Syntheses and conformations of persubstituted inverse calixarenes

Autor: Christian Weber, Thomas Oeser, Rolf Schätz, Hermann Irngartinger, U. Huber-Patz, Claus-W. von der Lieth, Gerhard Schilling, Rüdiger Pipkorn
Rok vydání: 1995
Předmět:
Zdroj: Liebigs Annalen. 1995:1401-1408
ISSN: 1099-0690
0947-3440
DOI: 10.1002/jlac.1995199508190
Popis: A series of ten inverse calix[n]arenes (2–11) bearing four to thirteen benzene units were prepared by starting from 3,4,5-trimethoxybenzaldehyde followed by LC separation on silica gel. In 2–11 the substitution pattern is interchanged compared with the usual calixarenes. The conformational analysis was undertaken by variable temperature 1H-NMR spectroscopy and by MM2 calculations. Calix[4]arene 2 is a rigid molecule and shows the 1,3-alternate conformation which in addition was proven by X-ray analysis. At low temperatures the calix[5]arene 3 adopts the uudod conformation, where a methyl group of one benzene unit residues in the cavity of the macrocycle. At low temperature calix[6]arene 4 forms an 1:2 equilibrium between the 1,3,5-alternate (ududud; 4E) and the uududu (4B) conformation. Conformation 4B can be regarded as an intramolecular combination of a cone and an alternate arrangement of the benzene units. The calix[8]-arene shows the highest ΔG* value of the series and adopts an uuududdd conformation at low temperature. The inverse calixarenes 5 and 7–11 bearing seven and nine to thirteen aromatic units, respectively, are conformationally highly flexible systems even at low temperatures.
Databáze: OpenAIRE
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