A stereoselective hetero-Diels–Alder approach to Carbon–Carbon linked disaccharides

Abstract

The chiral 1-oxabuta-1,3-diene 1 bearing the thiazol-2-yl ring at C-2 and the D-galacto-pentopyranosid-5-yl ring at C-4 reacts with ethyl vinyl ether 2 in an endo-specific hetero-Diels–Alder process to give a mixture of diastereoisomeric 3,4-dihydro-2H-pyran derivatives 3 and 4 in 4 : 1 ratio and 97% overall yield; these compounds are transformed by thiazole-to-formyl unmasking and hydroxylation into stereoisomeric C-3–C-5 linked dipyranosides 7 and 8.