Direct Oxidative Dearomatization of Indoles with Aromatic Ketones: Rapid Access to 2,2-Disubstituted Indolin-3-ones

A metal-free oxidative dearomatization of indoles with aromatic ketones mediated by TEMPO oxoammonium salt is described. The dearomatization proceeds smoothly and displays a broad substrate scope with respect to both indoles and aromatic ketones in the presence of H2SO4, affording the corresponding 2,2-disubstituted indolin-3-ones in good yields.