title: Cooperative Reactivity in an Extended-Viologen-Based Cyclophane.
abstract: A tetracationic pyridinium-based cyclophane with a box-like geometry, incorporating two juxtaposed alkyne functions, has been synthesized. The triple bonds are reactive through cycloadditions toward dienes and azides, promoted by the electron-withdrawing nature of the pyridinium rings, as well as by the strain inherent in the cyclophane. The cycloadditions proceeded in high yields, with the cyclophane reacting faster than its acyclic analogue. While the cyclophane contains two reactive triple bonds, there is no evidence for a stable monofunctional intermediate-only starting material and the difunctional product have been detected by (1)H NMR spectroscopy. Molecular modeling of the energy landscape reveals a lower barrier for the kinetically favored second cycloaddition compared with the first one. This situation results in tandem cascading reactions within rigid cyclophanes, where reactions at a first triple bond induce increased reactivity at a distal second alkyne.
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Dale
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Ferris
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Nicolaas A
authors.initials: NA
authors.lastname: Vermeulen
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: James J
authors.initials: JJ
authors.lastname: Henkelis
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Ilja
authors.initials: I
authors.lastname: Popovs
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.|Department of Chemistry, University of Basel , CH-4056 Basel, Switzerland.
authors.forename: Michal
authors.initials: M
authors.lastname: Juríček
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.|Department of Chemistry, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Barnes
authors.affiliation: Department of Chemistry, The University of Vermont , Burlington, Vermont 05405, United States.
authors.forename: Severin T
authors.initials: ST
authors.lastname: Schneebeli
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: J Fraser
authors.initials: JF
authors.lastname: Stoddart
mesh_terms: D000218:Adamantane / Q000737:chemistry; D000480:Alkynes / Q000138:chemical synthesis / Q000737:chemistry*; D001386:Azides / Q000737:chemistry; D001555:Benzene Derivatives / Q000138:chemical synthesis / Q000737:chemistry*; D061565:Cycloaddition Reaction; D003517:Cyclopentanes / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D011726:Pyridinium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013816:Thermodynamics; D014755:Viologens / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D000480:Alkynes; D001386:Azides; D001555:Benzene Derivatives; D003517:Cyclopentanes; D011726:Pyridinium Compounds; D014755:Viologens; D000218:Adamantane