Dynamic Covalent Metathesis in the C═C/C═N Exchange between Knoevenagel Compounds and Imines.

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.

Fluorescent chemosensors for anions and contact ion pairs with a cavity-based selectivity.

The association of a concave macrocyclic compound to one or multiple fluorophores is an appealing strategy for the design of chemosensors. Indeed, as with biological systems, a cavity-based selectivity can be expected with such fluorescent receptors. Examples of calix[6]arene-based systems using this strategy are rare in the literature, and to our knowledge, no examples of fluorescent receptors that can bind organic contact ion pairs have been reported.

Use of residual dipolar couplings in conformational analysis of meta-disubstituted calix[4]arenes.

Dimercuration of tetrapropoxy calix[4]arene followed by a reaction with isoamyl nitrite afforded dinitroso regioisomers with unique substitution patterns. The unusual conformational behaviour of these inherently chiral systems was revealed by the combination of dynamic NMR and residual dipolar coupling (RDC) techniques.

Dimercuration of calix[4]arenes: novel substitution pattern in calixarene chemistry.

A mercuration reaction of tetrapropoxycalix[4]arene immobilized in the cone conformation gave a mixture of two dimercurated products (meta,meta and meta,para) in approximately a 1:1 ratio. Both regioisomers represent inherently chiral compounds, which makes them very attractive for design of novel receptors. As demonstrated by Pd-catalyzed arylation, the different reactivity of HgCl functions in the meta,para-disubstituted isomer opens the door for regioselective introductions of two different functional groups to achieve a substitution pattern so far unknown in calixarene chemistry.

Meta-arylation of calixarenes using organomercurial chemistry.

A direct mercuration reaction combined with a subsequent Pd-catalyzed arylation was used to introduce the aryl moiety into the meta position of the calix[4]arene skeleton. The application of organomercurial intermediates thus allows the straightforward formation of meta-aryl-substituted derivatives representing a unique substitution pattern in calixarene chemistry.

meta-Bridged calix[4]arenes: a straightforward synthesis via organomercurial chemistry.

The regioselective mercuration of tetraalkylated calix[4]arenes with Hg(OCOCF3)2 leads to the formation of meta-substituted products which enabled Pd-catalysed intramolecular bridging within the calixarene skeleton. Bridged derivatives represent a completely novel substitution pattern in calixarene chemistry with extremely distorted cavities and possible applications in supramolecular chemistry.

Unprecedented meta-substitution of calixarenes: direct way to inherently chiral derivatives.

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.

High sensitive calixarene-based sensor for detection of dopamine by electrochemical and acoustic methods.

We synthesized 25,26,27,28-tetrakis(11-sulfanylundecyloxy)calix[4]arene (CALIX) sensitive to dopamine and confirmed its structure by (1)H NMR and mass spectrometry. Chemisorption of CALIX molecules or their mixtures with 1-dodecanethiols (DDT) or hexadecanethiols (HDT) resulted in formation of compact low permeable monolayers as revealed by cyclic voltammetry at presence of redox probe [Fe(CN)(6)](3-/4-). These self-assembled monolayers (SAMs) served as sensor for dopamine.