Heterocalixarenes. Part 4. Synthesis of oxocalix[1]heterocycle[2]arenes: a unique H-bonding network in calix[1]benzimidazol-2-one[2]arene· 1/2 H2O †

Abstract

The Friedel–Crafts aroylation of 2-methylanisole with 3-methylbenzoyl chloride followed by NBS bromination and cyclizations with 1,3-dihydrobenzimidazol-2-one, 1,3-dihydro-5,6-dinitrobenzimidazol-2-one, uracil, 6-methyluracil and quinazoline-2,4(1H,3H)-dione provide respective oxocalix[1]heterocycle[2]arenes 5–9. The X-ray crystal structure (solid) and 1H NMR spectral (solution) studies show them to have by and large inwardly flattened partial cone conformations which vary in torsion angles between the rings. The calix[1]benzimidazol-2-one[2]arene·½ H2O complex shows a unique array of H-bonds in which three of the four CH and the imide oxygen of the benzimidazol-2-one unit, carbonyl oxygen and water molecule are involved in H-bonding with surrounding calixarene molecules. This heterocalixarene, in contrast to earlier reported benzimidazol-2-one-based calixarenes, does not show heterocyclic π–π stacking.