PLASH VACUUM PYROLYSIS OF 1,5-BENZODIAZEPINES

Gas-phase pyrolysis of the 2,4-diphenyl- and 2,4-dimethyl-1,5-benzodia zepines 3 and 4 at 800-850 degrees C gave a range of heterocyclic prod ucts (e.g. quinoxalines 8, 10 and 11, indole 9, benzimidazole 5 and py razole 7) in low yields. The formation of most products is initiated b y cleavage of the 2,3-bond to give a diradical intermediate, though th e pyrazole is obtained by a mechanism involving a 1,5-hydrogen shift f ollowed by an unusual ring contraction. (C) 1998 Elsevier Science Ltd. All rights reserved.