Synthesis and Structure of N-Hetero-ortho-phenylene Hexamers Containing 2,3-Substituted Pyridine Moieties

• Published in: European journal of organic chemistry Vol. 2015; no. 35; pp. 7666 - 7669
• Main Authors: Tokoro, Yuichiro, Ohtsuka, Nobuhiko, Toh, Ayumi, Fukuzawa, Shin-ichi
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.12.2015; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: Arenes; C-H activation; Chemistry; Chemistry, Organic; Helical structures; Nitrogen heterocycles; NMR; Nuclear magnetic resonance; Physical Sciences; Science & Technology; Spectrum analysis; Stacking interactions; POLYMERS; CHIRAL RECOGNITION; Helical structures; C-H activation; POLYACETYLENE; Nitrogen heterocycles; Arenes; Stacking interactions; BASIS-SETS; HELICAL POLY(QUINOXALINE-2,3-DIYL)S; OLIGOMERS; CATALYZED DIRECT ARYLATION
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201501270

N‐Hetero‐ortho‐phenylene hexamers with two 2,3‐substituted pyridine moieties (i.e., 1a–c) were prepared by palladium‐catalyzed homocoupling with pyridine‐directed C–H cleavage as the key step. The conformations of the resulting hexamers in solution and in the solid state were investigated by computational methods, X‐ray analysis, and 1H NMR spectroscopy. Calculations at the SCS‐MP2/def2‐TZVPP//B97‐D3(bj)/def2‐SVP level suggested that helical folding of 1a as the pyridine moieties are stacked is thermally more stable than the equivalent folding in the unsubstituted ortho‐phenylene hexamer. The conformations of single crystals of 1 were consistent with the optimized structures obtained by DFT calculations. Except for rotation of the terminal phenyl groups, only one set of signals corresponding to a helical conformation was observed by analysis of 1 by 1H NMR spectroscopy in CDCl3 solution. Two pyridine rings are substituted for benzene rings in ortho‐phenylene hexamers, which are stacked in a helical conformation. Directive stacking of pyridine rings effectively stabilizes a 3:1 helical conformation, as compared with other possible conformers, even in CDCl3.