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Koichi Mikami

Publications and source records attributed to Koichi Mikami.

36 records · Page 2Linked to original sources
PubMed2003

Dipole interaction-controlled stereoselectivity in aldol reaction of alpha-CF3 enolate with fluoral.

The stereoselectivity of a reaction is generally determined by minimizing steric repulsion. However, the aldol reaction of alpha-CF(3)-ketone (Z)-enolate with fluoral anomalously gave an anti-aldol through a sterically demanding transition state, because of the strong dipole interaction of the two CF(3) groups. We have thus disclosed a paradigm shift from steric to electronic control of reaction stereoselectivity. [reaction: see text]

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PubMed2003

Highly enantioselective alkaloid synthesis via ene-type cyclizations catalyzed by cationic chiral palladium(II) complexes of PN-ligands with an achiral oxazoline unit.

A highly efficient asymmetric alkaloid synthesis via ene-type cyclizations catalyzed by cationic chiral palladium(II) complexes of PN-ligands with an achiral gem-dimethyl oxazoline unit is shown to give 5-membered products with a quaternary carbon center, including a spiro-amide, almost quantitatively with extremely high enantiomeric excesses.

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PubMed2003

(2,5)-Ene cyclization catalyzed by mesoporous solid acids: isotope labeling study and ab initio calculation for continuum from concerted to stepwise ene mechanism.

(2,5)-Ene reactions catalyzed by mesoporous solid acids are reported from the mechanistic point of view. The continuum (2,5)-ene mechanism from the concerted to the cationic cyclization followed by 1,2-hydride shift is evaluated. The solid-acid-catalyzed cyclization of the oxonium ion intermediate 4 derived from cyclic allylic lactol ether 3 bearing allylic hydroxy group affords the (2,5)-ene product as the enol form, eventually tautomerizing to the corresponding aldehyde 6. The continuum from the concerted to stepwise mechanism is experimentally and theoretically verified in the present ene cyclization of the oxonium ion intermediate such as 4. The stepwise cyclization leading to aldehyde 6 is thus shown to associate with the concerted version as a result of the stabilization of the beta-hydroxycarbenium ion intermediate.

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PubMed2003

Molecular design of DABNTf as a highly efficient resolving reagent for racemic Pd complex with Tropos biphenylphosphine (BIPHEP) ligand: circular dichroism (CD) spectra of enantiopure BIPHEP-Pd complex.

The racemic Pd complexes with chirally flexible (tropos) biphenylphosphine (BIPHEP) ligands can be resolved but transformed into the enantio- and diastereo-pure complex. The enantiopure metal complex of BIPHEP ligand is thus obtained through enantiomer-selective complexation of a racemic BIPHEP-Pd complex with enantiopure 1,1'-binaphthyl-2,2'-di(triflyl)amide, DABNTf. The differential CD spectra of the enantiopure BIPHEP-Pd complex is also reported.

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PubMed2002

"Asymmetric" catalysis by lanthanide complexes.

Catalysis with lanthanide (Ln) complexes has been underestimated for long time, although Ln(III) complexes have great advantages as Lewis acid catalysts for "asymmetric" carbon-carbon bond-forming reactions. Lanthanide complexes are highly active in ligand-substitution reactions, especially with hard ligands. The association with substrates and dissociation of products are achieved fast enough for high catalyst efficiency. The asymmetric catalysis of organic reactions can be greatly advanced by the use of Ln complexes with chiral ligands such as binaphthol (binol). Ln(II) complexes are good reducing agents, which can be used in a wide variety of synthetically important reactions; when chiral ligands are used, many of these reactions are highly stereoselective. In the context of "green chemistry", the development of asymmetric Ln catalysts, and their recyclable use, is of increasing importance. This review gives an overview of the most recent developments in catalysis with lanthanide(II) and lanthanide(III) complexes.

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PubMed2002

Palladium-catalyzed isobenzofuran generation under neutral conditions via oxidative addition to lactol methyl ether.

