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Cyclo[8]pyrrole–phosphonate complexes were synthesized via the anion exchange method from cyclo[8]pyrrole sulfate. The molecular structures were determined by X-ray diffraction studies.

During the preparative investigation of [Formula: see text]-expanded porphyrinoids based on the retro-Diels-Alder reaction of bicyclo[2.2.2]octadiene(BCOD)-fused precursors for benzo- and benzo[[Formula: see text]]fluorantho[9,10]-[[Formula: see text]]porphyrins by the [3+1] porphyrin synthesis using tripyrrane-1,14-dicarbaldehyde and BCOD-fused pyrroles, serendipitous formation of the corresponding corroles was observed. After elucidation of the reaction conditions, the [3+1] reaction afforded 21,31-dihydro-21,31-ethanobenzo[[Formula: see text]]fluorantho[9,10-[Formula: see text]]corrole in 23% yield as well as a trace amount of the corresponding porphyrin. In the sapphyrin synthesis by the [3+2] approach using the tripyrrane-1,14-dicarbaldehyde and a bipyrrole, the similar reaction conditions resulted in the formation of 5-pyrrolylcorrole in a 38% yield as well as isosmaragdyrin and the originally targeted sapphyrin.

Bicyclo[2.2.2]octadiene(BCOD)-fused 5,15-diazaporphyrins were synthesized via a metal-template aza-annulation of dipyrrin-metal complexes as a soluble precursor of tetrabenzodiazaporphyrin. 10-Azacorrole copper complex with a meso-imine bridge was serendipitously obtained via the same reaction using dimethylBCOD-fused dipyrrin-copper complex.

Dibenzofurans featuring a 2,2′-biazulene framework were prepared in good yields by Brønsted acid-promoted annulation of 2,3-di(1-azulenyl)benzofurans in 100% H3PO4.

π-Expanded homoHPHACs with thiocarbonyl and carbonyl bridges change their global aromaticity in response to external stimuli as observed in tropothione and tropone.

A "3+3" condensation reaction of 1,3-di(2-pyrrolyl)azulene with aryl aldehyde followed by an oxidative aromatization afforded diazuliamethyrin, [24]diazulihexaphyrin(0.1.0.0.1.0). X-ray diffraction analysis revealed a relatively planar structure of diprotonated diazuliamethyrin with a mean plane deviation of 0.37 Å. A 24π non- or antiaromatic character was confirmed by

Bicyclo[2.2.2]octadiene(BCOD)-fused dithiaamethyrin 4 was synthesized via a “3+3” condensation method. Thermal conversion of the BCOD moieties afforded tetrabenzodithiaamethyrin 5. The highly planar structures of 4 and 5 were confirmed by X-ray diffraction studies. The 1H NMR, absorption and MCD spectra, together with TD-DFT calculations revealed that both BCOD-fused and [Formula: see text]-extended dithiaamethyrins have a 24[Formula: see text] antiaromatic character.

Cyclo[9]pyrrole, a ring-expanded porphyrin without meso-bridges and having an odd number of pyrroles, was synthesized via the oxidative coupling of 2,2':5',2″-terpyrrole. X-ray crystallography showed a C2-like symmetry with a large root-mean-square deviation. The optical properties and electronic structures were analyzed using magnetic circular dichroism spectroscopy and time-dependent density functional theory calculations.

Performing bottom-up synthesis by using molecules adsorbed on a surface is an effective method to yield functional polycyclic aromatic hydrocarbons (PAHs) and nanocarbon materials. The intramolecular cyclodehydrogenation of hydrocarbons is a critical process in this synthesis; however, thus far, its elementary steps have not been elucidated thoroughly. In this study, we utilize the metal tip of a low-temperature noncontact atomic force microscope as a manipulable metal surface to locally activate dehydrogenation for PAH-forming cyclodehydrogenation. This method leads to the dissociation of a H atom of an intermediate to yield the cyclodehydrogenated product in a target-selective and reproducible manner. We demonstrate the metal-tip-catalyzed dehydrogenation for both benzenoid and nonbenzonoid PAHs, suggesting its universal applicability as a catalyst for nanographene synthesis.

