Org Lett. 2018 Oct 19;20(20):6564-6568. doi: 10.1021/acs.orglett.8b02902. Epub 2018 Oct 10.
The asymmetric allylation of 1-pyrroline-5-carboxylic esters has been accomplished through a synergistic Pd/Cu catalyst system under mild reaction conditions. The mechanistic studies suggested that (1) nucleophilic attack is the enantiodiscriminating step; (2) the cooperative action of two chiral reactive species, N-metalated azomethine ylides and π-allylpalladium, is most likely responsible for its high reactivity and excellent enantioselectivity (up to >99% ee); and (3) the steric hindrance and electronic factors of the allylic electrophiles and imino ester substrates are crucial for the formation of the linear products. A series of 3,4-2 H-pyrrole derivatives bearing a quaternary stereogenic center were easily synthesized in high yields and with high to excellent regioselectivity and enantioselectivity.
通过协同 Pd/Cu 催化剂体系，在温和的反应条件下，实现了 1-吡咯啉-5-羧酸酯的不对称烯丙基化反应。机理研究表明：（1）亲核进攻是对映选择性的关键步骤；（2）两种手性反应物种，N-金属化氮宾叶立德和π-烯丙基钯的协同作用，可能是其高反应性和优异对映选择性（高达＞99%ee）的原因；（3）烯丙基亲电试剂和亚胺酯底物的空间位阻和电子因素对于形成线性产物至关重要。一系列含有季立体中心的 3,4-2H-吡咯衍生物以高产率、高至优异的区域选择性和对映选择性很容易合成。
