Heterocalixarenes featuring the benzimidazol-2-one subunit. Synthesis and X-ray structural studies of solvent inclusions

Abstract

The heterocalixarenes 4a,b and 5a–f have been synthesized. Compounds 4a,b and 5a–d were obtained by two-step fragment condensation from benzimidazol-2-one and 1,3-bis(bromornethyl)benzene building elements using blocking/deblocking, high dilution and template (Cs₂CO₃) techniques to give 4a/5a and 4b/5b in an approximate 1 : 2 or 1 : 3 ratio of the cyclo oligomers. The cleavage of the methyl ether groups of 5a and 5b yielded the tetraphenols 5e and 5f, respectively. The calix hosts 4a, 5a–c and 5f form crystalline inclusion compounds with organic solvent molecules. X-Ray crystal structures of the solvent inclusions 5a·methylene chloride (1 : 1), 5b·toluene·water (1 : 2 : l), Sc·acetone·methylene chloride (1 : 1 : 1) and 5f·toluene (1 : 3) have been studied. The molecular structures show a general trend of having enhanced calix-forming ability compared with conventional calix[8]arenes of the same ring size. The shape of the host molecules appear to be determined by the packing of the symmetry centres of related host molecules on either one of the benzimidazolone rings yielding basket-like hosts (5a–c) or on one of the phenol rings resulting in a chair-like host shape (5f), always exhibiting base-stacking characteristics between the aromatic planes concerned.