Replacement of Stoichiometric DDQ with a Low Potential o-Quinone Catalyst Enabling Aerobic Dehydrogenation of Tertiary Indolines in Pharmaceutical Intermediates.

A transition-metal/quinone complex, [Ru(phd)3]2+ (phd = 1,10-phenanthroline-5,6-dione), is shown to be effective for aerobic dehydrogenation of 3° indolines to the corresponding indoles. The results show how low potential quinones may be tailored to provide a catalytic alternative to stoichiometric DDQ, due to their ability to mediate efficient substrate dehydrogenation while also being compatible with facile reoxidation by O2. The utility of the method is demonstrated in the synthesis of key intermediates to pharmaceutically important molecules.