Published papers

We developed two new catalytic transformations of anilines via oxidative addition of C-N bonds to ruthenium centers. One is ruthenium-catalyzed reductive deaminatoindeamination of N-alkylated o-acylanilines. The other one is catalytic coupling of N-alkylated o-acylanilines with olefins giving ortho-alkylated aromatic ketones via C-N bond cleavage. This reaction involves a ruthenium hydride species as an intermediate, formed after beta-hydride elimination from the ruthenium amide species. (C) 2013 Elsevier B.V. All rights reserved.

The reactivity of various o-acylaniline derivatives with ruthenium complexes was examined. The reaction of o-acylanilines with RuH 2(CO)(PPh3)3 (1) or an activated ruthenium species formulated as "Ru(CO)(PPh3)3" (4) gave amido hydrido complexes 3 and aryl amido complexes 6 formed via N-H and C-N bond cleavage, respectively. Addition of olefins, such as vinylsilanes, accelerates the C-N bond cleavage. The aryl amido complexes 6 can provide the C-N arylation product upon treatment with arylboronates. The relative reactivity of o-acylanilines bearing various substituents was investigated by competition experiments, and it was found that electron-donating substituents increase the relative facileness of the C-N bond cleavage in both stoichiometric and catalytic reactions. The trend observed here is different from the one observed for the previously reported tantalum-mediated C-N bond cleavage. © 2013 American Chemical Society.

Efficient, selective, transition-metal-catalyzed C-H functionalizations have been widely studied and are recognized as atom-and step-economical tools in organic synthesis. During the past two decades, a variety of catalytic reactions involving C-H bond cleavage have been developed. In this review, we briefly survey studies dealing with transition-metal-catalyzed efficient and selective C-H functionalization by electrochemical reactions.

We report here the ruthenium-catalyzed selective monoarylation of aromatic ketones bearing two ortho carbon-heteroatom (O or N) bonds. Under the newly developed catalyst system consisting of RuHCl(CO)(PiPr3)2, CsF, and styrene, the C-O arylation of 2′,6′-dimethoxyacetophenone with a phenylboronate gave the C-O monoarylation product selectively. The selective C-O monoarylation was applicable to a variety of arylboronates and aromatic ketones and proceeds with high regio- and chemoselectivities. A formal synthesis of altertenuol was also achieved using the C-O monoarylation of an aromatic ester as a key step.

Selective long-distance isomerization of terminal alkenes to silyl enol ethers proceeded via nondissociative chain walking using phenanthroline palladium catalysts. Notable features achieved taking advantage of the nondissociative chain walking mechanism include high efficiency obtained regardless of the chain length, high chemoselectivity toward terminal alkenes over internal ones, and retention of the stereoconfiguration of the stereocenter on the alkyl chain.

A catalyst system consisting of RuHCl(CO)-((PPr3)-Pr-i)(2), CsF, and a styrene derivative was found to be applicable to selective monoarylation of aromatic ketones via ortho C-H bond cleavage. The reaction of 2'-methoxyace-tophenone with arylboronates gave C-H arylation products without cleaving the ortho C-O bond. Acetophenone was also converted to monoarylation products with high selectivity. Cyclohexanone was found to be an effective solvent for the C-H arylation using the catalyst system.

Solution-phase assembly of a Rh complex using specific hydrogen bonding between BA and TAP moieties was achieved by tuning the substituent on TAP to control the solubility of the assembly

We report here ruthenium-catalyzed arylation of fluorinated aromatic ketones via ortho-selective carbon-fluorine bond cleavage. In the presence of trimethylvinylsilane and cesium fluoride, ortho carbon-fluoride bonds of aromatic ketones were phenylated by 5,5-dimethyl-2-phenyl-1,3,2-dioxaborinane using RuH2(CO)(PPh3)3 as a catalyst. Tandem C-F phenylation/C-H alkylation was observed for substrates bearing both one ortho hydrogen and one ortho fluorine atoms © 2011 Elsevier Ltd. All rights reserved.

Catalytic conversion of unreactive sp3 C-O bonds in alkyl ethers to C-C bonds is described. Alkyl ethers bearing 2- or 4-pyridyl groups were coupled with triarylboroxines in the presence of a ruthenium catalyst. Triarylboroxines bearing a variety of functional groups including electron-withdrawing and -donating groups can be used for the reaction. No additional base was required for the coupling with the organoboron reagents, and base-sensitive groups can be tolerated. The reaction is considered to proceed via dehydroalkoxylation followed by addition of triarylboroxines to form C-C bonds. © 2011 American Chemical Society.

