Zwitterionic spirocycles based on dinitrobenzofurazan and tropolone heteroanalogs

Zwitterionic spirocyclic σ-complexes were synthesized by reaction of 7-chloro-4,6-dinitrobenzofurazan with 2-(benzylamino)cyclohepta-2,4,6-trien-1-one, 2-(benzylamino)cyclohepta-2,4,6-triene-1-thione, and N-benzyl-7-(benzylimino)cyclohepta-1,3,5-trien-1-amine. The structure, stereodynamics, and stability of the spirocycles were studied by NMR spectroscopy, X-ray analysis, and DFT quantum chemical calculations at the B3LYP/6-31G** level of theory. The contribution of heteroatoms to positive charge delocalization and the thermodynamic and kinetic stabilities of the spirocycles increase in the series aminotropone < aminothiotropone < aminotropone imine.