Synthesis of 4-(4,6-di-0-benzyl-2,3-dideoxy-β-D-erythro-hex-2-enopyranosyl)pyrazoles from 3,4,6-tri-O-acetyl-D-glucal

3-(4,6-Di-O-benzyl-2,3-dideoxy-beta-D-erythro-hex-2-enopyranosyl)-2,4-pentanedione and its analogue 2-(4,6-di-O-benzyl-2,3-dideoxy-beta-D-erythro-hex-2-enopyranosyl)-1-phenyl-1,3-butanedione, prepared from 3,4,6-tri-O-acetyl-1,5-anhydro-2-deoxy-D-arabino-hex-1-enitol (3,4,6-tri-O-acetyl-D-glucal), reacted with hydrazine and its methyl-, phenyl-, p-tolyl, and p-methoxyphenyl-derivatives in ethanol, at room temperature, to afford, in 71-96% yields, a series of 4-(4,6-di-O-benzyl-2,3-dideoxy-beta-D-erythro-hex-2-enopyranosyl)-3-methylpyrazoles having the N-1 free or substituted by the foregoing groups, and the C-5 substituted by a methyl or phenyl group. The reactions of the 1-phenyl-1,3-butanedione derivative were highly regioselective. Catalytic hydrogenation of some of these novel compounds gave the respective 4',6'-di-O-deprotected-2',3'-saturated compounds in 51-67% yields. The acetolysis/methanolysis of one of the title compounds led to the formation of the 4',6'-di-O-debenzylated 2',3'-unsaturated pyrazole C-nucleoside in poor yield. (C) 1998 Elsevier Science Ltd. All rights reserved.