High-yield regioselective thiation of biologically important pyrimidinones, dihydropyrimidinones and their ribo, 2’-deoxyribo and 2‘, 3’-dideoxyribo nucleosides.

Convenient and high-yield regioselective thiation procedures based on the use of the Lawesson reagent in different solvents, are described for conversion of the 2- and 4-keto, and 2, 4-diketo pyrimidines to the corresponding 2(4)-thio, and 2, 4-dithio, derivatives. This method is applicable to thiation of the 4-keto groups of 5, 6-dihydropyrimidinones and pyrimidine nucleosides. The mild reaction conditions employed are such that it is the method of choice for compounds with labile glycosidic bonds, such as 5, 6-dihydropyrimidine nucleosides and the 2‘, 3’-dideoxynucleosides currently of interest as antiretroviral, including anti-HIV, agents.