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Aerobic Oxidation of Alkynes to 1,2‐Diketones by Organic Photoredox Catalysis

A method for the synthesis of 1,2‐diketones through the mild and metal‐free catalytic photooxygenation of alkynes is described. This reaction, using 9,10‐dicyanoanthracene as a catalytic sensitizer with/without biphenyl as a co‐sensitizer, readily furnished a variety of desired products upon visible‐light irradiation. Mechanistic studies indicated that a radical cation process might have been involved. This report provides the first examples of the transformation of alkynes via acetenyl radical cation intermediates, which have thus far not been explored in organic synthesis.