An approach to the synthesis of branched-chain amino sugars from C-methylene sugars

The reaction of 1,2:5,6-di-O-isopropylidene-3-C-methylene-alpha-D-ribo-hexofuranose (4) with mercuric azide in hot 50% aqueous tetrahydrofuran yielded, after reductive demercuration, 3-azido-3-deoxy-1,2:5,6-di-O-isopropylidene-3-C-methyl-alpha-D-glucofuranose (5). Partial, acid hydrolysis of 5 afforded the diol 7, which gave 3-azido-3-deoxy-1,2-O-isopropylidene-5,6-di-O-methanesulphonyl-3-C-methyl-alpha-D-glucofuranose (8) on sulphonylation. On hydrogenation over a platinum catalyst and N-acetylation, the dimethanesulphonate 8 furnished 3,6-acetyleprimino-3,6-dideoxy-1,2-O-isopropylidene-5-O-methanesulphonyl-3-C-methyl-alpha-D-glucofuranose (9), which was also prepared by an analogous sequence of reactions on 3-azido-3-deoxy-1,2-O-isopropylidene-5-O-methanesulphonyl-3-C-methyl-6-O-toluene-p-sulphonyl-alpha-D-glucofuranose (13). The formation of the N-acetylepimine 9 establishes the D-gluco configuration for 5. 1,2-O-Isopropylidene-3-C-methylene-alpha-D-ribo-hexofuranose (20) reacted with mercuric azide in aqueous tetrahydrofuran at approximately 85 degrees to give 3,6-anhydro-1,2-O-isopropylidene-3-C-methyl-alpha-D-glucofuranose (22) as a result of intramolecular participation by the C-6 hydroxyl group in the initial intermediate.