Synthesis of novel L-2',3'-dideoxy-2'-trifluoromethyl-4'- thiocytidines from alpha-trifluoromethyl-alpha,beta-unsaturated ester

A short and efficient synthesis of L-2',3'-dideoxy-2'-trifluoromethyl-4'-thiocytidines is described. (2R,4S/2S,4S)-5-(tert-Butyldimethylsiloxy)-2-trifluoromethylpentan-4-olide (3a and 3b) are prepared from alpha-trifluoromethyl-alpha,beta-unsaturated ester (1) in three steps and converted to compounds 6a and 6b. The corresponding 1-O-acetyl derivatives 8a and 8b were obtained via the usual Pummerer rearrangement from 6a and 6b in two steps, which were in turn used to synthesize L-4'-thiocytidines 10a and 10b.