The unusual 1,4-chelation-controlled nucleophilic addition to aldehydes with high stereoselectivity. A systematic study of stereoselectivity in the addition reaction of carbon nucleophiles to cis-substituted cyclopropanecarbaldehydes

Abstract

The addition reaction of carbon nucleophiles to cis-substituted cyclopropanecarbaldehydes was systematically investigated. Ab initio calculations of model cyclopropanecarbaldehydes suggested that the bisected s-cis and s-trans conformers are the only two minimum energy conformers, which are stabilized due to the π-donating stereoelectronic effect of the cyclopropane ring. The experimental results of a series of substrates, that is, cyclopropanecarbaldehydes 1– 5 bearing a cis-( tert-butyldiphenylsilyloxy)methyl group, a cis-benzyloxymethyl group, a cis-( p-methoxybenzyloxy)methyl group, cis- N,N-diethylcarbamoyl and trans-phenyl groups, and cis-( tert-butyldiphenylsilyloxy)methyl and trans-phenyl groups, respectively, showed that highly anti-selective Grignard additions could be realized. It turned out that it occurred via an unusual 7-membered 1,4-chelation-controlled pathway. Highly stereoselective Grignard addition via the chelation-controlled pathway occurred even in the reaction of the usually non-chelating silyl ether-type substrate 5 . The results have great importance because the 1,4-chelation-controlled stereoselective addition reactions can indeed be realized. Under non-chelation conditions, the syn-products were produced with moderate stereoselectivity, which are likely to be formed via the bisected s-cis conformation-like transition state stabilized by the characteristic orbital interaction. These reactions, especially the chelation-controlled reaction, should be useful because of their t stereoselectivity and stereochemical predictability.