Ryuta Sekiguchi

Synthesis of 2-Azulenyltetrathiafulvalenes by Palladium-Catalyzed Direct Arylation of 2-Chloroazulenes with Tetrathiafulvalene and Their Optical and Electrochemical Properties

Tetrathiafulvalene (TTF) derivatives with 2-azulenyl substituents 5-11 were prepared by the palladium-catalyzed direct arylation reaction of 2-chloroazulenes with TTF in good yield. Photophysical properties of these compounds were investigated by UV-vis spectroscopy and theoretical calculations. Redox behavior of the novel azulene-substituted TTFs was examined by using cyclic voltammetry and differential pulse voltammetry, which revealed their multistep electrochemical oxidation and/or reduction properties. Moreover, these TTF derivatives showed significant spectral change in the visible region under the redox conditions.

Synthesis of 2-Aminofurans by Sequential [2+2] Cycloaddition–Nucleophilic Addition of 2-Propyn-1-ols with Tetracyanoethylene and Amine-Induced Transformation into 6-Aminopentafulvenes

Synthesis of 2-aminofuran derivatives with an azulene or N,N-dimethylanilino substituent was established by the formal [2+2] cycloaddition-retroelectrocyclization of 3-(1-azulenyl or N,N-dimethylanilino)-2-propyn-1-ols with tetracyanoethylene, followed by intramolecular nucleophilic addition to the initially formed tetracyanobutadiene moiety of the internal hydroxyl group that come from 2-propyn-1-ol. The reaction proceeds under mild conditions with short reaction period. The products of the reaction are readily available through a simple purification procedure. 2-Aminofuran derivatives obtained by this reaction could be converted into 6-aminofulvene derivatives upon reaction with various amines. The structures of 2-aminofuran and 6-aminopentafulvene with a N,N-dimethylanilino substituent were confirmed by single-crystal X-ray structural analysis.

Synthesis of 1-azulenyl ketones by Brønsted acid mediated hydration of 1-azulenylalkynes

Preparation of 1-azulenyl ketones was achieved by metal-free hydration of 1-azulenylalkynes using trifluoroacetic acid as a Bronsted acid in good to excellent yields. The reaction was accomplished at a relatively low temperature with complete regioselectivity and compatibility of several functional groups.

Preparation of a cyclic polyphenylene array for a zigzag-type carbon nanotube segment.

Preparation of cyclic polyphenylene array 2, which corresponds to a complete carbon array of a zigzag-type CNT segment with (18,0)-structure, has been established by a Diels-Alder reaction of cyclic biphenylylene-acetylene derivative 1 with tetraphenylcyclopentadienone. The reaction of 2 with excess FeCl3 realized a presumed cyclodehydrogenation reaction and elimination of the alkyl chains that were introduced as a measure to counter the low solubility problem, but this resulted in the formation of a complicated mixture that included the mass region of a presumed zigzag-type CNT segment with (18,0)-structure. The rather efficient blue emission of cyclic compounds 1 and 2 was discussed utilizing fluorescence (FL) quantum efficiencies (Φ(FL)) and lifetimes (τ(FL)) in their crystalline state along with those in dichloromethane solution. Thermal analyses of these compounds revealed their characteristic phase transition behavior. The synthesis of a novel cyclic polyphenylene array by utilizing a Diels-Alder reaction of cyclic phenylene-acetylene compounds with tetraphenylcyclopentadienone should afford an attractive pathway to a novel belt-shaped CNT segment.

Synthesis of Azulene-Substituted Tetraarylpyrroles by Reaction of 1-Azulenyl Ketones with Benzoin and Ammonium Acetate

Tetraarylpyrroles with a 1-azulenyl substituent were prepared by the reaction of 1-azulenyl ketones, which have various aryl-substituents at their α-position, with benzoin in the presence of ammonium acetate as a nitrogen source of the pyrrole ring. Optical property of the tetraarylpyrroles obtained by the reaction was clarified by UV/Vis spectroscopy and/or time-dependent density functional theory (TD-DFT) calculations. INTRODUCTION A variety of synthetic methods for pyrrole derivatives have been developed so far, because the compounds having a pyrrole skeleton are found in numerous natural products and pharmaceuticals. In particular, the synthetic procedures for tetraarylpyrroles and their derivatives have been actively investigated in recent years, since the pyrrole derivatives with multiple aryl substituents have attracted the interest in the field of functional organic materials, such as luminescent materials, e.g., organic EL and LED, with high luminous efficiency and long emission lifetime. As a classical method, the dehydrative condensation reaction of 1,4-diketones with a primary amine, known as Paal-Knorr synthesis, has been employed for the synthesis of the pyrrole derivatives. However, there are some difficulties in the preparation of aryl-substituted 1,4-diketones, which become a good precursor for the arylpyrrole derivatives. As an alternative procedure, there is a dimerization method of aryl ketones in the presence of hydrazine via condensation reaction for the pyrrole synthesis, but this 1870 HETEROCYCLES, Vol. 94, No. 10, 2017

Synthesis of 2-Methyl-1-azulenyl Tetracyanobutadienes and Dicyanoquinodimethanes: Substituent Effect of 2-Methyl Moiety on the Azulene Ring toward the Optical and Electrochemical Properties

We describe the comparative study of optical and electrochemical properties of tetracyanobutadienes (TCBDs) and dicyanoquinodimethanes (DCNQs) with a 2-methyl-1-azulenyl group and their derivatives with a 1-azulenyl substituent examined under the same conditions. TCBDs and DCNQs with a 2-methyl-1-azulenyl substituent have been prepared by the Sonogashira-Hagihara alkynylation of the 2-methyl-1-iodoazulene with arylalkyne derivatives, followed by the formal [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction with tetracyanoethylene and 7,7,8,8-tetracyanoquinodimethane. The optical properties of the TCBDs and DCNQs with a 2-methyl-1-azulenyl group were investigated through the comparison with those of TCBDs and DCNQs with a 1-azulenyl substituent by employing the UV/vis spectroscopy and theoretical calculations. The electrochemical properties of the TCBD and DCNQ derivatives were also examined by cyclic voltammetry and differential pulse voltammetry experiments, which elucidated their multistep redox properties. Furthermore, noticeable spectral changes of these chromophores were identified by the spectroelectrochemical measurements.