o-Nitrobenzylidene compounds. Part 3. Formation of 4-arylamino-3-methoxycinnoline 1-oxides from N-o-nitrobenzylideneanilines, cyanide ion, methanol: the intermediacy of 2-aryl-3-cyano-2H-indazole 1-oxides

Abstract

The N-o-nitrobenzylidene derivatives of variously substituted anilines (7) have been cyclised by potassium cyanide in methanol, to give 4-arylamino-3-methoxycinnoline 1-oxides (9), the structures of which have been confirmed by independent synthesis of one representative [the p-toluidino-compound. (9b)]. These cinnoline oxides are the main products (sometimes the only isolated products) when the amine-derived ring in (7) is ortho-substituted; in other cases the cinnoline oxides are minor products formed along with 2- aryl-3-cyano-2H-indazoles (10).

In the latter group of reactions, the primary cyclisation products are 2-aryl-3-cyano-2H-indazole 1-oxides (8): these have then either been reduced to the indazoles in the basic methanolic medium, or have undergone ring-opening and recyclisation to give the cinnoline oxides (9). In the other group, where indazole oxides (8) cannot usually be isolated, their intermediacy in cinnoline oxide formation remains a possibility, although other mechanistic pathways can be envisaged.

Some ‘borderline’ cases are identified and discussed.