Electrosynthesis of C-3 Phosphorylated 2H-Indazoles from Trialkyl Phosphites and 2H-Indazoles

A facile and efficient direct electrochemical oxidation method for C-3 phosphorylation of 2H-indazoles with trialkyl phosphites as the phosphorylation reagents has been developed. Introducing electricity to the green and sustainable synthetic procedures allowed the reactions to be carried out under simple and mild conditions without any metal salts and additional oxidants. Electrochemical data asserted that the cation radical species which were generated from the oxidation of 2H-indazoles were stabilized by 1,1,1,3,3,3-hexafluoro-2-propanol and could be captured by trialkyl phosphites effectively to form C-3 phosphorylated 2H-indazoles. In an undivided cell, a board range of functional groups on various substrates were well tolerated and the yield of the desired phosphorylated products was up to 84%. Moreover, a plausible mechanistic proposal involving radical pathway was established based on the results of cyclic voltammetry, in situ FTIR and control experiments.