Ortho Substituent with the Nitrogen in -Anilines

Interactions of the Ortho Substituent with the Nitrogen in (-Anilines 

A variety of seemingly unrelated reactions have been reported in which a (-aniline with an ortho substituent of the type N—C—Y is converted into a benzimidazole with loss of a group from the ( nitrogen. 

All these cyclizations can be rationalized by the intermediacy of an imine (6) bearing a good leaving group (Y). Ring closure yields an unstable quaternary benzimidazole (7), which by loss of one of the nitrogen substituents (R3) attains aromaticity to give a 1,2-disub-stituted benzimidazole (8). 

The acetylation of o-aminodimethylaniline (1) already quoted1-6 is a typical example. Its acetyl derivative (9) is capable of further acetylation, the O-acetyl derivative (10) being the required intermediate for cyclization. Elimination of methyl acetate, which was isolated by Pinnow, gives the required product (2). 

The above type of reaction is of particular interest when the N,N-dialkyl substituents are part of a ring system7,8 (e.g., 11). It was found of advantage to replace the acetic anhydride by polyphosphoric 

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