Starting with the reaction of 2H-cyclohepta[b]furan-2-ones with an enamine, which was prepared from 4-tert-butylcyclohexanone and pyrrolidine, benz[a]azulenes having both formyl and tert-butyl groups were obtained in the three-step sequence. Subsequently, both the formyl and tert-butyl groups were eliminated by heating the benz[a]azulene derivatives in 100% H3PO4 to give benz[a]azulenes without these substituents in high yields. In terms of the product yield, this method is the best one ever reported for the synthesis of the parent benz[a]azulene so far. The conversion of the benz[a]azulene derivatives with a formyl group into cyclohept[a]acenaphthylen-3-one derivatives was also investigated via Knoevenagel condensation with dimethyl malonate, followed by Brønsted acid-mediated intramolecular cyclization. The structural features including the bond alternation in the benz[a]azulene derivatives were revealed by NMR studies, NICS calculations, and a single-crystal X-ray structural analysis. The optical and electrochemical properties of a series of benz[a]azulene derivatives were evaluated by UV/Vis, fluorescence spectroscopy and voltammetry experiments. As a result, we found that some benz[a]azulene derivatives showed remarkable luminescence in acidic media. In addition, the benz[a]azulene derivatives with the electron-withdrawing group and cyclohept[a]acenaphthylen-3-one derivative displayed good reversibility in the spectral changes under the electrochemical redox conditions.

Symmetrical octaphenyltetrabenzoporphyrins 3 were synthesized via cyclotetramerization from bicyclo[2.2.2]octadiene (BCOD)-fused pyrrole, followed by a thermal conversion based on retro Diels–Alder...

In this paper, we describe an efficient and atom-economical synthesis of highly functionalized pyrroles, pentafulvenes, and pyrrolopyridines by [2+2] cycloaddition-retroelectrocyclization of N-substituted propargylamines with tetracyanoethylene, followed by the treatment of the resulting tetracyanobutadiene derivatives with silica gel. In this reaction, silica gel plays an important role to promote the intramolecular cyclization to afford the heterocyclic products from the tetracyanobutadiene intermediates. The products were obtained selectively depending on the substituent on the nitrogen atom of the starting propargylamines.

A ring-contracted carbaporphyrin, azulitriphyrin(2.1.1), was synthesized via intramolecular McMurry coupling reaction. Absorption, NMR spectra and NICS calculations of protonated azulitriphyrin(2.1.1) revealed its Hückel aromatic character as a 14[Formula: see text] porphyrinoid.

Novel thermally convertible precursors of tetrabenzoporphyrin (TBP) were synthesized by tetramerization of the corresponding bicyclo[2.2.2]octadiene(BCOD)-fused pyrroles. These precursors showed hi...

Di(acenaphtho)-fused BODIPYs with four electron-withdrawing N,N-dimethylcarbamoyl groups were obtained by complexation of the corresponding dipyrrins, which were also proven to be a stable deep-red...

1,3-Dihydrothieno[3,4-a]- and 1,3,8,10-tetrahydrodithieno[3,4-a;3′4′-m]-HPHACs were prepared by the successive SNAr reactions of hexafluorobenzene with 1,3-dihydrothieno[3,4-c]pyrrole and 3,4-dihex...

The nucleophilic aromatic substitution (SNAr) reaction of diethyl 6-bromoazulene-1,3-dicarboxylate (1) with a variety of amines afforded the corresponding 6-aminoazulene derivatives 2a–2j in good-to-excellent yields. 6-Aminoazulene derivatives 3a–3f without the 1,3-diethoxycarbonyl functions were obtained by the deesterification of 2a–2f with 100% H3PO4. The reactivity of 6-aminoazulenes toward the bromination, SNAr, and palladium-catalyzed cross-coupling reactions was also clarified. 6-Arylazoazulenes 13a–13c were also prepared via the SNAr reaction of 1 with arylhydrazines, followed by oxidation with Pb(OAc)4 in the presence of N2H4. The structural, optical, and electrochemical properties of the 6-amino- and 6-arylazoazulenes were revealed by single-crystal X-ray structure analysis, UV/vis spectroscopy, voltammetry analysis, spectroelectrochemistry, and theoretical calculations.

