Synthesis of 1,2-unsaturated pyranosylphosphonate nucleosides from 3,4,6-tri-O-acetyl-D-glycal.

Ferrier rearrangement of 3,4,6-tri-O-acetyl-D-glucal (1) in the presence of triethylphosphite afforded the 2,3-unsaturated pyranose 2. Deacetylation and simultaneous migration of the double bond to 1,2-position in the sugar moiety was achieved by stirring in sodium ethoxide. Tosylation with one equivalent of tosyl chloride afforded 4. Nucleophile displacement of the tosylate of 4 with nucleobase in the presence of NaH/DMF followed by deprotection gave the desired 1,2-unsaturated pyranosylphosphonates 7a-c.