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ABSTRACT: The high utility of 2,4,6-trichlorophenyl formate, a highly reactive and easily accessible crystalline CO surrogate, is demonstrated. The decarbonylation with NEt(3) to generate CO proceeded rapidly at rt, thereby allowing external-CO-free Pd-catalyzed carbonylation of aryl/alkenyl halides and triflates. The high reactivity of the CO surrogate enabled carbonylation at rt and significantly reduced the quantities of formate to near-stoichiometric levels. The obtained trichlorophenyl esters can be readily converted to a variety of carboxylic acid derivatives in high yields.
Organic Letters 09/2012; 14(20):5370-3. · 5.86 Impact Factor
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ABSTRACT: Imidazole derivatives are revealed to be effective ligands in the Ru-catalyzed hydroesterification of alkenes using formates, affording one-carbon-elongated esters in high yields. Further, intramolecular hydroesterification was successfully performed to give lactones for the first time. Imidazole derivatives can contribute to promote the reaction as well as to suppress the undesired decarbonylation of formate. Toxic CO gas, a directing group, and large excess alkenes are not required.
Organic Letters 08/2012; 14(18):4722-5. · 5.86 Impact Factor
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ABSTRACT: Highly efficient palladium-catalyzed carbonylation of aryl, alkenyl, and allyl halides with phenyl formate is reported. This procedure does not use carbon monoxide and affords one-carbon-elongated carboxylic acid phenyl esters in excellent yields. The reaction proceeds smoothly under mild conditions and tolerates a wide range of functional groups including aldehyde, ether, ketone, ester, and cyano groups. Furthermore, a variety of heteroaromatic bromides can be converted to the corresponding phenyl esters in high yields.
Organic Letters 05/2012; 14(12):3100-3. · 5.86 Impact Factor
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ABSTRACT: A method for oligoarene synthesis involving chemoselective cross-coupling as the key reaction was developed. Boronic acids with a chloro or trifluoromethanesulfonyloxy group were used as the monomer precursors with either of two chemoselective catalytic systems: Pd with P(t-Bu)(3), and Pd with 1,1'-bis(diphenylphosphino)ferrocene (DPPF). This method enabled elongation by one benzene unit in every step and thus reduced the number of steps required for elongation of oligoarene chains with well-defined lengths and sequences of substituted benzene rings.
Organic Letters 05/2011; 13(9):2436-9. · 5.86 Impact Factor
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ABSTRACT: Site-selective cross-coupling of dihaloarenes constitutes a useful method for synthesis of multi-substituted arenes. In this paper, we report the site-selective cross-coupling of dichlorinated benzo-fused nitrogen-heterocycles having two chloro groups on the benzene ring. These dichlorinated heterocycles reacted with Grignard reagents in the presence of PdCl(2)(PCy(3))(2) at the positions ortho to the nitrogen-based substituents with high selectivities. A mechanism in which interaction between Lewis acidic Mg and Cl of the ortho position facilitates C-Cl bond cleavage is proposed.
Chemical & pharmaceutical bulletin 09/2010; 58(9):1255-8. · 1.70 Impact Factor
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ABSTRACT: A catalyst composed of Pd and hydroxyterphenylphosphine was found to be effective for one-pot benzo[b]furan synthesis from 2-chlorophenols and alkynes.
The Journal of Organic Chemistry 08/2010; 75(15):5340-2. · 4.45 Impact Factor
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Angewandte Chemie International Edition 12/2009; 49(4):772-5. · 13.45 Impact Factor
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ABSTRACT: High preference of substitution at the position ortho to the hydroxy group was observed for Ni-catalyzed cross-coupling reactions of dihalophenols with alkyl Grignard reagents. Reactions of 2,4-dihalophenols, with various combinations of F, Cl, and Br, were shown to afford ortho-cross-coupled products selectively. In addition, high ortho preference was also observed in competitive cross-coupling reactions between 2-halophenols and other halophenols.
Organic Letters 03/2009; 11(3):741-4. · 5.86 Impact Factor
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ABSTRACT: This feature article highlights our recent work on oligoarene-type catalysts. We developed a synthetic method for multifunctionalized oligoarenes using a repetitive two-step strategy. The method was then applied to the preparation of oligoarene-type phosphines, which were used for palladium-catalyzed cross-coupling of halobenzenes with Grignard reagents.
Chemical Communications 10/2008; · 6.17 Impact Factor
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ABSTRACT: Highly ortho-selective cross-coupling of dichlorobenzene derivatives with Grignard reagents was realized using a combination of Pd2(dba)3 and PCy3. Use of hydroxylated terphenylphosphines further improved the reactions of dichlorophenol and dichloroaniline.
Organic Letters 01/2008; 9(26):5593-5. · 5.86 Impact Factor
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ABSTRACT: A synthetic method for multifunctionalized oligoarenes using rapid Suzuki-Miyaura coupling of pinacol esters of hydroxyphenylboronic acids and subsequent triflation of the hydroxy group was developed.
Chemical Communications 07/2006; · 6.17 Impact Factor
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ABSTRACT: Catalytic asymmetric Mannich-type reactions of an alpha-hydrazono ester with silicon enolates in aqueous media have been developed by using ZnF2 and chiral diamines as catalysts. In these reactions, both Zn2+ and a fluoride anion were necessary to achieve high yields and enantioselectivities, suggesting a double activation mechanism, in which Zn2+ activates the alpha-hydrazono ester and the fluoride anion simultaneously activates the silicon enolate. When chiral diamine ligands bearing methoxy-substituted aromatic rings were employed, the reactions in aqueous THF were markedly accelerated. Furthermore, the use of these diamines facilitated the asymmetric Mannich-type reactions in water without any organic cosolvents. It is noteworthy that either syn or anti adducts were stereospecifically obtained from (E)- or (Z)-silicon enolates, respectively. Interestingly, these reactions proceeded smoothly only in the presence of water. On the basis of several experimental results, it can be concluded that the reaction mechanism is likely to be a fluoride-catalyzed one, in which the ZnF2 chiral diamine complex is regenerated from the Me3SiF formed during the reaction.
