Ken Takaki

Partial oxidation of methane over Ni/Mg-Al oxide catalysts prepared by solid phase crystallization method from Mg-Al hydrotalcite-like precursors

Ni-supported catalyst was prepared by the solid phase crystallization (spc) method starting from Mg-Al hydrotalcite (HT) anionic clay as the precursor; it was tested for the partial oxidation of CH4 to synthesis gas. The precursor based on [Mg6Al2(OH)16CO32−]·4H2O was prepared by co-precipitation method from nitrates of the metal components. The precursor was then thermally decomposed and reduced to form Ni-supported catalyst (spc-Ni/Mg-Al). Ni2+ can well occupy the Mg2+ sites in the hydrotalcite resulting in the formation of highly dispersed Ni metal particles on spc-Ni/Mg-Al. The spc-Ni/Mg-Al thus prepared, showed high activity and selectivity to synthesis gas even at high space velocity. When Ni was supported by impregnating Mg-Al mixed oxide prepared from Mg-Al HT, the activity of imp-Ni/Mg-Al was higher than those of Ni/α-Al2O3 and Ni/MgO while it was close to that of spc-Ni/Mg-Al. The relatively high activity of the imp-Ni/Mg-Al may be due to the regeneration of Mg-Al HT phase from the mixed oxide during the preparation resulting in incorporation of Ni2+ on the Mg2+ sites in the HT as seen in the spc method.

Copper-Catalyzed Three-Component Carboboration of Alkynes and Alkenes

Carboboration of alkynes was found to take place efficiently by a three-component coupling reaction with diboron and carbon electrophiles under copper catalysis to afford diverse multisubstituted borylalkenes in a stereoselective manner. The carboboration was also applicable to alkenes, leading to the formation of multisubstituted borylalkanes via regioselective carbon-boron and carbon-carbon bond-forming processes.

Three‐Component Coupling of Arynes and Organic Bromides

Arynes have been versatile tools in synthetic organic chemistry for the facile construction of benzoannulated structures and multisubstituted arenes. Despite the labile and transient character arising from the highly strained C C bonds, the use of a suitable combination of nucleophiles and electrophiles allows arynes to serve as connectors between these two components, thus leading to various three-component coupling reactions of high synthetic significance; in the reaction zwitterions (1,n-dipoles) generated from the arynes and nucleophiles act as key intermediates. 3] In view of the fact that almost all three-component coupling reactions reported so far employ classic electrophiles (e.g., carbonyl compounds, sulfonylimines, and CO2) as the third component, [4] there should be a number of unexploited three-component coupling reactions with potential synthetic utility that would be made feasible by employing a new type of third component. We report herein that 1,3or 1,4-dipoles generated in situ from arynes can be captured by alkynyl (or polyfluoroaryl) bromides, which serve as a source of bromine cations and alkynyl (or polyfluoroaryl) anions, thus leading to the direct construction of functionalized bromoarenes having diverse structures. We first conducted the reaction of benzyne (from 1a and KF/[18]crown-6), 1,1,3,3-tetramethylbutyl isocyanide (tOctNC; 2a), and phenylethynyl bromide (3a) in DME at 0 8C, and observed that two C C bonds and a C Br bond formed all in one pot to give the three-component coupling product 4a in 88% yield (Scheme 1). As described in Scheme 2, the reaction would be triggered by formation of the zwitterion (1,3-dipole) 5 from benzyne and 2a. Subsequent nucleophilic attack of the aryl anionic moiety on the bromo moiety of 3 a produces the phenylacetylide 7 and an aryl–Br bond in 8 through the bromine ate complex 6, with subsequent C C bond formation between 7 and the nitrilium cation 8 to furnish 4a. Products derived from various alkynyl bromides bearing a substituted aryl (4b–4d), thienyl (4e), or enynyl (4 f) moieties were obtained. The doubly coupled product 4g was produced from 1,4-bis(bromoethynyl)benzene in 66% yield (Scheme 1). The reaction was also applicable to aliphatic alkynyl bromides whose acetal or propargylic ether moiety remained intact (4h–4j), and moreover, the functionalized iodoarene 4 k could be synthesized by use of phenylethynyl iodide. Next, we examined the threecomponent coupling with substituted arynes. The respective products from dimethylbenzynes (4 l and 4m) and cyclo-

