Chemo-, stereo- and regioselective hydrogenolysis of carbohydrate benzylidene acetals. Synthesis of benzyl ethers of benzyl α-d-, methyl β-D-mannopyranosides and benzyl α-D-rhamnopyranoside by ring cleavage of benzylidene derivatives with the LiAlH4-AlCl3 reagent
Treatment of benzyl α-(1) and methyl β-d-mannopyranoside (2) with α,α-dimethoxytoluene gave the exo and endo isomers (3,5 and 4,6) of the dibenzylidene derivatives of 1 and 2. Hydrogenolysis of the exo isomers (3 and 5) with a molar equivalent of AlH2Cl gave the 3-0-benzyl-4,6-0-benzylidene derivatives (7 and 21), whereas the endo isomers (4 and 6) gave the 2-0-benzyl-4,6-0-benzylidene compounds (8