Hafnium(IV) tetratriflate in selective reductive carbohydrate benzylidene acetal opening reaction and direct silylation reaction

Hafnium(IV) tetratriflate was shown to be an effective catalyst for the regioselective reductive benzylidene ring opening with concurrent silylation reaction. The synthetic conditions were optimized, and the scope and limitations were identified. In addition to glucose and glycosamine derivatives, mannose and galactose were successfully employed as substrates. Various protecting groups such as acetyl, allyl, and benzyl were found to be stable under the reaction conditions. By using a deuterated reducing reagent, the reaction was deduced to proceed via an S_N1 mechanism.