Contrary to theoretical predictions, direct alkylation of 2,14-dithiacalix[4]arene provides only four out of five basic conformers (atropisomers). To prepare the missing 1,2 (C)-alternate conformer, the indirect alkylation strategy was applied using 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane as a protective agent. As proved by the combination of NMR and X-ray crystallography, the position of the disiloxane bridge on the macrocycle is not fixed and can be changed under basic conditions, representing thus so far unknown rearrangement of the siloxane moiety. The subsequent dialkylation/deprotection and dialkylation enabled the synthesis of the last missing conformer. As demonstrated by several examples, the mixed-bridge macrocycle (with both CH2 and S bridging units) enables preparation of unusual conformers or substitution patterns, which are difficult to obtain, if at all, in classical calixarene chemistry. This feature makes 2,14-dithiacalix[4]arene a very promising candidate for the role of molecular scaffold or platform in various supramolecular applications.

Department of Organic Chemistry University of Chemistry and Technology Prague Technická 5 166 28 Prague 6 Czech Republic

Department of Solid State Chemistry UCTP 166 28 Prague 6 Czech Republic

Laboratory of NMR spectroscopy UCTP 166 28 Prague 6 Czech Republic

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