Selective Hydroxylation And Amination Of Arylboronic Acids In Aqueous Ammonia By Electrochemically Generated Copper Species

The hydroxylation and amination of arylboronic acids have attracted increasing attentionbecause they are widely employed in the synthesis of natural products, materials andbiological and pharmaceutical compounds. In the reported methods, metal catalyst, oxidant,ligand, alkali base and organic solvent were added into the reactions, and the reactionsproceeded in low rates and were not suitable for all the substrates. It is important for theorganic synthesis to develop new highly efficient reactions with broader of substrate scopeand to realize its sustainable synthesis.Electro-organic chemistry is particularly favored by chemist because of its mild reactionconditions, easy control and lower toxicity. Highly reactive intermediate, generated either atthe anode or at the cathode, offer novel strategies for the construction of complex molecules.The history, development and present condition of electro-organic chemistry,hydroxylation and amination of arylboronic acids are reviewed in this paper. Electro-organicchemistry was widely used in the industry and environmentally friendly. In view of previousresearch results, we managed to realize the hydroxylation and amination of arylboronic acidschemo-selectively by the electrochemically generated CuIIIspecies.The project focuses on the electrochemical behaviors of arylboronic acids. Extensivestudies were directed to optimize the reaction conditions on voltage, current, electrode and theconcentration of aqueous ammonia. The studies have shown that in an undivided cell withcopper foils as anode and cathode, sat. aq KNO3as electrolyte, by changing the ammoniaconcentration and adjusting the potential, phenols and arylamines were obtainedchemo-selectively (up to60:1) in good yields (up to92%) at rt. For the electrochemicalhydroxylation and amination of arylboronic acids in aqueous ammonia, the reaction rate wasnoteworthy and no special ligand was added. Cyclic voltammetry studies had shown that awave, which corresponding to a CuIIIspecies was observed in the solution of electrochemicalreaction. For the control reaction under non-electrochemical conditions, the peak of CuIIIspecies in CV was not observed. Another control reaction run under N2indicated that air wasalso important in the catalytic cycle of copper for the electrochemical reaction. Hence, apossible reaction pathway which involved the active CuIIIspecies was proposed. Cyclicvoltammetry studies showed that CuIIIspecies might be formed by electro-oxidation, whichexhibited high activities towards the hydroxylation and amination of arylboronic acids.