C-Nucleoside studies. Part XI. Cine-substitution in 1,4-dinitropyrazoles; application to the synthesis of formycin via nitropyrazole derivatives

Abstract
Reaction of 1,4-dinitro-3-methylpyrazole with a variety of nucleophiles led to the formation of 5-substituted 3-methyl-4-nitropyrazoles 11–15 by a process of cine-substitution. This reaction has been applied as the key step in a novel synthesis of formycin. Treatment of 1,4-dinitro-3-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)pyrazole (17) with cyanide ion produced 3(5)-cyano-4-nitro-5(3)-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)pyrazole (19) in 89% yield. Catalytic reduction to the 4-amino compound 20 (84%), and subsequent reaction with formamidine acetate yielded formycin triacetate 21 (79%). Methanolysis of 21 produced formycin (1) in 90% yield.