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.