Yoichiro Kuninobu

Copper‐Catalyzed Intramolecular C(sp3)H and C(sp2)H Amidation by Oxidative Cyclization

The first copper-catalyzed intramolecular C(sp(3))-H and C(sp(2))-H oxidative amidation has been developed. Using a Cu(OAc)2 catalyst and an Ag2CO3 oxidant in dichloroethane solvent, C(sp(3))-H amidation proceeded at a terminal methyl group, as well as at the internal benzylic position of an alkyl chain. This reaction has a broad substrate scope, and various β-lactams were obtained in excellent yield, even on gram scale. Use of CuCl2 and Ag2CO3 under an O2 atmosphere in dimethyl sulfoxide, however, leads to 2-indolinone selectively by C(sp(2))-H amidation. Kinetic isotope effect (KIE) studies indicated that C-H bond activation is the rate-determining step. The 5-methoxyquinolyl directing group could be removed by oxidation.

Rhodium-catalyzed synthesis of silafluorene derivatives via cleavage of silicon-hydrogen and carbon-hydrogen bonds.

The rhodium-catalyzed synthesis of silafluorenes from biphenylhydrosilanes is described. This highly efficient reaction proceeds via both Si-H and C-H bond activation, producing only H(2) as a side product. Using this method, a ladder-type bis-silicon-bridged p-terphenyl could also be synthesized.

A meta-selective C–H borylation directed by a secondary interaction between ligand and substrate

Regioselective C-H bond transformations are potentially the most efficient method for the synthesis of organic molecules. However, the presence of many C-H bonds in organic molecules and the high activation barrier for these reactions make these transformations difficult. Directing groups in the reaction substrate are often used to control regioselectivity, which has been especially successful for the ortho-selective functionalization of aromatic substrates. Here, we describe an iridium-catalysed meta-selective C-H borylation of aromatic compounds using a newly designed catalytic system. The bipyridine-derived ligand that binds iridium contains a pendant urea moiety. A secondary interaction between this urea and a hydrogen-bond acceptor in the substrate places the iridium in close proximity to the meta-C-H bond and thus controls the regioselectivity. (1)H NMR studies and control experiments support the participation of hydrogen bonds in inducing regioselectivity. Reversible direction of the catalyst through hydrogen bonds is a versatile concept for regioselective C-H transformations.

Rhodium‐Catalyzed Asymmetric Synthesis of Spirosilabifluorene Derivatives

Chiral compounds occupy a large and important area of organic molecules, such as natural products, bioactive compounds, drugs, and functional materials. However, examples of the synthesis of chiral organosilicon compounds are still rare among organic compounds. It is important to construct a quaternary silicon atom to synthesize chiral organosilicon compounds. Our strategy for the construction of a quaternary silicon atom is a rhodium-catalyzed double dehydrogenative cyclization of bis(biphenyl)silanes through carbon–silicon bond formation (Scheme 1). 3] We report herein the asymmetric synthesis of chiral spirosilabifluorene derivatives from bis(biphenyl)silanes, bearing substituents on the aromatic rings, using a rhodium catalyst with a chiral phosphine ligand.

Palladium-catalyzed synthesis of dibenzophosphole oxides via intramolecular dehydrogenative cyclization

Dibenzophosphole oxides were obtained from secondary hydrophosphine oxides with a biphenyl group by dehydrogenation via phosphine-hydrogen and carbon-hydrogen bond cleavage in the presence of a catalytic amount of palladium(II) acetate, Pd(OAc)(2). By using this reaction, a ladder-type dibenzophosphole oxide could also be synthesized by double intramolecular dehydrogenative cyclization.

Rhenium-Catalyzed Diastereoselective Synthesis of Aminoindanes via the Insertion of Allenes into a C−H Bond

Aminoindane derivatives were synthesized diastereoselectively by the treatment of aromatic imines with allenes in the presence of a catalytic amount of a rhenium complex, [HRe(CO)(4)](n). The allenes inserted into the aromatic C-H bonds.

Palladium-Catalyzed Direct C–H Silylation and Germanylation of Benzamides and Carboxamides

A palladium-catalyzed regioselective activation of C(sp(2))-H and C(sp(3))-H bonds of benzamides and carboxamides, followed by coupling with disilanes to afford organosilanes in moderate to high yields, with the aid of 8-aminoquinoline as a directing group, is reported. Catalytic C(sp(2))-H germanylation of benzamides also proceeds under the same palladium catalysis. The reaction tolerates a wide variety of functional groups and is scalable without yield reduction. The bidentate directing group is readily removed and recovered by the reaction with a hydrazine, with concominant generation of an acyl hydrazide.

Indium-Catalyzed Construction of Polycyclic Aromatic Hydrocarbon Skeletons via Dehydration

Polycyclic aromatic compounds can be synthesized from 2-benzylic- or 2-allylbenzaldehydes using a catalytic amount of In(III) or Re(I) complexes. By using this method, polycyclic aza-aromatic compounds can also be prepared efficiently. In these reactions, only water is formed as a side product.

Manganese- and Borane-Mediated Synthesis of Isobenzofuranones from Aromatic Esters and Oxiranes via C–H Bond Activation

A manganese- and borane-mediated synthesis of isobenzofuranones from esters and oxiranes is developed. The reaction proceeded at aromatic, heteroaromatic, and olefinic C-H bonds with high functional group tolerance. This is the first example of a manganese-catalyzed C-H transformation using an oxygen-directing group. Triphenylborane played an important role in this reaction to cooperatively promote the annulation reaction. Kinetic isotope effect experiments revealed that C-H bond activation of the aromatic rings was the rate-determining step.

Rhenium-catalyzed insertion of nonpolar and polar unsaturated molecules into an olefinic C-H bond

Treatment of olefins bearing a directing group with alpha,beta-unsaturated carbonyl compounds, alkynes, or aldehydes in the presence of a catalytic amount of a rhenium complex, [ReBr(CO)(3)(thf)](2) gave gamma,delta-unsaturated carbonyl compounds, dienes, and allyl silyl ethers, respectively. This reaction proceeds via C-H bond activation, insertion of unsaturated molecules into the formed rhenium-carbon bond, and then reductive elimination (or transmetalation in the case of aldehydes).