Carbene-Catalyzed Indole 3‑Methyl C(sp³)–H Bond Functionalization

The metal-free catalytic functionalization of aromatic sp2-carbons and benzylic sp3-carbons remains challenging. Here we report a carbene-catalyzed functionalization of the 3-methyl sp3-carbon attached to 2-formyl-indoles. The reaction proceeds through an NHC-bound o-quinodimethane as the key intermediate generated from 2-formyl-3-methylindoles under oxidative conditions. Reactive ketones are found to be effective substrates to produce substituted hydropyrano­[3,4-b]­indoles in good to excellent yields.