Synthesis of 2',3'-dideoxy-2'-trifluoromethylnucleosides from alpha-trifluoromethyl-alpha,beta-unsaturated ester.

The treatment of alpha-bromo-alpha,beta-unsaturated esters 2 with FSO(2)CF(2)CO(2)Me and CuI in DMF/HMPA constitutes a new synthetic scheme for the preparation of alpha-trifluoromethyl-alpha, beta-unsaturated esters 3. The trifluoromethylation of (Z)/(E)-ethyl 3-[(S)-2,2-dimethyl-1,3-dioxolan-4-yl]-2-bromo-2-propenoate (2e), which is derived from 1-(R)-glyceraldehyde acetonide, yields the key intermediate alpha-trifluoromethyl-alpha,beta-unsaturated esters 3e. This is transformed into anomeric acetates 8a and 8b and is used for the synthesis of a number of 2', 3'-dideoxy-2'-trifluoromethylnucleosides.