CHEMICALLY MODIFIED CALIX[4]ARENES - REGIOSELECTIVE SYNTHESIS OF 1,3-(DISTAL) DERIVATIVES AND RELATED-COMPOUNDS - X-RAY CRYSTAL-STRUCTURE OF A DIPHENOL-DINITRILE

p-tert-Butylcalix[4]arene has been chemically modified in a regioselective manner at the 1,3-(distal) phenolic groups of the lower rim using electrophiles such as ethyl bromoacetate, chloroacetone, bromopinacolone, chloroacetonitrile, and prop-2-ynyl bromide. X-Ray diffraction analysis of one of these 1,3-derivatives reveals that it exists in a highly distorted cone conformation. Crystals of the dinitrile 7 are triclinic, space group P1BAR, with two molecules in a cell of dimensions a = 13.191(3), b = 16.755(3), c = 10.424(1) angstrom; alpha = 100.32(1), beta = 93.23(1), gamma = 84.89(2)-degrees. The structure was solved by direct methods and refined by full-matrix least squares calculations; R = 0.066 for 4155 observed reflections. The two phenolic rings (A and C) are tilted (interplanar angle 102.3-degrees) so as to place the hydroxy groups inside the cavity, whereas rings B and D bearing OCH2CN moieties are almost parallel to each other (interplanar angle 13.3-degrees). This arrangement allows for relatively facile intramolecular hydrogen bond formation between proximal hydroxy and ether functional groups [O(H)...O 2.941(3) and 2.903(3) angstrom]. These products are useful precursors of other 1,3-disubstituted derivatives including double calixarenes and of a variety of tetrasubstituted calix[4]arenes with dual functionality on the lower rim.