Factors which influence the formation of oxadiazoles from anthranilhydrazides and other benzoylhydrazines

The cyclization of o ‐aminobenzoylhydrazine ( 1a ) and its 5‐methyl derivative 1b with four equivalents and with one equivalent of triethyl orthoacetate (TEOA) was studied. 3‐Amino‐2‐methyl‐4(3 H )‐quinazolinone ( 2a ), 3,4‐dihydro‐2‐methyl‐5 H ‐1,3,4‐benzotriazepin‐5‐one ( 3a ) and an imino ether derivative of 2a , N ‐[2‐methyl‐4‐oxo‐3(4 H )quinazolinyl]ethanimidic acid ethyl ester ( 4a ) were obtained from the reaction of 1a with four equivalents of TEOA. These results were compared with those of Merour [1] who isolated 2a and 3a using the same conditions. When 1a was treated with one equivalent of TEOA, 2a, 3a , and a new product, 2‐(5‐methyl‐1,3,4‐oxadiazol‐2‐yl)benzenamine ( 5a ) were produced, and 4a was not. Similar results were obtained with the reactions of 1b with TEOA. Authentic samples of oxadiazoles 5a and b were prepared by alternate routes. Novel acid‐catalyzed rearrangements of benzotriazepinones 3a and b , to mixtures of aminoquinazolinones 2a and b and oxadiazoles 5a and b , respectively, were found. The different relative amounts of aminoquinazolinones 2 and oxadiazoles 5 which were produced from these rearrangements allowed us to choose between two potential mechanisms for these interesting rearrangements. Treatment of 5‐nitrobenzoylhydrazine ( 37 ) with four equivalents of TEOA gave three products which were characterized, but did not lead to benzotriazepinone formation.