Rob G. Janssen

Conformational isomerism and self-association of calixarene building blocks in non-polar solution studied by Fourier transform infrared spectrometry

In order to establish the conformational equilibrium of calix[6]arene derivatives, a series of phenolic building blocks differing in chain length (oligomers) have been studied in solution by Fourier transform infrared spectrometry (FT-IR). Different intramolecular OH ? X interactions have been established in the calixarene building blocks, i.e. OH ? ?, OH ? OH, OH ? OCH3 and a bifurcated OH ? OH/OCH3 or OH ? OH/OH one. Concentration-dependent measurements show that the ?biphenol? and ?triphenol? oligomers form cyclic dimers even at very low concentration ( 10?2 M). Preliminary MM3 calculations were performed to support conformational assignment.

Cryptocalix[6]arenes; molecules with a large cavity

A new type of cavitand molecules with large cavities (4a–g) has been synthesized by the covalent three-point linking of a p-tert-butylcalix[6]arene to a cyclotriveratrylene (CTV) and their dynamic behavior has been studied by 1H NMR spectroscopy.

Hydrogen bonded calix[4]arene aggregates

Chiral biaryl alcohols were readily transformed in a single step, with chiral non-racemic 1,2-diamines, PCl3, and sulfur in CDCl3 - all in a NMR tube - to their diastereomeric diazaphospholidines and their diastereomeric ratios (also ees) assessed directly.

Synthesis of calix[6]arenes partially functionalized at the upper rim

Several new examples of calix[6]arenes selectively functionalized at the upper rim are reported. Starting from calix[6]arenes 1,3,5-tri-, 1,2,4,5-tetra- and 1,2,3,4,5-pentaalkylated at the lower rim, it is possible to isolate macrocycles 2,4,6-tri-, 3,6-di- and 6-mono functionalized at the upper rim (18?94% yield) with nitro, formyl, bromo, chloromethyl and 2-propenyl groups. Modifications of these moieties allow the synthesis of macrocycles bearing amino, amido, hydroxymethyl, carboxy, cyano and chloromethyl functions which can be used for further transformation and preparation of new molecular receptors, based on calix[6]arenes, which have different geometries. Examples of di- and triquinones on the hexameric macrocycle are also reported.

Selective phosphorylation of p-tert-butylcalix[6]arene

The synthesis of selectively phosphorylated and thiophosphorylated p-tert-butylcalix[6] arenes is described; the solid-state structure of the 1,4-bis(thiophosphorylated)p-tert-butylcalix[6]arene is elucidated by X-ray crystallography.

Spectroscopic studies of hydrogen-bond structures and dynamics of partially methylated p-tert-butylcalix[6]arenes

Hydrogen-bond structures of partially methylated p-tert-butylcalix[6]arenes were investigated both in solution and the solid state by Fourier transform infrared spectroscopy (FTIR). The hydrogen bonds in these macrocycles are preferentially of the three-centred and cooperative types. The dynamic behaviour of these calix[6]arenes is characterized by fast rearrangement of the methoxy groups in the calix[6]arene annulus and was investigated by means of 2D NMR spectroscopy. The conformational behaviour is primarily dominated by an interplay of favourable hydrogen-bond formation and the tendency of selfinclusion of the methoxy groups