Synthesis and conformational studies of calixarene analogue chiral [3.3.1]metacyclophanes

Trihydroxy[3.3.1]metacyclophane, which can be regarded as an unsymmetrical or incomplete "homocalix[3]arene", has been prepared from rimethoxy[3.3.1]metacyclophane by demethylation with trimethylsilyl iodide in MeCN. Di-O-methylation at the lower rim of trihydroxy[3.3.1]metacyclophane in the presence of K2CO3 in acetone afforded a novel, inherently chiral calixarene-analogue, namely a macrocyclic [3.3.1]metacyclophane, possessing C1 symmetry. The inherent chirality of the two conformers was characterized by ¹H NMR spectroscopy by addition of an excess of Pirkle's chiral shift reagent [(S)-(+)-1-(9-anthryl)-2,2,2-trifluoroethanol], which caused a splitting of the OMe group and AB patterns corresponding to the methylene protons.