Organocopper complexes ketones

An RCu(LiI)/TMSI combination13 promotes conjugate addition to a,/)-unsaturated ketones, leading directly to TMS enol ethers from a presumed organocopper-enone jr-complex, thus ruling out significant amounts of enolate as an intermediate on the reaction pathway (equation 2). However, these results do not allow discrimination between an a-cuprio ketone or a /i-silyl copper species. 

Addition to ot, -acetylenic esters and ketones (3, 108 6, 163-164). The addition of organocopper reagents to conjugated acetylenic carbonyl compounds is usually not stereospeciflc, although cis-addition predominates. Japanese chemists have found that the stereoselectivity in the reaction with alkylcopper reagents is markedly enhanced by use of the complex RCu BRj. Thus the reaction of dimethyl acetylenedicarboxylate with n-butylcopper complexed with tri-n-butylboron (or triethylboron) results in exclusive formation of the cis-adduct. In the absence of a trialkylborane the cis- and adducts are formed in the-ratio 85 15. 

Discussed in this chapter, for the most part, are documented cases where complexes derived fiom (one or more equivalents of) a Grignard or organolithium reagent, in combination with a copper(I) salt, have been used to add to an aldehyde, ketone, imine, amide or nitrile moiety. In the majority of examples, the key issue is one of stereocontrol. Hence, where available, data within the organocopper manifold versus those for other organometallic reagents are provided for comparison. 

The mechanism of the transfer of the alkyl group from the organocuprate to the p-position of conjugated ketones is uncertain. Evidence points to an initial complexation of the organocopper(I) species to the enone (d-rr complex), followed... 

The nucleophilic reactivities of organocopper-lithium ate complexes are lower than those of either a Grignard reagent or organolithium compounds. Then they are able to add to the 1,4-position of the double bond conjugated with ketone or the other carbonyl groups [79]. 

Finally, not all applications of Cul involve organocuprates or related reagents. For example, Corey used Cul to catalyze intramolecular diazoalkene cyclization reactions, and Yates used Cul to catalyze the Wolff rearrangement of diazo ketones. Flouse recommended CuL(SBu2)2 for the intermolecular cyclo-propanation of alkenes with a-diazo ketones. The intermediates are undoubtedly organocopper species of some kind, perhaps Cu-carbene complexes however, it should be noted that Cu and Cu are more commonly used as catalysts in conjunction with diazo compounds. ... 

---