Ryoichi Kuwano

CATALYTIC ASYMMETRIC HYDROGENATION OF 5-MEMBERED HETEROAROMATICS

Catalytic asymmetric hydrogenation of heteroaromatics had been a formidable issue in organic synthesis. However, the catalytic asymmetric hydrogenation has remarkably progressed during the past decade. This review surveys the recent progress of the asymmetric hydrogenation of 5-membered heteroaromatics, indoles, pyrroles, furans, and benzofurans.

Reduction of amides to amines via catalytic hydrosilylation by a rhodium complex

Abstract Reduction of a wide range of tertiary amides with 2 molar equivalents of diphenylsilane was promoted by 0.1 mol% of RhH(CO)(PPh 3 ) 3 at room temperature, affording the corresponding tertiary amines in high yields. The synthetic utility is demonstrated by chemoselective reductions of amides having functional groups such as ester and epoxy groups which are not tolerated by the conventional reductions with LiAlH 4 and BH 3 .

Suzuki-Miyaura Coupling of Diarylmethyl Carbonates with Arylboronic Acids: A New Access to Triarylmethanes

Suzuki-Miyaura coupling of diarylmethyl carbonates with arylboronic acids proceeded in the presence of [Pd(eta3-C3H5)Cl]2-DPPPent (1,5-bis(diphenylphosphino)pentane) catalyst, yielding a variety of triarylmethanes.

Catalytic Asymmetric Hydrogenation of N-Boc-Imidazoles and Oxazoles

Substituted imidazoles and oxazoles were respectively hydrogenated into the corresponding chiral imidazolines and oxazolines (up to 99% ee). The highly enantioselective hydrogenation was achieved by using the chiral ruthenium catalyst, which is generated from Ru(η(3)-methallyl)(2)(cod) and a trans-chelating chiral bisphosphine ligand, PhTRAP. This is the first successful catalytic asymmetric reduction of 5-membered aromatic rings containing two or more heteroatoms.

Nickel‐Catalyzed Formation of a Carbon–Nitrogen Bond at the β Position of Saturated Ketones

Gone fishing: When propiophenone and related ethyl ketones are treated with morpholine in the presence of K(3)PO(4), chlorobenzene, and [Ni(cod)(2)]/PMe(3) catalyst, a carbon-nitrogen bond is formed selectively at the beta position (see scheme; cod = cycloocta-1,5-diene). Secondary amines were employed as substrates to give the corresponding beta-enaminones.

SYNTHESIS OF A TRANS-CHELATING CHIRAL DIPHOSPHINE LIGAND WITH ONLY PLANAR CHIRALITY AND ITS APPLICATION TO ASYMMETRIC HYDROSILYLATION OF KETONES

Abstract Optically active diphosphine (S,S)-2,2″-bis[(diethylphosphino)methyl]-1,1″-biferrocene (abbreviated to (S,S)-EtTRAP-H) was synthesized from ferrocenyloxazoline derived from l -valinol in 47% overall yield. The new chiral ligand, (S,S)-EtTRAP-H, which coordinates to a rhodium atom in a trans-chelating manner, was effective for asymmetric hydrosilylation of ketones to give optically active secondary alcohols with up to 94% ee.

Benzyl Protection of Phenols under Neutral Conditions: Palladium-Catalyzed Benzylations of Phenols

Benzyl protection of phenols under neutral conditions was achieved by using a Pd(eta3-C3H5)Cp-DPEphos catalyst. The palladium catalyst efficiently converted aryl benzyl carbonates into benzyl-protected phenols through the decarboxylative etherification. Alternatively, the nucleophilic substitution of benzyl methyl carbonates with phenols proceeded in the presence of the catalyst, yielding aryl benzyl ethers.

Catalytic Asymmetric Hydrogenation of Naphthalenes

The catalytic asymmetric hydrogenation of heteroarenes has been intensively studied during the last decade. Nowadays, various heteroaromatics, for example, indoles, pyrroles, and quinolines, can be reduced to the corresponding chiral heterocycles with high stereoselectivity through asymmetric catalysis. Glorius and co-workers recently found that a chiral N-heterocyclic carbene–ruthenium catalyst allowed the site-selective hydrogenation of the carbocyclic rings of some quinoxalines, producing chiral 5,6,7,8-tetrahydroquinoxalines with up to 88% ee. However, to the best of our knowledge, the catalytic asymmetric hydrogenation of aromatics containing no heteroatoms remains unexplored. Herein, we report the first successful enantioselective hydrogenation of carbocyclic arenes, naphthalenes, through asymmetric catalysis. Previously, we had developed the highly enantioselective hydrogenation of N-Boc indoles with a ruthenium catalyst generated from [{RuCl2(p-cymene)}2] and the chiral bisphosphine ligand, PhTrap. During the course of this study, we attempted the reduction of 2-naphthylindole 1 with the PhTrap–ruthenium catalyst (Scheme 1). To our surprise, none of the expected product 2 was obtained. The hydrogenation was accompanied by the partial reduction of the naphthalene ring, yielding tetrahydronaphthylindoline 3 with 90% ee. This observation suggested that the ruthenium complex was capable of reducing carbocyclic aromatic rings. In this context, we began to study the catalytic asymmetric hydrogenation of naphthalenes. In our initial attempt, a solution of dimethyl naphthalene2,6-dicarboxylate (4a) in 1,4-dioxane was stirred at 60 8C under hydrogen gas (50 atm) in the presence of [RuCl(p-cymene){(S,S)-(R,R)-PhTrap}]Cl (6) catalyst. Although formation of the hydrogenation product 5a was observed, the desired reaction was very sluggish and the enantiomeric excess of 5a was only 22% ee (Table 1, entry 1). Both the

Asymmetric aldol reaction of 2-cyanopropionates catalyzed by a trans-chelating chiral diphosphine–rhodium(I) complex: highly enantioselective construction of quaternary chiral carbon centers at α-positions of nitriles

Abstract The aldol reaction of 2-cyanopropionates with aldehydes proceeded under neutral conditions in the presence of a catalytic amount of the rhodium complex generated in situ from Rh(acac)(CO) 2 and triphenylphosphine, to give the corresponding β-hydroxy-α-cyanocarboxylates bearing a quaternary chiral carbon center at the α-position of the cyano group. A high degree of asymmetric induction for the aldol reaction was achieved by use of trans-chelating chiral diphosphine ligands, ( R , R )-2,2″-bis[( S )-1-(diarylphosphino)ethyl]-1,1″-biferrocenes (TRAPs). The asymmetric aldol reactions gave optically active β-hydroxy-α-cyanocarboxylates with up to 94% ee.

[4+2] Cycloaddition of o-xylylenes with imines using palladium catalyst

The cycloaddition of o-(silylmethyl)benzylic carbonates with imines proceeded in the presence of the Pd(eta(3)-C(3)H(5))Cp-DPPPent catalyst, affording the tetrahydroisoquinolines in good to high yields. The reaction rate was remarkably increased by a fluoride additive. In the catalytic cycloaddition, the palladium(0) reacted with the benzylic substrate to form 2-palladaindane, which works as an o-xylylene equivalent. The catalytic reaction is equivalent to the hetero-Diels-Alder reaction of o-xylylene with imines.