Chiral Calix [4] arenes

Abstract

syn-Dihydroxymetacyclophanes were converted to bridged calix [4] arene analogs by base-cat-alyzed condensation with formaldehyde. A remarkable template effect was observed on this condensation. Enlarged calix [4] arene analogs were synthesized by two different methods. All calix [4] arene analogs took the cone-type conformation and kept it even at high temperatures. From them, the unique chiral calixarenes were successfully synthesized by the following two methods : one is Williamson ether synthesis and the other is a stepwise ether cleavage with a mild Lewis acid. The high regioselectivity is recognized by the latter stepwise method. Also from them, the ionophores having oligoethylene glycol unit were obtained, which efficiently extracted larger alkali metal ions like K⁺, Rb⁺, and Cs⁺ than smaller ones like Li⁺ and Na⁺. Their ion selectivity apparently changed by the chain length of crown ether. All racemates obtained were resolved by the chiral HPLC column. The planar chiral calixarenes recognized the chirality of guest molecules. Thus, the (-) -receptor resolved strongly forms 1 : 1 complex with (R) - (+) - α-phenylethylammonium picrate.