Regio- and chemoselective reductive cleavage of 4,6-O-benzylidene-type acetals of hexopyranosides using BH3·THF–TMSOTf

Benzylidene-type cyclic acetals of carbohydrates undergo efficient reductive ring opening using BH3·THF and a catalytic amount of TMSOTf at room temperature. 4,6-O-Benzylidene-hexopyranosides afford the corresponding 4-O-benzyl ethers exclusively, in high yields. Other benzylidene-type acetals, such as naphthylmethylene and 4-methoxybenzylidene acetals are also cleaved with the same reagent. The conversions are highly regio- and stereoselective and afford benzyl-type ethers in excellent yields.