Hayato Tsurugi

Regioselective C−H Functionalization Directed by a Removable Carboxyl Group: Palladium-Catalyzed Vinylation at the Unusual Position of Indole and Related Heteroaromatic Rings

The palladium-catalyzed oxidative vinylation of indole-3-carboxylic acids with alkenes effectively proceeds via directed C-H functionalization and decarboxylation to produce the corresponding 2-vinylated indoles. Similarly, pyrrole-, furan-, and thiophenecarboxylic acids also undergo decarboxylative vinylation.

Palladium-Catalyzed Perarylation of 3-Thiophene- and 3-Furancarboxylic Acids Accompanied by C−H Bond Cleavage and Decarboxylation

3-thiophene- and 3-furancarboxylic acids efficiently undergo perarylation accompanied by cleavage of the three C-H bonds and decarboxylation upon treatment with excess aryl bromides in the presence of a palladium catalyst to give the corresponding tetraarylated products in good yields.

New tantalum ligand-free catalyst system for highly selective trimerization of ethylene affording 1-hexene: new evidence of a metallacycle mechanism.

Mild and salt-free reduction of MCl(5) (M = Nb, Ta) has been achieved by using 3,6-bis(trimethylsilyl)-1,4-hexadiene derivatives as reducing reagents. The salt-contact-free low-valent TaCl(3) exhibits high catalytic activity for the trimerization of ethylene to 1-hexene (>1000 TOF) with excellent selectivity (>98%). This salt-free tantalum system enables us to observe new evidence for a metallacycle mechanism.

Rhodium‐Catalyzed Oxidative Coupling between Salicylaldehydes and Internal Alkynes with CH Bond Cleavage To Produce 2,3‐Disubstituted Chromones

A direct oxidative coupling of salicylaldehydes with internal alkynes proceeds efficiently with cleavage of the aldehyde C--H bond to produce the corresponding chromone derivatives. A rhodium catalyst in combination with a cyclopentadiene ligand and a copper oxidant promote this straightforward annulation reaction. Solid-state luminescence was observed for certain chromone products.

End-functionalized polymerization of 2-vinylpyridine through initial C-H bond activation of N-heteroaromatics and internal alkynes by yttrium ene-diamido complexes.

We successfully introduced end-capping functional groups to poly(2-vinylpyridine)s by initial introduction of the functional groups on yttrium catalysts through C-H bond activation of heteroaromatics and internal alkynes to the Y center via alkylyttrium-mediated σ-bond metathesis.

Carbon radical generation by d0 tantalum complexes with α-diimine ligands through ligand-centered redox processes.

High-valent tantalum complexes having redox-active α-diimine ligands, (α-diimine)TaCl(n) (n = 3, 4), are prepared by the reaction of TaCl(5), α-diimine ligands, and an organosilicon-based reductant, 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene. Reductive cleavage of the C-Cl bond of polyhaloalkanes is accomplished by trichlorotantalum complexes having dianionic α-diimine ligands via electron transfer from the dianionic ligands, whereas oxidative decomposition of tetraphenylborate is observed using tetrachlorotantalum complexes with monoanionic α-diimine ligands through electron transfer to the monoanionic ligands. Chemically oxidized or reduced complexes of (α-diimine)TaCl(4) are isolated as ligand-centered redox products, [Cp(2)Co][(α-diimine)TaCl(4)] and [(α-diimine)TaCl(4)][WCl(6)], where the α-diimine ligand coordinates to the metal center as a dianionic or neutral ligand, respectively. On the basis of EPR measurements of (α-diimine)TaCl(4) complexes (which are key intermediates for reductive cleavage of C-Cl bond and oxidative decomposition of tetraphenylborate), two redox isomers--a tantalum-centered radical and ligand-localized radical--are present in solution.

Oxidant-free direct coupling of internal alkynes and 2-alkylpyridine via double C-H activations by alkylhafnium complexes.

We have developed a novel oxidant-free direct cross-coupling reaction of 2,6-lutidine and internal alkynes leading to five-membered carbocyclic compounds mediated by nonmetallocene cationic hafnium alkyl complexes. Mechanistic studies of the coupling reaction showed that the reaction begins with C(sp(3))-H bond activation via σ-bond metathesis, after which the coordinatively unsaturated hafnium center mediates further insertion, migration, and β-H elimination reactions to give five-membered carbocycles from readily available substrates.

Salt-Free Reducing Reagent of Bis(trimethylsilyl)cyclohexadiene Mediates Multielectron Reduction of Chloride Complexes of W(VI) and W(IV)

We developed a salt-free reduction of WCl6 using 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (MBTCD) in toluene to give a low-valent trinulcear tungsten complex involving W(II) and W(III) centers, while in the presence of redox active ligands such as α-diketone and α-diimine the same reduction produced W(IV) complexes with the corresponding redox-active ligands, (α-diketone)WCl4 and (α-diimine)WCl4. A W(VI) complex with two α-diketone ligands, (α-diketone)2WCl2, was found to be synthetically equivalent to low-valent W(IV) species that trapped azopyridine to give (α-diketone)WCl2(azopyridine).

Aminomethylation reaction of ortho-pyridyl C-H bonds catalyzed by group 3 metal triamido complexes.

Tris[N,N-bis(trimethylsilyl)amido] complexes of group 3 metals, especially yttrium and gadolinium, served as catalysts for ortho-C-H bond addition of pyridine derivatives and N-heteroaromatics into the C═N double bond of nonactivated imines to afford the corresponding aminomethylated products. Addition of catalytic amounts of secondary amines, such as dibenzylamine, dramatically improved the catalytic activity through the formation of a mixed ligated complex such as [(Me3Si)2N]2Y(NBn2)(THF) (4). Furthermore, kinetic studies using the isolated complex 4 provided a plausible reaction mechanism by which coordination of two pyridine derivatives afforded a penta-coordinated species as a key step.

Recent Developments in Homogeneous Organomagnesium Catalysis

Stoichiometric organomagnesium chemistry has continually progressed since its initiation by Victor Grignard over one century ago. Other than acting as a Lewis acid, however, homogeneous magnesium catalysis is a rare topic in the literature. Magnesium catalysts that govern reactions within the coordination sphere of magnesium have only recently begun to appear. This Concept covers recent progress in this young but potentially powerful new chapter of magnesium chemistry.