Methylation of Thiouracils and Thioxanthines with Trimethyl Phosphate

Abstract

Preparation of alkyl derivatives of thiouracils and thioxanthines has been carried out by ring cyclization¹ and sulfurization of alkyl derivatives of uracil and xanthines with phosphorus pentasulfide.^2–4 However, direct alkylation of thiouracils and thioxanthines has been described by a limited number of papers using dimethyl sulfate,^5,6 methyl iodide,^7,8 etc. Previously we reported that trimethyl phosphate (TMP) was useful for N-methylation of various azaaromatics.⁹ In view of the recent biological interest on methyl derivatives of natural products,¹⁰ we wish to communicate here the reactions of thiouracils and thioxanthines with TMP.