Fourfold tetraurea calix[4]arenes—potential cores for the formation of self-assembled dendrimers

Abstract

Wide rim tetraurea calix[4]arenes monofunctionalized at the narrow rim by COOH or NH₂ have been synthesized in five steps from t-butylcalix[4]arene tripropylether. Their covalent linkage via the narrow rim to a central calix[4]arene fixed in the 1,3-alternate conformation led to pentacalix[4]arenes 9 bearing four tetraurea derivatives in the cone conformation in a flexible tetrahedral arrangement. Their self-assembly via the formation of hydrogen bonded dimeric capsules has been studied under different conditions. A fourfold heterodimerisation of tetrakis-tetraurea derivatives of type 9 with tetratosylurea 10 has been confirmed by ¹H NMR-spectroscopy and dynamic light scattering.