Search

Mono- and tetrakis(aminomethyl)-substituted resorcinarene-based cavitands 1 and 2 and their clathrates 1 2·THF and 2·(THF)2 were investigated by FTIR spectroscopy and thermogravimetric analysis. Both hosts form stable clathrates with THF both in solution and in the solid state. Major intra- and intermolecular interactions could be identified and located by the use of vibrational spectroscopy. In all cases, dynamic cyclic intramolecular hydrogen bonds between the amino groups and neighbouring ether bridges are observable.

By comparison of the fully assigned vibrational spectra obtained for resorcarene-based cavitands 2a and 2b, their clathrates with toluene and ethanol respectively, and free guest molecules, good structural models for the clathrates could be obtained merely based on Fourier transform infrared data. Using this novel technique, various different interactions between the host and guest in the solid state as well as the orientation of the included guest could be identified. In the case of cavitand 2a, the model obtained by this methodology could be validated by comparison with an experimental crystal structure analysis.

Treatment of calix[4]arene bis-O-carbamates 4a,b-6a,b with LDA in THF results in the regio- and stereoselective introduction of both axial and equatorial carboxamide groups at the methylene bridges via a homologous anionic ortho-Fries rearrangement to give 7-16. The stereochemical outcome of the rearrangement is dependent on the reaction conditions and the conformation of the starting material. Stereochemical and structural proof has been secured by the X-ray crystal structure of calix[4]arene 10 having only one equatorial carboxamide moiety. The use of this novel class of methylene bridge-functionalized calix[4]arenes is illustrated by the formation of bis--lactone 19, while the enhanced acidity of the remaining hydroxyl groups, owing to the presence of axial carboxamide groups at the methine bridges, followed from the easy propylation of bisrearranged calix[4]arene 7.

3-7 with bromochloromethane. According to X-ray analysis of cavitand 19 and 1-D and 2-D NMR spectroscopy for 18, the cavitands possess a stereochemistry with two adjacent aryl substituents in the axial position and the two others in the equatorial position. The starting methylresorcin-[4]arenes 3-7 were obtained exclusively in the chair conformation in 30-98% yield upon condensation of 2-methylresorcinol with aryl aldehydes.

Fourfold homologous anionic ortho-Fries rearrangement in the twofold bridged tetra-O-carbamate 3 gave the tetrakis(carboxamidomethyl)resorc[4]arene 4 in 68% yield. Compound 3 was prepared by selective carbamoylation of methylresorc[4]arene 1, followed by the bridging of the remaining OH groups in tetra-O-carbamate 2.Key words: resorc[4]arenes, selective functionalizations, homologous anionic ortho-Fries rearrangement.