Palladium(II) and/or copper(II)-catalyzed carboxylation of small alkanes such as methane and ethane with carbon monoxide

Abstract Small alkanes such as methane and ethane react with carbon monoxide in the presence of transition metal catalysts to give the corresponding carboxylic acids in high yields. For the reaction of ethane, the Pd(OAc) 2 /Cu(OAc) 2 mixed catalyst is the best, whereas that of methane proceeds most efficiently by the Cu(OAc) 2 catalyst system. Kw]Palladium; Carbon monoxide; Alkane activation; Copper; Methane; Ethane

Palladium(II)-catalyzed carboxylation of benzene and other aromatic compounds with carbon monoxide under very mild conditions

Abstract Aromatic compounds such as benzene, toluene, chlorobenzene, anisole, and naphthalene were carboxylated by palladium(II) acetate catalyst with carbon monoxide in the presence of potassium peroxodisulfate in trifluoroacetic acid (TFA) at room temperature under atmospheric pressure. The aromatic carboxylic acids were formed in good yields; for example, the carboxylation of benzene with carbon monoxide proceeds quantitatively under the optimal conditions.

Intermolecular hydrophosphination of alkynes and related carboncarbon multiple bonds catalyzed by ytterbium–imine complexes

Abstract Catalytic intermolecular hydrophosphination of alkynes with Ph2PH has been achieved by using a ytterbium–imine complex, [Yb(η2-Ph2CNPh)(hmpa)6]. Thus, both terminal and internal alkynes were converted in high yields to the corresponding alkenylphosphines or phosphine oxides after oxidative workup. The present method was also applicable to various carboncarbon multiple bonds such as conjugated diynes and dienes, allenes and styrene derivatives.

Copper‐Catalyzed Three‐Component Borylstannylation of Alkynes

Regio- and stereoselective installation of boryl and stannyl moieties into a carbon-carbon triple bond of various alkynes has been achieved based on a three-component coupling reaction by using a diboron and a tin alkoxide with the aid of a copper(II) acetate-tricyclohexylphosphine complex, giving diverse vic-borylstannylalkenes in a straightforward manner. Carbon-tin and carbon-boron bonds of the resulting borylstannylation product are successively transformed into carbon-carbon bonds by a Migita-Kosugi-Stille and a Suzuki-Miyaura coupling, leading to the formation of (Z)-tamoxifen with anti-breast cancer activity.

Silver-Catalyzed Highly Regioselective Formal Hydroboration of Alkynes

A silver(I)-N-heterocyclic carbene complex has proven to be a potent catalyst for formal hydroboration of alkynes, providing a variety of borylalkenes in regio- and stereoselective manners. Under the silver catalysis, allenes also undergo regioselective hydroboration to give borylalkenes.

Tandem ene-reaction/hydroamination of amino-olefin and -allene compounds catalyzed by Bi(OTf)3

Bi(OTf)(3) was proven to act as an effective catalyst for tandem ene-reaction/hydroamination of amino-olefin and amino-allene compounds with some enophiles, giving rise to functionalized N-heterocycles in good yields.

Stereochemistry of conjugate addition to 4- and 5-substituted α,β-unsaturated δ-lactones

Conjugate addition, especially of the phenyldimethylsilylcuprate reagent, to 4- and 5-substituted α,β-unsaturated δ-lactones [(5) and (18)] is highly selective for the formation of the trans-products [(6), (7), (9), (10), and (19)], the silicon-containing products having 1H n.m.r. coupling constants indicative of distortions from the chair conformation; the silyl group can be converted into a hydroxy group to give the lactones (8) and (20).