Highly efficient synthesis of hydrogen-bonded aromatic tetramers as macrocyclic receptors for selective recognition of lithium ions

Persistently folded aromatic amide macrocycles comprising four monomeric units (biphenyl-cyclo[4]aramide) were synthesized with high efficiency via a one-step approach along with the larger cyclic oligomer, biphenyl-cyclo[8]aramide as a minor product. Such cyclic hydrogen-bonded aromatic tetramers feature four amide oxygens enclosing a cavity with small dimensions, enabling the selective complexation of alkali metal ions, particularly Li+, with high affinity. The cyclization efficiency and selectivity of smaller macrocycles was further improved using fragment coupling and Li+-based template approaches. In addition, the superior binding ability of biphenyl-cyclo[4]aramide towards Li+ over its acyclic analogues was observed, demonstrating a remarkable macrocyclic effect.