Highly stereoselective conjugate additions of heteroaryl alkyl sulfoxides

Conjugate additions of alkyl 1-methyl-2-imidazolyl and 2-pyridyl sulfoxides to alpha,beta -unsaturated esters proceeded in high yield and with excelle nt diastereoselectivity when LHMDS, rather than LDA, was used as the base. Additions to enones were complicated by competitive 1,2-addition. A benzyl imidazolyl sulfoxide underwent selective conjugate addition to an enone, bu t did not react with unsaturated esters. In contrast, a benzyl 2,4-dimethox yphenyl sulfoxide gave high yields and stereoselectivity in additions to un saturated eaters.