Steric course of cross coupling of organocopper reagents with allylic acetates

The trans- and cis-2-methyl-1-vinylcyclohexyl acetates (4b) and (5b) were prepared from 2-methylcyclohexanone (1). The stereochemistry of the reaction of these isomers when treated with lithium dialkylcopper reagents is investigated and the structures are confirmed by 13C n.m.r. spectroscopy. The stereoselectivity experienced in the conversion of the cis-compound (5b) into the E-olefins (7a and b) is not observed with the trans-analogue (4b). This is tentatively interpreted in terms of steric hindrance during the attack of the reagent in the case of (5b).