Purine studies. Part VIII. Formation of alkylthiopurines from 4,5-di-aminopyrimidine- or purine-thiones by means of orthoester–anhydride mixtures

Abstract

Treatment of 4,5-diaminopyrimidine-2-thione (1) with freshly prepared triethyl orthopropionate–propionic anhydride gives not only the expected 8-ethylpurine-2-thione (2; R = Et) but also 8-ethyl-2-ethylthiopurine (3; R¹= SEt. R²= Et). In the latter, the S- and 8-substituents are derived respectively from the alcoholic and acyl portions of the orthoester. The ratio of products depends on conditions. The same mixed reagents also cause S-ethylation of preformed purine-2(or 8)-thiones. Similar treatment of 2-thiouracil gives a separable mixture of its S- and N(1)-ethyl derivatives; 4-thiouracil yields the S- and N(3)-ethyl isomers.