Synthesis and properties of unsymmetrical azatrioxacirculenes†
Insights to the subtle reactivity patterns of hydroxy-substituted carbazoles allows the precise synthesis of unsymmetrical azatrioxacirculenes by the reaction of N-benzyl-2,7-di-tert-butyl-3,6-dihydroxycarbazole with two different 1,4-benzoquinones in the presence of an oxidant (chloranil) and a Lewis acid (BF3OEt2). The unique synthetic control obtained originates from the selectivity obtained upon reacting N-benzyl-2,7-di-tert-butyl-3,6-dihydroxycarbazole with an electron-rich benzoquinone to give first the C–C bond formation and then subsequently the dibenzofuran formation with high regioselectivity. Herein the first synthesis of unsymmetrical antiaromatic azatrioxacirculenes and the full characterization using NMR spectroscopy, optical spectroscopy, electrochemistry, computational techniques and single crystal X-ray crystallography is reported. The controlled stepwise condensation of N-benzyl-2,7-di-tert-butyl-3,6-dihydroxycarbazole with two different 1,4-benzoquinones gives selectively the unsymmetrical azatrioxacirculenes.