Chiral Quaternary Ammonium Bromide Research Articles

Efficient base-free asymmetric one-pot synthesis of spiro[indoline-3,3′-pyrrolizin]-2-one derivatives catalyzed by chiral organocatalyst

A 1,3-dipolar cycloaddition reaction has been performed under organocatalytic conditions with high enantioselectivity by the utilization of bipyridine-based chiral quaternary ammonium bromide as an organocatalyst. Here, the reaction of 1,3-dipolar cycloaddition of azomethine ylide generated in situ from the decarboxylative condensation of α-amino acids and non-enolizable 1,2-diketones to the above dipolarophiles takes place.

ChemInform Abstract: Highly Efficient Asymmetric Amination of β‐Keto Esters Catalyzed by Chiral Quaternary Ammonium Bromides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Highly efficient asymmetric amination of β-keto esters catalyzed by chiral quaternary ammonium bromides

A highly efficient asymmetric amination of β-keto esters was achieved under phase transfer conditions using chiral quaternary ammonium bromide as a catalyst. The amination products were obtained in quantitative yields with up to 97% ee. One of the amination products represents a key intermediate for the preparation of aldose reductase inhibitor AS-3201.

Practical Stereoselective Synthesis of β-Branched α-Amino Acids through Efficient Kinetic Resolution in the Phase-Transfer-Catalyzed Asymmetric Alkylations

Phase-transfer-catalyzed alkylation of glycinate Schiff base with racemic secondary alkyl halides proceeded with excellent levels of syn- and enantioselectivities under the influence of chiral quaternary ammonium bromide 1d and 18-crown-6. The alkylation product can be selectively converted to the corresponding anti isomer, allowing the preparation of all the stereoisomers of beta-alkyl-alpha-amino acid derivatives, an extremely valuable chiral building block.

Asymmetric phase-transfer catalysis of homo- and heterochiral quaternary ammonium salts: development and application of conformationally flexible chiral phase-transfer catalysts

Inspired by the considerable difference of catalytic activity and stereocontrolling ability between the conformationally rigid, homo- and heterochiral quaternary ammonium bromides 1, conformationally flexible, N-spiro chiral quaternary ammonium bromides of type 4 have been designed and synthesized. Reliable procedures for the preparation of the appropriately substituted biphenyl subunits have been established by the repeated use of ortho magnesiation–halogenation as a key synthetic tool. The relationship between the structure of achiral biphenyl moiety and the reactivity and selectivity of 4 has been evaluated in the asymmetric alkylation of glycinate Schiff base 2 under typical phase-transfer conditions, leading to the identification of 4l as an optimal catalyst structure to exhibit an excellent enantiocontrol in the reactions with various alkyl halides. The molecular structure of 4l was determined by X-ray crystallographic analysis and its unique behavior in solution was examined by a variable-temperature 1H NMR study. These investigations uncovered that the observed high chiral efficiency originated from the efficient asymmetric phase-transfer catalysis of homochiral- 4l, which rapidly equilibrated with heterochiral- 4l of low catalytic activity and stereoselectivity.

Highly Enantioselective Monoalkylation of p‐Chlorobenzaldehyde Imine of Glycine tert‐Butyl Ester under Mild Phase‐Transfer Conditions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

N‐Spiro Chiral Quaternary Ammonium Bromide Catalyzed Diastereo‐ and Enantioselective Conjugate Addition of Nitroalkanes to Cyclic α,β‐Unsaturated Ketones under Phase‐Transfer Conditions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Highly enantioselective monoalkylation of p-chlorobenzaldehyde imine of glycine tert-butyl ester under mild phase-transfer conditions

The selective monoalkylation of glycine tert-butyl ester aldimine Schiff base 3 has been realized in high chemical yield with excellent enantioselectivity under mild liquid–liquid phase-transfer conditions by the use of binaphthyl-derived chiral quaternary ammonium bromides 7 and 8 as catalysts. This achievement demonstrates that 3 can be used as a cost-effective substrate for the preparation of optically active α-alkyl-α-amino acid derivatives by chiral phase-transfer catalysis.

Importance of Chiral Phase‐Transfer Catalysts with Dual Functions in Obtaining High Enantioselectivity in the Michael Reaction of Malonates and Chalcone Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

N-Spiro Chiral Quaternary Ammonium Bromide Catalyzed Diastereo- and Enantioselective Conjugate Addition of Nitroalkanes to Cyclic α,β-Unsaturated Ketones under Phase-Transfer Conditions

[reaction, structure: see text] Conjugate addition of various prochiral nitroalkanes to cyclic alpha,beta-unsaturated ketones was found to be efficiently catalyzed by N-spiro C2-symmetric chiral quaternary ammonium bromide 1b possessing a 3,5-bis(3,4,5-trifluorophenyl)phenyl substituent under solid-liquid phase-transfer conditions to afford the corresponding gamma-nitro ketones in excellent chemical yields with unprecedented levels of diastereo- and enantiocontrol.

Importance of Chiral Phase-Transfer Catalysts with Dual Functions in Obtaining High Enantioselectivity in the Michael Reaction of Malonates and Chalcone Derivatives

[reaction: see text]. Highly enantioselective Michael addition of diethyl malonate to chalcone derivatives has been achieved under mild phase-transfer conditions by the successful utilization of N-spiro C(2)-symmetric chiral quaternary ammonium bromide 1 as a catalyst, which possesses diarylhydroxymethyl functionalities as a recognition site for the prochiral electrophile. This simple asymmetric Michael addition process was found to be quite effective for various chalcone derivatives, including those with heteroaromatic substituents.

