Attempted routes to benzazetes
Abstract
Vapour phase pyrolysis of the N-indazol-2-yl-SS-dimethylsulphoximides (21; R = H or Me) and of 3-methylindazol-2-ylimino(triphenyl)phosphorane (22) gave cis,cis-hepta- and octa-2,4-dien-6-ynenitriles; these could not be induced to isomerise to benzazetes. Pyrolysis of 1,2,3-benzotriazines above 450° resulted in fragmentation of the triazine ring to give benzyne, which dimerised to give biphenylene in good yield. 6-Methylpyrido[3,2-d][1,2,3]triazine however gave 6-methylpyridine-2-carbonitrile rather than the diazabiphenylenes. 1,2,4-Benzotriazines also gave benzyne but only at temperatures above 800° quinazoline, phthalazine, 2,3-diphenylquinoxaline, and 2-methyl-3,1-benzoxazin-4-one were unchanged at this temperature.