Metal-free Synthesis Of2-Oxindoles Via PHI（OAc）₂-Mediated Oxidative C-C Bond Formation

Oxindoles have received enduring synthetic interest from organic chemists since they are versatile building blocks for the synthesis of natural products and biologically active molecules. Specifically,3-monofunctionalized2-oxindoles have been identified as indispensible intermediates in the total synthesis of the naturally occurring horsfiline, welwitindolinone C, CPC-1and etc.A handful of strategies have been established to construct the oxindole skeleton. The most commonly used approaches are metal-catalyzed (Ir, Cu, Rh, Au and etc.) intramolecular cyclization of various amide derivatives.We report a new application of hypervalent iodine, that is, in constructing the3-monofunctionalized2-oxindole frameworks through its role of facilitating an intramolecular cyclization of anilide derivatives via an exclusive C(sp2)-C(sp2) bond forming reaction. A series of3-monofunctionalized2-oxindoles were conveniently synthesized from reactions between anilide and phenyliodine (III) diacetate (PIDA). In addition, this metal-free method, shown to provide direct access to an important oxindole intermediate, could be applied for the total synthesis of naturally-occurring horsfiline. We also studied the mechanism of the reaction process, and one possible mechanism was proposed.The highlights of the reported method, in comparison to the currently existing methods for the synthesis of oxindole products, include the mild reaction conditions, good functional group tolerance, the metal-free feature, and environmental friendly characteristic.