Tohoku University · Chemistry
Professor Naohiko Yoshikai's research lab specializes in the development of transition-metal-catalyzed C–H bond functionalization and cross-coupling reactions, with a strong focus on nickel, cobalt, and iron catalysis. The lab pioneers innovative ligand designs—particularly phosphine-based and bidentate ligands—that enable the activation of challenging substrates such as aryl fluorides, chlorides, and phenol derivatives under mild conditions. A key theme in their work is the synergistic effect between transition metals and main-group metals (e.g., Mg) in bimetallic catalytic systems, enhancing reactivity and chemoselectivity. The lab also explores the use of first-row transition metals like cobalt and iron as sustainable alternatives to noble metals in selective C–H functionalization.
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We report here that hydroxyphosphine ligands (PO ligands) significantly accelerate nickel-catalyzed cross-coupling reactions of unreactive aryl electrophiles and Grignard reagents. The new catalytic system based on the nickel-PO-Grignard combination allows facile activation of unreactive aryl halides such as fluorides, chlorides, polyfluorides, and polychlorides as well as phenol derivatives such as carbamates and phosphates to give the corresponding cross-coupling products in good to excellent
Direct alkenylation of the C2-position of indoles bearing an easily removable N-pyrimidyl group with alkynes has been achieved by using a cobalt catalyst complexed with a phosphine–pyridine bidentate ligand. This reaction has wide substrate scope and is highly efficient and stereoselective at room temperature. The alkenylated indoles serve as useful platforms for further synthetic transformations (some products of these transformations are shown in the scheme). Detailed facts of importance to sp
Nickel-catalyzed cross-coupling of Grignard reagents with aryl (poly)fluorides or (poly)chlorides can be achieved efficiently in the presence of a new triarylphosphine ligand bearing a nearby hydroxy group. The high reactivity and the unique chemoselectivity (ArF > ArOTf > ArSR) of the catalysis have been attributed to synergy of nickel and magnesium atoms preorganized on the ligand, as has been surmised on the basis of theoretical modeling of the reaction mechanism.
No Fe-ar: Iron catalyzes an imine-directed C-H bond activation to introduce an ortho-aryl group to an acetophenone-derived imine using a diarylzinc reagent (see scheme), whereas palladium catalyzes the conventional substitution reaction . The title reaction features mild and selective C-H bond activation in the presence of aryl bromide, chloride, or sulfonate groups, and 1,2-dichloroisobutane is essential to achieve such selectivity.
While chelation-assisted C-H bond activation by a transition-metal complex serves as a versatile platform for the development of regioselective C-H bond-functionalization reactions, the capability of first-row transition metals to catalyze such transformations has scarcely been explored. This highlight article illustrates how cobalt has recently emerged as a promising metal for chelation-assisted C-H bond functionalization.
Abstract Pyrroles, indoles, and carbazoles are among the most important families of nitrogen‐containing heterocycles that occur frequently in natural products, pharmaceuticals, agrochemicals, and other functional molecules. Consequently, improved syntheses of these compounds continue to interest synthetic chemists. This Focus Review describes recent advances in synthetic methods for producing these privileged heterocycles that feature transition‐metal‐catalyzed CH activation approaches. Because
C-C bond formation reactions that take place through organoiron species sometimes exhibit radical-like character. The reaction of N-(2-iodophenylmethyl)dialkylamine with a Grignard or diorganozinc reagent in the presence of a catalytic amount of Fe(acac)(3) gives the product resulting from arylation, alkenylation, or alkylation of the sp(3) C-H bond next to the amine group in good to excellent yield. Mechanistic studies including labeling experiments indicate that the reaction involves radical t
A copper-catalyzed condensation reaction of oxime acetates and α,β-unsaturated ketimines to give pyridine derivatives is reported. The reaction features mild conditions, high functional-group compatibility, and high regioselectivity with respect to unsymmetrical oxime acetates, thus allowing the preparation of a wide range of polysubstituted pyridines, many of which are not readily accessible by conventional condensation methods.
Migratory carbometalation: A cobalt–Xantphos complex catalyzes the addition of an arylzinc reagent to an unactivated internal alkyne; the reaction most likely involves insertion of the alkyne into an arylcobalt species and vinyl-to-aryl 1,4-cobalt migration, followed by transmetalation with the arylzinc reagent. Interception of the resulting ortho-alkenylarylzinc species with electrophiles allows access to 1-alkenyl arenes functionalized in the 2-position.
Directed activation: Cationic Cp*CoIII (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) complexes, either well-defined or in situ-generated, promote catalytic functionalization of arene CH bonds with a variety of electrophilic reaction partners by directed CH activation. These complexes not only emulate known reaction patterns of Cp*RhIII analogues, but also exhibit remarkable catalytic activity or unique reactivity. DG=Directing group.
Regiodivergent catalysis: Cobalt N-heterocyclic carbene (NHC) catalysts promote intramolecular olefin hydroarylation of indoles bearing an N-homoallyl or bis(homoallyl) tether and a C3 aldimine directing group to afford dihydropyrroloindoles and tetrahydropyridoindoles under mild conditions. The course of the cyclization is dependent on the tether, but can be controlled by the NHC ligand. As a service to our authors and readers, this journal provides supporting information supplied by the author
Mild mannered: Cobalt catalysts complexed with phenanthroline-type ligands and activated with Grignard reagents serve as inexpensive and effective catalysts for the ortho alkylation of aromatic imines with a variety of olefins (see scheme). The new catalytic systems feature remarkably mild reaction conditions for CH bond activation and functionalization.
Rapidly aSSembled: The combination of cobalt-catalyzed migratory arylzincation and copper-mediated/catalyzed chalcogenative cyclization allows the construction of benzothiophenes and benzoselenophenes from arylzinc reagents, alkynes, and elemental chalcogens. Benzothiophenes and benzoselenophenes diversely functionalized at the benzene ring moiety can be prepared, which are not readily accessible by conventional methods.
A cobalt-N-heterocyclic carbene catalyst, in combination with an appropriate Grignard reagent, promotes a chelation-assisted aromatic C-H functionalization reaction via addition to an aromatic aldimine.
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