Diastereoselectivity in the Lewis Acid Mediated Aldol Reaction of Chiral α, β-Epoxyaldehydes with a Ketene Silyl Acetal

Article abstract of DOI:10.1007/BF00807077

The Lewis acid mediated aldol reaction of chiral α, β-cis and trans epoxyaldehydes 1 and 2 with tert-butyl ketene silyl acetal proceeds mainly with anti diastereofacial preference. The best results were obtained for cis epoxyaldehyde 1 in the presence of catalytic amounts of BiCl₃ · 1.5 eq. ZnI₂ (anti:syn ～ 13:1), whereas the poorest stereoselectivity was observed when an excess of LiClO₄ was used (anti:syn ～ 1:1). The more stable epoxyaldehyde conformers were determined and the diastereofacial preference was found to be in agreement with a nucleophilic attack on the energetically more favoured conformers.