Controllable synthesis of diazocine - investigation on electroreduction mechanism for intramolecular cyclization of 2,2′- dinitrodibenzyl in the presence of CO2

Abstract

11,12-dihydrodibenzo[c,g][1,2]diazocine (Diazocine, 12), a molecular switch capable of reversible interconversion between (at least) two states by light, has been widely used in pharmacology and biochemistry. However, most of the synthetic methods so far have been limited by tedious steps, complicated derivatives, and long reaction times, resulting in poor synthetic yields of 12. Here, we propose a green, effective, and controllable strategy for synthesizing 12. The intramolecular cyclization (8-membered ring) of 2,2′-dinitrodibenzyl (1) was achieved by electrochemical reduction in the presence of CO₂, and 12 and its derivatives 11,12-dihydrodibenzo[c,g][1,2]diazocine-N-oxide (DDCG-N, 11) were synthesized. The electrochemical reduction mechanism of 1 in the presence of CO₂ was investigated by cyclic voltammetry (CV) and in situ FT-IR spectroelectrochemistry. The molecular structures of the electrolytic product (12) and intermediate (11) were confirmed by single-crystal X-ray diffraction, NMR, and MS. The results show that the electrochemical behavior of 1 in acetonitrile (AN) changes from a reversible two-step 1-electron transfer process (in the absence of CO₂) to an irreversible 8-electron transfer process (in the presence of CO₂). The 12 and 11 can be obtained by controlling the electrolytic potential and time. Under the optimum conditions, the yields of 12 and 11 were 84% and 71%, respectively.