Synthesis of Benzimidazoles by Phosphine-Mediated Reductive Cyclisation of ortho-Nitro-anilides
作者:Jan Duchek、Andrea Vasella
DOI:10.1002/hlca.201100123
日期:2011.6
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)3P 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
加热邻硝基N-酰苯胺1 - 3和2-甲基- ñ - (3-硝基吡啶-2-基)丙酰胺(5)与4当量。的导致了2-取代的苯并咪唑的膦6 - 8和所述咪唑并[4,5- b ]吡啶10分别在45和85%之间的收率。用(EtO)3 P加热1会实现环化和N乙基化,从而生成1乙基苯并咪唑6b。N-新戊酰硝基苯胺2b的缓慢环化可分离出中间体膦亚胺11慢慢转化为1 H-苯并咪唑7b。的结构11,通过晶体结构分析确定。当N-甲基化的邻-硝基乙酰苯胺3环化成1,2-二甲基-1 H-苯并咪唑(8)时,2-甲基丙酰苯胺4被转化为1-甲基-3-(1-甲基乙基)-2 H-苯并咪唑‐2‐1(9)。