toluene/pentane, –35 °C) to give dark brown needles; yield: 118.6 mg (92%).

1.4.5.1.1.8 Method 8: Synthesis of (η5-Cyclopentadienyl)cobalt–η5-Pentadienyl Complexes by Exchange of Ligands

The most general synthesis among others[31–34] of the η5-pentadienyl–cobalt(III) complexes 22 and 23 is the coordination and protolytic dehydration of penta-1,4-dien-3-ols in the presence of a labile source of cobalt(I) (▶ Scheme 15).[35,36]

▶ Scheme 15 Synthesis of Cationic (η5-Cyclopentadienyl)(η5-pentadienyl)cobalt(III) Salts[35,36]

R

1

R

2

R

3

R

4

R

5

Product

Yield (%)

Ref

Me

H

H

H

H

23

67

[

35

]

Me

Me

H

H

H

23

75

[

35

]

Me

H

Me

H

H

23

54

[

35

]

Me

Me

Me

H

H

23

59

[

35

]

Me

Me

Me

H

Me

23

30

[

35

]

Me

Ph

H

H

H

22

80

[

35

]

H

Me

H

H

H

22

61

[

36

]

H

H

H

H

H

22

78

[

36

]

H

H

Me

H

H

22

51

[

36

]

H

Me

Me

H

H

22

55

[

36

]

H

Ph

H

H

H

22

50

[

36

]

H

H

Me

Me

H

22

34

[

36

]

H

TMS

H

H

H

22

56

[

36

]

One of the possible mechanisms is the substitution of ethene by the alka-1,4-dien-3-ol substrate as first step to form the intermediate (η5-cyclopentadienyl)(η4-1,4-dien-3-ol)cobalt(I), which after protonation can undergo water elimination and valence isomerization to provide the cationic (η5-cyclopentadienyl)(η5-pentadienyl)cobalt(III) (▶ Scheme 16).

▶ Scheme 16 Mechanism of the Formation of Cationic (η5-Cyclopentadienyl)(η5-pentadienyl)cobalt(III) Salts[36]

CAUTION:

Tetrafluoroboric acid is extremely destructive to the skin, eyes, and respiratory tract.

In a drybox, Co(Cp)(H2C=CH2)2 (209.5 mg, 1.16 mmol) was weighed into a Schlenk flask and dissolved in THF (10 mL). The Schlenk flask was removed to a Schlenk line and cooled to –78 °C while under argon. After 5–10 min at –78 °C, (E)-hexa-1,4-dien-3-ol (128 mg, 1.16 mmol), itself at rt, was added via microsyringe into the stirring Schlenk flask. The flask was warmed to 0 °C and allowed to stir for 10 min (bubbling occurred). After stirring, the flask was again cooled to –78 °C, and HBF4•OEt2 (180 μL, 1.16 mmol) was added via microsyringe (with positive argon pressure). The mixture was allowed to warm to rt overnight (ca. 16 h). The volatiles were removed under reduced pressure and the crude product was purified by flash chromatography (silica gel, MeOH/CH2Cl2 3:97) to give a red powder; yield: 209 mg (61%).

1.4.5.1.1.9 Method 9: Synthesis of (η5-Cyclopentadienyl)cobalt–Alkyne Complexes

Substitution of (η5-cyclopentadienyl)cobalt(I)–bis(ligand) complexes by one alkyne was established using triphenylphosphine as the displaced ligand in the substrate, providing complexes 24 (▶ Scheme 17).[37–40] More recently, dicarbonyl(η5-cyclopentadienyl)cobalt(I) has been found to be a good starting material, using triple bond compounds with strong acceptor properties, for example to give complexes 25 (▶ Scheme 18).[41]

▶ Scheme 17 Synthesis of (η2-Alkyne)(η5-cyclopentadienyl)(triphenylphosphine)cobalt(I) Complexes[37–40]

R

1

R

2

Time (h)

Yield (%)

Ref

Ph

Ph

1

85

[

37

,

38

]

Me

CO

2

Me

12

74

[

38

]

