A one‐step synthesis of 2‐methylthio‐6‐oxopyrimidine derivatives: Preparation of fused pyrimidinones

Condensation of a ternary mixture of ethyl cyanoacetate, S‐methylisothiourea and aromatic aldehydes in pyridine afforded directly the 4‐aryl‐5‐cyano‐2‐methylthio‐6‐oxopyrimidines IV in good yields. Alkylation of IV with alkyl halides in alkaline medium yielded the 1‐alkyl derivatives V. The methylthio group in IV and V could be eliminated by aniline, hydrazine and phenylhydrazine and the corresponding 2‐anilino, VII, 2‐hydr‐azino, VIIIa,b, and 2‐phenylhydrazino, VIIIc,d, derivatives were obtained. Compounds VIIIa,b could be cyclised with nitrous acid to give the 3‐cyano‐4‐phenyltetrazolo[1,5‐a]pyrimidine‐2‐one (Xa) and the 1‐methyl analogue Xb, respectively. Some derivatives of VIII were prepared to help in elucidating the structures.