Tubular structures bearing channels in organic crystals composed of adamantane-based macrocycles Masahide Tominaga a, * , Hiroyuki Ukai a , Kosuke Katagiri a , Kazuaki Ohara a , Kentaro Yamaguchi a , Isao Azumaya b, * a Faculty of Pharmaceutical Sciences at Kagawa Campus, Tokushima Bunri University,1314-1 Shido, Sanuki, Kagawa 769-2193, Japan b Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan article info Article history: Received 22 July 2013 Received in revised form 1 February 2014 Accepted 4 February 2014 Available online 2 March 2014 Keywords: Macrocycle Adamantane Channel Tubular structure CH/p interaction abstract Five macrocyclic molecules (1e5) were efficiently synthesized from the dimerization and trimerization of di-substituted adamantane derivatives, which were composed of three different aromatic units and two different linker groups. Three single-crystals were obtained from these macrocyclic molecules, including a set of pseudopolymorphs (3a and 3b) of macrocycle 3 and another macrocycle 5 (5a). Single crystal X- ray analysis revealed that the three monocyclic compounds were rectangular or square in shape with solvent molecules in the cavity. Macrocycle 3 in 3a formed stacks to produce tubular structures with channels that assembled into three-dimensional networks through CH/p interactions. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction During the course of the last three decades, significant research efforts have been directed toward the development of molecular- based tubular structures, with these materials being used in a number of different areas including ion sensors and molecular sieves, as well as heterogeneous catalysis in materials science and biochemistry. 1,2 The development of tubular assemblies can be achieved by the self-assembly of a wide variety of different organic molecules through weak noncovalent interactions, such as hydro- gen bonding and p/p interactions. As a general method, macrocy- clic frameworks containing a central cavity 3,4 can be directly stacked into tubular architectures along one axis to form one- dimensional (1D) channels. 5e7 Ghadiri et al. demonstrated that peptide-based macrocycles can be aligned into tubular structures via the formation of hydrogen bonds from the amide groups. 8 Shimizu et al. described the construction of tubular architectures built from macrocycles bearing urea groups. 9 These tubular as- semblies based on macrocycles exhibited a range of interesting practical applications, including gas adsorption and selective chemical transformation. 10 Reports pertaining to the assembly of tubular structures from macrocycle compounds without hydrogen- bonding functional groups through weaker interaction, including CH/p and halogen/halogen interactions, however, are scarce. We recently reported the synthesis of an adamantane-based macro- cycle, where two di-substituted adamantane molecules bearing 2,6-dimethoxyphenyl moieties were covalently linked to each other through 1,6-dioxahexa-2,4-diyne spacers with relatively rigid and directional properties. 11 Unfortunately, however, this macro- cycle afforded a columnar structure without channels through CH/ p and CH/O interactions in the solid state (Fig. S1). We have sub- sequently designed a variety of different adamantane-based mac- rocycles using novel aromatic units and linkers to construct tubular structures in solid crystalline materials. In this paper, we report the facial synthesis of five adamantane-based macrocycles of different shapes and sizes. Single crystals X-ray analysis revealed that mac- rocycles exhibited nearly rectangular or square shapes when guest molecules were present in the cavity. Tubular structures with 1D channels were also constructed from the stacking of these macro- cycles through CH/p interactions in the solid state. 2. Results and discussion 2.1. Syntheses The adamantane-based macrocycles discussed in this study were derived from three different macrocycles bearing one of three * Corresponding authors. Tel.: þ81 87 899 7432; fax: þ8187 894 0181 (M.T.); tel./ fax: þ81 47 472 1589 (I.A.); e-mail addresses: tominagam@kph.bunri-u.ac.jp (M. Tominaga), isao.azumaya@phar.toho-u.ac.jp (I. Azumaya). Contents lists available at ScienceDirect Tetrahedron journal homepage: www.elsevier.com/locate/tet 0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tet.2014.02.006 Tetrahedron 70 (2014) 2576e2581