Novelp-Toluenesulfonylation and Thionocarbonylation of Unprotected Thymine Nucleosides

Abstract

A new procedure involving the use of both dibutyltin oxide and a quaternary ammonium salt along with p-toluenesulfonyl chloride or phenoxythiocarbonyl chloride leads in good yields to the desired monotosylate or to the 2′,3′-O -cyclic thiocarbonate of thymine nucleosides without prior modification of any hydroxyl group. It is noteworthy that with 5-methyl uridine, tosylation occurs regioselectively at the 2′- position, while the 3′-O-tosylate is formed when 5-methyl uridine is substituted on 1′ by a methyl (or cyano) group.