Equatorial Sulfur Atoms in Bambusurils Spawn Cavity Collapse.

This study confirms the hypothesis that bambusurils (BUs) with equatorial sulfur atoms cannot assume an anion-binding jigger conformation due to strong intramolecular van der Waals attractive interactions. NMR, X-ray crystallography, and computation with newly synthesized eq-semithio-BU[4] and ax-semiaza-eq-semithio-BU[4]s indicate that they all assume compact conformations. Intramolecular distances and a torsional angle serve as reliable indicators of the conformation of any BU. Chemoselective alkylation at the peripheral (equatorial) thiourea functions provides a convenient entry to novel hetero-BUs.