非对称氮杂环丙烷的亲核开环反应及其区域选择性

本文系统地总结了各类亲核试剂对非对称氮杂环丙烷(吖丙啶)的亲核开环反应及开环的区域选择性.氮杂环丙烷亲核开环的区域选择性是一种空间效应和电子效应平衡的结果,非芳基和非烯基取代的氮杂环丙烷的亲核开环通常发生在氮杂环丙烷取代少的碳原子上,空间效应起主导作用;而芳基和烯基取代的氮杂环丙烷的亲核开环通常发生在氮杂环丙烷芳甲位和烯丙位的碳原子上,电子效应起主导作用,烯基取代的氮杂环丙烷的亲核开环还可以发生在烯基的β-碳原子上;分子内的亲核开环反应主要受成环时环大小的控制,成环时的倾向是五元环>六元环>七元环.对于亲核试剂,一般的亲核试剂也同时受电子效应和空间效应的影响; 而亲核性强的亲核试剂通常只受空间效应的影响.容易生成稳定自由基的亲核试剂容易发生单电子转移机理的开环反应,生成相当于亲核试剂进攻氮杂环丙烷中取代多的碳原子得到的开环产物.

Nucleophilic Ring Opening Reaction of Unsymmetric Aziridines and Its Regioselectivity

Nucleophilic ring opening reaction of unsymmetric aziridines and its regioselectivity with various nucleo-philes was reviewed systematically. The regioselectivity is controlled by a balance between steric hindrance and electronic effect in an aziridine ring. Nucleophilic ring opening reaction of non-aryl and non-alkenyl substituted aziridines occurs generally on the less substituted carbon atom in their aziridine rings, controlled by steric hindrance. However, ihe reaction of aiyl and alkenyl substituted aziridines does on arylmethyl and allyl carbon atom, controlled by electronic effect, and the reaction of alkenyl substituted aziridines can also occur on the /3-carbon atom of the alkenyl group. The regiose-lectivity of intramolecular nucleophilic ring opening reaction of aziridines is controlled by the ring size of products, five-membered ring > six-membered ring > seven-membered ring. For a nucleophile, its regioselectivity is also controlled by both steric hindrance and electronic effect. However, a stronger nucleophile is generally just controlled by steric hin-drance. A nucleophile which prefers to form a stable free radical undergoes a single electron transfer mechanism in ring opening reaction of aziridines to generate products which could be obtained via its attacking on more substituted carbon at-om in an aziridine ring.