Iron-catalyzed oxidative bis-arylation of indolin-2-ones for direct construction of quaternary carbons

We describe a direct construction of all-carbon quaternary centers from secondary C(sp 3 )-H substrates through a dehydrogenative cross-coupling reaction. Using FeCl 2 ·4H 2 O as the catalyst and employing air (molecular oxygen) as the terminal oxidant, the cross-coupling of indolin-2-ones with indoles proceeded smoothly under mild, ligand-free and base-free conditions, providing 3,3-disubstituted oxindoles bearing all-carbon quaternary centers with excellent chemoselectivities. The cross-dehydrogenative coupling protocol is catalyzed by a simple iron salt, and air is used as the terminal oxidant under very mild conditions, offering a novel synthetic method for the direct construction of all-carbon quaternary centers.