A novel method for generation of isobenzofuran is developed from lactol methyl ether using palladium catalysts. This reaction can be carried out under neutral conditions and hence improves on the precedent methods under acidic or basic conditions and at high temperatures. Furthermore, this Pd-catalyzed isobenzofuran generation suggests the involvement of oxidative addition of Pd catalyst into benzylic or allylic methyl ethers. [reaction: see text]

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PubMed2002

Asymmetric deactivation of racemic BINAP-Ru(II) catalysts through complete enantiomer discrimination by dimethylbinaphthylamine: highly enantioselective hydrogenation of olefin and beta-keto ester.

[reaction: see text] 3,3'-Dimethyl-2,2'-diamino-1,1'-binaphthyl (DM-DABN) is designed as a "chiral poison" (deactivator) for complete enantiomer resolution of racemic BINAP-Ru(II) catalysts in a highly enantioselective hydrogenation of beta-keto ester and kinetic resolution of racemic 2-cyclohexen-1-ol.

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PubMed2002

Asymmetric activation of the Pd catalyst bearing the tropos biphenylphosphine (BIPHEP) ligand with the chiral diaminobinaphthyl (DABN) activator.

[reaction: see text] The enantio- and diastereomerically pure Pd complex of the tropos biphenylphosphine (BIPHEP) ligand is obtained through complexation of the enantiopure (R)-diaminobinaphthyl (DABN) with either enantiomer of the BIPHEP-Pd catalyst, followed by tropo-inversion of the less favorable (S)-BIPHEP-Pd/(R)-DABN diastereomer to the more favorable (R)-BIPHEP-Pd/(R)-DABN diastereomer. The enantiopure BIPHEP-Pd catalyst with DABN affords higher enantioselectivity and catalytic efficiency as an activated Lewis acid catalyst than the enantiopure BIPHEP-Pd catalyst without DABN.

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PubMed2002

Dynamic asymmetric catalysis by diphenylphosphinoferrocene (DPPF)-nickel complexes through control of axial chirality by chiral diamines.

[reaction: see text] The enantio- and diastereomerically pure metal complexes of a chirally dynamic diphenylphosphinoferrocene (DPPF) ligand are obtained through coordination of enantiopure diaminobinaphthyl (DABN) to control the axial chirality of DPPF-Pt, -Pd, and -Ni complexes. The DPPF-Ni catalyst with DABN affords higher enantioselectivity and catalytic efficiency than those attained by the Pd or Pt counterparts and [Ni[(R)-dabn]](SbF(6))(2) without DPPF ligand.

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PubMed2002

Resolution of Pd catalyst with tropos biphenylphosphine (BIPHEP) ligand by DM-DABN: asymmetric catalysis by an enantiopure BIPHEP-Pd complex.

[reaction: see text] The racemic Pd complex with the chirally flexible (tropos) biphenylphosphine (BIPHEP) ligand can be resolved with enantiopure 3,3'-dimethyl-2,2'-diamino-1,1'-binaphthyl (DM-DABN) as a resolving agent at room temperature. The enantiopure BIPHEP-Pd complex is obtained from complexation with enantiopure DABN followed by tropo-inversion into the single BIPHEP-Pd diastereomer at 80 degrees C and protonation at 0 degrees C. The enantiopure BIPHEP-Pd complex can be used as an efficient Lewis acid catalyst for the Diels-Alder reaction at room temperature to give high enantioselectivity (82% ee, 60%).

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PubMed2002

Practical asymmetric synthetic route to 4,4,4-trifluoro-3-hydroxybutyrate: head-to-tail and head-to-head crystallizations through double and single hydrogen bonds of hetero- and homochiral 4,4,4-trifluoro-3-hydroxybutyrophenones.

A practical asymmetric synthetic route to 4,4,4-trifluoro-3-hydroxybutyrophenone and the butyric acid phenyl ester is described using heterochiral crystallization through double hydrogen bonding assembly in head-to-tail fashion and sequential Baeyer-Villiger oxidation reaction by trifluoroperacetic acid.

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