Enantioselective Michael Additions with Optically Active Co<sup><scp>II</scp></sup>/Diamine Catalysts

Brunner, Henri; Hammer, Benedikt

doi:10.1002/anie.198403121

Cited by 108 publications

(25 citation statements)

References 10 publications

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“…Cinchona alkaloids have also been used since a long time, as chiral homogeneous catalysts for the Michael reaction. [128][129][130] First attempts to prepare organic-inorganic Cinchonabased catalysts showed very low diastereoisomeric excesses for the Michael addition of alkyl and aryl mercaptans to racemic 5-methoxy-2-(5H)-furanone. [131] However, a different catalyst preparation method has been used and yields better results (see Scheme 15).…”

Section: The Anchored [Sncl 5 ]mentioning

confidence: 99%

Silica‐Bound Homogenous Catalysts as Recoverable and Reusable Catalysts in Organic Synthesis

2006

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Very frequently the most costly components in a chemical reaction are not the starting materials or the reaction products, but the catalyst. In addition to the advantages from the economic point of view, recovery and reuse of the catalyst is equally important in order to avoid wastes, so improving the greenness of the process. There is a current tendency to transform homogeneous into heterogeneous catalysis, that will even be accelerated in the near future. Starting from a successful homogeneous catalyst, one general methodology allowing its recovery and reuse is to immobilize a suitable derivative of the active catalyst on an insoluble solid support. When the catalyst does not deactivate and is sufficiently stable under the reaction conditions, the ultimate immobilization methodology is to attach covalently the catalytically active species to the support. In this contribution, after introducing some general principles describing the fundamentals of the covalent anchoring, the emphasis is placed more on giving an overview of the most important types of covalently anchored catalysts, including Brçnsted and Lewis acids, covalently anchored bases and hydrogenation complexes. Hot topics such as silica-bound organocatalysts and the application of periodic mesoporous organosilicas as heterogeneous catalysts is also covered.

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Section: The Anchored [Sncl 5 ]mentioning

confidence: 99%

Silica‐Bound Homogenous Catalysts as Recoverable and Reusable Catalysts in Organic Synthesis

2006

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“…One of the first studies, carried out by Brunner et al, was a cobalt-catalyzed 1,4-addition: [42] The conjugate addition of Grignard reagents to a,bunsaturated ketones catalyzed by diaminezinc(ii) complexes has been reported. [43a] The reaction of isopropylmagnesium bromide with 2-cyclohexenone in the presence of catalyst 85 proceeded with 8 % enantiomeric excess.…”

Section: Alkylation Of Aldehydesmentioning

confidence: 99%

The Chemistry of Vicinal Diamines

Lucet

Gall

Mioskowski³

1998

Angewandte Chemie International Edition

963

416

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“…[70] This chiral complex [Co-(acac) 2 {(S,S)-dpen}] catalyzes the Michael addition reaction at À 50 8C to give the product in up to 66 % ee (Scheme 18). [74] The S,S configuration of the DPEN ligand means the D conformation of the cobalt complex is thermodynamically more stable than the L conformation. [70,75] Thus, the formation of R product is rationalized on the assumptions that the ketone group occupies an axial position and the ester group an equatorial one, and that methyl vinyl ketone is directed to the Si face of the ketoester complex by hydrogen bonding of the vinyl ketone oxygen to one of the NH groups (Scheme 18).…”

Section: Asymmetric Activation Of Catalyst With Chirallymentioning

confidence: 99%

Asymmetric Activation

Mikami

Terada

Korenaga

et al. 2000

Angew. Chem. Int. Ed.

157

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While nonracemic catalysts can generate nonracemic products with or without the nonlinear relationship in enantiomeric excesses between catalysts and products, racemic catalysts inherently give only a racemic mixture of chiral products. Asymmetric catalysts, either in nonracemic or racemic form, can be further evolved into highly activated catalysts with association of chiral activators. This asymmetric activation process is particularly useful in racemic catalysis through selective activation of one enantiomer of the racemic catalyst. Recently, a strategy whereby a racemic catalyst is selectively deactivated by a chiral additive has been reported to yield nonracemic products. However, reported herein is an alternative and conceptually opposite strategy in which a chiral activator selectively activates, rather than deactivates, one enantiomer of a racemic chiral catalyst. The advantage of this activation strategy over the deactivation counterpart is that the activated catalyst can produce a greater enantiomeric excess in the products—even with the use of a catalytic amount of activator relative to chiral catalyst—than that attained by the enantiomerically pure catalyst on its own. Therefore, asymmetric activation could provide a general and powerful strategy for not only the use of atropisomeric, racemic ligands but also chirally flexible and proatropisomeric ligands without enantiomeric resolution!

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Enantioselective Michael Additions with Optically Active Co^II/Diamine Catalysts

Cited by 108 publications

References 10 publications

Silica‐Bound Homogenous Catalysts as Recoverable and Reusable Catalysts in Organic Synthesis

Silica‐Bound Homogenous Catalysts as Recoverable and Reusable Catalysts in Organic Synthesis

The Chemistry of Vicinal Diamines

Asymmetric Activation

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Enantioselective Michael Additions with Optically Active CoII/Diamine Catalysts

Cited by 108 publications

References 10 publications

Silica‐Bound Homogenous Catalysts as Recoverable and Reusable Catalysts in Organic Synthesis

Silica‐Bound Homogenous Catalysts as Recoverable and Reusable Catalysts in Organic Synthesis

The Chemistry of Vicinal Diamines

Asymmetric Activation

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Product

Resources

About

Enantioselective Michael Additions with Optically Active Co^II/Diamine Catalysts