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[摘要]：Heating ortho-nitro-anilides 1-3 and 2-methyl-N-(3-nitropyridin-2-yl)propanamide (5) with 4 equiv. of a phosphine led to the 2-substituted benzimidazoles 6-8 and to the imidazo[4,5-b]pyridine 10, respectively, in yields between 45 and 85%. Heating 1 with (EtO)(3)P effected cyclisation and N-ethylation, leading to the 1-ethylbenzimidazole 6b. The slow cyclisation of the N-pivaloylnitroaniline 2b allowed isolation of the intermediate phosphine imide 11 that slowly transformed into the 1H-benzimidazole 7b. The structure of 11 was established by crystal-structure analysis. While the N-methylated ortho-nitroacetanilide 3 cyclised to the 1,2-dimethyl-1H-benzimidazole (8), the 2-methyl-propananilide 4 was transformed into 1-methyl-3-(1-methylethyl)-2H-benzimidazol-2-one (9). |
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