Metal-free synthesis of C2-quaternary indolinones by (NH4)2S2O8 mediated oxidative dearomatization of indoles.

An efficient metal-free, (NH4)2S2O8 mediated oxidative dearomatization of indoles for the construction of C2-quaternary indolinones was disclosed. A series of C2-quaternary indolinones derivatives with good functional group tolerance were obtained in moderate to excellent yields. This methodology provides an alternative approach for the direct generation of all-carbon quaternary centers at the C2 position of indoles. This catalytic approach represents a step-economic and convenient strategy for the oxidative dearomatization of indoles.