Electrochemical carboxylation of fluorocontaining imines with preparation of fluorinated N-phenylphenylglycines

A possibility of obtaining fluorine-containing N-phenylphenylglycine derivatives at yields of up to 85% via the electrochemical carboxylation of corresponding benzalanilines was shown. The influence of imineʹs electron structure, the nature of supporting electrolyte and cathodic material on such processes is examined. It was found, that increasing electron accepting ability of the substituents in benzylidene and aniline fragments of the imine molecule lead to decrease of amino acid yields. The dependence of the N-phenyl-p-fluorophenylglycine yield on the cathode material (Zn, GC, Cu, Ag, Pt) and on the nature of the supporting electrolytes (Bu4NBr, Et4NBr, Et4NClO4, PhCH2Me3NClO4, LiBF4, LiClO4, NaBF4 and KBF4) was investigated. The highest amino acid yields were obtained at cathodes (GC and Zn) that do not exhibit specific adsorption of fluorine-containing imines, as well as in the presence of background salts (Alk4NBr) whose cations do not show tendency to strong ion pairing with anion radicals formed by the electrochemical activation of the imines.