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Closed Pentaaza[9]helicene and Hexathia[9]/[5]helicene: Oxidative Fusion Reactions of ortho‐Phenylene‐Bridged Cyclic Hexapyrroles and Hexathiophenes

Abstract

Oxidative fusion reactions of ortho‐phenylene‐bridged cyclic hexapyrroles and hexathiophenes furnished novel closed helicenes in a selective manner. X‐Ray diffraction analysis unambiguously revealed the structures to be a closed pentaaza[9]helicene, the longest azahelicene reported so far, and an unexpected double‐helical structure of hexathia[9]/[5]helicene, whose formation was assumed to result from multiple oxidative fusion along with a 1,2‐aryl shift. The pentaaza[9]helicene exhibited well‐defined emission with high fluorescence quantum yield (ΦF=0.31) among the known [9]helicenes. Chiral resolution of the racemic pentaaza[9]helicene and hexathia[9]/[5]helicene were achieved by chiral‐phase HPLC and the enantiomers were characterized by circular dichroism spectra and DFT calculations.

Die oxidative Fusion von ortho‐Phenylen‐verbrückten cyclischen Oligomeren lieferte neuartige geschlossene Heterohelicene. Die Strukturen wurden durch Röntgenstrukturanalyse als Pentaaza[9]helicen und Hexathia[9]/[5]helicen als seltene Beispiele eines heteroaromatischen geschlossenen Helicens bzw. eines asymmetrischen Doppelhelicens bestätigt.

Authors:   Fengkun Chen, Takayuki Tanaka, Yong Seok Hong, Tadashi Mori, Dongho Kim, Atsuhiro Osuka
Journal:   Angewandte Chemie
Volume:   129
edition:   46
Year:   2017
Pages:   14880
DOI:   10.1002/ange.201708429
Publication date:   10-Oct-2017
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