Heterogeneous palladium-catalysed intramolecular C(sp3)-H alpha-arylation for the green synthesis of oxindoles

Herein, we present our results on the development of a waste-minimized protocol for the synthesis of oxindoles using cyclopentyl methyl ether (CPME) as a safe and green reaction medium and palladium on carbon (Pd/C) as a reusable catalyst. This protocol is efficiently applied to a variety of substrates affording products with excellent yields, minimal metal contamination and minimum waste production. The catalyst was recovered and reused for four consecutive runs without any apparent loss of efficiency. Moreover, products were isolated by simple precipitation from heptane with no need for chromatographic separations, and both CPME and heptane were recovered. Waste-minimization is reflected by the low E-factor calculated for the presented protocol.