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 a nd simultaneous migration of the double bond to 1,2-position in the sugar m oiety was achieved by stirring in sodium ethoxide. Tosylation with one equi valent of tosyl chloride afforded 4. Nucleophile displacement of the tosyla te of 4 with nucleobase in the presence of NaH/DMF followed by deprotection gave the desired 1,2-unsaturated pyranosylphosphonates 7a-c.