A new synthesis of α-L-fucose from D-glucose is described. The key intermediate is methyl 2, 3-di-O-acetyl-4, 6-O-benzylidene-α-D-altropyranoside (1), synthesized from methyl α-D-glucopyranoside by known procedures. Compound 1 was converted into methyl 2, 3-di-O-acetyl-4-O-benzoyl-6-bromo-6-deoxy-α-D-altropyranoside (2) by treatment with N-bromosuccinimide. Dehydrobromination of 2 afforded the 5, 6-unsaturated glycoside (4), which underwent reduction by hydrogen, mainly with inversion at C-5, to give methyl 2, 3-di-O-acetyl-4-O-benzoyl-6-deoxy-β-L-galactopyranoside (5) with a small amount of the isomeric methyl 2, 3-di-O-acetyl-4-O-benzoyl-6-deoxy-α-D-altropyranoside (3). The ratio of 3 to 5 was about 1 to 4. Deacylation of a mixture of 3 and 5 gave crystalline methyl β-L-fucopyranoside (6) and a syrupy methyl 6-deoxy-α-D-altropyranoside. Acidic hydrolysis of 6 afforded crystalline α-L-fucose in 19.3% yield from 1 via 5 steps.
