General Homologation Strategy for Synthesis of l -glycero- and d -glycero-Heptopyranoses

A general and stereospecific homologation strategy for the synthesis of heptopyranosides is reported. The strategy employs the Wittig olefination and proline-catalyzed α-aminoxylation to achieve one carbon elongation and stereoselective hydroxylation at the C6 position, respectively. The l-glycero- and d-glycero-heptopyranosides can be obtained with nearly perfect stereoselectivity. Further study reveals the difference in the chemical shift of the C6 proton of l/d-glycero-heptopyranosyl diastereomers, which is found to be useful for assignment of the configuration of heptopyranosides.