SYNTHESIS AND PHOTOLYSIS OF PROTECTED D-HEX-2-ULOPYRANOSYL AZIDES

Treatment of ,2:4,5-di-O-methylethylidene-beta-D-fructopyranose with t rimethylsilyl azide in the presence of trimethylsilyl triflate in dry acetonitrile led, after neutralization and desilylation, to an anomeri c mixture of -O-methyl-4,5-O-methylethylidene-D-fructopyranosyl azides in 94 % yield (alpha/beta similar to 1/10). Likewise, ,5-O-methylethy lidene-D-erythro-hex-2-ulopyranosyl azides were prepared from methylet hylidene-beta-D-erythro-hex-2-ulopyranose. The corresponding acetates and a mesylate were prepared in high yield under standard conditions. Photolysis of these azido sugars, in different solvents, led mainly to two labile, non-isolated imidates identified by NMR spectroscopy. For both alpha- and beta-azides, the preferred cleavage of the C-2-C-3 bo nd and migration of the C-3 carbon to the nitrene led to the major rin g-expanded photoproduct while migration of the C-1 carbon atom account ed for the structure of the minor N-substituted glycono-1,5-iminolacto nes formed. Migration of the ring oxygen atom was not observed, in kee ping with other observations from the photolysis of cyclic and acyclic azido ethers. Copyright (C) 1996 Elsevier Science Ltd