Shape-persistent, double-helically twisted macrocycles with two quaterphenyl moieties: Synthesis, structure and physicochemical properties for a chiral sensor

Shape-persistent macrocyclic diene and diyne, which consist of two quaterphenyl units, were synthesized by McMurry coupling of 5,5′-bis(3-formylphenyl)-2,2′-dimethoxybiphenyl as a key step. The macrocycles have achiral (meso) and chiral (racemic) conformational isomers owing to two asymmetric axes of the biaryl units. According to the theoretical calculations, the chiral conformers are about 1 kcal mol−1 lower than the corresponding achiral conformers in energy. The NMR spectra indicate that the interconversion between the diastereomers occurs with relatively low energy barrier (<10 kcal mol−1). An X-ray crystallographic analysis of the diyne reveals that it has a double-helically twisted chiral structure and low strain nature of the molecule as expected. Moreover, the molecules construct a layered structure with channels that are filled with two chloroform molecules. Potential utilities such as a chiral sensor were also investigated.