Nitrene Generation from Iminophosphoranes: Facilitating Ring-Closing C(sp²)-H Amidation for Disubstituted Oxindoles

Nitrenes serve as key reactive intermediates in ring-closing C-H amination reactions for the synthesis of heterocyclic compounds. In this study, we established an efficient method for preparing disubstituted oxindoles using iminophosphoranes as effective nitrene precursors. Our findings demonstrate that iminophosphoranes, upon activation by m-CPBA, can generate nitrene intermediates that enable ring-closure C-H amidation reactions. Detailed mechanistic insights were obtained through density functional theory (DFT) calculations and supporting control experiments. This protocol demonstrates excellent scalability to gram quantities and has been successfully applied in the total synthesis of the natural product coixspirolactam A and the bioactive CRTH2 receptor antagonist, underscoring its practical synthetic utility.