Published papers

An 8-quinolinolato rhodium catalyst was found to be effective for head-to-tail selective dimerization of arylacetylenes. Formation of substituted cyclopentene and allene derivatives via alkyne dimerization and subsequent addition of malonates was also catalyzed by the 8-quinolinolato rhodium catalyst in the presence of cesium fluoride. One-pot reaction using palladium-catalyzed alkyne dimerization in conjunction with rhodium-catalyzed addition of malonates was also possible.

The ruthenium-catalyzed coupling reactions of benzamides with alkynes in the presence of acetic acid as a promoter smoothly proceeded regio- and stereoselectively through a directed C-H bond cleavage to produce the corresponding ortho-alkenylated products. Phenylpyrazoles and related substrates also underwent a similar coupling to give dialkenylated products selectively. Several competitive experiments were performed to obtain mechanistic insight into both the mono- and dialkenylation reactions. © 2012 American Chemical Society.

We report here the first transition-metal-catalyzed anti-Markovnikov intermolecular hydroalkoxylation of terminal acetylenes to give enol ethers in high yields without using bases. Arylacetylenes as well as alkenyl- and alkylacetylenes were coupled with aliphatic alcohols, and the products were obtained with high Z selectivity in most cases. Effective catalysts were 8-quinolinolato rhodium complexes, which are structurally simple but have been relatively unexplored as catalysts. © 2010 American Chemical Society.

The palladium-catalyzed ortho-selective chlorination of N-quinolinylbenzamide derivatives with hydrochloric acid was achieved under anodic oxidation conditions. The use of 5,7-dichloro-8-quinolinyl group as directing group was effective for the selective chlorination, and the reaction was applicable to benzamide derivatives bearing various functional groups. Synthesis of vismodegib was also completed using the palladium-catalyzed electrochemical C-H chlorination in two different steps.

Palladium-catalyzed ortho-selective C-H iodination of N-(8-quinolinyl)benzamides proceeded using I-2 under both electrochemical and non-electrochemical conditions. The C-H iodination at 90 degrees C under base-free conditions provided high yields of the iodination products. The use of anodic oxidation increased the efficiency of the iodination at sterically-hindered positions.

A novel method for catalytic remote bismetalation of alkene substrates by the addition of dimetal reagents is accomplished by using chain walking. In the presence of a palladium catalyst, the reaction of various 1,n-dienes and diborons were converted into cyclopentane derivatives with two boryl groups at remote positions via facile regioselective transformation of an unactivated sp3 C-H bond to a C-B bond. Sequential construction of three distant bonds, which is difficult to achieve by any method, was accomplished for the reactions of 1,n-dienes (n ≥ 7).

The ruthenium-catalyzed alkenylation of C-H bonds with alkenylboronates has been explored for a series of aromatic ketones. The coupling reaction of pivalophenone (1) with 2-isopropenyl-5,5-dimethyl[1,3,2]dioxaborinane (2) gave the corresponding isopropenylation product in 73% yield. In the case of the reaction of a sterically congested alkenylboronate, such as 2-methylpropenylboronate (8), the yield was decreased slightly. When beta-styrylboronates were used, the corresponding coupling products were obtained in good yields. The reaction of acetophenone with alpha-styrylboronate afforded the corresponding 1:1 coupling product, exclusively.

Palladium-catalyzed remote arylative substitution was achieved for the reaction of arylboronic acids with alkenes possessing a distant acetoxy group to provide arylation products having an alkene moiety at the remote position. The use of β-acetoxy elimination as a key step in the catalytic cycle allowed for regioselective formation of unstabilized alkenes after chain walking. This reaction was applicable to various arylboronic acids as well as alkene substrates.

Anti-Markovnikov hydroamination of both aliphatic and aromatic terminal alkynes with primary amines was achieved using an 8-quinolinolato rhodium catalyst to form aldimines and enamines in high yields. This catalytic system realized high functional group tolerance including hydroxy, bromo, cyano, and thioester groups.

Upon electrochemical oxidation of configurationally stable (M)-4, 5-dimethyl-9, 10-dihydrophenanthrene attached with two spiroacridan units at the C9 and C10 positions [(M)-1c], a threeway-output response by UVvis, FL, and CD spectra was realized via clean conversion to the corresponding bond-dissociated dication (Rax)-2c2+. Similar gradual changes were induced upon standing of an aerated MeCN solution of (M)-1c after the addition of CF3CO2H because the elongated C9C10 bond was also cleaved by oxidative protonolysis to give (Rax)-2c2+.© 2014 The Chemical Society of Japan.

