Pyrolysis of 2-(2-azidobenzoyl)pyridine and 3-(2-Pyridyl)-2,1- benzisixazoles. Prepration and chemistry of some pyrido[1,2-b]cinnolin-6-ium hydroxide inner salts

The pyrolysis of 3-(2-pyridyl)-2,1-benzisoxazoles 5A, 5B, and 5C (A : unsubstituted; B : 5-bromo; C : 5,7-dibromo) at about 215° afforded 5,11-dihydro-11-oxopyrido 1,2-b] cinnolin-6-ium hydroxide inner salt 6A , the 2-bromo ( 6B ) and the 2,4-dibromo ( 6C ) compounds respectively in high yields. X-ray crystallographic analysis of 6B unambiguously confirmed the structure. The benzisoxazoles 5A-5C were obtained from the pyrolysis of the corresponding 2-(2-azidobenzoyl) pyridines 2A-2C at about 112°. While 2A and 2B afforded the corresponding benzisoxazoles 5a and 5B in 82% and 51% yields respectively, 2-(2-azido-3,5-dibromobenzoyl)pyridine ( 2C ) afforded a mixture of the benzisoxazole 5C and the tricyclic compound 6C , isolated 43% and 41% yields respectively. The properties of the novel mesoionic compounds of type 6 , their oxidative and reductive ring cleavage products together with alkylation and catalytic hydrogenation products are described. Electrophilic substitutions, substitutions in position 11 via the 11-thiones 11 and other miscellaneous trans of 6 are also presented.