ChemInform Abstract: Selective Ipso-Nitration of tert-Butylcalix(4)arene 1,3-Diethers: X- Ray Structure of an Unexpected Side Product.

ChemInform Abstract: Calixarenes: Some Recent Developments

Reversible Dimerization of Tetraureas Derived from Calix[4]Arenes

Calix[4]arene derivatives, substituted at the wider rim by four urea functions are easily available in great variety. In apolar solvents like benzene or chloroform they dimerize via NH…O=C hydrogen bonds encapsulating a single solvent molecule as guest. The exclusive formation of dimers has been proved in solution by NMR, while their shape has been characterized by single crystal X-ray analysis. The kinetic stability and the rate of the guest exchange have been studied by NOESY experiments using a derivative with lower symmetry.