TEMPO Oxidation of Phenylalkynes: A Green Approach to Diketophenols

Herein, we report a catalytic 2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPO)‐mediated oxidation of 4‐hydroxyphenylalkynes under molecular oxygen, affording 4‐hydroxybenzil efficiently. Mechanistic studies suggest that TEMPO oxidizes the phenolic alkyne to a quinoethylene intermediate, which is further transformed into diketones in the presence of oxygen and/or water. This metal‐free protocol avoids stoichiometric strong oxidants, providing a green and operationally simple route to valuable diketone compounds.