Synthesis of substituted oxindoles by chloroperoxidase catalyzed oxidation of indoles

Chloroperoxidase catalyzed oxidation of substituted indoles yields the corresponding oxindoles in virtually quantitative yield. These include 5-chloro-oxindole, a precursor for the anti-inflammatory agent Tenidap, which was obtained in 95% yield. The reactivity of the substituted indoles depends on the nature and the position of the substituent. Both electronic and steric effects of substituents appear to be important. All of the oxygen in the product is derived from hydrogen peroxide. A mechanism is proposed for the hydroxylation which is consistent with these observations.