Bridging between hetero- and homogeneous catalysis: copper powder catalyzed chemo- and regioselective benzylic C(sp3)–H oxidation Shantanu Nandi, Dr. Ranjan Jana Indian Institute of Chemical Biology, India Selective C‒H functionalization in a pool of proximal C‒H bonds, predictably altering their innate reactivity is a daunting challenge. We present here, an expedient synthesis of privileged biaryl seven-membered lactone, dibenzo[ c , e ]oxepin-5(7H)-one from the corresponding 2'-methyl-[1,1'-biphenyl]-2-carboxylic acid through a highly chemo- and regioselective benzylic C‒H activation. Notably, under present reaction conditions, the formation of vastly explored six-membered lactone via sp 2 C‒H bond activation is completely avoided. Importantly, here we use inexpensive metallic copper powder as the catalyst and di-tert-butyl peroxide (DTBP) as oxidant. Owing to the explosion hazards of stoichiometric DTBP, further for sustainable development, we replaced DTBP with molecular oxygen by coupling photocatalysis with copper powder catalysis. The origin of chemo-selectivity has been investigated where a heterogeneous bulk metal (Cu 0 ) transforms to substrate-bound soluble catalyst (Cu II ), performs the reaction and finally after completion, heterogeneous copper nanoparticles are formed (CuNPs) . Additionally, 1,5-aryl migration through Smiles rearrangement has been realized from the corresponding diaryl ether substrates. The present methodology is scalable, has been applied to the total synthesis of cytotoxic and neuroprotective natural product Alterlactone, and for synthesis of other privileged compounds. The catalyst is recyclable by simple filtration technique. Notably, the reaction has been demonstrated performing it simply in a commercial copper-bottle without any external catalyst. References 1. S. Nandi, S. Mondal and R. Jana, iScience , 2022, 25 , 104341. 2. J. Gallardo-Donaire and R. Martin, J. Am. Chem. Soc. , 2013, 135 , 9350-9353. 3. S.-E. Suh, S.-J. Chen, M. Mandal, I. A. Guzei, C. J. Cramer and S. S. Stahl, J. Am. Chem. Soc. , 2020, 142 , 11388-11393. 4. D. C. Fabry and M. Rueping, Acc. Chem. Res. , 2016, 49 , 1969-1979. 5. H. A. Malik, B. L. H. Tylor, J. R. Kerrigan, J. E. Grob, K. N. Houk, J. Du Bois, L. G. Hamann and A. W. Patterson, Chem. Sci. , 2014, 5 , 2352-2361.
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