SYNTHESIS OF 3'-AZIDO, 2',3'-DIDEHYDRO, AND 3',4'-DIDEHYDRO NUCLEOSIDES FROM 5-ALKOXYMETHYLURACILS

Reaction of methyl 5-tert-butyldiphenylsilyl-2, 3-dideoxy-3-iodo-D-thr eo-pentofuranoside (3) with silylated 5-alkoxymethyluracils 2a-c using trimethylsilyl trifluoromethanesulfonate as a catalyst afforded the a lpha nucleosides 4a-c and the beta nucleosides 5a-c. The corresponding 3',4'-and 4',5'-didehydro nucleosides 6-9 were prepared in an elimina tion reaction by treating the iodo nucleosides 4a-c or 5a-c with 10 eq uivalents of sodium methoxide in methanol under reflux. The deprotecte d 3'-azido nucleosides 10a-e and 11a-c of the AZT type as well as the 4',5'-didehydro nucleosides 7a-c and 9a-c were prepared by treating 4a -c and 5a-c, respectively, with sodium azide and subsequently with tet rabutylammonium fluoride.