Chiral designer phase-transfer catalysts for practical asymmetric synthesis

Abstract A series of C 2-symmetric, spiro-type chiral quaternary ammonium bromides have been designed as new, purely synthetic chiral phase-transfer catalysts, and readily prepared from commercially available optically pure (R)- or (S)-1,1'-bi-2-naphthol as a basic chiral unit. The structures of the assembled N-spiro chiral quaternary ammonium bromides were unequivocally determined by single-crystal X-ray diffraction analysis. The reactivity and selectivity of these chiral ammonium bromides as chiral phase-transfer catalysts have been evaluated in the asymmetric alkylation of N-(diphenylmethylene)glycine tert-butyl ester under mild liquid–liquid phase-transfer conditions, and the optimization of the reaction variables (solvent, base, and temperature) has also been conducted. Furthermore, the scope and limitations of other asymmetric transformations have been thoroughly investigated with a variety of substrates, in which the advantage of the unique N-spiro structure of our chiral phase-transfer catalysts and dramatic effect of the steric as well as the electronic properties of the aromatic substituents on the 3,3'-position of one binaphthyl moiety have been particularly emphasized.

Asymmetric Synthesis of Functionalized Aza-Cyclic Amino Acids with Quaternary Stereocenters by a Phase-Transfer-Catalyzed Alkylation Strategy

[Reaction: see text] Practical asymmetric synthesis of functionalized aza-cyclic alpha-amino acid derivatives possessing quaternary stereocenters has been achieved by the phase-transfer-catalyzed alkylation of 2 or 3 using chiral quaternary ammonium bromide 1 as catalyst. Subsequent reduction and alkylation of the 3-keto carbonyl moiety of 4 proceeded with complete diastereochemical control to afford the corresponding beta-hydroxy aza-cyclic alpha-amino acid derivatives having stereochemically defined consecutive quaternary carbon centers.

Highly Enantioselective Conjugate Addition of Nitroalkanes to Alkylidenemalonates Using Efficient Phase‐Transfer Catalysis of N‐Spiro Chiral Ammonium Bromides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Catalytic Asymmetric Synthesis of a Nitrogen Analogue of Dialkyl Tartrate by Direct Mannich Reaction under Phase‐Transfer Conditions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly enantioselective conjugate addition of nitroalkanes to alkylidenemalonates using efficient phase-transfer catalysis of N-spiro chiral ammonium bromides.

Highly enantioselective conjugate addition of nitroalkanes to alkylidenemalonates has been accomplished for the first time by the utilization of efficient phase-transfer catalysis of N-spiro C2-symmetric chiral quaternary ammonium bromide 1. For instance, simple mixing of nitropropane (2, R1 = Et), diisopropyl benzylidienemalonate (3, R2 = Ph), Cs2CO3 (1 equiv), and (S,S)-1 (1 mol %) in toluene at 0 degrees C for 2.5 h gave rise to the desired conjugate addition product 4 (R1 = Et, R2 = Ph) quantitatively (anti/syn = 86:14) with 97% ee (anti isomer). The applicability of this procedure has been demonstrated with other representative alkylidenemalonates and nitroalkanes. Since 4 can be readily transformed into the corresponding gamma-amino acid hydrochloride 5 without loss of diastereo- and enantioselectivity, the present method provides a new and practical access to various optically active gamma-amino acid derivatives.

Catalytic asymmetric synthesis of a nitrogen analogue of dialkyl tartrate by direct mannich reaction under phase-transfer conditions.

[reaction: see text] Phase-transfer-catalyzed direct Mannich reaction of glycinate Schiff base 3 with alpha-imino ester 4 has been accomplished with high enantioselectivity by the utilization of N-spiro C(2)-symmetric chiral quaternary ammonium bromide 2 as a catalyst. This methodology enables the catalytic asymmetric synthesis of differentially protected 3-aminoaspartate, a nitrogen analogue of dialkyl tartrate. The product (syn-5) was converted into a precursor (6) of streptolidine lactam.

Stereoselective terminal functionalization of small peptides for catalytic asymmetric synthesis of unnatural peptides.

The asymmetric phase-transfer catalytic alkylation of peptides has been achieved by the use of designed C(2)-symmetric chiral quaternary ammonium bromide 1 as catalyst. Excellent stereoselectivities were uniformly observed in the alkylation with a variety of alkyl halides and the efficiency of the transmission of stereochemical information was not affected by the side-chain structure of the preexisting amino acid residues. This method also enables an asymmetric construction of noncoded alpha,alpha-dialkyl-alpha-amino acid residues at the peptide terminal. Since this chirality can be efficiently transferred to the adjacent amino acid moiety, our approach provides a general procedure not only for the highly stereoselective terminal functionalization of peptides but also for the sequential asymmetric construction of unnatural oligopeptides, which should play a vital role in the peptide-based drug discovery process.

A New N‐Spiro C2‐Symmetric Chiral Quaternary Ammonium Bromide Consisting of 4,6‐Disubstituted Biphenyl Subunit as an Efficient Chiral Phase‐Transfer Catalyst.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Practical asymmetric synthesis of vicinal diamines through the catalytic highly enantioselective alkylation of glycine amide derivatives.

Phase-transfer catalysis (PTC) by a designer chiral quaternary ammonium bromide facilitated the direct, highly enantioselective introduction of a wide variety of substituents including cycloalkyl side chains at the α position of the prochiral glycine amide derivative 1. A general, practical procedure for the asymmetric synthesis of structurally diverse monosubstituted vicinal diamines of type 2 is presented. Dpm=diphenylmethyl.