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Here, we present a protocol for the synthesis of dibenzo[c,e]oxepin-5(7H)-ones starting from 2'-alkyl-[1,1'-biphenyl]-2-carboxylic acids. This technique uses two copper(0)-catalyzed benzylic C(sp 3 )-H activation strategies taking either di -tertbutyl peroxide or gaseous oxygen as an oxidant. We detail a photocatalytic thermal approach for copper powder-catalyzed reaction with oxygen. We also describe a procedure for catalyst recycling in both the strategies. The product has been successfully synthesized both in mmol and gram scale. For complete details on the use and execution of this protocol, please refer to Nandi et al. (2022)., Competing Interests: The authors declare no competing interests., (© 2022 The Author(s).)

Selective C‒H functionalization in a pool of proximal C‒H bonds, predictably altering their innate reactivity is a daunting challenge. We disclose here, an expedient synthesis of privileged seven-membered lactones, dibenzo[ c , e ]oxepin-5(7H)-one through a highly chemoselective benzylic C(sp 3 )‒H activation. Remarkably, the formation of widely explored six-membered lactone via C(sp 2 )‒H activation is suppressed under the present conditions. The reaction proceeds smoothly on use of inexpensive metallic copper catalyst and di- tert -butyl peroxide (DTBP). Owing to the hazards of stoichiometric DTBP, further, we have developed a sustainable metallic copper/rose bengal dual catalytic system coupled with molecular oxygen replacing DTBP. A 1,5-aryl migration through Smiles rearrangement was realized from the corresponding diaryl ether substrates instead of expected eight-membered lactones. The present methodology is scalable, applied to the total synthesis of cytotoxic and neuroprotective natural product alterlactone. The catalyst is recyclable and the reaction can be performed in a copper bottle without any added catalyst., Competing Interests: The authors declare no competing interests., (© 2022 The Authors.)