An improved procedurtx for the preparation of purinc4thiols by the reaction of 4, 5- diaminopyrirnidines with carbon disiilfide in N,,+ r-dimethylformamide is described. Application of this procedure to 4, 5-dianiinopyrimidines containing a group in the 6-position susceptible to nucleophilic attack resulted in intramolecular displacement of this group by the intermediate dithiocarbamate anions to give thiazolo [5, 4-d] pyrimidine-2-thiols. The ...