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SPATIAL STRUCTURE AND NONTRIVIAL STEREODYNAMICS OF TRICYCLIC PERHYDRO-1,2,4,5-TETRAZINES

Rafael R. Kostikov, Tatiana A. Kornilova, Alexander F. Khlebnikov, Gennady V. Shustov, Alexander Yu. Ivanov, Vitaly V. Suslonov, Nikolay V. Shesternin, Mikhail A. Kuznetsov
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Abstract


Thermolysis of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes in methanol leads to the respective dimers, 5,11-diaryltetrahydro-1H,7H-dipyrazolo[1,2-a:1',2'-d]tetrazines. X-ray structural analysis of these compounds reveals the perhydrotetrazine ring adopting a chair conformation with the equatorially fused five-membered rings and with the equatorial orientation of the aryl substituents. A hindered rotation of the aryl substituents around the C–Ar bonds was observed by low-temperature NMR. Another NMR-observed process that takes place at low temperature is a reversible isomerization of the major eeee conformer into a slightly less stable aeee isomer. Density functional theory calculations (B3LYP/6-31+G(d)) on the conformational transformations of the parent tricyclic perhydrotetrazine and its 5,11-diphenyl derivative are in good agreement with the experimental findings and reveal that a conformation with the orthogonal orientation of the planes of the aryl substituents in respect to the average plane of the six-membered ring has the lowest energy.

Keywords


perhydro-1,2,4,5-tetrazines; conformations of tricyclic perhydrotetrazines; DFT quantum-chemical calculations; variable temperature NMR spectra; X-ray structures

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