Palladium(II) catalyzed transfer vinylation reactions of monosaccharides
A novel approach for the conversion of a sugar hydroxyl function to a vinyl ether was developed using a palladium(II) catalyzed transfer vinylation reaction. Optimum reaction conditions were established on the model systems ethylene glycol and cyclohexanol with ethyl and butyl ether as the vinyl source. Applied to a polyhydroxyl compound, e.g. levoglucosan, the reaction gives a mixture of all seven possible vinylated products (mono-, di-, and pervinylated levoglucosan) in a 78% overall yield, i.e. the catalyst does not induce any regioselectivity. When applied to protected sugars containing a single free hydroxyl function, the reaction vinylates primary, secondary and anomeric hydroxyls in moderate to good yields (36%-79%). The potential use of vinyl glycosides as glycosyl donors was demonstrated through a glycosylation reaction between vinyl 2,3,4,6-tetra-'O'-benzyl-[alpha]- D-glucopyranoside and methyl 2,3,6-'tri'-[alpha]- D-glucopyranoside.