Synthesis of Long Oxahelicenes by Polycyclization in a Flow Reactor

• Published in: Angewandte Chemie Vol. 129; no. 21; pp. 5933 - 5937
• 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: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 15-05-2017; Wiley-VCH Verlag
• Subjects: Asymmetrische Synthesen; Backbone; Benzene; Chemical Sciences; Chemistry; Chiralität; Cobalt; Conductivity; Construction; Flow; Folding; Helicale Strukturen; Heterocyclen; Isomerization; Leitfähige Materialien; Nickel; Pyridines; Rhodium; Synthesis
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201700341

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.
Große Ziele setzen: Oxahelicene aus bis zu 19 kondensierten Ringen (siehe Beispiel) wurden durch mehrfache Cobalt(I)‐vermittelte Cycloisomerisierungen von Oligoinen in einem Strömungsreaktor synthetisiert. Die stereogenen Zentren in enantiomerenreinen Substraten dirigierten die diastereoselektiven Polycyclisierungen. Die Einzelmolekülleitfähigkeit eines Pyridooxa[9]helicens wurde mit der Break‐Junction‐Methode untersucht.