Photoinduced alkylation of unactivated arenes via Halogen Atom Transfer Krishnakumar Sachidanandan, Ben Niu, Alexandra S. Kelley, and Sébastien Laulhé Indiana University-Purdue University Indianapolis, Department of Chemistry & Chemical Biology Alkylation of aromatic rings to form C(sp2)–C(sp3) bonds has attracted significant attention due to the importance of these chemical connections across pharmaceuticals and bioactive compounds. Traditional ways to obtain these bonds have used the Friedel-Crafts alkylation reaction. Unfortunately, this method proceeds via a carbocation intermediate that often rearranges and the reaction conditions afford little functional group compatibility. More recently, photoredox methods have been successfully used to generate these C(sp2)–C(sp3) bonds, but they require the pre-functionalization of the aromatic ring, often in the form of an aryl halide. The direct alkylation of unactivated C–H arenes would represent a more straightforward and atom-economical approach that would enable facile late-stage functionalization of arene moieties in drugs and bioactive compounds. To this day, only one example of photoinduced alkylation of unactivated arenes exists but it utilizes an expensive palladium-based catalyst, a relatively strong base, and the scope of the reaction is limited to liquid arenes as it required neat conditions. Herein we present the first example of a photoinduced metal-free, halogen-atom-transfer mediated alkylation of unactivated arenes. The reaction enables the efficient coupling of a wide variety of arenes with alkyl halides via a radical pathway. This methodology efficiently converts both liquid and solid arenes to their respective alkylated products in the presence of synthetically valuable functional groups. Mechanistic work, substrate scope, and reaction optimization will be presented.

Photoinduced alkylation of unactivated arenes via halogen atom transfer

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