Asymmetric Synthesis of 3-Spiro-Fused 2-Oxindoles <i>via</i> Organocatalyst/<i>N</i>-Iodosuccinimide/Hydrogen Peroxide-Mediated Oxidative Cyclization

A squaramide organocatalyst was employed to efficiently promote asymmetric oxidative lactonization to construct spiro-fused 2-oxindoles in moderate-to-good yield and enantioselectivity (up to 81% enantiomeric excess (ee)). Herein, we report the first study accomplishing stereoselective oxidative cyclization from indole propionic acid using an organocatalyst, N-iodosuccinimide (NIS), and hydrogen peroxide under metal-free and mild reaction conditions.