The reaction of 1,2-diformylazulenes with several maleimides in the presence of PPh3 gave the corresponding azulenophthalimides with an ester function at the five-membered ring in moderate to good yields. The removal of the ester function from the azulenophthalimide with an N-cyclohexyl function was also achieved by the treatment with 100% H3PO4. The optical and electrochemical properties of the azulenophthalimides were investigated by UV/Vis measurements, voltammetry experiments and DFT calculations. The azulenophthalimide without the ester function exhibited remarkable emission under acidic conditions. Moreover, the azulenophthalimides displayed a significant spectral change under electrochemical reduction conditions.

The reaction of several azulenylalkynes having an aryl substituent with elemental sulfur afforded the corresponding azuleno[2,1-b]thiophenes in moderate to good yields. Decarboxylation of an azuleno[2,1-b]thiophene derivative with an ester function was also achieved by treatment with 100% H3PO4. The structural features of the azuleno[2,1-b]thiophene derivatives were revealed by X-ray single-crystal analysis. The optical and electrochemical properties of the azuleno[2,1-b]thiophene derivatives were investigated by UV/Vis spectroscopy, voltammetry experiments and theoretical calculations.

Radially π-extended hexapyrrolohexaazacoronene (HPHAC 2) was synthesized in two steps with 2,5-di-tert-butyl-acenaphtho[1,2-c]pyrrole and hexafluorobenzene. Like its parent HPHAC 1a, 2 exhibited re...

A bicyclo[2.2.2]octadiene(BCOD)-fused bis(dipyrromethane) derivative was reacted with methylal in the presence of trifluoroacetic acid followed by oxidation with chloranil to give a doubly N-confused phlorin derivative, which did not undergo the retro-Diels-Alder reaction extruding an ethylene molecule on heating. In contrast, a 7-tert-butoxybicyclo[2.2.1]heptadiene(7-BuOBCHD)-fused bis(dipyrromethane) yielded benzene-ring-fused doubly N-confused porphyrins by following similar reaction sequences.

A core-expanded, pyrrole-fused azacoronene analogue containing two unusual N-doped heptagons was obtained from commercially available octafluoronaphthalene and 3,4-diethylpyrrole in two steps as a heteroatom-doped nonplanar nanographene. Full fusion with the formation of the tetraazadipleiadiene framework and the longitudinally twisted structure was unambiguously confirmed by single-crystal X-ray diffraction analysis. The edge-to-edge dihedral angle along the acene moiety was 63°. This electron-rich π-system showed four reversible oxidation peaks. Despite the nonplanar structure, the Hückel aromaticity owing to a peripheral π-conjugation in the dicationic state was concluded from the bond-length alternation and nucleus-independent chemical shift (NICS) and anisotropy of the induced current density (ACID) calculations.

The adsorption configurations of heptahelicene ([7]H) molecules on Cu(001) are investigated with noncontact atomic force microscopy (ncAFM) and scanning tunneling microscopy (STM). Because of the suppression of thermal diffusion at 5 K, racemic [7]H molecules exist as monomers, dimers, trimers, and tetramers on the surface. The terminal naphthaleno part of the molecule is attached horizontally to the substrate so that the two benzene ring centers are located at the hollow sites, whereas the other terminal is protruded toward a vacuum. A procedure for picking a [7]H molecule up from the surface (vertical manipulation) enables us to functionalize the tip apex to enhance the spatial resolution of ncAFM. The ncAFM images with the helicene tip clarify that whereas the tetramers are homochiral, the dimers and trimers are heterochiral. In contrast, homochiral dimers and trimers are unobservable probably because of the rapid formation of the stable homochiral tetramers. Thus, ncAFM imaging can identify the geomet...

Benzene-fused bis(acenaphthoBODIPY)s prepared by retro-Diels–Alder reaction of bicyclo[2.2.2]octadiene-fused precursors showed strong absorption bands in the near-infrared region and very weak absorptions in the visible region.

The preparation of azulene-substituted benzofurans and isocoumarins was established by two types of intramolecular cyclization reaction of 1-ethynylazulenes. 2-(1-Azulenyl)- and 2,3-bis(1-azulenyl)benzofurans were prepared by the palladium-catalyzed cross-coupling reaction of 1-iodoazulenes with 2-ethynylphenol and that of 1-ethynylazulenes with 2-iodophenol under Sonogashira-Hagihara reaction conditions following the intramolecular nucleophilic addition of the oxygen nucleophile to the presumed 1-arylethynylazulenes. In contrast, 1-(phenylethynyl)azulenes bearing an o-methoxycarbonyl function on the substituted phenyl moiety exhibited intramolecular cyclization either in the presence of trifluoroacetic acid or N-iodosuccinimide (NIS) to afford azulene-substituted isocoumarins and 4-iodoisocoumarins, and the structures were clarified by single-crystal X-ray analysis. The optical properties of these compounds were also investigated by UV/vis spectroscopy and theoretical calculations.

