Corona[5]arenes Accessed by a Macrocycle-to-Macrocycle Transformation Route and a One-Pot Three-Component Reaction

Corona[5]arenes, a novel type of macrocyclic compound that is composed of alternating heteroatoms and para-arylenes, were synthesized efficiently by two distinct methods. In a macrocycle-to-macrocycle transformation approach, S₆-corona[3]arene[3]tetrazine underwent sequential S_NAr reactions with HS-C₆H₄-X-C₆H₄-SH (X=S, CH₂, CMe₂, SO₂, and O) to produce the corresponding corona[3]arene[2]tetrazines. Different corona[3]arene[2]tetrazine compounds were also constructed in a straightforward manner by a one-pot three-component reaction of HS-C₆H₄-X-C₆H₄-SH (X=S, CH₂, CMe₂, SO₂, and O) with diethyl 2,5-dimercaptoterephthalate and 2 equiv of 3,6-dichlorotetrazine under very mild conditions. All corona[5]arenes adopted 1,2,4-alternate conformational structures in the crystalline state yielding similar nearly regular pentagonal cavities. Both the cavity size and the electronic property of the acquired macrocycles were fine-tuned by the nature of the bridging element X.