Formation of para-quinomethanes via 4-aminobutylcatechol oxidation and ortho-quinone tautomerism
作者:Edward J. Land、Christopher A. Ramsden、Patrick A. Riley、Gnanamoly Yoganathan
DOI:10.1039/b305219m
日期:——
Enzymatic and chemical oxidation of 4-(4-N,N-dialkylaminobutyl)catechols leads to formation of 1,1-dialkylpyrrolidinium salts in good yield. It is proposed that these products are formed by tautomerism of the initially formed ortho-quinones to para-quinomethanes. The corresponding secondary amines do not form para-quinomethanes but cyclise giving tetrahydro-1H-benzo[b]azepine-7,8-diones. The failure of the dialkylaminobutyl derivatives to cyclise to bicyclic betaines, in a manner analogous to lower homologues and monoalkylaminobutyl derivatives, is attributed to steric hindrance. This proposal is supported by evidence that the sterically hindered N-tert-butylaminobutyl derivative, in contrast to other secondary amines, does not cyclise but gives a para-quinomethane-derived product. Based on pulse radiolysis and spectrophotometric evidence, para-quinomethane formation appears to be much slower than cyclisation and only occurs when cyclisation is unfavourable. The ortho-quinones formed from 5-aminopentylcatechols neither cyclise nor tautomerise suggesting that the chain length in these derivatives is too long for both cyclisation and intramolecular deprotonation.
对 4-(4-N,N-二烷基氨基丁基)儿茶酚进行酶促和化学氧化后,可生成 1,1-二烷基吡咯烷盐,收率很高。据推测,这些产物是通过最初形成的原醌与对醌甲烷的同分异构作用形成的。相应的仲胺不会形成对位喹啉甲烷,而是环化生成四氢-1H-苯并[b]氮杂卓-7,8-二酮。二烷基氨基丁基衍生物不能以类似于低级同系物和单烷基氨基丁基衍生物的方式环化成双环甜菜碱,这归因于立体阻碍。与其他仲胺不同的是,受立体阻碍的 N-叔丁基氨基丁基衍生物不会环化,而是生成一种对醌甲烷衍生产物,这一证据支持了上述观点。根据脉冲辐射分析和分光光度法的证据,对位喹啉甲烷的形成似乎比环化慢得多,而且只有在环化不利时才会发生。5-aminopentylcatechols 形成的邻醌既不会环化,也不会发生同分异构,这表明这些衍生物的链长过长,不适合环化和分子内去质子化。