Daniel A. Decato

A Halogen-Bond-Induced Triple Helicate Encapsulates Iodide.

The self-assembly of higher-order anion helicates in solution remains an elusive goal. Herein, we present the first triple helicate to encapsulate iodide in organic and aqueous media as well as the solid state. The triple helicate self-assembles from three tricationic arylethynyl strands and resembles a tubular anion channel lined with nine halogen bond donors. Eight strong iodine⋅⋅⋅iodide halogen bonds and numerous buried π-surfaces endow the triplex with remarkable stability, even at elevated temperatures. We suggest that the natural rise of a single-strand helix renders its linear halogen-bond donors non-convergent. Thus, the stringent linearity of halogen bonding is a powerful tool for the synthesis of multi-strand anion helicates.

Advantages of organic halogen bonding for halide recognition

Abstract The synthesis of a bidentate halogen bonding receptor and a nearly isostructural hydrogen bonding analogue is described. Crystal structures reveal the interactions of each receptor with anions in the solid state, while NMR titrations elucidate bidentate binding and association constants in solution. Of the two, the halogen bonding receptor demonstrates stronger, water resistant halide binding in competitive solvents.

Redetermination and absolute configuration of berkeleydione

The crystal structure of the title compound, berkeleydione [systematic name; (5aS,7R,9S,11R,11aS)-methyl 9-hydroxy-1,1,5,7,9,11a-hexamethyl-14-methylidene-3,8,10-trioxo-1,3,4,5a,6,7,8,9,10,11,11a,12-dodecahydro-7,11-methanocycloocta[4,5]cyclohepta[1,2-c]pyran-11-carboxylate], C26H32O7, has been reported previously [Stierle et al. (2004 ▸). Org. Lett. 6, 1049–1052]. However, the absolute configuration could not be determined from the data collected with Mo Kα radiation and has now been determined by refinement of the Flack parameter with data collected using Cu Kα radiation. It is in agreement with the previous circular dichroism assignment, and the crystal packing is similar to that described previously.

Crystal structure and absolute configuration of preaustinoid A1.

The absolute structure of the title compound preaustinoid A1 [systematic name: (5aR,7aS,8R,10S,12R,13aR,13bS)-methyl 10-hydroxy-5,5,7a,10,12,13b-hexamethyl-14-methylene-3,9,11-trioxohexadecahydro-8,12-methanocycloocta[3,4]benzo[1,2-c]oxepine-8-carboxylate], C26H36O7, has been determined by resonant scattering using Cu Kα radiation [Flack parameter = 0.07 (15)]. The structure is consistent with that reported previously [Stierle et al. (2011). J. Nat. Prod. 74, 2272–2277], determined by detailed analysis of MS and NMR data. The molecule consists of a fused four-ring arrangement. The seven-membered oxepan-2-one ring has a chair conformation, as do the central cyclohexane rings, while the outer cyclohexa-1,3-dione ring has a boat conformation. In the crystal, molecules are linked via O—H⋯O hydrogen bonds, forming helical chains propagating along [100].

The synthesis of lactone-bridged 1,3,5-triphenylbenzene derivatives as pi-expanded coumarin triskelions

Two triply lactone-bridged 1,3,5-triphenylbenzene derivatives with solubilizing moieties have been synthesized in five and six steps from commercially available starting materials. Compounds containing the 1,3,5-triphenylbenzene core with two atom bridges are relatively unknown. This new class of pi-expanded coumarins contain triskelion architectures and X-ray crystallographic studies of one of the triskelions indicates that the 1,3,5-triphenylbenzene core adopts a near-planar geometry. This is the only known example of a two atom-bridged 1,3,5-triphenylbenzene derivative to adopt a planar structure.

Anion–Arene Interactions and the Anion–π Phenomenon

Aromatic rings are involved in nearly every aspect of chemistry, and as a result, over a century of research has been devoted to understanding their complexes and reactivity. The attractive interaction between anions and the π faces of electron-deficient aromatic rings and π systems has recently received extraordinary attention. The so-called anion–arene (or sometimes anion–π) interaction can be considered as a continuum of stabilization that occurs between electron-deficient π systems and anions. The strength and nature of the interaction depends on the nucleophilicity of the anion and the electron deficiency of the π system, resulting in both off-center and centered binding modes. The interaction is composed of electrostatics, polarization, and covalency. This article details the systematic investigations that have been employed to understand the attraction between acidic π systems and anions in the gas, solid, and solution phases. Although still lacking a formal definition, the anion–arene interaction is already becoming a standard tool to control molecular form and function.

Steric effects of pH switchable, substituted (2-pyridinium)urea organocatalysts: a solution and solid phase study

ABSTRACT The study of hydrogen bonding organocatalysis is rapidly expanding. Much research has been directed at making catalysts more active and selective, with less attention on fundamental design strategies. This study systematically increases steric hindrance at the active site of pH switchable urea organocatalysts. Incorporating strong intramolecular hydrogen bonds from protonated pyridines to oxygen stabilizes the active conformation of these ureas thus reducing the entropic penalty that results from substrate binding. The effect of increasing steric hindrance was studied by single crystal X-ray diffraction and by kinetics experiments of a benchmark reaction. Graphical Abstract

Crystal structure of [1,1':3',1''-ter-phenyl]-2',3,3''-tri-carb-oxy-lic acid.

The asymmetric unit of the title compound, C21H14O6, comprises two symmetrically independent molecules that form a locally centrosymmetric hydrogen-bonded dimer, with the planes of the corresponding carboxylic acid groups rotated by 15.8 (1) and 17.5 (1)° relative to those of the adjacent benzene rings. The crystal as a whole, however, exhibits a noncentrosymmetric packing, described by the polar space group Pca21. The dimers form layers along the ab plane, being interconnected by hydrogen bonds involving the remaining carboxylic acid groups. The plane of the central carboxylic acid group forms dihedral angles of 62.5 (1) and 63.0 (1)° with those of the adjacent benzene rings and functions as a hydrogen-bond donor and acceptor. As a donor, it interconnects adjacent layers, while as an acceptor it stabilizes the packing within the layers. The ‘distal’ carboxylic acid groups are nearly coplanar with the planes of the adjacent benzene rings, forming dihedral angles of 1.8 (1) and 7.1 (1)°. These groups also form intra- and inter-layer hydrogen bonds, but with ‘reversed’ functionality, as compared with the central carboxylic acid groups.