Direct Conversion of Indoles to 3,3-Difluoro-2-oxindoles <i>via</i> Electrophilic Fluorination

3,3-Difluoro-2-oxindoles can be obtained directly from indoles in moderate yields <i>via</i> electrophilic fluorination using <i>N</i>-fluorobenzenesulfonimide as a mild fluorinating reagent. The presence of <i>tert</i>-butyl hydroperoxide during the reaction, together with additional heating after quenching the reaction with triethylamine, is beneficial to the formation of the desired product