Hemisphere-shaped calixarenes and their analogs: synthesis, structure, and chiral recognition ability

The hemisphere-shaped calixarene 1a and its split-hemisphere-shaped isomer 1b were synthesized from [2.1.2.1]metacyclophane (MCP) 3 by pinacol rearrangement and subsequent intramolecular acetalization. Their structures were revealed by X-ray crystallography and ¹H NMR spectroscopy. The temperature-dependence of the intramolecular acetalization to provide 1a and 1b was examined. The results indicated that 1a is the dominant product at high temperatures, and the values of ΔH° and ΔS° were estimated to be −18.3±0.37 kJ mol⁻¹, −59.1±1.12 kJ mol⁻¹ K⁻¹, respectively. The dinitro derivative 7 and tetranitro derivatives8 were obtained by ipso-nitration at the upper rims of 1a. The optical resolution and chiral recognition ability of racemic mixture 7 were investigated by HPLC systems.