Heterocuprate reagents

Nucleophilic Addition to Carboxylic Acid Derivatives Table 7 Comparison of Heterocuprate Reagents for Acylation with Benzoyl Chloride... 

Since only one of the organic groups of homocuprates is usually utilized, a non-trans-ferable group bonded to copper, such as RC C, 2-thienyl, PhS, r-BuO, R2N, Ph2P, or Me3SiCH2, is employed for the preparation of heterocuprate reagents. These cuprates are usually thermally more stable (less prone toward P-elimination of Cu-H), and a smaller excess of the reagent may be used. 

Table 6 Acylation of Heterocuprate Reagents Derived from Oiganolithiums and Cuprous r-Butoxide...

Annelation, The Gilman ate reagents derived from acetone N,N-dimethyl-hydrazone, either the homocuprate derivative (7, 149) or the more recently developed phenylthio heterocuprate derivative, add in a conjugate fashion to ethyl 1-cyclohexene-1-carboxylate (1) to afford the keto ester (2, 60-70% yield) after hydrolysis of the N,N-dimethylhydrazone group. The keto ester 2 serves as a versatile intermediate tor the preparation of several complementary annelation products 4-8. 

There have been few transformations of vinylcupiate reagents with acid chlorides (Section 1.13.3.1.1). Marino and Linderman have reported a gener preparation of divinyl ketones useful in a Nazarov sense for the formation of cyclopentenones (Scheme 33). Addition of various cuprate species to ethyl propio-late formed a mixed cuprate which is peibaps best represented as the allene (91). In the case of heterocuprates (89) and (90), acylation proceeded in good yield to form the divinyl ketone. Dimethylcuprate afforded none of the desired product but instead produced 1-acetylcyclohexene. The method was generalized for several different acid chlorides. 

The organocopper reagents used for conjugate additions to enones are homocuprates, heterocuprates, higher-order cuprates, and Grignard reagents in the presence of catalytic amounts of copper salts (CuX). 

HETE, a new higher-order heterocuprate of the type RCu(CN)2NBiuLi was the only reagent to provide satisfactory yields in the coupling of a 1,4-dienylcuprate with an alkyl iodide. 

---