Synthesis of a (2,3-dideoxyglyc-2-enopyranosyl)thymine and a (2,3-dideoxyglycopyranosyl)thymine via a 2,2′-anhydro-nucleoside

Abstract

2,2′-Anhydro-1-(4,6-O-benzylidene-3-O-methylsulphonyl-β-D-mannopyranosyl)thymine (5), prepared quantitatively from the 2′,3′-bismethanesulphonate (3), was converted into the corresponding unsaturated nucleoside (8) in 56% yield by the action of sodium iodide in boiling NN-dimethylformamide. Debenzylidenation of (8) with acid gave a free unsaturated nucleoside (12) in 91% yield. Reduction of (12) over palladium–carbon gave the (2,3-dideoxyhexopyranosyl)thymine (14). A mechanism for the formation of unsaturated nucleoside is described.