A novel iron-catalyzed cross-dehydrogenative coupling of two different C(sp3)–H bonds to synthesize olefins by using air as an ideal oxidant.

We describe an unprecedented dual C–H functionalization of indolin-2-one via an oxidative C­(sp3)–H/N–H/X–H (X = N, C, S) cross-coupling protocol, which is catalyzed by a simple iron salt under mild and ligand-free conditions and employs air (molecular oxygen) as the terminal oxidant. This method is readily applicable for the construction of tetrasubstituted carbon centers from methylenes and provides a wide variety of spiro N-heterocyclic oxindoles.

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.

A new class of bridged alkyl ionic liquids has been successfully developed and they are shown to be efficient catalysts for the synthesis of a wide range of densely functionalized spiro[4Hpyran-3,3'-oxindole] derivatives. With only 1 mol% catalyst, all the reactions underwent smoothly in aqueous ethanol solution at ambient temperature and afforded the corresponding products in good to excellent yields within a short reaction time. This is a simple and green protocol with significant advantages such as the use of environmentally friendly solvent, mild conditions, easy work up, no chromatographic separation, and applicability for large-scale synthesis. The catalyst could be reused eight times at least. 2 3 4 5 6 7 8