In this study, a benzene-fused bis(thiaporphyrin) was synthesized by the retro-Diels–Alder reaction of a bicyclo[2.2.2]octadiene (BCOD)-fused bis(thiaporphyrin) precursor. This precursor was prepared by the double [3+1] porphyrin synthesis of the BCOD-fused dipyrrole with thiatripyrrane. The ultraviolet–visible (UV–vis) spectrum of benzene-fused bis(thiaporphyrin) in dichloromethane was extremely different from that of the corresponding benzene-fused bis(porphyrin). In contrast, extremely similar spectra were obtained in the presence of trifluoroacetic acid. The similar electronic structures in the protonated states were supported by X-ray analysis and time-dependent density-functional theory (TD-DFT) calculations.

Controlling the structural deformation of organic molecules can drive unique reactions that cannot be induced only by thermal, optical or electrochemical procedures. However, in conventional organic synthesis, including mechanochemical procedures, it is difficult to control skeletal rearrangement in polycyclic aromatic hydrocarbons (PAHs). Here, we demonstrate a reaction scheme for the skeletal rearrangement of PAHs on a metal surface using high-resolution noncontact atomic force microscopy. By a combination of organic synthesis and on-surface cyclodehydrogenation, we produce a well-designed PAH—diazuleno[1, 2, 3-cd:1′, 2′, 3′-fg]pyrene—adsorbed flatly onto Cu(001), in which two azuleno moieties are highly strained by their mutual proximity. This local strain drives the rearrangement of one of the azuleno moieties into a fulvaleno moiety, which has never been reported so far. Our proposed thermally driven, strain-induced synthesis on surfaces will pave the way for the production of a new class of nanocarbon materials that conventional synthetic techniques cannot attain., 金属表面で分子を曲げて骨格を変える新・有機合成法を開発 --原子間力顕微鏡を用いて炭素骨格変換の可視化に成功--. 京都大学プレスリリース. 2017-07-24.

The SNAr reaction of 2-chloroazulene derivative 1 with ethoxycarbonyl groups at the 1,3-positions of the azulene ring with several amines afforded the corresponding 2-aminoazulenes 3-9 in excellent yields. 2-Chloroazulene (2) without the electron-withdrawing groups reacted with highly nucleophilic cyclic amines (i.e., morpholine, piperidine and pyrrolidine) under the high-temperature conditions in a sealed tube to produce the corresponding 2-aminoazulenes 10-12 in good yields. 2-Aminoazulenes 10-14 without the electron-withdrawing groups were also obtained in good yields by the treatment of compounds 3-7 with 100% H3PO4, but in the cases of the reaction of 8 and 9 with a secondary amine function, the decomposition of the products resulted. The synthesis of 2-arylazoazulenes 15-18 was also established via the SNAr reaction of 1 with arylhydrazines. The optical and electrochemical properties of the 2-arylazoazulene derivatives were examined by UV/Vis spectroscopy, theoretical calculations and voltammetric experiments., Article, ORGANIC & BIOMOLECULAR CHEMISTRY. 94(10):3917-3923 (2017)

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., Article, CHEMISTRY-A EUROPEAN JOURNAL. 23(21):5126-5136 (2017)

The protonation behavior of bicyclo[2.2.2]octadiene (BCOD)-fused thiaporphyrin and thiabenzoporphyrin was examined by titration with trifluoroacetic acid. Neutral, monorotonated, and diprotonated species of thiaporphyrins were easily detected by UV–vis spectral measurement. The first (K1) and second (K2) equilibrium constants were found to be K1 = 520 and K2 ≈ 7.1 for BCOD-fused thiaporphyrin and K1 = 1.4 × 104 and K2 ≈ 1.4 for thiabenzoporphyrin. The difference between K1 and K2 values of thiaporphyrins is larger than that observed for porphyrins (N4-porphyrins). The main contributing conjugation pathways for thiaporphyrins in both protonated species were investigated by NICS and AICD quantum calculations using their atomic geometries obtained by X-ray structural analysis. The 18π-conjugation pathways of the neutral, monoprotonated, and diprotonated species thiaporphyrins were found to contain 18, 19, and 20 atoms, respectively. Results of 1H NMR studies also support the major contributing pathways.

