Recoverable chiral sulfoxides for asymmetric synthesis: application to stereoselective carbonyl reduction and the asymmetric synthesis of allylic alcohols

The enantiomerically pure cyclic sulfinamide S(s)R-(+)-3 reacts with the sodium enolates of ketones to give the corresponding homochiral sulfoxides. Reduction of the carbonyl group in these products may be achieved using a variety of reducing agents the best of which were DIBAL-H or DIBAL-H/ZnBr2, which give complementary products of high diastereoisomeric excess. Reduction of the hydroxy sulfoxides with Raney nickel proceeds in low yield and causes partial racemisation of the products. However the combined use of a directed reduction followed by a facile sulfenic acid elimination provides a synthesis of allylic alcohols in high enantiomeric excess.