SYNTHESES AND OPTICAL RESOLUTION OF CALIX[4]ARENES WITH MOLECULAR ASYMMETRY - SYSTEMATIC CLASSIFICATION OF ALL POSSIBLE CHIRAL ISOMERS DERIVABLE FROM CALIX[4]ARENE

All possible chiral isomers that can be derived from calix[4]arene by modification of the OH groups were systematically classified. Molecular asymmetry can be generated not only by different substituents but also by conformational isomerism. The numbers of chiral isomers are 24 for tetra-O-substituted calix[4]arenes, 10 for tri-O-substituted calix[4]arenes, 3 for di-O-substituted calix[4]arenes, and 0 for mono-O-substituted calix[4]arenes. This implies that calix[4]arene is a useful building block for the design of novel asymmetric ring structures. In order to demonstrate asymmetry in these chiral calix[4]arenes, we synthesized several tetra-, tri-, and di-O-substituted calix[4]arenes by using the metal template method, the stepwise synthesis method, the protection-deprotection method, etc., which were developed in efforts directed toward regioselective O-alkylation and control of conformational isomerism in calix[4]arenes. Finally, we succeeded in complete optical resolution of chiral calix[4]arenes by an HPLC method using a chiral-packed column or by the formation of diastereomers with the (-)-menthoxyacetyl group. This article thus contains all of the molecular design concepts, syntheses, and optical resolutions of chiral calix[4]arenes.