Synthesis and properties of unsymmetrical azatrioxa[8]circulenes.
Insights to the subtle reactivity patterns of hydroxy-substituted carbazoles allows the precise synthesis of unsymmetrical azatrioxa[8]circulenes 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 azatrioxa[8]circulenes 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 azatrioxa[8]circulenes.
Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark. pittel@kiku.dk.
Malene
M
Plesner
Thomas
T
Hensel
Bjarne E
BE
Nielsen
Fadhil S
FS
Kamounah
Theis
T
Brock-Nannestad
Christian B
CB
Nielsen
Christian G
CG
Tortzen
Ole
O
Hammerich
Michael
M
Pittelkow