FeCl3 ⋅ 6H2O Mediated Sequential Oxidative Cleavage and Spiro Coupling of Peroxyoxindole with Cyclic-1,3-diketone/1-Naphthol for the Synthesis of Spirooxindolo-Xanthene Derivatives

Abstract

Herein, an efficient approach to synthesize various hexahydro-1H-xanthene-1,8-dione or dibenzo xanthene containing bioactive spirooxindole derivatives is reported by using FeCl3 ⋅ 6H2O mediated spiro coupling of 1,3-diketone or naphthalene-1-ol with peroxyoxindole. This new approach proceeds via a sequential oxidative cleavage of the C−C bond of peroxyoxindoles to generate the isatin intermediate and further reaction with two molecules of cyclic-1,3 diketones through a series of reactions such as Knoevenagel condensation, Michael addition, and dehydration in one-pot conditions. Furthermore, this sequential reaction of peroxyoxindole with malononitrile afforded 2-(2-oxoindolin-3-ylidene)malononitriles in very good yields in the presence of the most abundant Fe-catalyst. A plausible mechanistic pathway in this transformation has been supported with experimental evidence and control experiments.