Synthesis of Oxindoles by Direct Intramolecular Oxidative Coupling

Significance

Kündig and Jia reported here the synthesis of 3,3-disubstituted oxindoles by direct coupling of Csp^²-H and Csp^³-H centers. The best results have been obtained using 2.2 equivalents of CuCl₂ as oxidant and five equivalents of t-BuONa as base. The authors proposed a mechanism involving radical formation by amide enolate oxidation followed by cyclization onto the aromatic ring and aromatization. They showed that the Csp^²-H bond breaking was not involved in the rate-determining step by the observation of a ­secondary isotope effect in the reaction of substrate 1.