Fast and reversible dynamic covalent C═C/C═N exchange takes place without catalyst in nonpolar solvents between barbiturate-derived Knoevenagel (Kn) compounds and imines. A detailed study of the reaction indicates that it proceeds by an associative organo-metathesis mechanism involving the formation of a four-membered ring azetidine intermediate by addition of the imine C═N group to the C═C bond of the Kn compound. This intermediate could be generated cleanly and stabilized at low temperature by condensation of the o,p-dinitrophenyl Kn derivative with the cyclic imine 1-azacyclohexene. It was characterized by extensive NMR and mass spectrometric studies. The process described represents a genuine dynamic covalent organo-metathesis through a four-membered ring adduct as intermediate. It paves the way for the exploration of a wide set of dynamic systems involving (strongly) polarized C═C bonds and various imines, extending also into covalent dynamic polymers and polymolecular assemblies.

Electrophilic aromatic substitution in the calix[n]arene series is a well-established procedure leading exclusively to para-substituted derivatives. An unprecedented regioselectivity of the mercuration reaction leading to the meta-substituted calix[4]arenes is described. These compounds represent a new type of substitution pattern in classical calixarene chemistry and open the door for the straightforward synthesis of inherently chiral receptors based on calixarenes.