Asymmetric induction in the additions of anions of allylic sulfoxides to benzaldehyde

Addition reactions of anions of aryl allyl sulfoxides to benzaldehyde proceed readily in moderate yields and afford mixtures of products resulting from α- and γ-attack on the allyl anion. The γ-products all possess the (E)-configuration around the double bond, and asymmetric induction occurs in the addition to the extent that the major/minor diastereomer ratio exceeds 2 : 1, generally. Electronic factors are believed to be responsible for this 'remote' asymmetric induction. Mixtures of all four possible diastereomers are observed in the products from α-attack and evidence is presented which suggests that the ratios of these products are as a result of epimerization of two of the chiral centres by [2,3] sigmatropic rearrangement.