Synthesis of 4-(4,6-di-O-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-β-d-erythro-hex-2-enopyranosyl)-2,4-pentanedione and its analogue 2-(4,6-di-O-benzyl-2,3-dideoxy-β-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-β-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.