Synthesis of 9,10-Bis-ketoenaminoanthryl and 9,10-Bisi-isoxazolylanthryl Linked Biscalix[4]arenes: Atropisomers and Molecular Recognitions

An efficient synthetic pathway for the synthesis of biscalix[4]arenes 5-10 using 1,3-dipolar cycloaddition reactions is reported. Biscalix[4]arene 10 is capable of forming a complex with methyl viologen because of favorable cation-pi interactions and a proper cavity size to accommodate the guest. Moreover, biscalix[4]arenes 8a and 8b were found to be atropisomers at room temperature. These two conformers were unable to exchange at room temperature because of the restricted rotation of the C-9-C-11 or C-10-C-12 bonds of the beta-amino-alpha,beta-unsaturated ketones of anthracene.