TMS

Ts

24

100

[

39

]

TMS

SO

2

Ph

18

80

[

40

]

▶ Scheme 18 Synthesis of [η2-Bis(tert-butylsulfonyl)acetylene]carbonyl(η5-cyclopentadienyl)cobalt(I) Complexes[41]

R

1

Time (d)

Yield (%)

Ref

H

3

73

[

41

]

Me

2

85

[

41

]

TMS

6

78

[

41

]

CO

2

Me

11

39

[

41

]

Diphenylacetylene (0.9 g, 5 mmol) was added to a soln of Co(Cp)(PPh3)2 (3.6 g, 5 mmol) in benzene (25 mL) (CAUTION:carcinogen) and the mixture was allowed to stand at rt. After 1 h, hexanes (50 mL) was added to precipitate shiny black crystals, which were separated by decantation and washed with hexanes; yield: 2.4 g (85%).

[η2-Bis(tert-butylsulfonyl)acetylene]carbonyl(η5-cyclopentadienyl)cobalt(I) (25); General Procedure:[41]

To a soln of bis(tert-butylsulfonyl)acetylene (890 mg, 3.34 mmol) in CH2Cl2 (50 mL) was added the dicarbonyl(η5-cyclopentadienyl)cobalt(I) substrate (1.67 mmol). The mixture was stirred at rt for 2–11 d, the solvent was removed under reduced pressure, and the product 25 was isolated by chromatography (silica gel); yield: 39–85%.

1.4.5.1.1.10 Method 10: Synthesis of (η5-Cyclopentadienyl)cobaltacycles

1.4.5.1.1.10.1 Variation 1: Synthesis of (η5-Cyclopentadienyl)cobaltacyclobutenes

Cobaltacyclobutenes were first described as intermediates during the reaction of (η5-cyclopentadienyl)(η2-diphenylacetylene)(triphenylphosphine)cobalt(I) complexes with alkyl diazoacetates to give a mixture of cobalt–diene complexes.[42] However, depending upon the substituents on the alkyne in the starting complex, the reaction can lead to stable cobaltacyclobutenes such as 26 (▶ Scheme 19).[39,43–46]

▶ Scheme 19 Synthesis of (Cyclopentadienyl)cobaltacyclobutenes[39,46]

R

1

Yield (%)

Ref

Et

84

[

39

]

(CH

2

)

2

CH=CH

2

67

[

46

]

To a soln of (η5-cyclopentadienyl)[η2-1-(phenylsulfonyl)-2-(trimethylsilyl)acetylene](triphenylphosphine)cobalt(I) (312 mg, 0.5 mmol) in benzene (30 mL) (CAUTION:carcinogen) was added Ph3P (1.31 g, 5 mmol) and but-3-enyl diazoacetate (350 mg, 2.5 mmol). After being stirred at reflux for 2 h, the dark red soln was subjected to chromatography (silica gel, EtOAc/hexanes 3:17) and recrystallized (MeOH, 0 °C) to give the product as an air-stable, dark red crystalline solid; yield: 245 mg (67%); mp 139.5–140 °C.

1.4.5.1.1.10.2 Variation 2: Synthesis of (η5-Cyclopentadienyl)cobaltasilacyclopentenes

The use of 1-silabenzocyclobutenes allows the formation of new cobaltasilacyclopentene complexes by a regioselective oxidative addition of the starting dicarbonyl(η5-cyclopentadienyl)cobalt(I) complex into the C(sp2)—Si bond (▶ Scheme 20). The 1-cobalta-2-silacyclopentenes 27 have unexpected air stability for cobalt(III) organometallic species.[47]

▶ Scheme 20 Synthesis of 1-Cobalta-2-silacyclopentenes by Oxidative Addition onto Silabenzocyclobutenes[47]

R

1

Yield (%)

Ref

Ph

88

[

47

]

4-MeOC

6

H

4

46

[

47

]

iPr

33

[

47

]

A soln of 1,1-diphenyl-1-silabenzocyclobutene (274 mg, 1 mmol) and Co(Cp)(CO)2