A general arene C–H functionalization strategy via electron donor-acceptor complex photoactivation Leendert van Dalsen, Abhishek Dewanji, James A. Rossi-Ashton, Eloise Gasson, Giacomo E. M. Crisenza, David J. Procter Department of Chemistry, The University of Manchester, UK The emerging field of electron donor-acceptor (EDA) complex photoactivation has led to the development of sustainable, selective, and versatile alternatives to photoredox catalysis, for the generation of radical species. 1 Rather than relying on precious photocatalysts, EDA complexes take advantage of charge transfer interactions between electron-rich donors and electron-deficient acceptors - which alone are colourless – to generate visible light absorbing aggregates. Photoexcitation of EDA complexes induces an intracomplex single electron transfer (SET), which drives the formation of radical species. 1 However, for aryl radical formation, EDA photoactivation has been held back by limitations with regard to the aromatic radical precursor, with electron-deficient aryl halide acceptors being required. Thus, general strategies for aryl radical generation via EDA complex photoactivation have so far proved elusive. Recently, our group used triarylsulfonium salts, readily synthesised by C–H sulfenylation of aromatic substrates, with photoexcited organic photocatalysts to efficiently produce aryl radicals. 2 We now introduce triarylsulfonium salts as acceptors in photoactive EDA-complexes, used in combination with catalytic amounts of newly-designed amine donors. The sulfonium salt tag renders inconsequential the electronic features of the aryl radical precursor and, more importantly, it is installed regioselectively in native aromatic compounds by C–H sulfenylation. Using this general synthetic platform for aryl radical formation, we have developed site-selective, metal-free protocols for the aromatic C–H alkylation and cyanation of arenes, and showcased their application in both the synthesis and the late-stage modification of pharmaceuticals and agrochemicals. 3
References 1. G. E. M. Crisenza, D.Mazzarella,andP. Melchiorre, Synthetic Methods Driven by the Photoactivity of Electron Donor− Acceptor Complexes., J. Am. Chem. Soc., 2020, 142 , 5461−5476. 2. M. H. Aukland, M.Šiaučiulis, A. West, G. J. P.Perry,and D. J.Procter, Metal-Free Photoredox-Catalyzed C–H/C–H Coupling of Arenes Enabled by Interrupted Pummerer Activation., Nat. Catal., 2020, 3 , 163−169. 3. A.Dewanji, et al., A general arene C–H functionalization strategy via electron donor-acceptor complex photoactivation., Nat. Chem. ,2023, 15 , 43-52.
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