An efficient electrochemical approach for the synthesis of oxindoles has been developed from electrolysis of a mixture of sodium sulfinate and acrylamide. The chemistry avoids the utilization of additional conducting salt and proceeds in a simple undivided cell employing catalytic amount of NH₄Br (10 mmol %) as a redox catalyst. The protocol is practical that is proved by the one-pot, two-step procedure and scaled-up experiments. Mechanical studies reveal that the electrochemical approach involves the formation of sulfonyl radicals via homolytic cleavage of the in-situ generated sulfonyl bromide.

Scheme 1. Oxidative radical coupling for the synthesis of oxindoles