David J. Walton

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

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.

Anodic acetamidosulphenylation of alkenes

Anodic oxidation of disulphides in acetonitrile in the presence of an alkene gives acetamidosulphides.

The electrochemical reduction of the 6-phenyl-2,3-dihydro-1,4-diazepinium cation and its 1-methyl and 5-methyl derivatives: formation and some properties of pyrrolodiazepines

The 6-phenyl-2,3-dihydro-1,4-diazepinium cations (VIa–c), dissolved in dimethylformamide, undergo one-electron single reduction waves at –1.2 to –1.5 V. The reductions were studied by polarography, cyclic voltammetry, and preparative electrochemistry. Rapid chemical reactions follow the initial reduction and the isolated products are pyrrolodiazepines (VIIa–c). The latter compounds are reversibly protonated to provide pyrrolodihydrodiazepinium cations (IX) and appear to form dications and stable cation radicals when they are, respectively treated with triphenylmethyl perchlorate or oxidised electrochemically.

Electrochemical reduction of the 5,7-diphenyl-2,3-dihydro-1,4-diazepinium cation

The 5,7-diphenyl-2,3-dihydro-1,4-diazepinium cation (II), dissolved in dimethylformamide, is reduced in two steps. The first wave, at –1.23 V with respect to an aqueous Ag–AgCl–KCl (saturated) reference, provides a radical which disproportionates to give the corresponding dihydrodiazepine base (I) and a tetrahydrodiazepine (IV). The second wave is at –2.00 V and produces the anion (IV). The reduction was studied by polarography, cyclic voltammetry, and preparative electrochemistry. The dihydrodiazepine base is electroinactive to –2.1 V, whereat it displays an apparently two-electron reduction wave.

Surprising electrochemical reduction product from a dihydrodiazepinium salt

Electrochemical reduction of 6-phenyldihydrodiazepinium perchlorate provides unexpectedly, in high yield, a pyrrolodiazepine; an interesting base–salt equilibrium between pyrrole and dihydrodiazepinium systems is observed.