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 (B(OH)), 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.