Alkylchromium(<scp>III</scp>) Dichlorides, Highly Selective Reagents for the Addition of Nucleophiles to Aldehydes

Kauffmann, Thomas; Hamsen, Angelika; Beirich, Christoph

doi:10.1002/anie.198201441

Cited by 30 publications

(4 citation statements)

References 6 publications

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“…Although Kauffmann's transmetallation provided the first reactions of simple alkylchromium reagents with aldehydes, 37,178,181 the use of alkyl halides as starting materials only became available with Takai's application of nucleophilic cobalt catalysts. 182 The method is based on the early findings of an alkyl transfer from cobalt to chromium by Espenson et al 220,221 As stabilized nucleophilic cobalt(I) complexes, the most prominent one being reduced vitamin B 12 , react with alkyl halides to the alkylcobalt(III) complexes, the combination can be used to create a catalytic cycle with Co(I/III) to generate alkylchromiums (Scheme 25).…”

Section: Reactions Of Non-activated Haloalkyl Derivativesmentioning

confidence: 99%

Recent Advances in Chromium(II)- and Chromium(III)-Mediated Organic Synthesis

Wessjohann¹,

Scheid²

1999

Synthesis

215

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Synthetic transformations utilizing chromium(II) or chromium(III) reagents, mainly CÐC-coupling reactions, are discussed. Chromium reagents find increasing application in complex total syntheses where other organometallics are difficult to apply. They are easy to prepare and exhibit extraordinary chemoselectivity and high diastereoselectivity. In this article emphasis is laid on recent results in synthetic procedures, on little known general aspects of (organo)chromium chemistry, and on areas not reviewed before. The most important recent advances include reactions catalytic in chromium ions, anti -selective Reformatsky-type aldol reactions with excellent asymmetric induction, domino radical/carbanion reactions, asymmetric chromium(III) catalyzed epoxide openings and homogeneous alkene polymerization catalysts. Some progress is also made in ligand controlled enantioselective reactions with Cr(II) reagents, but satisfying solutions remain a major challenge in the field.

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Section: Reactions Of Non-activated Haloalkyl Derivativesmentioning

confidence: 99%

Recent Advances in Chromium(II)- and Chromium(III)-Mediated Organic Synthesis

Wessjohann¹,

Scheid²

1999

Synthesis

215

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Section: Metal-assisted Generation Of Carbanion Equivalentsmentioning

confidence: 99%

“…In the case of chromium, the nucleophilic organochromium species is generally only capable to attack aldehydes as electrophiles, while less active ketones are mostly unsuitable substrates. 9,46 The group of Glorius exploited this strategy for the generation of carbanion equivalents in α-position to amines. 47 In this transformation, α-TMS amines (27) were used as radical precursors (Figure 9C).…”

Section: Metal-assisted Generation Of Carbanionmentioning

confidence: 99%

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Strategies for the Photocatalytic Generation of Carbanion Equivalents for Reductant-Free C–C Bond Formations

Donabauer

König

2020

Acc. Chem. Res.

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Conspectus The use of photocatalysis in organic chemistry has encountered a surge of novel transformations since the start of the 21st century. The majority of these transformations are driven by the generation and subsequent reaction of radicals, owing to the intrinsic property of common photocatalysts to transfer single electrons from their excited state. While this is a powerful and elegant method to develop novel transformations, several research groups recently sought to further extend the toolbox of photocatalysis into the realm of polar ionic reactivity by the formation of cationic as well as anionic key reaction intermediates to furnish a desired product. Our group became especially interested in the photocatalytic formation of anionic carbon nucleophiles, as the overall transformation resembles classical organometallic reactions like Grignard, Barbier, and Reformatsky reactions, which are ubiquitous in organic synthesis with broad applications especially in the formation of valuable C–C bonds. Although these classical reactions are frequently applied, their use still bears certain disadvantages; one is the necessity of an (over)stoichiometric amount of a reducing metal. The reducing, low-valent, metal is solely applied to activate the starting material to form the organometallic carbanion synthon, while the final reaction product does generally not contain a metal species. Hence, a stoichiometric amount of metal salt is bound to be generated at the end of each reaction, diminishing the atom economy. The use of visible light as mild and traceless activation agent to drive chemical reactions can be a means to arrive at a more atom economic transformation, as a reducing metal source is avoided. Beyond this, the vast pool of photocatalytic activation methods offers the potential to employ easily available starting materials, as simple as unfunctionalized alkanes, to open novel and more facile retrosynthetic pathways. However, as mentioned above, photocatalysis is dominated by open-shell radical reactivity. With neutral radicals showing an intrinsically different reactivity than ionic species, novel strategies to form intermediates expressing a polar behavior need to be developed in order to achieve this goal. In the last couple of years, several methods toward this aim have been reported by our group and others. This Account aims to give an overview of the different existing strategies to photocatalytically form carbon centered anions or equivalents of those in order to form C–C bonds. As the main concept is to omit a stoichiometric reductant source (like a low-valent metal in classical organometallic reactions), only redox-neutral and reductant-free transformations were taken into closer consideration. We present selected examples of important strategies and try to illustrate the intentions and concepts behind the methods developed by our group and others.

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Addition of Organochromium Reagents to Carbonyl Compounds

Takai

2004

Organic Reactions

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Organochromium compounds can be prepared by two methods: (1) transmetallation from the corresponding organolithium, ‐magnesium, or –zinc compounds with chromium(III) halides, and (2) reduction of organic substrates, such as halides and unsaturated compounds with chromium(II) salts. The second method is usually the one ised because the first method suffers from low solubility of chromium(III) salts in ethereal solvents and from the difficulty of preparing organolithium compounds. Low‐valent chromium species are reducing agents. Reduction of various types of organic halides and compounds having unsaturated hetero‐hetero bonds with the chromium (II) species is discussed. Also described are the transmetallation to organochromium compounds from other organometallics, the nature of the carbon‐chromium bonds, and the X‐ray structure of chromium compounds. Reactions of organochromium reagents with carbonyl compounds and their scope and limitations are described. Included in this discussion are the geminal chromium reagents. Other reagents discussed are the chromium‐nickel compounds and alkylchromium and other organochromium reagents.

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Alkylchromium(III) Dichlorides, Highly Selective Reagents for the Addition of Nucleophiles to Aldehydes

Cited by 30 publications

References 6 publications

Recent Advances in Chromium(II)- and Chromium(III)-Mediated Organic Synthesis

Recent Advances in Chromium(II)- and Chromium(III)-Mediated Organic Synthesis

Strategies for the Photocatalytic Generation of Carbanion Equivalents for Reductant-Free C–C Bond Formations

Addition of Organochromium Reagents to Carbonyl Compounds

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