We report a Brønsted acid-catalyzed C6 functionalization of 2,3-disubstituted indoles with 2,2-diarylacetonitriles for efficient construction of cyano-substituted all-carbon quaternary centers with excellent yields. The synthetic utility was demonstrated by the conversion of the cyano-group which enables the divergent preparation of aldehydes, primary amines and amides. Control experiments suggested that this process involves C-H oxidation of 2,2-diarylacetonitriles to in situ generate δ,δ-disubstituted p-quinone methide intermediates. This protocol provides an efficient method for C6 functionalization of 2,3-disubstituted indoles to construct all-carbon quaternary centers.