ASYMMETRIC 1,6-INDUCTION IN HETERO-DIELS-ALDER REACTIONS OF CHIRAL OXABUTADIENES FOR A DE-NOVO SYNTHESIS OF ENANTIOMERICALLY PURE CARBOHYDRATES - LEWIS-ACID DEPENDENT REVERSAL OF FACIAL SELECTIVITY

Excellent endo/exo selectivity and very good induced diastereoselectivity are achieved by hetero‐Diels‐Alder reactions of oxabutadienes such as 1, accessible from chiral oxazolidinones, with the enol ether 2 in the presence of Lewis acids. The facial selectivity can be reversed by varying the Lewis acid. The endo product is formed almost exclusively from 1 and 2 with Me2AlCl as promotor. In contrast, the other endo product 4 predominates with trimethylsilyltriflate (TMS‐OTf) as initiator. (Figure Presented.) Copyright © 1994 by VCH Verlagsgesellschaft mbH, Germany