Synthesis and Dimerization Properties of Cup- and Bowl-shaped Cyclic Trilactams

Abstract

Two chiral trilactams, cup-shaped (−)-1 and bowl-shaped (−)-2, were synthesized. Single crystal X-ray analysis revealed that (−)-1 formed dimer structure by the formation of three NH⋅⋅⋅O type complementary hydrogen bonds at three amide moieties. The equilibrium constant (Keq) and kinetic parameters ▵H° and ▵S° of the dimer formation phenomenon of (−)-1 were determined by variable temperature proton NMR. Further binding energy calculation on both (−)-1 and (−)-2 dimers confirmed the more favourable formation of (−)-1 dimer than (−)-2 dimer, explaining the significant solubility difference of the two against the less polar solvent, such as CHCl3. Trilactam (−)-1 afforded coordination polymer by complexation with Zn2+, keeping the capsule-like structure.