Macrotricycles featuring a π-basic tetrahedral cavity:: Preference for NH4+ detected by electrospray ionization mass spectrometry

Cation-pi interactions play an important role in biology. The title compounds are C-3-symmetric macrotricycles built from resorcinol, a pi 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-pi interactions.