First enantiopure calix[6]aza-cryptand: synthesis and chiral recognition properties towards neutral molecules

The synthesis of the first enantiopure calix6]aza-cryptand was achieved in five steps from the known 1,3,5-tris-O-methylated calix6]arene. A ¹H NMR spectroscopic study has shown that the chiral tren cap constrains the calixarene core in a straight cone conformation ideal for host–guest chemistry applications. As a result, the tetra-protonated derivative displays remarkable host properties towards polar neutral molecules and enantioselective recognition processes have been evidenced with chiral guests.