Kazuaki Oniwa

Pd-Catalyzed Cascade Crossover Annulation of o-Alkynylarylhalides and Diarylacetylenes Leading to Dibenzo[a,e]pentalenes

A novel and selective Pd-catalyzed cascade crossover-annulation of o-alkynylarylhalides and diarylacetylenes for the synthesis of dibenzo[a,e]pentalenes has been reported. Various arylacetylenes with a wide range of functional groups were tolerated, producing the corresponding multisubstituted dibenzopentalenes with the different substituents on the aromatic rings in good to high yields under the optimized reaction conditions. The reaction proceeds through a Pd-catalyzed cascade carbopalladation and C-H activation. The use of the combined DBU and CsOPiv bases is crucial for the successful implementation of the present cross-annulation.

N-Methyl Transfer Induced Copper-Mediated Oxidative Diamination of Alkynes.

A novel intramolecular oxidative diamination of bis(2-aminophenyl)acetylene for the synthesis of the structurally intriguing π-conjugated polyheterocyclic scaffold, 5,10-dihydroindolo[3,2-b]indole (DHII), has been developed under Cu(hfacac)2/O2 oxidation systems. The structure design of bis(2-aminophenyl)acetylene bearing both N,N-dimethylamine and primary amine groups is crucial for constructing the corresponding DHII scaffold. Notably, an intermolecular N-methyl transfer from the nitrogen atom of N,N-dimethylamine to the primary amine takes place, which is a critical step for the successful implementation of the present annulation process.

Triflic Acid Mediated Cascade Cyclization of Aryldiynes for the Synthesis of Indeno[1,2‐c]chromenes: Application to Dye‐Sensitized Solar Cells

A new triflic acid (TfOH)-mediated cascade cyclization of ortho-anisole-substituted aryldiynes is described for the construction of indeno[1,2-c]chromenes. The cascade cyclization proceeds through an unusual TfOH-induced alkyne-alkyne cyclization followed by nucleophilic attack of the methoxy group on the benzylidene cation, which is completely different to the cyclization of ortho-aniline- or ortho-thioanisole-substituted aryldiynes. A new class of organic dyes with the indeno[1,2-c]chromene framework as both donor and π-linker were synthesized. These compounds exhibit high photovoltaic performances in dye- sensitized solar cells (DSCs).

Synthesis of 5,10,15-triazaporphyrins—effect of benzo-annulation on the electronic structures

Novel triazaporphyrins were synthesized using 1,9-dibromodipyrromethene as a key starting material. These triazaporphyrins exhibit comparatively intense Soret and Q bands in the UV/vis region due to their hybrid properties between porphyrins and phthalocyanines.

Thieno[2,3,a]carbazole donor-based organic dyes for high efficiency dye-sensitized solar cells

A new series of donor–π-acceptor organic K-dyes based on the thieno[2,3,a]carbazole moiety as a new electron donor, trithiophene as a π-linker and cyanoacrylic acid as an electron acceptor were designed and synthesized for achieving high performances in dye-sensitized solar cells (DSCs). The substituent effect and the molecular planarity for photophysical properties and DSC performances of K-dyes have been investigated, and the highest power conversion efficiency of 7.4% has been achieved. EIS and IMVS were employed to study the effect of the molecular structure on the charge transfer process and electron lifetime.

Deuterium Isotope Effect on Bulk Heterojunction Solar Cells. Enhancement of Organic Photovoltaic Performances Using Monobenzyl Substituted Deuteriofullerene Acceptors

A series of novel monobenzyl-substituted deuteriofullerenes (BnDCs) were synthesized efficiently through Co-catalyzed selective monofunctionalization of C60. Bulk heterojunction solar cells, based on poly(3-hexylthiophene) as the donor and BnDCs as the acceptors, exhibited higher photovoltaic performances as compared to the corresponding protonated BnHCs devices.

Synthesis of extended polycyclic aromatic hydrocarbons by oxidative tandem spirocyclization and 1,2-aryl migration

The extended polycyclic aromatic hydrocarbons (PAHs) have received significant interdisciplinary attention due to their semiconducting applications in diverse organic electronics as well as intriguing structural interests of well-defined graphene segments. Herein, a highly efficient oxidative spirocyclization and 1,2-aryl migration tandem synthetic method for the construction of extended polyaromatic hydrocarbons (PAHs) has been developed. The CuCl-catalyst/PhCO3 tBu or DDQ oxidation system in the presence of trifluoroacetic acid enables the selective single-electron oxidation to take place preferentially at the more electron-rich alkene moiety of o-biphenylyl-substituted methylenefluorenes, giving rise to the subsequent tandem process. A variety of structurally diverse extended PAHs including functionalized dibenzo[g,p]chrysenes, benzo[f]naphtho[1,2-s]picene, hexabenzo[a,c,fg,j,l,op]tetracene, tetrabenzo[a,c,f,m]phenanthro[9,10-k]tetraphene, tetrabenzo[a,c,f,k]phenanthro[9,10-m]tetraphene, tetrabenzo[a,c,f,o]phenanthro[9,10-m]picene and S-type helicene have been readily synthesized.

A μ-oxo hetero dimer of silicon phthalocyanine and naphthalocyanine

A novel μ-oxo hetero dimer of silicon phthalocyanine and silicon naphthalocyanine was synthesized. Its unique optical properties, such as a single Q band, which is unusual for hetero dimer species, and solvatochromic behavior, were revealed to be better interpreted by taking interchromophore interactions into consideration.

Pd-Catalyzed Consecutive C−H-Arylation-Triggered Cyclotrimerization: Synthesis of Star-Shaped Benzotristhiazoles and Benzotrisoxazoles

Star-shaped π-extended molecules comprising discotic aromatic cores and peripheral π-conjugated arms have attracted significant attention as diverse optoelectronic materials in terms of their large π-surface, tunable self-assembly, enhanced charge transport and fluorescence, and liquid crystallinity. Although many efforts have been made in the construction of various aromatic discotic cores, a new class of C3 -symmetric star-shaped discotic π-molecules consisting of electron-deficient benzotristhiazole and benzotrisoxazole cores, which are expected to exhibit distinct optoelectronic properties, remains unexplored owing to the unachievable synthetic approaches involved in their synthesis. Herein, we report a novel and highly efficient Pd-catalyzed cyclotrimerization of the functionalized thiazoles or oxazoles for the construction of a new class of discotic molecules of benzotristhiazole and benzotrisoxazole central cores with star-shaped π-conjugated arms. The combination of [Pd2 (dba)3 ]/XPhos (dba=dibenzylideneacetone) catalyst systems with the 4-bromo-substituted thiazole enables the formation of a sufficiently stable thiazole-Pd species that participates in the subsequent C-H arylations consecutively to form the corresponding cyclic trimer products. This new class of star-shaped discotic π-extended products showed tunable energy levels and high fluorescence quantum yields that make them promising candidates for optoelectronic applications.