The electrochemical reduction of NN′-disubstituted 6-phenyl-2,3-dihydro-1,4-diazepinium salts: formation of bis(tetrahydrodiazepinyls) and a di-imidazolidinylbutadiene

Abstract

The NN′-disubstituted 6-phenyl-2,3-dihydro-1,4-diazepinium cations (la–c), in solution in dimethylformamide, undergo one-electron single reduction waves at –0.9 to –1.3 V with respect to Ag–AgCl–KCl (saturated). The reductions were studied by polarography, cyclic voltammetry, and constant potential electrolysis. Rapid chemical reactions follow the initial reduction and isolated products were the bis(tetrahydrodiazepinyls)(IV) and (VI) and a di-imidazolidinylbutadiene (V). These products were hydrolysed by concentrated hydrochloric acid to give the corresponding NN′-disubstituted ethylenediamine dihydrochloride and also, in the case of (V), 2,5-diphenylhexa-2,4-diene-1,6-dial. The meso-isomer (IVa) was converted into its racemic isomer (IVb) when heated in dimethyl-formamide. Compound (IVb) was quantitatively converted into the diene (V) in a cold mixture of chloroform and ethanol. Cyclic voltammetry studies of (IV) indicated that they were oxidised to bis(dihydrodiazepinium) cations, and that (V) was reduced, with similar behaviour to the reduction of 1,4-diphenylbuta-1,3-diene.