Double stereodifferentiation in the lewis acid promoted crotylation of (S)-2-Alkoxypropanal with chiral β-Alkyl (E)-Crotylsilanes

The sense and level of 1,2-asymmetric induction have been evaluated in the Lewis acid promoted addition of (E)crotylsilanes (S)-1 and (R)-2 to (S)-2-alkoxypropanal 3 and 7. These aldehydes are substituted at the α-position with benzyloxy (OBn) to reinforce chelation and tert-butyldiphenylsilyloxy (TBDPSO) groups to prevent chelation with bidentate Lewis acids. The nature of the Lewis acid and the chirality of the silane reagent were found to playa pivotal role in the direction and levels of carbonyl diastcreoface selectivity.