Studies on diazepines. XVII. Synthesis of monocyclic 1,3-diazepines. (2). Substituent effects on the thermal ring-conversion of 1,2-diazepines into 1,3-diazepines.

Abstract

The thermolysis of 1, 2-diazepines (7a-f and 11) having an electron-donating substituent in the 4- or 6-position resulted in the formation of the 1, 3-diazepines (9 and 12) and 2-aminopyridines (10), whereas 1, 2-diazepines (7g-k) having an electron-withdrawing substituent in the same position gave only 2-aminopyridines (10) and no 1, 3-diazepines. However, the thermolysis of 3-, 5-, or 7-substituted 1, 2-diazepines with either an electron-donating or-withdrawing substituent did not give 1, 3-diazepines. Heating of the bicyclic compounds (8) also gave the corresponding 1, 3-diazepines. Based on these results, we concluded that the presence of an electron-donating substituent is essential for this ring-conversion of 1, 2-diazepines into 1, 3-diazepines. These substituent effects and the reaction mechanism are discussed.