华中师范大学陈加荣团队报道了双光氧化还原/镍催化β-酮酯和叠氮化乙烯的不对称[3+2]光环加成。相关研究成果发表在2023年5月24日出版的国际学术期刊《美国化学会杂志》。

光催化[3+2]环加成和立体化学的控制仍然是一个巨大的挑战，特别是在杂环合成的背景下；零星的成功实例包括氧化还原活性的含直接基团的环丙烷和烯烃之间的对映选择性[3+2]光环加成，以产生环戊烷。

该文中，研究人员报道了一种合作催化体系，该体系包括手性镍-路易斯酸催化剂和以可见光照射为燃料的有机光催化剂，该体系能够在氧化还原中性条件下，β-酮酯与叠氮乙烯酯进行迄今为止难以实现的不对称[3+2]光环加成。该方案能够高度对映选择性地构建具有两个连续的四取代碳立体中心的多环稠取代的3，4-二氢-2H-吡咯杂环，包括有用的手性N，O-酮基序，而该基序用其他催化方法不容易获得。机理研究表明，整体反应性依赖于镍催化剂的双重作用的无缝整合，通过催化形成底物/Ni复合物，辅助光氧化还原反应和对映选择性自由基加成。

附：英文原文

Title: Asymmetric [3 + 2] Photocycloaddition of β-Keto Esters and Vinyl Azides by Dual Photoredox/Nickel Catalysis

Author: Xue-Song Zhou, Zhihan Zhang, Wen-Yuan Qu, Xiao-Peng Liu, Wen-Jing Xiao, Min Jiang, Jia-Rong Chen

Issue&Volume: May 24, 2023

Abstract: Photocatalytic [3 + 2] cycloadditions and control of stereochemistry have remained a substantial challenge, particularly in the context of heterocycle synthesis; sporadic successful examples have involved enantioselective [3 + 2] photocycloaddition between redox-active direct group-containing cyclopropanes and alkenes for creation of cyclopentanes. Herein, we report a cooperative catalytic system comprising a chiral nickel Lewis acid catalyst and an organic photocatalyst fueled by visible-light irradiation that allows for the hitherto elusive asymmetric [3 + 2] photocycloaddition of β-keto esters with vinyl azides under redox-neutral conditions. This protocol enables highly enantioselective construction of polycyclic densely substituted 3,4-dihydro-2H-pyrrole heterocycles featuring two contiguous tetrasubstituted carbon stereocenters, including a useful chiral N,O-ketal motif that is not easily accessible with other catalytic methods. Mechanistic studies revealed that the overall reactivity relies on the seamless integration of dual roles of nickel catalysts by the catalytic formation of the substrate/Ni complex, assisting both photoredox event and enantioselective radical addition.

DOI: 10.1021/jacs.3c02485

Source: https://pubs.acs.org/doi/10.1021/jacs.3c02485