Chemistry 02/2006; 12(4):1205-15. · 5.93 Impact Factor
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ABSTRACT: New types of P,N-ligands, cis- and trans-3, containing a tetrahydroisoquinoline skeleton as an N-donor were synthesized from (1R,2S)-1-phenylphospholane-2-carboxylic acid (phenyl-P-proline, 1). The cis isomer, cis-3, was found to act as an excellent ligand in palladium-catalyzed asymmetric allylic substitution reactions. The reactions of 1,3-diphenyl-2-propenyl acetate (5) with several nucleophiles in the presence of [Pd(π-allyl)Cl]2, cis-3 (Pd : ligand=1 : 2), and a base afforded the desired products in high yields with high enantioselectivity. It was suggested that these ligands did not serve as P,N-bidentate ligands but as P-monodentate ligands in these reactions.
Advanced Synthesis & Catalysis 12/2005; 347(15):1893 - 1898. · 6.05 Impact Factor
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ABSTRACT: New types of Lewis acids as water-stable catalysts have been developed. These Lewis acids activate substrates such as aldehydes efficiently in aqueous media. Furthermore, surfactant-aided Lewis acid catalysis has also been used for reactions in water without using any organic solvents.
11/2005: pages 1 - 12; , ISBN: 9783527605743
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ABSTRACT: [reaction: see text] Catalytic asymmetric hydroxymethylation of silicon enolates with an aqueous formaldehyde solution has been developed using a chiral bismuth complex. This is the first example of highly enantioselective reactions using a chiral bismuth catalyst in aqueous media. In this paper, we have added Bi(OTf)(3)-1 complex as a "water-compatible Lewis acid". Bi(OTf)3 is unstable in the presence of water but is stabilized by the basic ligand.
Organic Letters 11/2005; 7(21):4729-31. · 5.86 Impact Factor
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ABSTRACT: [reaction: see text] An operationally simple and environmentally benign protocol for the catalytic asymmetric ring opening of meso-epoxides with aromatic amines has been developed. The reactions proceeded smoothly in the presence of 1 mol % of Sc(OSO3C12H25)3 and 1.2 mol % of a chiral bipyridine ligand in water to afford beta-amino alcohols in high yields with excellent enantioselectivities.
Organic Letters 11/2005; 7(21):4593-5. · 5.86 Impact Factor
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ABSTRACT: The catalytic Pictet-Spengler reactions proceeded in high yields with high regioselectivity in the presence of a catalytic amount of Yb(OTf)3 and a dehydrating agent at room temperature. High regioselectivities were obtained in these reactions, and it is suggested that the reactions proceeded under kinetic control.
Bioorganic & Medicinal Chemistry 10/2005; 13(17):5154-8. · 2.92 Impact Factor
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ABSTRACT: A synthetic route to enantiomerically pure (1R,2S)-1-phenylphospholane-2-carboxylic acid (1), which is a phosphorus analogue of proline, has been established. A key step is the deprotonation-carboxylation of the 1-phenylphospholane borane complex 3 by using sBuLi/1,2-dipiperidinoethane (DPE). Configurational stability of the key intermediate, the amine-coordinated alpha-phosphinoalkyllithium borane complex 4, was investigated by employing lithiodestannylation-carboxylation of both diastereomers of the 1-phenyl-2-trimethylstannylphospholane borane complex 7 in the presence of several kinds of amines, and as a result, 4 was found to be configurationally labile even at -100 degrees C. The key intermediate, the DPE-coordinated trans-1-phenyl-2-phospholanyllithium borane complex 9, was isolated, and the structure was identified by X-ray crystal structure analysis. This is the first X-ray crystal structure determined for an alpha-monophosphinoalkyllithium borane complex. Remarkably, the alkyllithium complex is monomeric and tricoordinate at the lithium center with a slightly pyramidalized environment, and the existence of a Li--C bond (2.170 A) has been confirmed. Moreover, (1)H-(7)Li HOESY and (6)Li NMR analyses suggested the structure of 9 in solution as well as the existence of an equilibrium between 9, its cis isomer, and the ion pair 8 at room temperature, which was extremely biased towards 9 at -100 degrees C. Finally, 1 was used as a chiral ligand in a palladium-catalyzed allylic substitution, and the desired product was obtained in high yield with good enantioselectivity.
Chemistry 01/2005; 11(1):361-8. · 5.93 Impact Factor
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ABSTRACT: Catalytic asymmetric hydroxymethylation of silicon enolates has been achieved. In this reaction, an aqueous solution of formaldehyde can be used to realize an easy and safe procedure, and high enantioselectivities have been obtained. This is the first example of catalytic asymmetric reactions in aqueous media with a chiral scandium complex.
Journal of the American Chemical Society 11/2004; 126(39):12236-7. · 9.91 Impact Factor
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ABSTRACT: Catalytic asymmetric Mannich-type reactions in water proceeded in high yields and selectivities using a combination of ZnF2 and a chiral diamine that has the methoxy groups on the aromatic rings. In these reactions, either syn- or anti-Mannich adducts were stereospecifically obtained from (E)- or (Z)-silicon enolate, in contrast with most asymmetric Mannich-type reactions.
Journal of the American Chemical Society 07/2004; 126(25):7768-9. · 9.91 Impact Factor