We report here on a C-H alkylation reaction, in which the coupling of aromatic ketones with alkenes proceeds in the presence of only a simple Fe(PMe3)(4) catalyst. The anti-Markovnikov addition of ortho C-H bonds in various ketones occurs with excellent regioselectivity under relatively mild reaction conditions. A strikingly wide variety of alkenes can be used for this reaction, and the high-yielding anti-Markovnikov addition of aromatic C-H bonds to enol ethers was achieved for the first time using this catalyst system.

Sequential formation of distant bonds in organic molecules was achieved for the palladium-catalyzed hydrosilylation/cyclization of various 1,n-dienes by chain walking of the metal catalyst. The reaction was applicable to various 1,n-dienes, including a 1,13-diene, to form a cyclopentane ring as well as a carbon-silicon bond at a remote site. The use of "nondissociative" chain walking provides a fascinating strategy in organic synthesis to functiorudize distant parts of organic molecules, in a particular order, within a catalytic cycle by effectively moving the reactive center from a remote position.

"Nondissociative" chain walking is a mechanism where an alkylmetal species undergoes rapid beta-hydride elimination and reinsertion to move the metal center along the alkyl chain without dissociating an alkene intermediate during the migration process. This digest summarizes the unique characteristics of the nondissociative chain walking mechanism compared to the stepwise alkene isomerization mechanism and their use in catalytic organic synthesis. (C) 2019 Elsevier Ltd. All rights reserved.

© The Royal Society of Chemistry 2018. Bis(dicyanomethylene)-substituted quinoidal π-conjugated systems possess a high electron-accepting nature and thus have been extensively investigated for application as n-type semiconductors. We focus on the utilization of benzene-annelation for the stabilization of the quinoidal electronic structure against the biradicaloid structure by designing quinoidal thiophenes 3-mer (BTQ) and 6-mer (BTQ-6) that have benzo[c]thiophene units. We also develop quinoidal oligothiophenes (BTQ-F) consisting of both benzo[c]thiophene and fluorinated thiophene units. The influence of benzo[c]thiophene on the quinoidal electronic structure is investigated by theoretical studies and property measurements. The molecular structure of BTQ-F is unambiguously confirmed through single-crystal X-ray diffraction. Analyses of cyclic voltammetry reveal that the lowest unoccupied molecular orbital energy levels of these compounds lie below -4.0 eV, leading to good electron-transporting characteristics even under ambient conditions in organic field-effect transistors (OFETs). Due to an increased highest occupied molecular orbital energy level, ambipolar transport is observed in BTQ-6, indicating the versatility of quinoidal π-conjugated systems incorporating benzo[c]thiophene.

Transition-metal-catalyzed C–H functionalizations have been extensively studied as atom- and step-economical methods in organic synthesis. Oxidative C–H functionalization is one of the most extensively studied reactions in this area, but it is often necessary to deactivate the remaining oxidants and to remove the wastes derived from chemical oxidants. During the past few years, a combination of transition-metal-catalyzed C–H activation and electrochemical oxidation has become a commonly-used environmentally-benign strategy for catalytic oxidative C–H functionalization. In this review, we briefly survey studies regarding the transition-metal-catalyzed oxidative C–H functionalization with the aid of electrochemical oxidation.

The reaction mechanism of the Ru(H)2(CO)(PPh3)3-catalyzed addition of C–H bonds in aromatic esters to olefins was studied by means of deuterium-labeling experiments and measurement of the 13C kinetic isotope effect. The deuterium-labeling experiment revealed a rapid equilibrium among the intermediates prior to the reductive elimination, and the 13C NMR kinetic isotope effect indicated that C–C bond formation is the rate-determining step in this reaction.

Catalyst-specific C-H/olefin as well as C-H/acetylene coupling has been accomplished for aromatics which contain both keto and imino substituents by simply changing the catalyst. By using Ru(H)2(CO)(PPh3)3 as the catalyst, the C-H bond at the position ortho to the carbonyl group reacted to add across an olefin. When Ru3(CO)12 is used as the catalyst, the C-H bond at the position ortho to the imino group reacted with the olefin.

A new strategy for catalytic functionalization of C-H bonds by means of electrochemical oxidation is described. Combination of palladium-catalyzed aromatic C-H bond cleavage and halogenation with electrochemically generated halonium ions enables highly efficient, selective halogenations of aromatic compounds in a green-sustainable manner. The required reagents for this reaction are an arene and an aqueous hydrogen halide as substrates, a palladium salt as a catalyst, and an organic solvent. No further additives such as electrolytes, oxidants, or ligands are necessary to achieve effective catalytic activity. Several remarkable advantages of the use of the electrochemical method are also described.