Synthesis and Conformational Properties of Nonsymmetric Pillar[5]arenes and Their Acetonitrile Inclusion Compounds

Abstract The catalytic cyclocondensation of 1‐butoxy‐4‐methoxy‐2,5‐bis(methoxymethyl)benzene ( 1d ) affords a statistical mixture of the regioisomeric pillar[5]arenes 3a – d in high yield. The alkoxy groups are arranged stereoselectively in a mode so that they avoid steric interactions. The rotation of the benzene rings is, at room temperature, fast in terms of the NMR timescale and leads to a de facto C s symmetry for 3a – c and a C 5 h symmetry for 3d . All four structural isomers can encapsulate two CH 3 CN guest molecules. The structure determinations are based on four crystal structure analyses (constitutions) and NMR spectroscopic measurements (conformations).