Fumitoshi Kakiuchi

Catalytic C-H/olefin coupling

The cleavage and addition of ortho C-H bonds in various aromatic compounds such as ketones, esters, imines, imidates, nitrile, and aldehydes to olefins and acetlylenes can be achieved catalytically with the aid of ruthenium catalysts. The reaction is generally highly efficient and useful in synthetic methods. The coordination to the metal center by a heteroatom in directing groups such as carbonyl and imino groups is the key. The reductive elimination to form a C-C bond is the rate-determining step.

Palladium-Catalyzed Aromatic C−H Halogenation with Hydrogen Halides by Means of Electrochemical Oxidation

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.

Ruthenium(II)-catalyzed regio- and stereoselective hydroarylation of alkynes via directed C-H functionalization.

The ruthenium-catalyzed hydroarylation of alkynes with benzamides proceeds regio- and stereoselectively through a directed C-H bond cleavage. Preliminary mechanistic investigations indicate that the reaction involves amide-directed ortho-metalation, carbometalation of alkyne, and protonolysis. Similarly, phenylazoles also add to alkynes regioselectively.

Atropselective alkylation of biaryl compounds by means of transition metal-catalyzed C-H/olefin coupling

Abstract The reaction of 2-(1-naphthyl)-3-methylpyridine with olefins in the presence of [RhCl(coe)2]2 and PCy3 as the catalyst resulted in the alkylation of the naphthyl ring at the 2-position in good yield. The replacement of PCy3 with the chiral ferrocenyl phosphine, (R),(S)-PPFOMe, as the ligand resulted in atropselective alkylation of the naphthylpyridine derivatives. Ethylene reacted with the biaryl compounds to give the corresponding addition products in moderate yields with fair to good ees (up to 49% ee).

Activation of C-H Bonds: Catalytic Reactions

Direct use of the carbon-hydrogen bond in organic synthesis with the aid of the homogeneous transition metal complexes has been the subject of recent interest. This review surveys some of the recent advances in the field of the transition metal-catalyzed functionalization of carbon-hydrogen bonds.

Cleavage of C-N bonds in aniline derivatives on a ruthenium center and its relevance to catalytic C-C bond formation.

The first observation of cleavage of unactivated aromatic C-N bonds on a late-transition-metal center was achieved using o-acylanilines and a ruthenium complex. Use of olefins as additives dramatically improved the rate of C-N bond cleavage. The carbon fragment remaining on the ruthenium after C-N bond cleavage was coupled with a phenylboronate to form a biphenyl framework. The present results suggest that ruthenium-catalyzed C-C bond formation from o-acylaniline and organoboronate proceeds via direct C-N bond cleavage on the ruthenium center.

Ruthenium-Catalyzed Amino- and Alkoxycarbonylations with Carbamoyl Chlorides and Alkyl Chloroformates via Aromatic C−H Bond Cleavage

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.

Completely selective synthesis of (E)-β-(triethylsilyl) styrenes by Fe3(CO)12-catalyzed reaction of styrenes with triethylsilane

Abstract Using Fe3(CO)12 as the catalyst, the reaction of styrenes (C6H5CHCH2, p-CH3C6H4CHCH2, p- ClC6H4CHCH2, and p-CH3OC6H4CHCH2) with triethyisilane gave (E)-β-(triethylsilyl)styrenes (2a, (E)-C6H5CHCHSiEt3; 2b, (E)-p-CH3C6H4CHCHSiEt3; 2c, (E)-p-ClC 6H4CHCHSiEt3; 2d, (E)-p-CH3OC6H4CHCHSiEt3) in 66–89% yields with complete selectivity. Similarly, Fe2(CO)9 also catalyzed dehydrogenative silylation again, with complete selectivity but in low yields. The reaction of styrene with treithylsilane, catalysed by OS3(CO)12, gave a mixture of the corresponding vinylsilane (dehydrogenative silylation product) and alkylsilane (hydrosilylation product).

Ruthenium-catalyzed addition of olefinic C-H bonds in conjugate enones to acetylenes to give conjugate dienones

Abstract Addition of a β C–H bond in conjugate enones to internal acetylenes to give conjugate dienones proceeded with the aid of RuH 2 (CO)(PPh 3 ) 3 as the catalyst. The reaction of pivaloylcyclohexene with diphenylacetylene gave the corresponding dienone in high yield. Acylpyranes can also be used in these olefinic C–H/acetylene coupling reactions. Phenyltrimethylsilylacetylene is also able to serve as a C–H bond acceptor.

Regioselective C-H bond cleavage/alkyne insertion under ruthenium catalysis.

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.