Regioselective ipso-nitration of calix[4]arenes

A novel protection/deprotection method leading to the regioselective ipso-substitution of calix4]arenes is described. The introduction of nosyl (p-nitrobenzenesulfonyl) groups into the lower rim of partly alkylated tert-butylcalix4]arenes leads subsequently to the exclusive ipso-nitration of the alkylated phenol rings, while the protecting groups can be easily removed in the next step. This method gives dialkoxy- or trialkoxy-substituted calix4]arenes with nitro groups on the alkylated rings and tert-butyl groups on the remaining ones. The above substitution pattern is complementary to the isomers so far known in the chemistry of calix4]arenes and could be used in the design of novel type of calixarene-based receptors.