Synthesis of enantiomerically pure 2 ',3 ',5 '-trideoxy-4 '-[(diethoxyphosphoryl)difluoromethyl]thymidine analogues

D- and L- (diethoxyphosphoryl) difluoromethyl nucleoside analogues 10 have been synthesized using the building block approach, starting from chiral fl uorinated molecules. The key steps of the synthetic sequence were condensat ion of 2-methyl-5-(4-methylphenylsulfinyl)pent-2-ene (1) and ethyl 2-(dieth oxyphosphoryl)-2,2-difluoroacetate (2), reduction of the thus formed ketone s 3 to alcohols 4, reductive removal of the sulfur moiety to give hydroxy p hosphonates 6, and oxidative cyclization to give furanose derivatives 8.