Cyclic esters of calixarenes with phthalic acid and pyromellitic acid; synthesis and X-ray molecular structures

Abstract

The reaction of phthaloyl dichloride with tert-butylcalix[4]-, calix[5]- and calix[6]-arene has been studied. While the 1,2-bridged macrocyclic ester is the main product in the case of calix[4]- and calix[6]-arene, the intramolecular bridging of the calix[5]arene occurs mainly in the 1,3-position. The derivatives of calix[4]- and calix[6]-arene could be further O-alkylated and the ester bonds may be easily hydrolysed in these derivatives. 1,2-Singly bridged derivatives of calix[4]- and calix[6]-arene were also obtained with ClCH₂Br. Reaction of tert-butylcalix[4]arene with pyromellitic acid tetrachloride leads to the formation of a new double calixarene.

The structures of two cyclic esters have been determined by X-ray crystallography. Crystals of compound 6c·0.2 McOH are triclinic, space group P, with two molecules in a unit cell of dimensions a= 10.9292(6), b= 15.0534(10), c= 16.8534(14)Å, α= 94.195(6)°, β= 90.044(6)°, γ= 100.171(5)°, R= 0.075 for 2187 observed reflections. Crystals of compound 8·0.83 C₇H₈·0.38 C₆H₁₄ are monoclinic, space group P2₁/n, with 4 molecules in a unit cell of dimensions a= 14.5554(13), b= 35.3802(24), c= 15.0160(12)Å, β= 99.782(7)°, R= 0.072 for 4028 observed reflections. The phthaloyl residue is enclathrated in the molecular cavity of a neighbouring calix[6]arene in a self-inclusion process resulting from C–H⋯π(arene) hydrogen-bonding interactions.