Department of Applied Chemistry, Graduate School of Engineering Osaka University MINAKATA Lab. Synthetic Organic Chemistry Research Group

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論文 Publication List at MINAKATA Lab.

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"Catalytic Activation of 1-Cyano-3,3-dimethyl-3-(1H)-1,2-benziodoxole with B(C6F5)3 Enabling the Electrophilic Cyanation of Silyl Enol Ethers"
Takaya Nagata, Hiroki Matsubara, Kensuke Kiyokawa*, and Satoshi Minakata*
Org. Lett. ASAP DOI:10.1021/acs.orglett.7b02313

Abstract: The Lewis acidic activation of a hypervalent iodine reagent containing a transferable cyano group, 1-cyano-3,3-dimethyl-3-(1H)-1,2-benziodoxole (CDBX), with B(C6F5)3, to achieve the catalytic electrophilic cyanation of silyl enol ethers is presented. Mechanistic studies indicate that CDBX is activated through coordination of its cyano group to B(C6F5)3, thus enabling the electrophilic cyanation reaction to occur.

"An optical and electrical study of full thermally activated delayed fluorescent white organic light-emitting diodes"
Daniel de Sa Pereira,* Paloma L. dos Santos, Jonathan S. Ward, Przemyslaw Data, Masato Okazaki, Youhei Takeda, Satoshi Minakata, Martin R. Bryce, and Andrew P. Monkman
Sci. Rep. 2017, 7, 6234/1-8. DOI:10.1038/s41598-017-06568-3

*Open-access Article!

Abstract: We report on the engineering of full thermally activated delayed fluorescence – based white organic light emitting diodes (W-OLEDs) composed of three emitters (2,7-bis(9,9-dimethyl-acridin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DDMA-TXO2), 2,7-bis(phenoxazin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DPO-TXO2) and 3,11-di(10H-phenoxazin-10-yl)dibenzo[a,j]phenazine (POZ-DBPHZ) in two different hosts. By controlling the device design through the study of the emission of DDMA-TXO2 and DPO-TXO2, the behaviour of POZ-DBPHZ in a device with more than one emitter, and the combination of the three materials, respectively, we show that external quantum efficiencies as high as 16% can be obtained for a structure with a correlated colour temperature close to warm white, together with colour rendering index close to 80. However it is in their performance stability that provides the true breakthrough: at 1000 cd/m2 the efficiencies were still above 10%, which is one of the best for this type of devices.

"Hypervalent Iodine(III)-Mediated Decarboxylative Ritter-Type Amination Leading to the Production of α-Tertiary Amine Derivatives"
Kensuke Kiyokawa*, Tomoki Watanabe, Laura Fra, Takumi Kojima, and Satoshi Minakata*
J. Org. Chem. ASAP DOI:10.1021/acs.joc.7b01202

Abstract: We report on the decarboxylative Ritter-type amination of carboxylic acids bearing an α-quaternary carbon center using a combination of PhI(OAc)2 and molecular iodine (I2) to produce the corresponding α-tertiary amine derivatives. This reaction proceeded at ambient temperature on the benchtop with a fluorescent light. Mechanistic investigations suggest that the reaction proceeds via the formation of an alkyl iodide and a higher oxidation state iodine(III) species as key intermediates. The present method represents a useful tool for the synthesis of ATAs that are difficult to prepare by conventional methods.

"Oxidative Cyclization of β,γ-Unsaturated Carboxylic Acids Using Hypervalent Iodine Reagents: An Efficient Synthesis of 4-Substituted Furan-2-ones"
Kensuke Kiyokawa*, Kenta Takemoto, Shunsuke Yahata, Takumi Kojima, and Satoshi Minakata*
Synthesis 2017, 49, 2907–2912. (Published as part of the Special Topic "Modern Strategies with Iodine in Synthesis") DOI:10.1055/s-0036-1588987


Abstract: The oxidative cyclization of β-substituted β,γ-unsaturated carboxylic acids using a hypervalent iodine reagent, to provide 4-substituted furan-2-one products, is reported. In this cyclization, the use of a highly electrophilic PhI(OTf)2, which is in-situ prepared from PhI(OAc)2 and Me3SiOTf, is crucial. Depending on the substitution pattern at the α-position of the substrates, furan-2(5H)-ones and furan-2(3H)-ones are produced. Thus, the present method offers a useful tool for accessing various types of 4-substituted furan-2-ones that are important structural motifs in the field of organic chemistry and medicinal chemistry.

"Thermally Activated Delayed Fluorescent Phenothiazine-Dibenzo[a,j]phenazine-Phenothiazine Triads Exhibiting Tricolor-Changing Mechanochromic Luminescence"
Masato Okazaki, Youhei Takeda*, Przemyslaw Data*, Piotr Pander, Heather Higginbotham, Andrew P. Monkman, and Satoshi Minakata*
Chem. Sci. 2017, 8, 2677–2686. DOI:10.1039/C6SC04863C

*Open-access Article!
*Highlighted in ResOU, Chem-Station, AlphaGalileo, EurekAlert!, Phys Org, ScienceDaily, and UPI, Asian Scientist, American Laboratory!


Abstract: Novel U-shaped donor-acceptor-donor (D-A-D) π-conjugated multi-functional molecules comprising of dibenzo[a,j]phenazine (DBPHZ) as an acceptor and phenothiazines (PTZ) as donors have been developed. Most importantly, the D-A-D compounds exhibit not only distinct tricolor-changeable mechanochromic luminescence (MCL) properties but also efficient thermally activated delayed fluorescence (TADF). Quantum chemical calculations, X-ray diffraction analysis, and systematic studies on photophysical properties have indicated that the “two-conformation-switchable” PTZ units play a highly important role in achieving multi-color-changing MCL. Time-resolved photophysical measurements have revealed that developed D-A-D compounds also exhibit efficient orange-TADF. Furthermore, organic light-emitting diode (OLED) devices fabricated with the new TADF emitters have achieved high external quantum efficiencies (EQEs) up to 16.8%, which significantly exceeds theoretical maximum (~5%) with conventional fluorescent emitters.

"Oxidative Self-annulation of 2,5-Diaryl-3,4-diaminothiophene via C–C and C–S Bond Cleavage of the Thiophene Ring: A New Synthesis of an Amino-substituted Triarylthieno[3,4-b]pyrazines and Their Photophysical Properties"
Youhei Takeda*, Satoshi Ueta, and Satoshi Minakata*
Heterocycles, 2017, 95, 137–144. (a Special Issue in honor of Professor Dr. Masakatsu Shibasaki on 70th Birthday) DOI:10.3987/COM-16-S(S)11


Abstract: A novel oxidative self-annulation of 2,5-diaryl-3,4-diaminothiophenes that accompanies C–C and C–S bonds cleavage of a thiophene ring to produce 3,5,7-triaryl-2-aminothieno[3,4-b]pyrazines in moderate to good yields has been discovered. Photophysical properties of this new family of thienopyrazines have also been disclosed.

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