Parikh–Doering oxidation of diethyl 9-hydroxy-2,6-dimethyl-4,8-dihydro-4,8-methanopyrrol[3,4-f]isoindole-1,7-dicarboxylate produced diethyl 9-oxo-2,6-dimethyl-4,8-dihydro-4,8-methanopyrrol[3,4-f]isoindole-1,7-dicarboxylate. This carbonyl derivative spontaneously underwent cheletropic extrusion of carbon monoxide, producing diethyl 2,6-dimethylpyrrol[3,4-f]isoindole-1,7-dicarboxylate, which showed 14π-electronic aromaticity on the whole five-six-five ring system.

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.

Azulene-substituted tetracyanobutadienes (AzTCBDs) and dicyanoquinodimethanes (AzDCNQs) connected with naphthalene cores were prepared by the reaction of 1-azulenylalkynes with tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) in a formal [2 + 2] cycloaddition-retroelectrocyclization. The characteristic intramolecular charge transfer (ICT) characters were investigated by using UV/Vis spectroscopy and theoretical calculation. The redox behaviors of AzTCBDs and AzDCNQs were examined by cyclic voltammetry and differential pulse voltammetry, which revealed their properties of multi-electron transfer depending on the number of AzTCBD and AzDCNQ moieties. Moreover, significant color changes were observed by visible spectroscopy under the electrochemical reduction conditions., Article, HETEROCYCLES. 95(1):353-369 (2017)

Synthesis of an azacoronene, in which both pyrrole and azulene moieties are circularly fused, was achieved just in three steps. This new azacoronene exhibited multistep reversible oxidations under electrochemical and chemical conditions. Formation of an aromatic 22π-electron conjugation and a tropylium cation (6π-electron conjugation) in the dicationic state was revealed by the single-crystal X-ray crystallographic analysis as well as the nucleus-independent chemical shift (NICS) and anisotropy of the induced current density (ACID) calculations.

The synthesis of 1,2-biazulenes was established by palladium-catalyzed homocoupling reactions of the corresponding 1-haloazulenes in the presence of ferrocene. The optical properties of the novel 1,2-biazulenes were investigated by UV/Vis spectroscopy and theoretical calculations. The redox behaviors of 1,2-biazulenes were also examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV)., Article, SYNTHESIS. 89(11):2438-2448 (2016)

Tris[(3-phenyl-1-azulenyl)tetracyanobutadiene]s and tris(aryltetracyanobutadiene)s connected to a 1,3,5-tri(1-azulenyl)benzene core (tris-AzTCBDs) have been prepared by the Pd-catalyzed alkynylation of tris(3-iodo-1-azulenyl)benzene derivative with the corresponding 1-ethynylazulene or ethynylbenzene derivatives under Sonogashira–Hagihara cross-coupling conditions, followed by the reaction with tetracyanoethylene (TCNE) in a formal [2 + 2] cycloaddition-retroelectrocyclization (CA–RE) reaction. The intramolecular charge-transfer (ICT) interactions of the new chromophores were investigated by the comparison with those of the model tetracyanobutadiene derivatives with azulene substituents (AzTCBDs), which were prepared by the reaction of the corresponding 1-ethynylazulene derivative with iodoarenes, followed by the CA–RE reaction with TCNE, utilizing UV/Vis spectroscopy and theoretical calculations. The redox behavior of the alkyne precursors and the tetracyanobutadiene derivatives was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their multistep electrochemical reduction properties. Moreover, significant color changes of these compounds were observed by visible spectroscopy under the electrochemical reduction conditions.

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.

Ferrocene-substituted 1,1,4,4-tetracyano-1,3-butadienes (FcTCBDs) connected by arylamine and azobenzene spacers were prepared by the reaction of a variety of alkynes with tetracyanoethylene (TCNE) ...