SYNTHESIS AND X-RAY MOLECULAR-STRUCTURES OF P-TERT-BUTYLCALIX[4]ARENES WITH DIAMIDE BRIDGES SPANNING THE 1,3-(DISTAL) POSITIONS ON THE LOWER RIM

Reaction of a 1,3-diacid dichloride ld of p-tert-butylcalix[4]arene with various aliphatic diamines including diaza-1 5-crown-5 and diaza-1 8-crown-6 yields calixarenes capped by diamide bridges, in yields of 19-95%. The tendency for capping is so pronounced with ethylenediamine that cyclic diamide 2a is formed even in the presence of an excess of diamine. Crystals of the ethylenediamine adduct 2a and of the N,N'-dimethylethylenediamine adduct 2c were studied by X-ray diffraction. Crystals of adduct 2a are monoclinic, space group C2/c, a = 36.140(4), b = 11.879(3), c = 25.801(6) angstrom, beta = 114.66(2)-degrees with R = 0.077 for 3044 observed reflections. Crystals of adduct 2c are triclinic, space group P1, a = 10.272(2), b = 12.474(3), c = 19.351(4) angstrom, alpha = 93.799(18), beta = 95.524(15), gamma = 91.584(18)-degrees with R = 0.076 for 2317 observed reflections. While adduct 2a includes a molecule of dichloromethane in its hydrophobic cavity, the distortion of the cone conformation in adduct 2c is too severe to allow the inclusion of a guest. This distorted chiral conformation of adduct 2c (C2 symmetry) is also stable in solution at room temperature.