A new and efficient route to the synthesis of pyrazole and pyrimidine C-nucleoside derivatives

A new route to the synthesis of pyrazole and pyrimidine C-nucleosides, involving as the key step a metal catalysed reaction of beta-D-ribofuranosyl ketoesters with alkyl cyanoformates, is described. 2,3,5-Tri-O-benzoyl-beta-D-ribofuranosyl cyanide (1) reacts with alpha-bromoesters, in the presence of zinc dust, to give beta-D-ribofuranosyl-enaminoesters 2 which are easily hydrolised to beta-ketoesters 3. The reactions of compounds 3 with alkyl cyanoformates, in the presence of catalytic amounts of [Cu(acac)(2)], afford C-glycosyl enaminoketosters 4. These compounds react with benzylhydrazine and acetamidine to give pyrazole and pyrimidine C-nucleosides 5 and 6 respectively. (C) 1998 Elsevier Science Ltd. All rights reserved.