Synthesis of 2′,3′ - Dideoxy-2′-difluoromethyl Azanucleosides

Methyl (2S,4S)-N-tert-butoxycarbonyl-4-difluoromethylpyroglutamate (9a) was synthesized from trans-4-hydroxy-l-proline (5). Compound 9a was converted to (5S,3S)-N-benzyloxycarbonyl-5-(tert-butyldimethylsilyloxymethyl-3-difluoromethyl-2-pyrrolidone (15) over 4 steps in 66% yield, which was used as a key intermediate for the synthesis of 2′,3′-dideoxy-2′-difluoromethyl azanucleosides