Tetsuo Iwanaga

The intramolecular C–F⋯HO hydrogen bond of 2-fluorophenyldiphenylmethanol

The intramolecular C–F⋯HO hydrogen bond of 2-fluorophenyldiphenylmethanol was observed by X-ray crystallographic analysis and NMR spectroscopy. The features of the spectra were compared to triphenylmethanol (a fluorine-free analog) and 2-fluorophenyldiphenylmethane.

Chemistry of anthracene–acetylene oligomers. XVII. Synthesis, structure, and dynamic behavior of 1,8-anthrylene pentamers and hexamers with acetylene linkers

Three types of cyclic oligomers consisting of five or six 1,8-anthrylene units with acetylene linkers were synthesized by macrocyclization of the corresponding acyclic precursors with coupling reactions. DFT calculations at the M05/3-21G level revealed that the pentamers had a relatively rigid structure with strained alkyne carbons. Meanwhile, out of several possible conformers the hexamers preferred to take parallelogram-prism structures due to transannular π···π interactions, and conformational interconversions via rotation about the acetylene axes took place rapidly at room temperature. NMR spectra and electronic spectra are discussed on the basis of molecular structures. The enantiomers of the chiral hexamer with one diacetylene linker were resolved by chiral HPLC, and showed optical activity.

Stereogenic Motif Consisting of Rigid Ring and Intraannular Chains: Isolation and Structures of Stereoisomers of 9-Alkyl-1,8-anthrylene−Butadiynylene Cyclic Dimers(1)

Stereoisomers of the title pi-conjugated compounds with intraannular propyl and butyl groups were isolated by chromatography. The high barrier to isomerization is attributed to the steric hindrance between the alkyl chains and the rigid framework.

Intramolecular Charge-Transfer Interaction of Donor–Acceptor–Donor Arrays Based on Anthracene Bisimide

We designed anthracene bisimide (ABI) derivatives having two triphenylamine (TPA) groups as donor units at the 9,10-positions to form a novel π-conjugated donor-acceptor system. These compounds and their analogues with ethynylene linkers were synthesized by Suzuki-Miyaura and Sonogashira coupling reactions, respectively. In UV-vis spectra, the linker-free derivatives showed broad absorption bands arising from intramolecular charge-transfer interactions. Introducing ethynylene linkers resulted in a considerable red shift of the absorption bands. In fluorescence spectra, the ethynylene derivatives showed intense emission bands at 600-650 nm. Their photophysical and electrochemical properties were compared with those of the corresponding mono TPA derivatives on the basis of theoretical calculations and cyclic voltammetry to evaluate the intramolecular electronic interactions between the donor and acceptor units.

Macrocyclic 2,7-Anthrylene Oligomers

A macrocyclic compound consisting of six 2,7-anthrylene units was successfully synthesized by Ni-mediated coupling of the corresponding dibromo precursor as a novel π-conjugated compound. This compound was sufficiently stable and soluble in organic solvents due to the presence of mesityl groups. X-ray analysis showed that the molecule had a nonplanar and hexagonal wheel-shaped framework of approximately S6 symmetry. The dynamic process between two S6 structures was observed by using the dynamic NMR technique, the barrier being 58 kJ mol(-1) . The spectroscopic properties of the hexamer were compared with those of analogous linear oligomers.

Efficient 2-amino-2-thiazolin-4-ones or 2-iminothiazolidin-4-ones formation from thioureas and maleimides under solvent-free conditions

A facile method for the construction of 2-thiazolin-4-one or thiazolidin-4-one structure is described. Condensation reactions of thiourea (la) and maleimides (2) under solvent-free conditions gave 2-amino-2-thiazolin-4-ones (3) via Michael-type reaction, while similar reactions of N-substituted thioureas (1b-d) with 2 afforded 2-iminothiazolidin-4-ones (4). Since the solvent-free reactions of 1 with 2a afforded 3 in good yields, the synthetic method was found to be effective from the viewpoint of green chemistry.

Three-Dimensional Aromatic Networks

Three-dimensional (3D) networks consisting of aromatic units and linkers are reviewed from various aspects. To understand principles for the construction of such compounds, we generalize the roles of building units, the synthetic approaches, and the classification of networks. As fundamental compounds, cyclophanes with large aromatic units and aromatic macrocycles with linear acetylene linkers are highlighted in terms of transannular interactions between aromatic units, conformational preference, and resolution of chiral derivatives. Polycyclic cage compounds are constructed from building units by linkages via covalent bonds, metal-coordination bonds, or hydrogen bonds. Large cage networks often include a wide range of guest species in their cavity to afford novel inclusion compounds. Topological isomers consisting of two or more macrocycles are formed by cyclization of preorganized species. Some complicated topological networks are constructed by self-assembly of simple building units.

Synthesis of 1,2-Bis(2-aryl-1H-indol-3-yl)ethynes via 5-exo-Digonal Double Cyclization Reactions of 1,4-Bis(2-isocyanophenyl)buta-1,3-diyne with Aryl Grignard Reagents

New π-conjugated 1,2-bis(2-aryl-1H-indol-3-yl)ethynes 1a-j having various substituents on the two aryl groups were efficiently synthesized via unusual 5-exo-digonal double isocyanide-acetylene cyclization reactions of 1,4-bis(2-isocyanophenyl)buta-1,3-diyne 3 and aryl Grignard reagents (R-MgBr, R = C6H5 (1a), 4-H3CC6H4 (1b), 2-H3CC6H4 (1c), 3-MeOC6H4 (1d), 3-(CH3)2NC6H4 (1e), 4-F3CC6H4 (1f), 4-FC6H4 (1g), 3-FC6H4 (1h), 4-PhOC6H4 (1i), and 2-Naph (1j)) in 19-85% yields. The UV-vis spectra were rationalized in detail using time-dependent DFT and single point calculations. The fluorescence emission peaks for 1a-j were observed at around 450 nm. Especially for 1f and 1j, those spectra displayed broad emission bands and relatively large Stokes shifts (3977-4503 cm-1), indicating the contribution of an intramolecular charge transfer. The absolute quantum yields (0.50-0.62) of 1a-j were higher than those of parent 8 (0.19) and 2-phenyl-1H-indole (0.11). The electrochemical features for 1a-j were investigated by cyclic voltammetry. The frontier molecular orbital levels for 1a-j were estimated based on the combination of oxidation potentials, UV-vis, and DFT calculated data. The structural property of 1,2-bis(2-phenyl-1H-indol-3-yl)ethyne 1a was characterized by several spectroscopic methods and finally determined by X-ray analysis of a single crystal of 1a recrystallized from ethyl acetate. The structural features of 1a-j were also supported by DFT calculations.

A comparison of coordination ability of hetero atoms: a Li+ and Na+ selective pyridinophane-based cryptand

A pyridinophane-based cryptand showed Li + and Na + selectivities. Crystallographic analysis of the Li + cryptate indicates that the coordination ability of the heteroatoms is in the following order: unsaturated nitrogen>oxygen>saturated nitrogen atom.

Molecular folding screen: folding and unfolding of 1,8-anthrylene–ethynylene oligomers by photochemical cycloaddition and thermal cycloreversion

Molecular folding screens consisting of anthracene plates and acetylene linkers stereoselectively fold into a zigzag form by [4 + 4]photocycloaddition, and unfold by thermal cycloreversion.