New functionalization at the 5-position of uracils by selenenylation^†

Electrophilic substitution of phenylselenenyl chloride at the 5-position of uracils in the presence of silver reagents, such as Ag₂O, AgBF₄, or CF₃CO₂Ag, afforded the corresponding 5-phenylselenenyluracils in excellent yields. 1,3-Dimethyl-5-phenylselenenyluracil(2a), 5-phenylselenenyl-(2′,3′,5′-tri-O-acetyl)uridine(2b), 5-phenylselenoxyl-1,3-dimethyluracil(3a) and 5-phenylselenoxyl-(2′,3′,5′-tri-O-acetyl)uridine(3b) were used for various transformations at C-5 or C-6 of pyrimidine bases via nucleophilic substitution, a free radical process, and a Michael-type addition utilizing the unique properties of organo-seleno groups located on C-5 of pyrimidine bases.