From 4-nitrotoluene and 4,4′-dinitrobibenzyl to E -4,4′-dinitrostilbene: an electrochemical approach

The dianions formed by the electroreduction of Z -O 2 NC 6 H 4 CHCHC 6 H 4 NO 2 , E -O 2 NC 6 H 4 CHCHC 6 H 4 NO 2 , O 2 NC 6 H 4 CH 2 –CH 2 C 6 H 4 NO 2 or O 2 NC 6 H 4 CMeH–CMeHC 6 H 4 NO 2 , as well as the anion radical arising from 4-nitrotoluene, are stable, in the time scale of cyclic voltammetry (DMF + 0.10 M NBu 4 BF 4 ). However, in the electrolysis time scale (from minutes to hours), only the dianion O 2 NC 6 H 4 CMeH–CMeHC 6 H 4 NO 2 2− remains stable, since the reduced species, Z -O 2 NC 6 H 4 CHCHC 6 H 4 NO 2 2− , O 2 NC 6 H 4 CH 2 –CH 2 C 6 H 4 NO 2 2− or O 2 NC 6 H 4 Me˙ − , evolve to form the E -O 2 NC 6 H 4 CHCHC 6 H 4 NO 2 2− dianion. This intermediate is recovered as the neutral species E -O 2 NC 6 H 4 CHCHC 6 H 4 NO 2 with concomitant water reduction after the work-up with water, as demonstrated by combined electrolysis, cyclic voltammetry experiments, UV-spectroelectrochochemistry and theoretical calculations. Bulk electrolysis under optimized conditions (ACN + 0.10 M NBu 4 BF 4 ) provides 40% and 67% isolated yields of E -4,4′-dinitrostilbene from 4-nitrotoluene and 4,4′-dinitrobibenzyl, respectively.