Asymmetric transformation in synthesis: chiral amino acid enolate equivalents

Vedejs, E.; Fields, Stephen C.; Schrimpf, Michael R.

doi:10.1021/ja00077a076

Cited by 75 publications

(39 citation statements)

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“…[129] The optimized reaction procedure involves catalytic amounts of Cu(OAc) 2 A comparison between the efficiency of these reagents with that of the aryl boronic acids (yields given in red) revealed that the organotrifluoroborate salts give higher yields. However, although standard methods to prepare these salts are known, [130] increased commercial availability is required for this method to attract more widespread use.…”

Section: Pentavalent Organotrifluoroborate Reagents As the Aryl Donormentioning

confidence: 99%

Modern Synthetic Methods for Copper‐Mediated C(aryl)O, C(aryl)N, and C(aryl)S Bond Formation

Ley,

Thomas

2003

Angew Chem Int Ed

2,496

816

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The copper-mediated C(aryl)[bond]N, C(aryl)[bond]O, and C(aryl)[bond]S bond formation is an important transformation and has been developed to include a wide range of substrates. This Review highlights the recent developments in the copper-mediated (both stoichiometric and catalytic) reactions of aryl boronic acids, aryl halides, iodonium salts, siloxanes, stannanes, plumbanes, bismuthates, and trifluoroborate salts as aryl donors. In particular, the recent introduction of boronic acids as reaction partners in both O- and N-arylation has been a significant discovery and will occupy centre-stage in this review. Clear improvements can be obtained by the correct choice of copper source, base, ligands, and other additives. Mechanistic investigations should provide insight into the catalytically active species, which would aid in the development of milder, more-efficient methods.

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Section: Pentavalent Organotrifluoroborate Reagents As the Aryl Donormentioning

confidence: 99%

Modern Synthetic Methods for Copper‐Mediated C(aryl)O, C(aryl)N, and C(aryl)S Bond Formation

Ley,

Thomas

2003

Angew Chem Int Ed

2,496

816

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“…The most successful method for formation of the enolates relies on the use of lithium diisopropylamide (LDA) or hexamethyldisilazanide (LHMDS) . All the common electrophiles such as H f , D + , alkyl, allyl, and benzyl halides, a-haloesters and amides, aldehydes, ketones, a$-unsaturated carbonyl compounds, and nitroolefins together with the more unusual ones such as tricarbonyl(benzene)- [84] is alkylated via its K-enolate, and the boron atom serves as the stereogenic center. (This has been applied to phenybdldnine.…”

Section: Chiral Heterocyclic Enolates Of 2-amino- 2-hydroxy- and 2-mentioning

confidence: 99%

Self‐Regeneration of Stereocenters (SRS)—Applications, Limitations, and Abandonment of a Synthetic Principle

Seebàch¹,

Sting²,

Hoffmann³

1996

Angew. Chem. Int. Ed. Engl.

517

299

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In the same manner that the Nasobem, Stiimpke's mythical creature, teaches his child the peculiar way of life of the species Nasobema lyricum, the work of Seebach et al. on the self-regeneration of stereocenters has been governed by a fanciful idea. On the way, many tricks have been learned and much knowledge gained. Finally, they have come back down to earth and find themselves once again in the unimaginative world of enantiomer separation for the synthesis of enantiomerically pure compounds. In order to replace a substituent at a single stereogenic center of a chiral molecule without racemization, a temporary center of chirality is first generated diastereoselectively, the original tetragonal center is then trigonalized by removal of a substituent, a new ligand is introduced, again diastereoselectively, and finally, the temporary center is removed. By means of these four steps (the "Self-Regeneration of Stereocenters", SRS), 2-and 3-amino-, hydroxy-, and sulfanylcarboxylic acids have been successfully alkylated with formation of tertiary carbon centers and without the use of a chiral auxiliary. Use of this methodology has allowed the potential of these inexpensive chiral building blocks to be expanded considerably. This article aims to demonstrate (using, in part, examples from natural product syntheses) that chiral heterocyclic acetals with enamine, enol ether, enolate, dienolate, enoate, radical, and acyliminium functionalities and also those that are potential reactants for Michael additions and pericyclic processes (for example, electron-rich and electronpoor dienophiles and dienes) are now easily accessible, more often than not, in both enantiomeric forms. Stereogenic nitrogen atoms of aziridines, boron atoms of cyclic or linear systems, and stereogenic planes of x-complexes can also be used as the temporary chirality element in other approaches to the realization of the SRS principle. Enantiomerically pure derivatives of, for example, glycine, hydroxy-and sulfanylacetic acid, 3-aminopropanoic acid, and 3-oxocarboxylic acids can be prepared by resolution of racemic mixtures via diastereoisomeric salts or by chromatography on a chiral column. Hence, the extensive reactivity of compounds developed to test the SRS principle and, above all, the outstanding stereoselectivities of the reactions can be put to good use even when no suitable chiral precursor is availabl-ven though this amounts to an abandonment of the principle! The readily available 2-tertbutyl-l,3-imidazolidin-3-one, -0xazolid-in-5-one, -dioxin-3-one, and -hydropyrimidinone (all of which contain a single stereogenic center at the acetal C atom) can thus be used in the preparation of a vast range of 2-amino-and 3-hydroxycarboxylic acids, and no chiral auxiliary has to be removed or regenerated during these procedures. (One example is the synthesis of 4-fluoro-MeBmt, a derivative of the C, amino acid found in cyclosporin.) In the final chapter we will discuss the most useful findings gained from investigations into both the self-regeneration of ste...

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“…Over the last decade, several groups have reported the utility of organotrifluoroborate salts [10] as air-and moisturestable reagents that act as synthetic equivalents to boronic acids. [11,12] While most reports of these salts have focused on their use for cross-coupling chemistry, [10] other synthetically useful applications have also emerged. For example, additions to electrophiles, including carbonyl groups and imines, under a variety of conditions, including the use of Lewis acid, phase transfer catalysis, montmorillonite K10 clay, indium and rhodium(I) catalysis, have been reported.…”

mentioning

confidence: 99%

Regio‐ and Stereoselective Allylation and Crotylation of Indoles at C2 Through the Use of Potassium Organotrifluoroborate Salts

Nowrouzi

Batey

2012

Angew Chem Int Ed

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Asymmetric transformation in synthesis: chiral amino acid enolate equivalents

Cited by 75 publications

References 0 publications

Modern Synthetic Methods for Copper‐Mediated C(aryl)O, C(aryl)N, and C(aryl)S Bond Formation

Modern Synthetic Methods for Copper‐Mediated C(aryl)O, C(aryl)N, and C(aryl)S Bond Formation

Self‐Regeneration of Stereocenters (SRS)—Applications, Limitations, and Abandonment of a Synthetic Principle

Regio‐ and Stereoselective Allylation and Crotylation of Indoles at C2 Through the Use of Potassium Organotrifluoroborate Salts

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