C-nucleoside studies. Part 12. Synthesis of 3-α- and 3-β-(D-xylofuranosyl)pyrazoles

3-(2,3:4,5-Di-O-isopropylidene-D-gulo-pentahydroxypentyl)pyrazole (13) was prepared in four steps (45% overall yield) from D-gulonolactone (9). Treatment with 1-fluoro-2,4-dinitrobenzene and triethylamine followed by reaction with methanesulphonyl chloride in pyridine afforded 1-(2,4-dinitrophenyl)-3-(1-O- methylsulphonyl-2,3:4,5-di-O-isopropylidene-D-gulo-pentahydroxypentyl)pyrazole (15) which, on treatment with boron trichloride and subsequent methanolysis, followed by exposure to methanolic ammonia, yielded 3-(a-D-xylofuranosyl) pyrazole (5). Oxidation of the pyrazole (13) and subsequent hydride reduction afforded, stereoselectively, 3-(2,3:4,5-di-O-isopropylidene-D-ido- pentahydroxypentyl)pyrazole(18); treatment of this in the same manner as the pyrazole (13) yielded 3-(ß-D-xylofuranosyl)pyrazole (7). The reactions of sodium benzoate in dimethylformamide with 1-methylsulphonyl-3-(1-O- methylsulphonyl-2,3:4,5-di-O-isopropylidene-D-gulo-pentahydroxypentyl)pyrazole (24) and with its D-ido-isomer (27) appear to involve a common fulvene-type intermediate (30).