New and stereoselective synthesis of 1,4-disubstituted buten-4-ols (homoallylic alcohol alpha-adducts) from the corresponding gamma-isomers (3,4-disubstituted buten-4-ols) via an acid-catalyzed allyl-transfer reaction with aldehydes

The gamma-adducts of homoallylic alcohols 3, derived from aldehydes via the usual reaction with common allylic metals I. were convened to the correspo nding alpha-adducts 6 by an acid-catalyzed allyl-transfer reaction. In the allyl-transfer reaction, anti- and syn-gamma-adducts 3 gave E- and Z-alpha- adducts 6, respectively, and the optical purity of the gamma-adducts 3 was transferred to the alpha-adducts 6 with >98%ee. This suggests that the ally l-transfer reaction proceeds stereoselectively via six-membered cyclic tran sition states [T]. The reaction was catalyzed by various metal triflates as well as Lewis acids and Bronsted acids.