Pd/C-Catalyzed transfer hydrogenation of N–H indoles with trifluoroethanol and tetrahydroxydiboron as the hydrogen source

Under the guidance of the known mechanism of the hydrogenation of indoles and transfer hydrogenation with tetrahydroxydiboron (B2(OH)4), Pd/C catalyzed transfer hydrogenation of N–H indoles with trifluoroethanol and tetrahydroxydiborane as the hydrogen source has been developed. This provides an efficient strategy and catalytic system for the reduction of un-activated N–H indoles, and N–H indolines are obtained with good to excellent yields. In addition, a series of the isotopic labelling experiments were carried out to probe the mechanism.