A Low-Temperature, Transition Metal-Free Cross Dehydrogenative Coupling Protocol for the Synthesis of 3,3-Disubstituted Oxindoles

A new low-temperature procedure for the synthesis of 3,3-disubstituted 2-oxindoles via cross dehydrogenative coupling (CDC) is reported. The use of a strong, non-reversible base in these reactions has been found to effect a dramatic drop in reaction temperature (to room temperature) relative to the current state-of-the-art (>100 °C). When employing iodine as an 'oxidant', new evidence suggests that this transformation may occur via a transiently stable iodinated intermediate rather than by direct single-electron oxidation.