Catalyst-free photochemical C(sp3)-H arylation of amides in a solvent-caged EDA complex
Jaspreet Kaur 1 , Ahmed Shahin 1,2 , Joshua P. Barham 1 1 Universität Regensburg, Germany, 2 Benha University, Egypt
Amides and lactams are important moieties in polymers, peptides, functional materials and bioactive organic molecules. An alternative approach to the condensation of amines with carboxylic acids is the direct C(sp3)-H functionalization of simple amide feedstocks. 1 Hydrogen atom transfer (HAT), affording alpha-amido radicals, is an elegant vehicle for the functionalizationof amides that circumvents otherwise high oxidation potentials needed for their activation by single electron transfer. Radicals derived from persulfate are ideally matched to engageamide C(sp3)-H bonds. The activation of persulfate in this way can be achieved at hightemperatures, 2 but also under ambient conditions using visible light. 3,4 For example, Stephenson and co-workers reported an elegant photochemical method employing transition metal photocatalyst [Ru(bpy)3]2+ and ammonium persulfate for a C(sp3)-H arylation of amides with electron rich arene partners. 4 We serendipitously found this reaction proceeds without any photocatalyst, using only visible light at ambient temperature. 5 UV-vis spectra revealed anelectron- donor acceptor (EDA) complex between electron rich arenes and persulfate is key toreactivity. Mechanistic studies including quantum yield measurements and radical trapping experiments corroborated the reaction taking place within a solvent cage, offering promise to theability to control photochemical reaction outcomes through confined spaces. References 1. J. P. Barham, S.Tamaoki, H. Egami, N. Ohneda, T. Okamoto, 2. H. Odajima, Y. Hamashima, Org. Biomol. Chem. 2018, 16 , 7568-7573. 3. J. Wang, J. Li, J. Huang, Q. Zhu, J. Org. Chem. 2016, 81 , 3017-3022. 4. Y. Zhang, K. B. Teuscher, H. Ji, Chem. Sci. 2016 , 7 , 2111-2118.C. Dai, F. Meschini, J. M. R. Narayanam, C. R. J. Stephenson, J. Org. Chem. 2012, 77 , 425-4431. 5. J. Kaur, A. Shahin, J. P. Barham, Org. Lett. 2021, 23 , 2002-2006.
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