m-Terphenyl-3,3″-dioxo-derived oxacalixaromatics: synthesis, structure, and solvent encapsulation in the solid state

The synthesis of oxacalix[2]terphenylene[2]aromatics with enlarged macrocyclic holes by cyclooligomerization reaction of 5′-tert-butyl-(1,1′:3′,1″-terphenyl)-3,3″-diol 1 with electron-deficient dihalogenated benzene and azaheterocycles is described. The structures of the macrocycles were characterized by NMR, HRMS spectroscopic and X-ray diffraction techniques. Single crystal X-ray analysis revealed that the terphenyl-3,3″-dioxo unit incorporated in the oxacalix[4]aromatics scaffold can adopt all three possible conformations (I, II, III). The cis-conformational terphenyl-3,3″-dioxo (I and II) derived oxacalix[4]aromatics were found to adopt both chair and boat conformations, resulted in creation of molecular cavities capable of hosting solvent molecules of chloroform. The trans-conformational terphenyl-3,3″-dioxo (III) derived oxacalix[4]aromatics, however, adopt a twisted chair conformation with a narrow void space incapable of hosting any guest molecules.