The cross-coupling of maleimides with electron-deficient alkenes such as acrylates proceeds smoothly under ruthenium catalysis. This unique C-C coupling provides a simple, straightforward synthetic method for preparing alkylidene succinimide derivatives.

Ruthenium-catalyzed selective monoalkenylation of ortho C-O or C-N bonds of aromatic ketones was achieved. The reaction allowed the direct comparison of the relative reactivities of the cleavage of different carbon-heteroatom bonds, thus suggesting an unconventional chemoselectivity, where smaller, more-electron-donating groups are more easily cleaved. Selective monofunctionalization of C-O bonds in the presence of ortho C-H bonds was also achieved. Smaller is better: The title reaction for ortho C-O and C-N bonds of aromatic ketones was achieved. Direct comparison of the cleavage of the carbon-heteroatom bonds suggested an unconventional chemoselectivity, where smaller, more-electron-donating groups are more easily cleaved. Selective monofunctionalization of C-O bonds in the presence of ortho C-H bonds was also achieved.

Mechanistic studies of the ruthenium-catalyzed reaction of aromatic ketones with olefins are presented. Treatment of the original catalyst, RuH2(CO)(PPh3)(3), with trimethylvinylsilane at 90 degrees C for 1-1.5 h afforded an activated ruthenium catalyst, Ru(o-C6H4PPh2)(H)(CO)(PPh3)(2), as a mixture of four geometric isomers. The activated complex showed high catalytic activity for C-H/olefin coupling, and the reaction of 2'-methylacetophenone with trimethylvinylsilane at room temperature for 48 h gave the corresponding ortho-alkylation product in 99% isolated yield. The activated catalyst was thermally robust and showed excellent catalytic activity under refluxing toluene conditions. H-1 and P-31 NMR studies of the C-H/olefin coupling at room temperature suggested that an ortho-ruthenated complex, P,P'-cis-C,H-cis-Ru(2'-(6'-MeC6H4C-(O)Me))(H)(CO)(PPh3)(2), participated in the reaction as a key intermediate. Isotope labeling studies using acetophenone-d(5) indicated that the rate-limiting step was the C-C bond formation, not the C-H bond cleavage, and that each step prior to the reductive elimination was reversible. The rate of C-H/olefin coupling was found to exhibit pseudo first-order kinetics and to show first-order dependence on the ruthenium complex concentration.

Ru/C also exhibits catalytic activity for carbonylation at ortho-C-H bonds in 2-phenylpyridines.

The RuH2(CO)(PPh3)(3)-catalyzed C-H functionalization of aromatic esters with 5,5-dimethyl-2-aryl-[1,3,2]dioxaborinanes (arylboronates) gave the ortho arylation products. This coupling reaction can be performed with various combinations of isopropyl benzoate derivatives and arylboronates. Introduction of CF3 group in the aromatic ring increased the reactivity of the esters. Pinacolone effectively served as an acceptor of a hydride generated by C-H bond cleavage, and the amount of pinacolone used also affected the yield of the arylation product. (C) 2010 Elsevier B.V. All rights reserved.

Ruthenium-catalyzed regioselective direct amino- and alkoxycarbonylations of aromatic rings via C-H bond cleavage using chlorocarbonyl compounds are described. A broad generality of amide and ester groups was achieved taking advantage of the wide availability of carbonylating agents. Alkyl chloroformates, inapplicable to usual Friedel-Crafts methods, can also be used for direct catalytic alkoxycarbonylation.

The RuH2(CO)(PPh3)(3)-catalyzed reaction of 2-amino-6-methylacetophenone with phenylboronic acid 2,2-dimethyl-1,3-propanediol ester in refluxing toluene gave the corresponding phenylation product in 83% yield via aryl carbon-nitrogen bond cleavage. This reaction involves two notable features: (1) the coupling proceeds via the oxidative addition of an aryl carbon-nitrogen bond in anilines to the ruthenium complex, and (2) C-C bond formation takes place via transmetalation between the Ru-NR2 species and organoboronates.

The first catalytic intermolecular [2 + 2] cycloaddition of terminal alkynes with electron-deficient alkenes is reported. The reaction proceeds with an 8-quinolinolato rhodium/phosphine catalyst system to give cyclobutenes from various substrates having polar functional groups in high yields with complete regioselectivity. © 2013 American Chemical Society.