Selective upper rim functionalization and lower rim bridge building with calix[4]arenes and calix[6]arenes

Selective upper rim functionalization of calix[6]arenes has been achieved by selective lower rim benzoylation at the 1,2,4,5 positions followed by AlCl3-induced removal of the tert-butyl groups of the unesterified aryl residues and introduction of various functionalities into the vacated para positions, including bromo (5), dialkylamino, (7-11) cyanomethyl (12), and (propargyloxy)methyl (13) groups. Lower rim bridge building has been achieved via oxidative coupling reactions between the aryne moieties of calix[4]arenes and calix[6]arenes in which O-benzyl groups carry one (from 23 and 24) or two (from 25) propargyloxy residues. In the calix[4]arene series both a single-spanned (32) and a double-spanned (33) double-cavity calixarene were obtained. In the calix[6]arene series only a single-spanned double cavity calixarene (36) could be characterized.