Deoxygenative Olefin Insertion of Cyclic Alcohols Promoted by Sulfoxide Cation Radicals

Herein we report a novel strategy to expand aliphatic cyclic alcohols via deoxygenative olefin insertion. Acridinium-catalyzed formation of sulfoxide radicals selectively converts unfunctionalized alcohols to alkoxy radicals, which undergo selective β-scission of the weakest adjacent C-C bond. The resulting alkyl radical undergoes a Giese addition with a vinyl phosphonate acceptor. Subsequent treatment of this ketophosphonate with mild base allows for a highly efficient Horner-Wadsworth-Emmons (HWE) reaction to proceed, generating the two-carbon-expanded product. The products notably possess an internal double bond, which is unique with respect to ring expansion methodologies. Further, this approach does not rely on preactivated starting alcohols, is applicable to the formation of 5-7-membered cycloalkenes, and proceeds with a broad array of functional group tolerance in moderate to excellent yields.