Sydnone Ribosides as a Platform for the Synthesis of Pyrazole <i>C</i>-Nucleosides: A Unified Synthesis of Formycin B and Pyrazofurin

Abstract

The <i>C</i>-nucleoside natural products formycin B and pyrazofurin were synthesized in seven steps employing a sydnone riboside as common intermediate. Sydnone ribosides were synthesized via a direct Lewis acid catalyzed dehydrative glycosylation reaction. We demonstrated that these can be used for the diversity-oriented synthesis of pyrazole <i>C</i>-nucleoside analogues via thermal 1,3-dipolar cycloaddition reactions with various alkynes, giving access to the pyrazole <i>C</i>-nucleoside natural products, as well as opening new avenues for exploring nucleoside chemical space.