Synthesis of 4-(2-hydroxyphenyl)-1-phenyl-1,2,4-triazolidine-3,5-dione derivatives through cyclic transformations of 3-(2-phenylcarbazoyl)-2(3H)-benzoxazolone derivatives

Four 3-(3-benzylidene-2-phenylcarbazoyl)-2(3H)-benzoxazolone derivatives 3 have been synthesized from benzoxazolone derivatives 1 and benzaldehyde N-chloroformylphenylhydrazone 2. By acid hydrolysis, these compounds yielded 3-(2-phenylcarbazoyl)-2(3H)benzoxazolone derivatives 4 which were not isolated and were transformed via an intramolecular reaction into 4-(2-hydroxyphenyl)-1-phenyl-1,2,4-triazolidine-3,5-dione derivatives 5 in a good yield. Attempts to cyclize these compounds by intramolecular elimination of water into tricyclic compounds 6 with various dehydrating agents were unsuccessful.