Various kinds of ethyl pyruvate 2-(2-substituted phenyl)hydrazones (1) were subjected to Fischer indolization with acid catalysts. All the phenylhydrazones gave corresponding normal 7-substituted indoles (2). In addition, phenyl-hydrazones whose ortho-substituent is electron-donative or has a central atom with an unshared electron pair tended to give the 4- or 5-substituted indole (3), which was produced by migration of the ortho-substituent during cyclization, whereas those whose ortho-substituent is electron-attractive tended to give little or no such abnormal product. The kind of acid catalyst used had some effect on the yield ratio of products but not on the kind of products.
各种
丙酮酸乙酯 2-(2-取代苯基)酰
肼(1)在酸催化剂作用下进行费歇尔
吲哚化反应。所有的苯
肼都得到了相应的 7-取代
吲哚(2)。此外,如果苯
肼的正位取代基是电子疏导型的,或者其中心原子上有一个未共享的电子对,则往往会产生 4 或 5 取代的
吲哚(3),这是由正位取代基在环化过程中发生迁移而产生的;而如果苯
肼的正位取代基是电子吸引型的,则往往很少或根本不会产生这种异常产物。所使用的酸催化剂对产物的产率有一定影响,但对产物的种类没有影响。