Synthesis and assembly of self-complementary cavitands

Cavitands with self-complementary shapes (3 and 4) were prepared by the cov alent attachment of adamantane guest molecules to the upper rim of the host structures. Relatives of the "self-folding" cavitands 2, these new structu res possess a seam of intramolecular hydrogen bonds that stabilize the fold ed conformation. Their self-complementary shapes result in the formation of noncovalent dimers of considerable kinetic and thermodynamic stability (-D elta G(295) = 4.5 kcal/mol for 3a and 6.5 kcal/mol for 4a in p-xylene-d(10) ). The dimerization of cavitands 3 and 4 is reversible and subject to contr ol by solvent and temperature. The dimerization process is enthalpically fa vored and entropy opposed and occurs with significant enthalpy-entropy comp ensation.