Asymmetric Phase-Transfer Catalysis

Nelson, Adam

doi:10.1002/(sici)1521-3773(19990601)38:11<1583::aid-anie1583>3.0.co;2-e

Cited by 182 publications

(39 citation statements)

References 15 publications

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“…Previous studies with acetic [36], mandelic [37], and tiglic [38] acids have indicated similar rotational restrictions, in those cases because the carboxylate ion fits in the bridging position of the open conformation of cinchonidine via a bidentate coordination [36]. All this is quite relevant to the performance of the cinchona alkaloids in catalysis, because their protonated quaternary quinuclidine nitrogen has been found to promote an array of asymmetric phase transfer reactions such as a-alkylation of carbonyl compounds, Michael additions, and epoxidation of enones [11,[39][40][41]. Protonation also appears to help in heterogeneous catalysis [42,43], and may be responsible for the medical properties of quinine [18].…”

Section: Solution Chemistrymentioning

confidence: 99%

The Physico-chemical Properties of Cinchona Alkaloids Responsible for their Unique Performance in Chiral Catalysis

Mink

Olsen

et al. 2008

Top Catal

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The physico-chemical properties of cinchona alkaloids have been characterized in connection to their use for catalytic enantioselective conversions. Adding to the previous identification of their active site at the nitrogen atom in the quinuclidine ring and the chiral environment provided by the carbon centers of the neighboring alcohol linker, an argument is made here for the importance of the adoption of certain rotational conformations by those cinchona alkaloids in optimizing their chiral promotion. Because catalysis with cinchona alkaloids involves a liquid phase, there is a dynamic conformation isomerization process controlled by a number of factors having to do with the exact structure of the cinchona as well as with the nature of the solvent used and, in the case of heterogeneous catalysis, the presence of a solid surface. Solvents of intermediate polarity have been found to be the best for dissolving the cinchona, for establishing rapid adsorption equilibria with metal surfaces, and for promoting chiral catalysis. Protonation also leads to a dramatic change in performance, locking the cinchona molecule in a specific conformation held in place by the counter anion of the acid used, and modifying the chemical and biological activity of the system. Comparative studies with several cinchona indicate that molecular groups attached to peripheral positions also exert a great influence on the conformational and adsorption behavior of these molecules.

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Section: Solution Chemistrymentioning

confidence: 99%

The Physico-chemical Properties of Cinchona Alkaloids Responsible for their Unique Performance in Chiral Catalysis

Mink

Olsen

et al. 2008

Top Catal

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“…[1] For example, the CH 2 group in CH 2 CHR can be replaced by 16-electron transition metal fragments [L n M] to give carbene complexes [L n M CHR], the CH group in HC CR can be replaced by 15-electron transition metal fragments [L n M] to give carbyne complexes [L n M CR], and a CH group in benzene can be replaced by 15-electron transition metal fragments to give metallabenzenes. [2] In principle, a carbon atom in benzyne could also be replaced by 14-electron transition metal fragments to give metallabenzynes.…”

Section: Methodsmentioning

confidence: 99%

“…[1] Following the seminal work by O Donnell et al [2a] and Grabowski et al [2b] dramatic improvements in the asymmetric efficiency of PTC reactions were achieved by introducing (9-anthracenylmethyl)cinchonidinium (1 a, R allyl, benzyl, H) and other cinchoninium salts as catalysts for the enantioselective alkylation of N-(diphenylmethylene)glycine esters with electrophiles. [2c±e] Purely synthetic, chiral, C 2 -symmetrical ammonium salts were recently prepared and shown to be highly efficient in the same set of reactions.…”

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confidence: 99%

Highly Efficient Catalytic Synthesis of -Amino Acids under Phase-Transfer Conditions with a Novel Catalyst/Substrate Pair

Belokoń

Кочетков

Churkina

et al. 2001

Angew. Chem. Int. Ed.

