2'3'-Carbonates in the synthesis of uridine 5'-deoxy and 2',5'-dideoxy derivatives

Detritylation of 2',3'-O-carbonyl-5'-O-trityluridine (Ia) with ethereal hydrogen chloride affords 2',3'-O-carbonyluridine (Ib; 83%) which is converted by mesylation to the 5'-mesylcarbonate Ic (75%). Reaction of compound, Ic with tetrabutylammonium bromide in DMF affords the 5'-bromo carbonate Id (77%) which is reduced with tributyltin hydride to the 5'-deoxyuridine 2',3'-cyclic carbonate Ie (70%). When heated with imidazole, compound Ie affords the 2,2'-anhydro derivative IIa (76%) which is converted to the 2'-chloro derivative IIIa (88%) on heating with HC1/DMF. The tributyltin hydride reduction of compound IIIa gives 2',5'-dideoxyuridine (IIIb; 68%). When heated with NaHCO3 in DMF, the 5'-bromo carbonate Id affords the anhydro bromo derivative IIb (50%) which is converted to the 2',5'-dichloro derivative IIIc (86%) on heating with HC1/DMF. The tributyltin hydride reduction of compound IIIc affords the 2',5'-dideoxy derivative IIIb (59%). Alkaline hydrolysis of the 2,2'-anhydro derivative IIa affords the arabinosyl derivative IVa which is converted to the diacetyl derivative IVb (34%) by acetylation. When refluxed in water, the 2',3'-cyclic carbonates Ib, Id, and Ie are hydrolysed to the parent nucleosides, namely, uridine (Va; 81%), 5'-bromo-5'-deoxyuridine (Vb; 78%), and 5'-deoxyuridine (Vc; 83%). Hydrolysis of carbonates Ib and Ie is accompanied by the formation of the 2,2'-anhydro derivatives IIc (10%) and IIa (5%) as by-products.