Zeolite-catalyzed Helferich-type glycosylation of long-chain alcohols. Synthesis of acetylated alkyl 1,2- trans glycopyranosides and alkyl 1,2- cis C2-hydroxy-glycopyranosides

Zeolite-catalyzed glycosylation of long-chain alcohols, using the inexpensive and readily available peracetylated β- d-gluco- and galactopyranoses as glycosyl donors under solvent free conditions, has been explored for the first time. Among the various forms (H-, Na-, Fe- and Zn) of β zeolite examined as catalysts in the reaction of 1,2,3,4,6-penta- O-acetyl-β- d-galactopyranose with cetyl alcohol, Fe-β zeolite gave the maximum yield of 63% of cetyl 2,3,4,6-tetra- O-acetyl-β- d-galactopyranoside and cetyl 3,4,6-tri- O-acetyl-α- d-galactopyranoside. Fe-β Zeolite-catalyzed glycosylation was found to be general affording the title compounds in each case in a moderate yield, but with a good stereoselectivity. The yield of synthetically valuable acetylated long-chain alkyl 1,2- cis C2-hydroxy-glycopyranosides obtained in the present single-step procedure is considerably higher than that of the previously reported multi-step method employing the Stork silicon tether approach.