An Unexpected α-Oxidation of Cyclic Ketones with 1,4-Benzoquinone by Enol Catalysis.

The first direct and asymmetric α-aryloxylation of cyclic ketones via enol catalysis has been achieved using quinones as the reaction partners. Catalytic amounts of a phosphoric acid promote the exclusive formation of α,α-disubstituted ketones from the corresponding α-substituted ketones in good yields and enantioselectivities (up to 96.5:3.5 er). Preliminary mechanistic experiments suggest that this reaction proceeds via a proton-coupled electron transfer (PCET) followed by radical recombination.