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Electrophilic Aromatic Coupling of Hexapyrrolylbenzenes. A Mechanistic Analysis
journal contribution
posted on 2019-11-19, 20:37 authored by Maksim Navakouski, Halina Zhylitskaya, Piotr J. Chmielewski, Marika Żyła-Karwowska, Marcin StępieńOxidative transformation of hexapyrrolylbenzenes into
azacoronenes
using bromine electrophiles as alternative coupling agents is shown
to occur according to a distinct mechanism, different from those proposed
for typical high-potential oxidants. It is shown that consecutive
cyclizations do not involve brominated intermediates and can be rationalized
by assuming a relayed arenium cation attack followed by deprotonation
and conjugate elimination. The final cyclization is incompatible with
this mechanism and is found to involve double-electrophilic bromination
followed by thermal elimination of dibromine. These findings provide
insight into the reactivity of sterically congested aromatic systems
and may help in designing new methods of C–C bond formation.
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bromine electrophilesarenium cation attackazacoronenestericallyagentHexapyrrolylbenzenealternativeinsightcyclizationreactivitymechanismhexapyrrolylbenzeneElectrophilic AromaticdeprotonationMechanistic Analysis Oxidative transformationfindingbondmethoddibrominehigh-potential oxidantsconjugate eliminationdouble-electrophilic brominationbrominated intermediates
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