Site-Selective Deuteration of N-Heterocycles via Iridium-Catalyzed Hydrogen Isotope Exchange

The application of iridium(I) NHC/phosphine catalysts has delivered highly selective deuteration of indole, azaindole, and pyrrole N-heterocycles, which represent an important and relatively underexplored class of labeling substrates. Common N-protecting groups have been used to selectively direct C–H activation and can be removed under mild conditions with retention of the deuterium label. The method is exemplified by the labeling of the drug molecule sumatriptan. Complementary DFT studies have been conducted to facilitate the rationalization of the very good selectivity offered by the mild and convenient labeling process.