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

Abstract

AbstractN‐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.