Synthesis of Long Oxahelicenes by Polycyclization in a Flow Reactor. Issue 21 (18th April 2017)

• Record Type: Journal Article
• 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
• Is Part Of: Angewandte Chemie international edition. Volume 56:Issue 21(2017)
• Page Start: 5839
• Page End: 5843
• Publication Date: 2017-04-18
• Subjects: asymmetric synthesis -- chirality -- conducting materials -- helical structures -- heterocycles; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201700341
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: A series of oxahelicenes composed of ortho / meta ‐annulated benzene/pyridine and 2 H ‐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. Abstract : 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.