Department of Applied Chemistry, 1001 Ta-Hseuh Road, National Chiao Tung University, Hsinchu 300-10, Taiwan, Republic of China.
Amar Chemistry Pvt. Ltd., G1A, Ackruti Corporate Park, Mumbai 400078, India.
Org Biomol Chem. 2022 Aug 31;20(34):6854-6862. doi: 10.1039/d2ob00906d.
A Rh(III)-catalyzed cascade C-H activation and cyclization of 2-aryl benzimidazoles with maleimides for the synthesis of benzimidazole-fused isoquinolines and benzimidazole-spiro isoindoles is reported. Switchable selectivity towards the formation of these two distinct products can be achieved using unsubstituted and substituted benzimidazoles at the -position of the phenyl ring. Mechanistically, C-H activation followed by migratory insertion of maleimide forms a Heck-type intermediate. Unsubstituted benzimidazole undergoes aza-Michael addition to form a (4 + 2) fused product, whereas -substituted phenyl benzimidazole causes steric clash to deliver a (4 + 1) spiro-adduct favorably acid-catalyzed intramolecular annulation.
报告了一种 Rh(III)催化的 2-芳基苯并咪唑与马来酰亚胺的级联 C-H 活化和环化反应，用于合成苯并咪唑并异喹啉和苯并咪唑螺异吲哚。使用苯环上未取代和取代的苯并咪唑，可以实现对这两种不同产物的可切换选择性。从机理上看，C-H 活化后马来酰亚胺进行迁移插入形成 Heck 型中间体。未取代的苯并咪唑发生氮杂-Michael 加成，形成（4+2）稠合产物，而取代的苯基苯并咪唑由于空间位阻导致有利于酸催化的分子内环化的（4+1）螺加合物的形成。
