Gathering precise knowledge on weak supramolecular interactions is difficult yet is of utmost importance for numerous scientific fields, including catalysis, crystal engineering, ligand binding, and protein folding. We report on a combined theoretical and experimental approach showing that it is possible to vastly improve the sensitivity of current methods to probe weak supramolecular interactions in solution. The concept consists of using a supramolecular platform involving a highly cooperative configurational transition, the perturbation of which (by the modification of the molecular building blocks) can be monitored in a temperature scanning experiment. We tested this concept with a particular bisurea platform, and our first results show that it is possible to detect the presence of interaction differences as low as 60 J/mol, which may be due to steric repulsion between vinyl and alkyl groups or may be the result of solvation effects.

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The synthesis of a limited series of non-racemic atropisomeric 1-(2-(4-methyl-2-thioxothiazol-3(2H)-yl)phenyl)-3-(hetero)aryl-(thio)ureas is described. Using NMR titration experiments monitoring the shift of the two NH of the (thio)urea and the C-5 hydrogen of the heterocycle, the binding constants for some optically pure (thio)-ureas with the enantiomers of N-protected amino acid tetrabutylammonium salts were determined in CD3CN. The obtained enantioselectivities were modest. Contrary to what was expected on the basis of the NH acidity in thiourea versus urea group, the association constants were smaller with the thiourea than with the corresponding urea. X-ray data, DFT calculations, and NMR provided the explanation of that unexpected behavior: the urea presents a pre-organized (Z,Z) conformation suitable for a double hydrogen bond with the carboxylate anion, the thiourea presents a (Z,E) conformation, which must be reorganized in a constrained (Z,Z) conformation in the complex. An intramolecular hydrogen bond between one NH and the thiocarbonyl group of the heterocycle, which is present in the thiourea and absent in the urea, might also contribute to the smaller K(ass) for the thiourea. The possible implication of these observations in the field of bifunctional organocatalysis is briefly discussed.

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3-Alkyl-thiazolo[3,2-a]benzimidazole derivatives are obtained in high yields via the corresponding 4-alkyl-N-3-(2-aminophenyl)-thiazoline-2-thiones which are easily prepared from 1,2-diaminobenzene, CS2 and halogenoketones. This new route compares advantageously with the classical mercaptobenzimidazole routes in term of simplicity, isolated yields and availability of the starting materials.

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In this paper we present a study concerning the basicity of some new carbanion monosubstituted pyridazinium, 3-methyl-pyridazinium, 3-(p-halogenophenyl)-pyridazinium and phtalazinium ylids. The pk a values of the conjugated acids (salts) of ylids have been experimentaly determinated. Consequently, we have evaluated their basicity (k b ) using the titration curves. The basicity depends mainly on the structure of the ylids carbanion itself, however the heterocycle's structures also has some influence on bacisity. Having in view the basicity, we have established certain correlations between basicity, structure and stability of the analised ylids.

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