Macrotricycles Featuring a π-Basic Tetrahedral Cavity:  Preference for NH₄⁺ Detected by Electrospray Ionization Mass Spectrometry

Cation-π interactions play an important role in biology. The title compounds are C₃-symmetric macrotricycles built from resorcinol, a π electron-rich arene. They were prepared in up to 18% yield by intramolecular cyclization of 1,3,5-trisubstituted benzene tripods bearing pendant resorcinol groups, with methylene acetal bridges. Positive ESI-MS showed that these receptors recognize NH₄⁺ over K⁺, and poorly respond to the large t-BuNH₃⁺ cation, suggesting that they bind NH₄⁺ intramolecularly, presumably via cation-π interactions.