Acylation and Cyclodehydration of Benzofuran-, Benzothiophene-, and Indolyl-3-acetic Acid Arylamides. Synthesis of Novel Benzofuro[2,3-c]-, Benzothieno[2,3-c], and Indolo[2,3-c]pyrilium and Pyridine Derivatives

The acylation of benzo[b]furan-, benzo[b]thiophene, and indolyl-3-acetic acid arylamides using acetic anhydride in the presence of 70% perchloric acid occurs at the -position of the heterocycle to give 2-acetylbenzo[b]furan-, 2-acetylbenzo[b]thiophene, and 2-acetylindolyl-3-acetic acid arylamides. Depending on the amount of perchloric used in the reaction they undergo cyclodehydration to 3-arylamino-1-methylhetero[2,3-c]pyrilium salts and to N-aryl-1-methyl-3(2H)hetero[2,3-c]pyridones.