Takashi Ooi 교수

The use of chiral nonracemic onium salts and crown ethers as effective phase-transfer catalysts have been studied intensively primarily for enantioselective carbon-carbon or carbon-heteroatom bond-forming reactions under mild biphasic conditions. An essential issue for optimal asymmetric catalysis is the rational design of catalysts for targeted reaction, which allows generation of a well-defined chiral ion pair that reacts with electrophiles in a highly efficient and stereoselective manner. Thi

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTMolecular Design of a C2-Symmetric Chiral Phase-Transfer Catalyst for Practical Asymmetric Synthesis of α-Amino AcidsTakashi Ooi, Minoru Kameda, and Keiji MaruokaView Author Information Department of Chemistry Graduate School of Science, Hokkaido University Sapporo 060-0810, Japan Cite this: J. Am. Chem. Soc. 1999, 121, 27, 6519–6520Publication Date (Web):July 14, 1999Publication History Received5 April 1999Published online14 July 1999Published i

A series of C(2)-symmetric chiral quaternary ammonium bromides 10 and 11 have been designed as a new, purely synthetic chiral phase-transfer catalyst, and readily prepared from commercially available optically pure 1,1'-bi-2-naphthol as a basic chiral unit. The details of the synthetic procedures of each requisite chiral binaphthyl subunit have been disclosed, and the structures of the assembled N-spiro chiral quaternary ammonium bromides 11a and 11f were unequivocally determined by single-cryst

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTPractical Catalytic Enantioselective Synthesis of α,α-Dialkyl-α-amino Acids by Chiral Phase-Transfer CatalysisTakashi Ooi, Mifune Takeuchi, Minoru Kameda, and Keiji MaruokaView Author Information Department of Chemistry, Graduate School of Science Hokkaido University, Sapporo 060-0810, Japan Department of Chemistry, Graduate School of Science Kyoto University, Sakyo, Kyoto 606-8502, Japan Cite this: J. Am. Chem. Soc. 2000, 122, 21, 5228–5229Publi

Abstract Der Einsatz chiraler nichtracemischer Oniumsalze und Kronenether als wirksame Phasentransferkatalysatoren ist intensiv untersucht worden. Gesucht wurde dabei vorrangig nach Wegen zur enantioselektiven Knüpfung von Kohlenstoff‐Kohlenstoff‐ oder Kohlenstoff‐Heteroatom‐Bindungen unter milden Bedingungen in Zweiphasensystemen. Eine Voraussetzung für optimale asymmetrische Katalysen ist die Abstimmung des Katalysators auf die jeweilige Reaktion und, daraus resultierend, die Bildung definiert

A new chiral ammonium bromide, 1-Br, possessing diarylmethanol functionality as a substrate recognition site has been designed as a promising, dual-functioning catalyst for the highly enantioselective epoxidation of alpha,beta-unsaturated ketones under mild phase-transfer conditions. For instance, vigorous stirring of a mixture of chalcone, 1-Br (3 mol %), and 13% NaOCl in toluene at 0 degrees C for 24 h gave rise to epoxy chalcone quantitatively with 96% ee. A variety of alpha,beta-unsaturated

Unique organocatalysis of both naturally occurring cinchona alkaloid-derived and purely synthetic chiral quaternary ammonium fluorides in synthetically useful stereoselective bond-forming reactions is overviewed. The development of this chemistry was initiated by the in situ generation of generally hygroscopic ammonium fluorides from the corresponding easy-to-handle ammonium salts in the presence of excess metal fluorides and their direct use for subsequent enantioselective reactions. On the oth

Designer chiral quaternary ammonium bifluoride 1 has been prepared, and both its catalytic and its chiral efficiency have been clearly demonstrated by achieving the first catalytic asymmetric nitroaldol reaction of silyl nitronate with aldehydes. For instance, the reaction of trimethylsilyl nitronate 2 (R(1) = Me) with benzaldehyde (R(2) = Ph) in THF in the presence of (S,S)-1 (2 mol %) proceeded smoothly at -78 degrees C, giving the corresponding nitroaldol adduct 3 (R(1) = Me, R(2) = Ph) in 92

The phase-transfer-catalyzed, highly enantioselective cyanation of aldimines using aqueous KCN has been realized based on the molecular design of chiral quaternary ammonium iodide 2c bearing a stereochemically defined tetranaphthyl backbone. For example, vigorous stirring of a mixture of cyclohexanecarboxaldimine (R = c-Hex) and (R,R,R)-2c (1 mol %) in toluene-KCN aqueous solution (1.5 equiv) at 0 degrees C for 2 h gave rise to the corresponding protected amino nitrile (R = c-Hex) in 89% yield w

A highly efficient direct asymmetric aldol reaction of a glycinate Schiff base with aldehydes has been achieved under mild organic/aqueous biphasic conditions with excellent stereochemical control, using chiral quaternary ammonium salt 1b as a phase-transfer catalyst. The initially developed reaction conditions, using 2 equiv of aqueous base (1% NaOH (aq)), exhibited inexplicably limited general applicability in terms of aldehyde acceptors. The mechanistic investigation revealed the intervention

A practical and environmentally benign chemical process for the synthesis of optically active β-hydroxy-α-amino acids involves the reaction of an aldehyde, glycine Schiff base 2, in the presence of catalytic N-spiro chiral quaternary ammonium bromide 1. The cross-aldol product 3 is obtained with excellent stereochemical control (see scheme; a) (R,R)-1 (2 mol %), toluene/aqueous NaOH (1 %), 0° C, 2 h; b) HCl (1 n)/THF). Supporting information for this article is available on the WWW under http://

The designer ammonium salt (S,S)-1 catalyzes highly enantioselective phase-transfer alkylation and Michael reaction of β-keto esters. This approach provides a reliable route for the asymmetric synthesis of polyfunctionalized compounds having chiral quaternary carbon atoms. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2003/z51469_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionalit

[reaction: see text] Phase-transfer-catalyzed direct Mannich reaction of glycinate Schiff base 3 with alpha-imino ester 4 has been accomplished with high enantioselectivity by the utilization of N-spiro C(2)-symmetric chiral quaternary ammonium bromide 2 as a catalyst. This methodology enables the catalytic asymmetric synthesis of differentially protected 3-aminoaspartate, a nitrogen analogue of dialkyl tartrate. The product (syn-5) was converted into a precursor (6) of streptolidine lactam.

A simple yet powerful strategy for the molecular design of chiral phase-transfer catalysts: Conformationally flexible, N-spiro chiral quaternary ammonium bromides of type 1 have been newly designed and are found to exert high chiral efficiency by taking advantage of the considerable difference of activity between the diastereomeric homo- and heterochiral isomers through rapid conformational interconversion.

[reaction: see text]. Highly enantioselective Michael addition of diethyl malonate to chalcone derivatives has been achieved under mild phase-transfer conditions by the successful utilization of N-spiro C(2)-symmetric chiral quaternary ammonium bromide 1 as a catalyst, which possesses diarylhydroxymethyl functionalities as a recognition site for the prochiral electrophile. This simple asymmetric Michael addition process was found to be quite effective for various chalcone derivatives, including