Two-in-One Strategy for Palladium-Catalyzed C-H Functionalization in Water.

Transition metal catalyzed C-H functionalizations have been developed as powerful methods for C-C bond formations. Directing groups, removable directing groups, traceless directing groups, and transient directing groups (TDGs) have been successfully used to improve the reaction efficiencies. For the development of greener and more sustainable methods, C-H functionalization using a TDG that also serves as a reagent in aqueous solvent was investigated. The palladium-catalyzed C-H functionalization of tryptamine derivatives using ketones in water successfully generated tetrahydro-β-carbolines with a quaternary carbon center at C1. Deuterium-labeling experiments are discussed to provide insight into the mechanism. The C2-position of pyridine was also successfully functionalized by this strategy.