Cavity effect of calix[4]arenes in electrophilic aromatic substitution reactions

Calix[4]arene dimers; self-assembly via hydrogen bonding at the upper rim

“…7 The hydrogen-bonded dimer 5ؒ5 adopts the pinched cone conformation in which the aromatic units bearing the carboxylic acid groups are oriented face-to-face whereas the other two aromatics are 'flattened'. The intermolecular O ؒ ؒ ؒ O distances of the hydrogen-bonded carboxylic acid groups are O(2) ؒ ؒ ؒ O(8Ј) 2.644 (10) and O(1) ؒ ؒ ؒ O(7Ј) 2.621(10) Å. The carboxylic acid groups of the 5ؒ5 are oriented in the plane with respect to the aromatic units.…”

Inherently chiralcone-calix[4]arenesviaa subsequent upper rim ring-closing/opening methodology

“…For example, interconversion for upper-rim unsubstituted compounds can be observed only below 250 K. 25 Such high proximity between distal positions can be covalently "trapped", as witnessed by a number of reports in which these two positions were connected by 3-, [26][27][28][29][30] 2-, [31][32][33][34] and even a 1-atom bridge. 35 In the recent past, we have exploited this high proximity with a simple method for the desymmetrization of a symmetrical cone distal-diformylcalix [4]arene. 36 The strategy was based on a highly efficient intramolecular hydride transfer during a Cannizzaro reaction (aldehyde disproportionation) with an Effective Molarity 37 (EM) as high as 600 M. 36 The procedure was then extended to AAAH trifunctionalized cone-derivatives, for which regiospecificity of the two reactive functions on the distal aromatic rings was observed.…”

A novel host molecule p-[1-(4-hydroxyphenyl)-1-methylethyl]calix[8]arene. Synthesis and complexation properties in non-aqueous polar solution

“…The complexation and catalytic properties of calixarenes and their derivatives have been extensively studied. [13][14][15][16][17][18] It has been well established that calixarenes can include small molecules in the solid state. 13, 14 Unambiguous evidence for inclusion complexes of calixarenes in solution has also been reported.…”

“…There are only a few examples of the complexation of neutral molecules in non-aqueous solutions. 17, 18 It seems to us that some calixarene derivatives should also be able to bind nonpolar substrates in a polar non-aqueous medium and in this case the driving force for the complexation is lipophobic interactions. In the present work we wish to report the synthesis of p-[1-(4-hydroxyphenyl)-1-methylethyl]calix- [8]arene 1 for the first time, and demonstrate that this calixarene can form inclusion complexes with a variety of aromatic compounds in polar non-aqueous solutions.…”