Sydnone Ribosides as a Platform for the Synthesis of Pyrazole -Nucleosides: A Unified Synthesis of Formycin B and Pyrazofurin.

The -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 -nucleoside analogues via thermal 1,3-dipolar cycloaddition reactions with various alkynes, giving access to the pyrazole -nucleoside natural products, as well as opening new avenues for exploring nucleoside chemical space.