Diastereoselectivity in asymmetric allylations: The role of vicinal chirality in the allyl nucleophile for SE2′ reactions with aldehydes

A series of nonracemic homoallylic alcohols have been prepared by asymmetric allylation using the (R,R)- and (S,S)-1,2-diamino-1,2-diphenylethane bis-sulfonamide controller ligands for in situ formation of chiral B-allyl-1,3,2-diazaborolidines. Diastereofacial selectivity is influenced by adjacent stereochemistry incorporated into the allyl moiety at C-2, in addition to the expected role of the chiral auxiliary. Additional asymmetry in the aldehyde reactant introduces threefold stereodifferentiation. A model is developed to identify reinforcing stereochemical relationships, and examples have ascertained the relative significance of these factors. The methodology supports the construction of complex homoallylic alcohols in a highly convergent fashion.Key words: asymmetric allylation, diastereofacial selectivity, 1,4-stereocontrol, homoallylic alcohols.