Treatment of the 1H-1, 2-thienodiazepine (1) and the 1H-1, 2-benzodiazepines (7) having an electron-donating substituent in the 7-position with ethyl chloroformate, acetyl chloride, or benzoyl chloride in benzene results in ring-conversion to give the corresponding 1, 3- diazepines (3) and (12).