Regioselective reductive ring-opening of 4-methoxybenzylidene acetals of hexopyranosides. Access to a novel protecting-group strategy. Part 1

Reduction of fully protected 4,6-O-(4-methoxybenzylidene) hexopyranosides with sodium cyanoboro-hydride–trifluoroacetic acid in NN′-dimethylformamide, or trimethylsilyl chloride in acetonitrile, gives the 6- and 4-O-(4-methoxybenzyl) ethers, respectively, in good yield and good regioselectivity. The 4-methoxybenzyl ether linkage in products containing benzyl ethers or other protective groups is selectively cleaved upon treatment with cerium(IV) ammonium nitrate in aqueous acetonitrile.