Thieno[2,3‐d]pyrimidines. I. A new method for the preparation of esters and amides of thieno[2,3‐<i>d</i>] pyrimidine‐6‐carboxylic acids

Abstract

Abstract A novel method for the preparation of esters and amides of thieno[2,3‐ d ]pyrimidine‐6‐carb‐oxylic acids was described. A typical example was the direct formation of ethyl 5‐amino‐2‐methylthiothieno[2,3‐ d ]pyrimidine‐6‐earboxylate(IIIa) from 4‐chloro‐2‐methylthio‐5‐pyrimidine‐carbonitrile (Ia) and ethyl mercaptoacetate in refluxing ethanol containing sodium carbonate. Displacement of the methylthio group in IIIa by various amines gave the corresponding amino derivatives. The reactions of IIIa and related compounds with acetylating agents such as acetic anhydride or chloroacetyl chloride gave various products. Treatment of 5‐carbethoxy‐4‐chloro‐2‐phenylpyrimidine(IV) with methyl mercaptoacetate afforded the dechloro intermediate diester Va, which cyclized on reaction with sodium ethoxide to form methyl 5‐hydroxy‐2‐phenylthieno‐[2,3‐ d ]pyrimidine‐6‐carboxylate (Vla). The synthesis was expanded to include the preparation of various new 2,4,5‐trisubstituted thieno[2,3‐ d ]pyrimidine‐6‐carboxylic acid esters and amides (Charts I‐V).