Some aspects of the chemistry of benzodiazoles.

When the mononitroindazoles were methylated under neutral conditions, by methyl iodide in dimethyl sulphoxide and by methyl toluene-p-sulphonate in nitrobenzene, 4-, 6- and 7-nitroindazole gave the 2-methyl isomer as the main product, whereas 5-nitroindazole formed mainly the 1-methyl isomer. Methylation of 4-nitroindazole under acidic conditions, using diazomethane in the presence of boron trifluoride etherate, gave equal amounts of the 1- and 2-methyl isomers; however 6-nitroindazole yielded only the 1-methyl isomer and 5-nitroindazole solely the 2-methyl isomer. The separation of the products was achieved mainly by column chromatography. The methylation of 6-hydroxyindazole by methyl iodide and dimethyl sulphate under alkaline conditions and by diazomethane under acidic and neutral conditions, gave 6-methoxyindazole and 6-methoxy- 2-methylindazole, It was found that the addition of nitrobenzene doubled the yield of 6-methoxyindazole in the Dennler Frasca synthesis. A convenient synthesis of 1, 2-dimethylindazoline, via 1, 2-dimethyl-3-iodoindazolium iodide, was accomplished in good yield. 6-Nitroindazole hydroformlated at 20 yielded l-hydroxymethyl-6-nitroindazole, whilst at 60 it gave solely l-methoxymethyl-6-nitroindazole. Cyanoethylation gave both the 1- and 2- isomers. When 3-methylindazole was reacted with dichlorocarbene under neutral and basic conditions, no ring expansion occurred, but under the latter conditions a small amount of tri (3-methyl-l-indazolyl) methane was formed. 3-Phenyl-2-hydroxyindazole heated in xylene gave benzophenone and 3-phenylindazole (Section 1). The position of quaternisation of 1, 2, 3-benzothiadiazole has been established by a direct synthesis of 3-ethyl-1, 2, 3-benzo- thiadiazolium bromide. 2-Aminophenylbenzyl sulphide was converted to N-ethyl-2-hydrazinophenylbenzyl sulphide by acetylation, reduction, nitrosylation and finally reduction with lithium aluminium hydride. This hydrazine was ring closed to give the quaternary salt (Section II). Aniline and certain aromatic primary amines with an o or p electron donating group, were oxidised by ethereal monochloramine under mild conditions to give the corresponding azobenzenes, often as both cis- and trans- isomers. Under similar conditions, benzyl alcohol, diphenylmethanol and cyclohexanol gave the respective carbonyl compounds (Section III).