Takeo Kawabata 교수

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTNonenzymatic Kinetic Resolution of Racemic Alcohols through an "Induced Fit" ProcessTakeo Kawabata, Minoru Nagato, Kiyosei Takasu, and Kaoru FujiView Author Information Institute for Chemical Research Kyoto University, Uji, Kyoto 611, Japan Cite this: J. Am. Chem. Soc. 1997, 119, 13, 3169–3170Publication Date (Web):April 2, 1997Publication History Received17 September 1996Published online2 April 1997Published inissue 1 April 1997https://pubs.acs.

An organocatalytic method for the chemo- and regioselective acylation of monosaccharides has been developed. Treatment of octyl beta-D-glucopyranoside with isobutyric anhydride in the presence of 10 mol % of a C2-symmetric chiral 4-pyrrolidinopyridine catalyst (1) at -50 degrees C gave the 4-O-isobutyryl derivative as the sole product in 98% yield. Thus, chemoselective acylation, favoring a secondary hydroxyl group in the presence of a free primary hydroxyl group, and regioselective acylation, f

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMemory of chirality: enantioselective alkylation reactions at an asymmetric carbon adjacent to a carbonyl groupTakeo Kawabata, Kiyoshi Yahiro, and Kaoru FujiCite this: J. Am. Chem. Soc. 1991, 113, 25, 9694–9696Publication Date (Print):December 1, 1991Publication History Published online1 May 2002Published inissue 1 December 1991https://doi.org/10.1021/ja00025a057RIGHTS & PERMISSIONSArticle Views1598Altmetric-Citations130LEARN ABOUT THESE METRICSArticle

The crucial intermediate A with a racemization barrier of 16 kcal mol−1 at −78 °C is proposed for the asymmetric α-methylation of 1 to give 2 in 81 % ee and 96 % yield (see scheme). The asymmetric α-methylation occurs in other amino acid derivatives (Dopa, Val, Leu, Trp, His, Tyr) in 78–93 % ee. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2000/z14334_s.pdf or from the author. Please note: The publisher is not responsible for the

Short total syntheses of natural glycosides (ellagitannins) were performed through sequential and regioselective functionalization of the hydroxy groups of unprotected glucose. The key reactions are β-selective glycosidation of a gallic acid derivative by using unprotected glucose as a glycosyl donor and catalyst-controlled regioselective introduction of a galloyl group into the inherently less reactive hydroxy group of the glucoside.

Acylative kinetic resolution of racemic cyclic cis-amino alcohol derivatives with a chiral nucleophilic catalyst proceeds enantioselectively (s = 10–21) at ambient temperature to give enantiopure recovered materials, and the % conversion of the acylation can be readily controlled by the amount of acid anhydride.

In this chapter we show that the chirality of a ketone and some α-amino acid esters can be preserved in their enolate forms, and asymmetric synthesis is possible via the strategy shown later in the chapter. In these reactions the chirality of the starting material appears to be memorized in the enolate intermediates, so we call this type of asymmetric transformation “memory of chirality.” The design, development, and rationale of the memory of chirality are described.

Enolate chemistry has been extensively used for stereoselective C-C bond formation, in which metal amide bases are frequently employed in strictly anhydrous solvents at low temperatures. However, we found that asymmetric intramolecular C-C bond formation via axially chiral enolate intermediates proceeded in up to 99% ee at 20 degrees C using powdered KOH in dry or wet DMSO as a base. The enantioselectivity was even higher than that of the corresponding reactions with potassium hexamethyldisilazi

N-(omega-Bromoalkyl)-amino acid derivatives, readily prepared from natural alpha-amino acids, gave cyclic amino acids with a quaternary stereocenter by treatment with potassium hexamethyldisilazaide in DMF. The chirality of parent amino acids was almost completely preserved during an enolate-formation and cyclization process, giving aza-cyclic amino acids in up to 98% ee in retention of configuration. This method is applicable to the asymmetric synthesis of azetidine, pyrrolidine, piperidine, an

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDirect Asymmetric .alpha.-Alkylation of Phenylalanine Derivatives Using No External Chiral SourcesTakeo Kawabata, Thomas Wirth, Kiyoshi Yahiro, Hideo Suzuki, and Kaoru FujiCite this: J. Am. Chem. Soc. 1994, 116, 23, 10809–10810Publication Date (Print):November 1, 1994Publication History Published online1 May 2002Published inissue 1 November 1994https://pubs.acs.org/doi/10.1021/ja00102a066https://doi.org/10.1021/ja00102a066research-articleACS Publicatio

An enantiodivergent asymmetric cyclization of N-Boc-N-omega-bromoalkyl-alpha-amino acid derivatives has been developed. With potassium amide bases in DMF, cyclization proceeds with retention of configuration, while inversion of configuration was observed with lithium amide bases in THF. Chirality of the parent amino acids was preserved during enolate formation and cyclization to give aza-cyclic amino acids in up to 98% ee with retention of configuration or inversion of configuration, depending o

This review describes the recent advances in asymmetric reactions based on memory of chirality. The memory of chirality is a unique concept concerning an advanced type of chiral pool-based asymmetric synthesis, in which reactions take place at the sole stereogenic center of the starting materials. The original sp³ chirality of the starting material is retained as dynamic sp² chirality in the intermediate, and then transferred to sp³ chirality of the product. Thes

Novel chiral binaphtyl surrogates with an inner hydrogen bond have been created. The NH appears at 13.0-13.3 ppm in thier (1)H NMR spectrum, indicating extremely strong hydrogen bonding. Enantiomers of these compounds were stable at ambient temperature and separable by HPLC with a chiral stationary phase. The half-lives of racemization of the enantiomer are in the range 3 months to 2 years at 20 degrees C, and the barriers for racemization are in the range 27.0 to 28.2 kcal/mol. An X-ray crystal