Synthesis of 9,10-bis-ketoenaminoanthryl and 9,10-bis-isoxazolylanthryl linked biscalix[4]arenes: atropisomers and molecular recognitions

An efficient synthetic pathway for the synthesis of biscalix4]arenes 5-10 using 1,3-dipolar cycloaddition reactions is reported. Biscalix4]arene 10 is capable of forming a complex with methyl viologen because of favorable cation-π interactions and a proper cavity size to accommodate the guest. Moreover, biscalix4]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 β-amino-α,β-unsaturated ketones of anthracene.