Elektrosynthese von N‐substituierten DL‐Arylglycinestern und 1,2‐Diarylamino‐1,2‐diarylethanen durch Kathodische Reduktion von Azomethinen in Gegenwart von CO₂

Abstract

Electosynthesis of N‐Substituted DL‐Arylglycineesters and 1,2‐Diarylamino‐1,2‐diarylethanes by Cathodic Reduction of Azomethines in the Presence of Carbon Dioxide The electroreduction of the N‐arylidene‐arylamines 1–12 in CO2‐saturated solvents of low proton availability as DMF at markedly more positive potentials than carbon dioxide end up in carboxylating the C‐atom and hydrogenating the nitrogen of the double bond. The resulting N‐arylsubstituted DL‐arylglycines and traces of carbamates may be isolated as esters, adding ethylchloride during the electrolysis. A competing pathway of the electrocarboxylation is the CC‐hydrodimerisation and the hydrogenation of the double bond, whose importance increases with the water content of the solvent. Based on cyclic‐voltametric evidence and product analysis the mechanism of the reductive electrocarboxylation reaction is discussed in terms of nucleophilic attack of the azomethine anion radical on a proton or CO2.

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

“…The possibility of forming similar dimers has been shown in Refs. [13,14] in the case of some imines, that does not contain fluorine atoms. The similar dimers can be formed in the case of electrochemical reduction of fluorocontaining imines that confirm with results of chromatography-mass spectrometry study of the products of preparative electrolysis of imine 1 (cathode, GC; anode, Al; Bu 4 NBr, DMF).…”

“…The preparative carboxylation was made in a DMF solution, under a constant CO 2 flow, in an undivided cell using the different cathodes and a soluble aluminium anode. After electrolysis DMF was distilled off and the carboxylation product was isolated via acidification of the residue followed by extraction with diethyl ether, purified and analysed by 1 H, 13 C, 19 F NMR and IR spectroscopy, mass spectrometry and elemental analysis. The conditions for preparative electrosyntheses and analytical data of the products are given in detail in Section 4.…”

“…In particular, electrochemically activated introduction of CO 2 to the C N bond can result in a-amino acids [13,14].…”

Electrochemistry for a better environment

“…The studies showed that in most cases the reaction is almost unselective, leading (i) not only to the desired monocarboxylation, and to (ii) the corresponding N-substituted amino acid with yields not exceeding 60% but also to (iii) products of monocarboxylation on the nitrogen atom, (iv) of dicarboxylation, (v) of carbon-carbon coupling, or (vi) of hydrogenation [178,[189][190][191]. Electrocarboxylation with A1 sacrificial anodes [192,193] in a diaphragmless cell appears to be more selective.…”

“…The first studies on the electrocarboxylation of the > C = N -double bond of imines were performed on conventional systems [178,188,189]. The studies showed that in most cases the reaction is almost unselective, leading (i) not only to the desired monocarboxylation, and to (ii) the corresponding N-substituted amino acid with yields not exceeding 60% but also to (iii) products of monocarboxylation on the nitrogen atom, (iv) of dicarboxylation, (v) of carbon-carbon coupling, or (vi) of hydrogenation [178,[189][190][191].…”