Enantioselective Phase-transfer Alkylation Research Articles

H-Bond Mediated Phase-Transfer Catalysis: Enantioselective Generating of Quaternary Stereogenic Centers in β-Keto Esters.

In this work, we would like to present the development of a highly optimized method for generating the quaternary stereogenic centers in β-keto esters. This enantioselective phase-transfer alkylation catalyzed by hybrid Cinchona catalysts allows for the efficient generation of the optically active products with excellent enantioselectivity, using only 1 mol% of the catalyst. The vast majority of phase-transfer catalysts in asymmetric synthesis work by creating ionic pairs with the nucleophile-attacking anionic substrate. Therefore, it is a sensible approach to search for new methodologies capable of introducing functional groups into the precursor’s structure, maintaining high yields and enantiomeric purity.

Diastereo- and enantioselective phase-transfer alkylation of 3-substituted oxindoles with racemic secondary alkyl halides.

A catalytic asymmetric alkylation of fully substituted enolates with racemic, non-activated secondary alkyl halides is described. The chiral 1,2,3-triazolium ion enables excellent diastereo- and enantiocontrol via enantiofacial discrimination of prochiral enolates and kinetic resolution of secondary halides.

Enantioselective Phase-Transfer Alkylation of Sulfenate Anions to Sulfoxides

Key words phase-transfer catalysis - pentanidium salts - sulfenate ions - sulfoxides

Bicyclic guanidinium-catalyzed enantioselective phase-transfer alkylation: direct access to pyrroloindolines and furoindolines

Highly enantioselective phase-transfer alkylation of 3-substituted-2-oxindoles with activated bromomethanes is disclosed with a broad substrate scope by using bicyclic guanidinium as a catalyst and a Lewis acid as the co-catalyst. The alkylation adducts are versatile intermediates to accomplish the syntheses of pyrroloindolines and furoindolines.

Enantioselective phase transfer alkylation using orthopalladated complex in chiral ionic liquid

The optically active orthopalladated phenanthrylamine phase transfer catalyst has been produced and explored for asymmetric glycine alkylation. The catalyst (10 mol%) in toluene/chloroform with 50% aqueous KOH (25 °C) promoted benzylation of benzophenone imine tert-butyl glycine. The product was obtained in 85% yield and 15% enantiomeric excess (ee). Addition of the chiral ionic liquid N,N-dimethyl ephedrinium bis(trifluoromethansulfon)imidate enhanced reactivity and selectivity for PTC glycine alkylation. It appears that the chiral ionic liquid has a cooperative effect to boost the ee content of an asymmetric reaction.

Asymmetric PTC Alkylation of Glycine Imines: Variation of the Imine Ester Moiety.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Asymmetric PTC Alkylation of Glycine Imines: Variation of the Imine Ester Moiety

Studies into the enantioselective phase-transfer alkylation of a series of glycine imine esters are presented. Using a quaternary ammonium salt catalyst derived from α-methylnaphthylamine, high enantioselectivities were obtained in reactions involving imines containing tert-butyl, benzhydryl, and benzyl esters. In contrast, a quaternary ammonium salt catalyst derived from dihydrocinchonidine gave highest enantioselectivities with tert-butyl and ethyl esters. Application of the benzhydryl ester alkylation in the preparation of a differentially protected aspartic acid derivative is also presented.

Highly enantioselective construction of quaternary stereocenters on beta-keto esters by phase-transfer catalytic asymmetric alkylation and Michael reaction.

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 functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

An unusual electronic effect of an aromatic-F in phase-transfer catalysts derived from cinchona-alkaloid.

[structure: see text] Various N-benzylcinchonidinium salts were prepared to study electronic factors in the catalytic enantioselective phase-transfer alkylation of glycine anion equivalent. An ortho-fluoro substituent on the benzyl group in the quaternary ammonium salt dramatically increased the enantioselectivity in the alkylation. O(9)-Allyl-N-2',3',4'-trifluorobenzylhydrocinchonidinium bromide (27), which gave the highest enantioselectivity of the catalysts studied, was used to prepare 12 alpha-alkylated amino acid derivatives in 94 approximately >99% ee.

Chiral quaternary benzophenone hydrazonium salt derivatives; Efficient chiral catalysts for the enantioselective phase-transfer alkylation of imines. Application to synthesis of chiral primary amines

(2S)-1-Methyl-1-[N-(diphenylmethylene)]-2-hydroxymethylpyrrolidine hydrazonium iodide I-a has been designed to catalyse the enantioselective phase-transfer alkylation of N-(diphenylmethylene) benzenemethanamine II . Although the weak acidic character of the latter, alkylations have been performed within reasonable reaction times. Optically active primary amines III a-e have been prepared in good chemical yields and up to 94% e.e. using 2–5 mol-% of the chiral catalyst only.