title: Synthesis and conformational study of the first triply bridged calix[6]azatubes.
abstract: [reaction: see text] The first C(3)(v)- and D(3)(h)-symmetrical triply bridged calix[6]azatubes were prepared in good yields from the known 1,3,5-tris-methylated calix[6]arene through an efficient [1 + 1] macrocyclization reaction. A remarkably regioselective hexa ipso-nitration reaction led to a calix[6]azatube substituted at the wide rim in alternate position by tBu and nitro groups. A (1)H NMR study showed that, whereas the parent bis-calix[6]arenes self-include their methoxy groups, thereby closing their inner tube, the nitro-substituted calix[6]azatube undergoes a conformational change with the expulsion of the methoxy groups, hence presenting a three-dimensional structure open for host-guest applications.
authors.affiliation: Faculté des Sciences et Techniques, URCOM, Université du Havre, 25 rue Philippe Lebon, BP 540, 76058 Le Havre Cedex, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Le Gac
authors.forename: Xianshun
authors.initials: X
authors.lastname: Zeng
authors.forename: Olivia
authors.initials: O
authors.lastname: Reinaud
authors.forename: Ivan
authors.initials: I
authors.lastname: Jabin