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, 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...

An organocatalytic method for the chemo- and regioselective acylation of monosaccharides has been developed. Treatment octyl β-d-glucopyranoside with isobutyric anhydride in presence 10 mol % a C2-symmetric chiral 4-pyrrolidinopyridine catalyst (1) at −50 °C gave 4-O-isobutyryl derivative as sole product 98% yield. Thus, chemoselective acylation, favoring secondary hydroxyl group free primary group, one three groups, took place perfect selectivity. A competitive between alcohol...

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...

Is it really true that racemization must occur in reactions via enolates unless the reaction takes place a chiral environment (below)? We discuss "memory of chirality", phenomenon which chirality starting material is preserved reactive intermediate for limited time.

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

Using a bottom-up method, we prepared series of oligonaphthofurans composed alternating naphthalene rings and furan rings. The largest compound (compound 25) contained 8 units 7 units. DFT calculations revealed that these compounds were fan-shaped molecules each ring was oriented in an alternate mountain-valley fold conformation because steric repulsion by the hydrogens at peri-positions. We investigated optical properties derived from their sequences. As number aromatic increased, peaks...

This review describes the recent advances in asymmetric reactions based on memory of chirality. The chirality is a unique concept concerning an advanced type chiral pool-based synthesis, which take place at sole stereogenic center starting materials. original sp³ material retained as dynamic sp² intermediate, and then transferred to product. These were found proceed through various types intermediates with nature. phenomena observed proceeding radical, cationic, anionic...

Asymmetric synthesis of mechanically planar chiral rotaxanes and topologically catenanes has been a long-standing challenge in organic synthesis. Recently, an excellent strategy was developed based on diastereomeric with mechanical chirality followed by removal the auxiliary. On other hand, its enantioselective approach quite limited. Here, we report preparation kinetic resolution racemates via remote asymmetric acylation hydroxy group axis component, which provides unreacted enantiomer up...

Organocatalytic regioselective acylation of mono- and disaccaharides with various functionalized acid anhydrides has been developed. Acylation octyl beta-D-glucopyranoside derived from alpha-amino acids, cinnamic acid, gallic took place at C(4)-OH 67-94% regioselectivity in the presence catalyst 1. Regioselective disaccharides was also achieved 78-94% selectivity. Especially, a disaccharide seven free hydroxy groups (X = OH, R' H) underwent 78% Thus, functional group tolerance catalyzed by 1...

Enolate chemistry has been extensively used for stereoselective C-C bond formation, in which metal amide bases are frequently employed strictly anhydrous solvents at low temperatures. However, we found that asymmetric intramolecular formation via axially chiral enolate intermediates proceeded up to 99% ee 20 degrees C using powdered KOH dry or wet DMSO as a base. The enantioselectivity was even higher than of the corresponding reactions with potassium hexamethyldisilazide DMF -60 C....

Acylation of lanatoside C in the presence organocatalyst 5 gave C(4'''')-O-acylate up to 90% regioselectivity (catalyst-controlled regioselectivity). Various functionalized acyl groups can be introduced at C(4'''')-OH by a mixed anhydride method or related organocatalyst. On other hand, DMAP-catalyzed acylation C(3'''')-O-acylate 97% (substrate-controlled Thus, diverse regioselective introduction among eight free hydroxy was achieved.

A method for asymmetric α-arylation of amino acid derivatives has been developed. The arylation was performed by Clayden rearrangement ester enolates via memory chirality to give hydantoins with an aryl-substituted tetrasubstituted carbon up 99% ee.

The first total syntheses of punicafolin (1) and macaranganin (2) were achieved in seven steps, respectively, from commercial α-d-glucose. characteristic features the synthesis are sequential site-selective introduction adequate galloyl groups into unprotected d-glucose by a catalyst-controlled manner stereodivergent construction 3,6-HHDP bridge oxidative phenol coupling common intermediate via ring-flipping process glucose core. Because no protective used for throughout process, extremely...

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

[reaction: see text] A total synthesis of spirotryprostatin B was accomplished via asymmetric nitroolefination as a key step.

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 acylation can be readily controlled by amount acid anhydride.

A new combination system consisting of boron trifluoride etherate and dimethyl sulfide has proved to be useful especially for the selective removal benzyl protecting group in a molecule having Michael acceptor or carbonyl (s).

An enantiodivergent asymmetric cyclization of N-Boc-N-omega-bromoalkyl-alpha-amino acid derivatives has been developed. With potassium amide bases in DMF, proceeds with retention configuration, while inversion configuration was observed lithium THF. Chirality the parent amino acids preserved during enolate formation and to give aza-cyclic up 98% ee or depending on reaction conditions. Thus, both enantiomers cyclic a tetrasubstituted stereocenter were prepared high enantiomeric purity from...

Novel chiral binaphtyl surrogates with an inner hydrogen bond have been created. The N—H appears at 13.0−13.3 ppm in thier 1H NMR spectrum, indicating extremely strong bonding. Enantiomers of these compounds were stable ambient temperature and separable by HPLC a stationary phase. half-lives racemization the enantiomer are range 3 months to 2 years 20 °C, barriers for 27.0 28.2 kcal/mol. An X-ray crystal analysis compound (R = CHPh2) shows that pseudonaphthyl skeleton including C═N···H—N is...

Electronic tuning: Nitroxyl radical 1 is shown to be an efficient catalyst for the oxidation of secondary alcohols, and promotes through oxoammonium species which highly reactive because adjacent electron-withdrawing ester groups. Chemoselective benzylic alcohols in presence aliphatic observed proposed proceed by a rate-determining hydride transfer.

The first total syntheses of multifidosides A-C have been achieved. synthetic strategy is characterized by catalytic site-selective acylation unprotected glycoside precursors in the final stage synthesis. High functional-group tolerance acylation, promoted an organocatalyst, enabled conventionally difficult molecular transformation a predictable and reliable manner. An advantage this to avoid risks undesired side reactions during removal protecting groups at

Acylpyridinium ions have been known as catalytically active species in acylation reactions catalyzed by 4-dimethylaminopyridine and its analogues. carboxylates were found to be 800–1300 times more reactive than the corresponding acylpyridinium chlorides. A catalytic cycle was developed, which generated situ counteranion exchange from catalyst loading low 0.01 mol % turnover number of up 6700 achieved for site-selective a carbohydrate.

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