Organic charge-transfer complex induces chemoselective decarboxylation to aryl radicals for general functionalization

• Published in: Chem Vol. 9; no. 10; pp. 2997 - 3012
• Main Authors: Hu, Chun-Hong, Sang, Yueqian, Yang, Ya-Wei, Li, Wen-Wen, Wang, Hui-Lin, Zhang, ZiYing, Ye, Chen, Wu, Li-Zhu, Xue, Xiao-Song, Li, Yang
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 12.10.2023
• Subjects: aryl carboxylic acids; charge-transfer complex; chemoselective decarboxylation; organic photocatalysis; visible light; charge-transfer complex; aryl carboxylic acids; SDG3: Good health and well-being; visible light; chemoselective decarboxylation; organic photocatalysis; SDG9: Industry, innovation, and infrastructure
• ISSN: 2451-9294; 2451-9294
• DOI: 10.1016/j.chempr.2023.06.022

Aryl radicals are used as versatile intermediates for arylations for the preparation of natural products, drugs, and functional materials. Photoinduced direct decarboxylation of aryl carboxylic acids to aryl radicals is considered attractive because of the wide availability and stability of aryl carboxylic acids and mild conditions. However, direct decarboxylation has been clearly shown to be very challenging because aryl carboxyl radicals favor strongly competitive addition to arene pathways. Herein, we demonstrate a solution to this challenge: a charge-transfer complex of aryl carboxylate via n-π∗ and π-π interactions induces chemoselective decarboxylation to aryl radicals for general functionalization. Presumably, the triplet complex significantly slows the rate of second-order aryl carboxyl radical addition to the aryl ring, resulting in selective decarboxylation to aryl radicals. Our studies should inspire numerous arylations in various fields under mild conditions with the use of easily available and stable aryl carboxylic acids, as well as new photoredox catalytic modes for selective radical transformations. [Display omitted] •Charge-transfer complex induces chemoselective decarboxylation to aryl radicals•General functionalization using aryl carboxylic acids under mild conditions•Transition-metal-free visible-light photoredox catalysis Photoinduced direct decarboxylation of native aryl carboxylic acids to aryl radicals is highly desirable because these radicals are widely applicable in various synthetic fields and because the availability and bench stability of aryl carboxylic acids are superior to those of surrogates. This direct decarboxylation, unfortunately, is also very challenging because hydrogen-atom abstraction and aryl carboxyl radical addition to arene pathways are highly competitive. We have developed a charge-transfer complex that undergoes direct chemoselective decarboxylation to aryl radicals for its general functionalization, presumably via selective decarboxylation in a triplet complex, while significantly slowing the rate of second-order aryl carboxyl radical addition to arenes. Our work should enable the use of aryl carboxylic acids as aryl radical precursors for various arylations and extensive applications under transition-metal-free and mild conditions. Furthermore, insights into the catalytic pathway of the charge-transfer complex should inspire exploration of new photoredox catalytic modes in the complex. An organic charge-transfer complex between a photocatalyst and an aryl carboxylate via n-π∗ and π-π interactions chemoselectively induces decarboxylation to aryl radicals for general functionalization. Presumably, the triplet complex significantly slows the rate of second-order aryl carboxyl radical addition to the aryl ring, a well-established and highly competitive pathway, resulting in selective decarboxylation to aryl radicals. Our studies should inspire numerous arylations using aryl carboxylic acids and new photoredox catalytic modes for selective radical transformations.