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“…Many useful catalytic asymmetric phase-transfer alkylation reactions have been developed where the chiral counter-cation (Y*) ϩ is a quaternary ammonium salt (14,15). The synthesis of 6 is exemplary (Scheme 4) (16).…”

Section: Combination Of Chiral Carbon Nucleophiles With Carbon Electrmentioning

confidence: 99%

Catalytic asymmetric synthesis of all-carbon quaternary stereocenters

Douglas

Overman

2004

Proc. Natl. Acad. Sci. U.S.A.

798

177

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Only a few catalytic asymmetric COC bond-forming reactions have been shown to be useful for constructing all-carbon quaternary stereocenters. This Perspective examines the current state of such methods.C arbon atoms bonded to four carbon substituents (all-carbon quaternary centers) pose a particular challenge for synthesis because creation of such centers is complicated by steric repulsion between the carbon substituents. When the four substituents differ, quaternary stereocenters become a singular challenge for achieving efficient asymmetric syntheses of chiral organic molecules (1-4). The invention of catalytic methods for asymmetric synthesis is one of the foremost recent achievements of chemistry (5), with the 2001 Nobel Prize in Chemistry recognizing William S. Knowles, Ryoji Noyori, and K. Barry Sharpless for their pioneering development of catalytic asymmetric hydrogenation and oxidation reactions. At present, many broadly useful methods for catalytic asymmetric oxidation and reduction exist; however, far fewer catalytic asymmetric methods for forming COC bonds have been invented to date (5). As disclosures in this special feature will attest, this latter area of catalytic asymmetric synthesis is a current focus of intense investigation worldwide.At present only a few catalytic asymmetric COC bond-forming reactions have been shown to be useful for constructing quaternary carbons, undoubtedly reflecting the additional steric challenge involved in forming all-carbon quaternary centers. This Perspective will examine the current state of such methods. The focus will be on reactions for which some generality has been documented, and several examples exist of reactions that proceed with enantiomeric selectivities of at least 9:1 [enantiomeric excesses (ees) Ͼ80%]. The discussion is organized by general reaction types that have proven useful, not by the more commonly used organizations that focus on one specific transformation or one family of asymmetric catalysts. It is hoped that this organization will highlight the many opportunities that exist for future discoveries in this area. The less general approach for forming allcarbon quaternary stereocenters in which a group-selective catalytic asymmetric reaction is used to desymmetrize a prochiral intermediate containing a quaternary carbon will be briefly mentioned also. No attempt to summarize this latter field will be made, as any catalytic asymmetric reaction could in principle be used in this approach. In four areas, catalytic methods for directly forming all-carbon stereocenters are most developed: Diels-Alder reactions, the combination of chiral carbon nucleophiles with carbon electrophiles, reactions of allylmetal intermediates with carbon nucleophiles, and intramolecular Heck reactions. Our discussion will begin with these reaction types. Asymmetric Diels-Alder ReactionsThe Diels-Alder reaction provides two approaches for forming quaternary stereocenters contained within the cyclohexene framework (Scheme 1). In reactions of type I, electron-rich dienes c...

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Asymmetric Phase-Transfer Catalysis

Abstract: Both in the laboratory and industrially, phase-transfer catalysis offers the potential to induce asymmetry into reactions with anionic intermediates. Equation (a) provides an example (conditions: a) 10 mol % phase-transfer catalyst, BnBr, CsOH⋅H O, PhMe, 15-24 h, -78°C).

Cited by 182 publications

References 15 publications

The Physico-chemical Properties of Cinchona Alkaloids Responsible for their Unique Performance in Chiral Catalysis

The Physico-chemical Properties of Cinchona Alkaloids Responsible for their Unique Performance in Chiral Catalysis

Highly Efficient Catalytic Synthesis of -Amino Acids under Phase-Transfer Conditions with a Novel Catalyst/Substrate Pair

Catalytic asymmetric synthesis of all-carbon quaternary stereocenters

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