Selective functionalization of calix[4]arenes via tricarbonylchromium complexes

Tricarbonylchromium complexes of 25,26,27,28-tetrapropoxycalix-[4] arene conformers (1(4)Pr) were synthesized. Since the benzene ring is activated through complexation with Cr(CO)(3), the functional groups (e. g. -D, -CH3, and -CHO) could be selectively introduced into the Cr(CO)(3)-complexed benzene ring. The substitution reaction occurred mainly at the p-position. The para selectivity was attributed to the steric crowding being relatively lower than that around the meta and benzyl position. This view was supported by the X-ray crystallographic study of 1,3-alternate-1(4)Pr center dot(CO)(3). This is a novel and general methodology for selective introduction of functional groups into calix [n] arenes.