A convenient method for the synthesis of 2',3'-didehydro-2',3'-dideoxy nucleosides

9-(2,3-Dideoxy-β-D-glyceropent-2-enofuranosyl)adenine (2',3'-didehydro- 2',3'-dideoxyadenosine, 9a), 9-(2,3-dideoxy-β-D-glyceropent- 2-enofuranosyl)hypoxanthine (2',3'-didehydro-2',3'-dideoxyinosine, 9b) and 4-amino-7-(2,3-dideoxy-β-D-glyceropent-2-enofuranosyl) pyrrolo[2,3-d]pyrimidine (2',3'-didehydro-2',3'-dideoxy-tubercidin, 9c) were prepared via a free radical -elimination of bromo and phenoxy(thiocarbonyl) leaving groups from appropriate 5'-O-(2-acetoxyisobutyryl)-2'(3')-phenoxy(thoiocarbonyl)-3'(2')-bromo derivatives of adenosine, inosine and tubercidin with tributyltin hydride and subsequent deprotection of the resulting 5'-O-(2-acetoxyisobutyryl)-2',3'-didehydro-2',3'-didesoxy nucleosides