Cuprates, conjugate additions, aldehydes/ketones

This reaction illustrates a stereoselective preparation of (Z)-vinylic cuprates, 5 which are very useful synthetic Intermediates. They react with a variety of electrophiles such as carbon dioxide,5,6 epoxides,5,6 aldehydes,6 allylic halides,7 alkyl halides,7 and acetylenic halides 7 they undergo conjugate addition to a,6-unsaturated esters,5 6 ketones,6 aldehydes,6 and sulfones.8 Finally they add smoothly to activated triple bonds6 such as HCSC-OEt, HC3C-SEt, HC=C-CH(0Et)2. In most cases these cuprates transfer both alkenyl groups. The uses and applications of the carbocupration reaction have been reviewed recently.9 The configurational purity in the final product 1s at least 99.951 Z in the above transformations. 

Conjugate additions. The silyl cuprate rcapcnt (PhMc,Si),CuLi (1) undergoes conjugate addition to a,(3-unsaturated aldehydes, ketones, or esters to form (3-silyl carbonyl compounds. Methylation of the intermediate enolate in acyclic systems is highly dia-stereoselective in favor of the isomer in which the silyl and methyl groups have the anti-... 

Conjugate Addition Reactions. In the presence of TMSCl, cuprates undergo 1,2-addition to aldehydes and ketones to afford sUyl enol ethers (eq 29). In the case of a chiral aldehyde, addition of TMSCl follows typical Cram diastereofacial selectivity (eq 30). - ... 

With this in mind, let s now explore the outcome of a reaction in which an enolate ion is used as a nucleophile to attack an a,(3-unsaturated aldehyde or ketone. In general, enolates are less reactive than Grignard reagents but more reactive than lithium dialkyl cuprates. As such, both 1,2-addition and 1,4-addition are observed, and a mixture of products is obtained. In contrast, doubly stabilized enolates are sufficiently stabifized to produce 1,4 conjugate addition exclusively. 

Several syntheses of aldehydes and ketones based on the insertion of carbon monoxide have been reported. Reaction of norbornadiene with monosubstituted acetylenes in the presence of octacarbonyldicobalt gives the fused cyclopen-tenone (35) in high yield conjugate addition of a cuprate and vacuum pyrolysis completes a simple synthesis of 2,3-disubstituted cyclopent-4-enones (36) (Scheme 30)." Conjugated dienes with methyl iodide in the presence of the same cobalt reagent yield conjugated dienones (37) [equation (8)]." In a review of carbonyl insertion reactions, the same reagent is reported to catalyse the reaction... 

Conjugate Addition to a, -Unsaturated Carbonyl Compounds Other than Ketones. In addition to a, 8-unsaturated ketones, the silylcuprate reagent also reacts with a, 8-unsaturated aldehydes, esters (eq 13), amides, and nitriles, and with vinyl-sulfoxides without needing Lewis acid catalysis as carbon-based cuprates do. With esters, the intermediate enolates, which have the E geometry (20), may be used directly in highly diastereoselective... 

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