N‑Heterocyclic Carbene-Catalyzed [3+4] Cycloaddition and Kinetic Resolution of Azomethine Imines

The
first N-heterocyclic carbene (NHC)-catalyzed
[3+4] cycloaddition of azomethine imines and enals is disclosed. Oxidative
catalytic remote activation of enals affords 1,4-dipolarophile intermediates
that react with 1,3-dipolar azomethine imines to generate dinitrogen-fused
seven-membered heterocyclic products with high optical purities. Our
approach also provides effective kinetic resolution of azomethine
imines, in which the substrate chiral center that is remote from the
NHC catalyst can be well resolved.

本项研究揭示了首例N-杂环卡宾（NHC）催化的[3+4]环加成反应，涉及亚胺和烯醛。通过氧化催化远程激活烯醛，可获得1,4-二极性亲电中间体，与1,3-二极性亚胺反应生成高光学纯度的氮气融合七元杂环产物。本研究方法还提供了亚胺的有效动力学拆分，其中远离NHC催化剂的底物手性中心得以有效分辨。