Synthesis of 3‐Acyl‐5,6‐dihydro‐2‐phenylthieno(‐furo‐)[2,3‐ d ]pyrimidin‐4(3 H )‐ones

The reactions of 2‐benzamido‐4,5‐dihydro‐3‐thiophene(‐3‐furan‐)carbonitriles 1a–c (and 11a–c ) with acetic (or propionic) anhydride in the presence of tin(IV) chloride give the corresponding 3‐acetyl‐5,6‐dihydro‐2‐phenylthieno(‐furo‐)‐[2,3‐ d ]pyrimidin‐4(3 H )‐ones 2a–c (and 12a–c ) or 5,6‐dihydro‐2‐phenyl‐3‐propionylthieno(‐furo‐)[2,3‐ d ]pyrimidin‐4(3 H )‐ones 3a–c (and 13a–c ). Hydrolysis of compounds 2a–c (and 12a–c ) or 3a–c (and 13a–c ) leads to the corresponding N ‐acetyl‐2‐benzamido‐4,5‐dihydro‐3‐thiophene‐(‐3‐furan‐)carboxamides 4a–c (and 14a–c ) or 2‐benzamido‐4,5‐dihydro‐ N ‐propionyl‐3‐thiophene‐(‐3‐furan‐)carboxamides 5a–c (and 15a–c ). The reaction of compounds 4a, b (or 14a, b ) with acid anhydrides in the presence of potassium carbonate or triethylamine gives the corresponding 3‐acyl‐2‐benzamido‐4,5‐dihydrothiophenes (or furans) 9, 10, 16 , and 17 .