Catalytic Ring Expansions of Cyclic Alcohols Enabled by Proton-Coupled Electron Transfer.

Zhao K , Yamashita K , Carpenter J , Sherwood TC , Ewing WR , Cheng PTW , Knowles RR
Journal of the American Chemical Society
We report here a catalytic method for the modular ring expansion of cyclic aliphatic alcohols. In this work, proton-coupled electron transfer (PCET) activation of an allylic alcohol sub-strate affords an alkoxy radical intermediate that undergoes subsequent C-C bond cleavage to furnish an enone and a tethered alkyl radical. Recombination of this alkyl radical with the revealed olefin acceptor in turn produces a ring-expanded ketone product. The regioselectivity of this C-C bond-forming event can be reliably controlled via substituents on the olefin substrate, providing a means to convert a simple N-membered ring substrate to either N+1 or N+2 ring adducts in a selective fashion.

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