Synthesis of Long Oxahelicenes by Polycyclization in a Flow Reactor

A series of oxahelicenes composed of ortho/meta‐annulated benzene/pyridine and 2H‐pyran rings were synthesized on the basis of the cobalt(I)‐mediated (or rhodium(I)‐ or nickel(0)‐mediated) double, triple, or quadruple [2+2+2] cycloisomerization of branched aromatic hexa‐, nona‐, or dodecaynes, thus...

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Published in:Angewandte Chemie International Edition 2017-05, Vol.56 (21), p.5839-5843
Main Authors: Nejedlý, Jindřich, Šámal, Michal, Rybáček, Jiří, Tobrmanová, Miroslava, Szydlo, Florence, Coudret, Christophe, Neumeier, Maria, Vacek, Jaroslav, Vacek Chocholoušová, Jana, Buděšínský, Miloš, Šaman, David, Bednárová, Lucie, Sieger, Ladislav, Stará, Irena G., Starý, Ivo
Format: Article
Language:English
Subjects:
asymmetric synthesis
Backbone
Benzene
chirality
Cobalt
conducting materials
Conductivity
Construction
Folding
helical structures
heterocycles
Isomerization
Nickel
Pyridines
Rhodium
Synthesis
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Summary:A series of oxahelicenes composed of ortho/meta‐annulated benzene/pyridine and 2H‐pyran rings were synthesized on the basis of the cobalt(I)‐mediated (or rhodium(I)‐ or nickel(0)‐mediated) double, triple, or quadruple [2+2+2] cycloisomerization of branched aromatic hexa‐, nona‐, or dodecaynes, thus allowing the construction of 6, 9, or 12 rings in a single operation. The use of a flow reactor was found to be beneficial for the multicyclization reactions. The stereogenic centers present in some of the oligoynes steered the helical folding in such a way that the final oxa[9]‐, [13]‐, [17]‐ and [19]helicenes were obtained in both enantiomerically and diastereomerically pure form. Specifically, the oxa[19]helicenes beat the current record in the length of a helicene backbone. Single‐molecule conductivity was studied by the mechanically controllable break‐junction method with a pyridooxa[9]helicene. Think big: Oxahelicenes comprising up to 19 fused rings (see example) were synthesized by multiple cobalt(I)‐mediated cycloisomerization reactions of oligoynes, most efficiently in a flow reactor. The stereogenic centers in enantiomerically pure substrates steered the diastereoselective polycyclization of the oligoynes. Single‐molecule conductivity was studied in a pyridooxa[9]helicene by the break‐junction method.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201700341