Synthesis, structure (NMR and mass spectrometry) and conformational analysis of heterocyclic analogues of dibenzo[a,e]cycloocta-1,5-diene: 5,6,12,13-tetrahydrobispyrazolo [1,2-a:1',2'-e][1,2,5,6] tetraazocinediium dihalides

Several 5,6,12,13-tetrahydrobispyrazolo[1,2-a:1',2'-e][1,2,5,6]tetraazocinediium dihalides 4a-d and 8 are prepared from pyrazole, 3,5-dimethylpyrazole, 4-(1-adamantyl)pyrazole and campho[2,3-c]pyrazole by stepwise alkylation with 1,2-dibromoethane or 1,2-dichloroethane, Their structural characterization has been achieved by NMR and mass spectrometry. Dynamic NMR spectroscopy allowed the measurement of the barrier for the chair-chair interconversion in the case of the parent compound 4a and the 1,3,8,10-tetramethyl derivative 4b, These barriers as well as the preferred chair conformation are rationalized through semi-empirical and molecular mechanics calculations with regard to dibenzo [a,e]cycloocta-1,5-diene. The study of doubly charged bispyrazolium salts allows demonstration of their reduction by addition of a hydride ion [C++ + H- --> (C + H)(+)] during FABMS experiments.