Steric Hindrance Underestimated: It is a Long, Long Way to Tri-<i>tert</i>-alkylamines
作者:Klaus Banert、Manuel Heck、Andreas Ihle、Julia Kronawitt、Tom Pester、Tharallah Shoker
DOI:10.1021/acs.joc.8b00496
日期:2018.5.4
temperature. Furthermore, tertiary amines with bulky alkyl substituents underwent Hofmann-like elimination when heating in toluene to form an olefin and a secondary amine. Since the tendency to take part in this decay reaction correlated with the degree of steric hindrance around the nitrogen atom, Hofmann elimination at ambient temperature, which made the isolation of the tertiary amine difficult, was observed
测试了十种不同的方法(方法A–J)来制备带有庞大烷基的叔胺。尤其是在三氟甲磺酸1-金刚烷基酯的帮助下,仲胺的S N 1烷基化(方法D)和N的反应-氯二烷基胺与有机金属试剂(方法H)的结合,但后者试剂对亚胺盐的攻击(亚胺的N-烷基化在原位生成的亚胺盐)(方法J)导致三烷基胺具有前所未有的空间拥堵。这些产物显示出绕C–N键旋转的限制。因此,旋转异构体的平衡在NMR时间尺度上很慢,导致在室温下可区分出一组NMR数据。此外,当在甲苯中加热以形成烯烃和仲胺时,具有大的烷基取代基的叔胺经历霍夫曼样消除。由于参与该衰变反应的趋势与氮原子周围的空间位阻程度相关,因此在环境温度下霍夫曼消除反应使叔胺的分离变得困难,