Chiral Phase-transfer Catalysts Research Articles

Rh(II)-catalyzed enantioselective synthesis of acuminatin through a C–H insertion reaction of a non-stabilized carbenoid

An efficient and practical asymmetric synthesis of the 2,3-dihydrobenzo[b]furan neolignan acuminatin was achieved by using trans-isoeugenol as the starting material. The key step is an intramolecular C–H insertion through a non-stabilized carbenoid, prepared by decomposition of a tosylhydrazone in the presence of an anthracenyl-derived cinchonidine quaternary ammonium salt as a chiral phase-transfer catalyst.

ChemInform Abstract: Alkaloid Derived Auxiliaries: Cinchona Alkaloids and Derivatives

AbstractReview: use of cinchona alkaloids and their derivatives as chiral auxiliaries, organoctalysts and phase transfer catalysts; 291 refs.

Recent Developments in Asymmetric Phase‐Transfer Reactions

Phase-transfer catalysis has been recognized as a powerful method for establishing practical protocols for organic synthesis, because it offers several advantages, such as operational simplicity, mild reaction conditions, suitability for large-scale synthesis, and the environmentally benign nature of the reaction system. Since the pioneering studies on highly enantioselective alkylations promoted by chiral phase-transfer catalysts, this research field has served as an attractive area for the pursuit of "green" sustainable chemistry. A wide variety of asymmetric transformations catalyzed by chiral onium salts and crown ethers have been developed for the synthesis of valuable organic compounds in the past several decades, especially in recent years.

ChemInform Abstract: Synthesis of a Calixarene‐Based Chiral Phase‐Transfer Catalyst Derived from Cinchonine and Its Application in Asymmetric Alkylation.

The synthesis of a novel calixarene-based chiral phase-transfer catalyst derived from cinchonine has been achieved in four steps from p-t-butylcalix[4]arene. Its catalytic properties were evaluated...

Immobilization of Cinchona Quaternary Ammonium Salts as the Chiral Phase Transfer Catalysts on Multi-walled Carbon Nanotubes and Their Application in Enantioselective Alkylation

The pyrene-tagged cinchona quaternary ammonium salt, the chiral phase transfer catalysts (PTC-1), was synthesized and immobilized on multi-walled carbon nanotubes (MWCNTs). The new catalysts (PTC-1/MWCNTs) were employed in enantioselective alkylation of N-(diphenylmethyene)glycine tert-butyl ester. UV-Vis absorption spectra show the effect of different organic solvents on the adsorption and desorption of PTC-1 onto and from MWCNTs, respectively. The results show that 5.3 mg PTC-1 can be loaded on 10 mg MWCNTs in toluene, and 0.02025 mg PTC-1 was desorbed from 12.7 mg PTC-1/MWCNTs when washed by CHCl3. In the enantioselective alkylation of different halohydrocarbons with N-(diphenylmethyene)glycine tert-butyl ester using PTC-1/MWCNTs as a catalyst, the alkylating products were obtained with high yield and ee value. Furthermore, PTC-1/MWCNTs catalyst can be recovered and used repeatedly. PTC-1/MWCNTs as a new catalyst is effective in enantioselective alkylation of multiple halohydrocarbon.

Efficient approach for the design of effective chiral quaternary phosphonium salts in asymmetric conjugate additions

An efficient approach for the design of chiral quaternary phosphonium bromides as chiral phase-transfer catalysts was demonstrated. A catalyst library of phosphonium salts with various structures was readily constructed using commercially available chiral phosphines as catalyst precursors, and an optimized catalyst was successfully applied to highly enantioselective conjugate additions under base-free phase-transfer conditions with low catalyst loading.

Hydrolytic Enantioselective Protonation of Cyclic Dienyl Esters and a β-Diketone with Chiral Phase-Transfer Catalysts

Hydrolytic enantioselective protonation of dienyl esters and a β-diketone catalyzed by phase-transfer catalysts are described. The latter reaction is the first example of an enantio-convergent retro-Claisen condensation. Corresponding various optically active α,β-unsaturated ketones having tertiary chiral centers adjacent to carbonyl groups were obtained in good to excellent yields and enantiomeric ratios (83-99%, up to 97.5:2.5 er).

ChemInform Abstract: Chiral Quaternary Phosphonium Salts: A New Class of Organocatalysts

AbstractReview: 50 refs.

Investigations Concerning the Syntheses of TADDOL-Derived Secondary Amines and Their Use To Access Novel Chiral Organocatalysts.

A structurally carefully diversified library of novel TADDOL-derived chiral secondary amines was synthesized and investigated for their applicability to obtain new organocatalysts like chiral Lewis bases and chiral phase-transfer catalysts. The scope and limitations of the developed syntheses routes to access these catalysts as well their catalytic performance in different benchmark reactions were systematically investigated. The most powerful of the catalysts prepared was found to be highly useful for the phase-transfer catalyzed α-alkylation of glycine Schiff base (high yields and up to 93% ee).

