Ortho Substituent with the a-Methylene Group in -Anilines

Interactions of the Ortho Substituent with the a-Methylene Group in t- Anilines 

The reactions which fall into this category conform to a basic mechanism as outlined below for an unsaturated ortho substituent (A=B) capable of mesomerism (61) - (62). The polarized mesomer 

Most of the known examples involve the following groups (—A=B) —N=0 (including — N02), —N=C, —N=N, —C=N, and — C=0. Many observations were unexpected and unwanted results arising from simple laboratory procedures such as reduction or acylation. The reactions, therefore, were occasionally misinterpreted and as a consequence incorrect structures were assigned to the products. 

The following discussion will be divided into sections according to the functional group situated at the ortho position. 

Pinnow2-5,26-27 was the first to observe the interaction of the nitro group with a tertiary amino function. In a series of papers from 1895 onward he noticed that during the reduction of o-nitrodimethyl-anilines (68) with tin and hydrochloric acid, significant quantities of a 1-methylbenzimidazole (69) were formed together with the amine (70) and a chlorinated product (71). He proposed that the benzimidazole arose by reduction of the nitro to a nitroso group which then 

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