Synthesis, Structure, and Molecular Recognition of S6- and (SO2)6-Corona[6](het)arenes: Control of Macrocyclic Conformation and Properties by the Oxidation State of the Bridging Heteroatoms

We report herein the synthesis, structure, and molecular recognition of S-6- and (SO2)(6)-corona[6](het)arenes, and demonstrate a unique and efficient strategy of regulating macrocyclic conformation and properties by adjusting the oxidation state of the heteroatom linkages. The one-pot nucleophilic aromatic substitution reaction of 1,4-benzenedithiol derivatives, biphenyl-4,4-dithiol and 9,9-dipropyl-9H-fluorene-2,7-dithiol with 3,6-dichlorotetrazine afforded S-6-corona[3]arene[3]tetrazines. These compounds underwent inverse-electron-demand Diels-Alder reaction with enamines and norbornadiene to produce S-6-corona[3]arene[3]pyridazines. Facile oxidation of sulfide linkages yielded (SO2)(6)-corona[3]arene[3]pyridazines. All corona[6](het)arenes adopted generally hexagonal macrocyclic ring structures; however, their electronic properties and conformation could be fine-tuned by altering the oxidation state of the sulfur linkages. Whereas (SO2)(6)-corona[3]arene[3]pyridazines were electron-deficient, S-6-corona[3]arene[3]pyridazines acted as electron-rich macrocyclic hosts that recognized various organic cations in both aqueous and organic solutions.