Mechanism of calixarene formation

The X-ray crystal structure of the complex between benzene and the linear tetramer from p-cresol shows the benzene to be in a cavity formed by two intermolecularly hydrogen-bonded linear tetramers Usui, S. Deyama, K. Fukazawa, Y. Sone, T. Ohba, Y. Chem. Lett. 1991, 1387. Vocanson, F. Lamartine, R. Supramol. Chem. 1996,7,19. 

A hemicalixarene precursor to the calixarenes has also been suggested for the genesis of the 6 (see ref 1, p. 56), but recent experiments may refute this possibility. A reaction employing the Organic Synthesis conditions for preparing 6 was monitored by GC and TLC which showed that at the end of the first step relatively little linear trimer and tetramer are present but that significant amounts of the linear hexamer have formed, suggesting that the immediate precursor for 6 is a pseudocalixarene (i.e. a linear hexamer) rather than a hemicalixarene (i.e. a pair of linear trimers). 

Until recently, the acid-catalyzed synthesis of calixarenes was limited to the calixresorcarenes. A kinetic and molecular modeling study of the acid-catalyzed reaction of acetaldehyde and resorcinol comes to the conclusions that 

Konishi, H. Ohata, K. Morikawa, O. Kobayashi, K. J. Chem. Soc., Chem. Commun. 1995, 309. 

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Although it is generally accepted that the f-butylcalix[8]arene is the kinetically and the -calix[4]arene the thermodynamically controlled product while the formation of the -calix[6]arene seems to be due to a template effect, not much is really known about the mechanism of calixarene formation. The hypothesis that 2a is formed from 2e by an intramolecular step ( molecular mitosis ) could not be confirmed by isotopic labelling, which proves a more or less statistical fragmentation and recombination. ... 

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