Alkoxyl Migration in Displacement of a 5-Trifluoromethanesulfonyloxy Group from Ribofuranosides

Article abstract of DOI:10.1021/jo00343a008

Methyl 2,3-O-isopropylidene-5-O-triflyl-β-D-ribofuranoside (2) reacts at room temperature with primary aralkanols such as benzyl alcohol and the steroid alcohols 3a,b in dichloromethane and in the presence of sodium sulfate to give the corresponding aralkyl 2,3-O-isopropylidene-5-O-methyl-β-D-ribofuranosides 5a,b and 11 in 40-45percent yields.Migration of the methoxyl group from C-1 to C-5, via a tricyclic oxonium ion (7a), is suggested as the basis of formation of the new β-glycoside.Anchimeric assistance by a benzyloxy group in the displacement of the sulfonate is observed in the reaction of benzyl 2,3-O-isopropylidene-5-O-triflyl-β-D-ribofuranoside (14) with methanol, which affords methyl 5-O-benzyl-2,3-O-isopropylidene-β-D-ribofuranoside (15) in 40percent yield on treatment with Na2SO4 in CH2Cl2.The elements of anomeric control in these facile transformations remain to be elaborated.