ENANTIOMERICALLY PURE ALPHA,BETA-UNSATURATED 5-MEMBERED-RING ALDEHYDES BY RING CONTRACTION OF EPOXYHEXOPYRANOSIDES

A series of epoxyhexopyranosides, variously substituted in the 6-posit ion, were each transformed by ring contraction into a single, enantiom erically pure, alpha,beta-unsaturated furanosidic aldehyde. Similar ri ng contraction of a C-propylglycosidic analog of one of the epoxyhexop yranosides gave a mixture of two diastereomeric aldehydes. This findin g supports the previously suggested mechanism of the reaction and indi cates that O-glycosidic epoxypyranosides also rearrange into two aldeh ydes, one of which is unstable.