STEREOCHEMICALLY CONTROLLED DECOMPOSITION OF SILVER-CATIONIZED METHYLGLYCOSIDES

Silver ion adducts of several methyl glycopyranosides were generated b y fast atom bombardment of 1 : 1 mixtures of the glycosides with silve r nitrate. The unimolecular decompositions of [M + Ag]+ ions showed dr amatic differences related to the relative positions of both the hydro xyl group on C(2) and the anomeric methoxyl group. When these groups w ere in the cis position, methanol was exclusively expelled. When they were in the trans position, silver hydride was preferentially lost. Th e stereoselective elimination reaction is proposed to proceed through a five-membered silver-containing intermediate complex. from the oxyge n on C(2) to the anomeric substituent (methoxyl group or hydrogen atom ).