Energy-Transfer-Enabled Dearomative Cycloaddition Reactions of Indoles/Pyrroles via Excited-State Aromatics

• DOI: 10.1021/acs.accounts.2c00412
• Publication Date: 2022-08-09T15:12:55Z
• Authors: Min Zhu; Xiao Zhang; Chao Zheng; Shu-Li You
• Keywords: Indoles; Cycloaddition Reaction; Energy Transfer; Oximes; Pyrroles; 7. Clean energy; 01 natural sciences; 0104 chemical sciences

Exploring the enormous chemical space through an expedient building-up of molecular diversity is important goal organic chemistry. The development synthetic methods toward molecules with unprecedented structural motifs lays foundation for wide applications ranging from pharmaceutical chemistry to materials science. In this regard, dearomatization arenes has been recognized as a unique strategy since it provides novel retrosynthetic disconnections various spiro or fused polycyclic increased saturation and stereoisomerism. However, inherent thermodynamic challenges are associated processes. disruption aromaticity arene substrates usually requires large energy inputs, which makes harsh conditions necessary many ground-state reactions. Therefore, further expansion scope reactions remains major problem not fully solved in chemistry.The past decade witnessed tremendous progress on photocatalytic under visible light. Particularly, via transfer mechanism have unlocked new opportunities Mediated by appropriately chosen photosensitizers, aromatic can be excited. This kind precise input might make feasible some that otherwise unfavorable thermal because significant increases substrates. Nevertheless, lifetimes key intermediates energy-transfer-enabled reactions, such excited-state aromatics downstream biradical species, quite short. How regulate reactivities these transient achieve exclusive selectivity certain reaction pathway among possibilities crucial issue addressed.Since 2019, our group reported series visible-light-induced dearomative cycloaddition indole pyrrole derivatives. It was found units excited irradiation light presence suitable photosensitizer. These readily undergo [m + n] tethered unsaturated functionalities including alkenes, alkynes, N-alkoxy oximes, (hetero)arenes, vinylcyclopropanes. yield indolines pyrrolines highly strained small- and/or medium-sized rings embedded, possess bridge- cagelike topologies. Systematic mechanistic studies confirmed involvement process. Density functional theory (DFT) calculations revealed correlation between substrate structure excitation efficiency, accelerated optimization parameters. Meanwhile, DFT demonstrated competition kinetically thermodynamically controlled pathways open-shell singlet intermediates, allowed complete switches [2 2] 1,5-hydrogen atom oximes [4 naphthalene. Furthermore, ab initio dynamics (AIMD) simulations uncovered post-spin crossing dynamic effects, determine regioselectivity recombination step pyrrole-derived vinylcyclopropanes.An increasing number scientists joined research contributed more elegant examples area. mechanism, although still its infancy, exhibited great potential synthesis hardly accessed other methods. We believe future will push boundary find related disciplines.