Synthesis of a Calixarene-Based Chiral Phase-Transfer Catalyst Derived from Cinchonine and its Application in Asymmetric Alkylation

The synthesis of a novel calixarene-based chiral phase-transfer catalyst derived from cinchonine has been achieved in four steps from p-t-butylcalix[4]arene. Its catalytic properties were evaluated over a range of conditions by carrying out the phase-transfer alkylation of N-(diphenylmethylene)glycine t-butyl ester with benzyl bromide. Under the optimal conditions the alkylated product was formed in 96% yield with 91% ee.

ChemInform Abstract: Asymmetric Phase‐Transfer‐Catalyzed Conjugate Addition of Glycine Imine to Exocyclic α,β‐Unsaturated Ketones: Construction of Polycyclic Imines Containing Three Stereocenters.

We developed a facile, one-pot, multistep transformation between glycine imine and exocyclic α,β-unsaturated ketones in reactions catalyzed by chiral phase-transfer catalysts (PTC). A series of polycyclic imines containing three adjacent stereocenters were obtained in good to high yields with high diastereo- and enantioselectivities. Further transformation of the imines could afford N-fused polycyclic compounds with four adjacent stereocenters.

Synthesis of L-arabinose-based crown ethers and their applications as enantioselective phase transfer catalysts

New chiral monoaza-15-crown-5 type macrocycles anellated to 3,4-O-isopropylidene-�-L- arabinopyranose ( 5a-b), to �-L-arabinopyranose ( 6) and to 3,4-O-benzyliden-�-L- arabinopyranose (11 ) have been synthesized. The cation binding ability of the new lariat ethers was evaluated by the picrate extraction method in liquid-liquid system. Some representatives of these crown ethers showed moderate asymmetric induction as chiral phase transfer catalysts, among them 11 with a benzylidene group proved to be the most efficient one inducing 64% ee in the Michael addition of 2-nitropropane to chalcone and 61% ee in the addition of diethyl acetamidomalonate to trans -�-nitrostyrene. An induction of 65% ee was observed in the epoxidation of a chalcone analogue with tert -butyl hydroperoxide in the presence of catalyst 5a.

New chiral phase-transfer catalysts possessing a 6,6′-bridged ring on the biphenyl unit: application to the synthesis of α,α-dialkyl-α-amino acids

A new chiral phase-transfer catalyst possessing a 6,6′-bridged ring on the biphenyl unit has been developed for the practical synthesis of α,α-dialkyl-α-amino acids. This catalyst shows very high activity for the asymmetric alkylation of an alanine derivative to give α,α-dialkyl-α-amino acid derivatives with high enantioselectivities.

Catalyzing Synthesis of Chiral Nitrendipine

This paper describes the chiral synthesis of R-2,6-dimethyl-4-(3-nitro phenyl)-1,4- dihydro-pyridine-3,5-dicarboxylic acid 3-ethyl ester 5-methyl ester (R-Nitrendipine) using chiral phase transfer catalyst. The structure of the obtained nitrendipine crystals was determined with single crystal X-ray diffraction. The crystal is monoclinic, with the space group of P21/c and unit cell constants of a=8.8577(15), b=15.581(3), c=12.999(2)Å, β=92.458(4)°, V=1792.3(5)Å3, Z=4, Dc =1.335g/cm3, F(000)=760. X-ray analysis reveals that the product is a chiral nitrendipine with R-configuration of the dihydropyridine ring. And measurement of polarimeter reveals that the synthesized nitrendipine is a chiral molecular.

Asymmetric Fluorination of Enamides: Access to α-Fluoroimines Using an Anionic Chiral Phase-Transfer Catalyst

The use of a BINOL-derived phosphate as a chiral anionic phase-transfer catalyst in a nonpolar solvent allows the enantioselective fluorination of enamides using Selectfluor as the fluorinating reagent. We demonstrate that a wide range of stable and synthetically versatile α-(fluoro)benzoylimines can be readily accessed with high enantioselectivity. These compounds have the potential to be readily elaborated into a range of highly stereodefined β-fluoroamines, compounds that constitute highly valuable building blocks of particular importance in the synthesis of pharmaceuticals.

Asymmetric Phase-Transfer-Catalyzed Conjugate Addition of Glycine Imine to Exocyclic α,β-Unsaturated Ketones: Construction of Polycyclic Imines Containing Three Stereocenters

We developed a facile, one-pot, multistep transformation between glycine imine and exocyclic α,β-unsaturated ketones in reactions catalyzed by chiral phase-transfer catalysts (PTC). A series of polycyclic imines containing three adjacent stereocenters were obtained in good to high yields with high diastereo- and enantioselectivities. Further transformation of the imines could afford N-fused polycyclic compounds with four adjacent stereocenters.

Designer chiral phase-transfer catalysts for green sustainable chemistry

A series of chiral quaternary ammonium salts derived from commercially available (R)- or (S)-binaphthol have been designed as new C 2-symmetric chiral phase-transfer catalysts. In order to realize the flexible design of these phase-transfer catalysts, the combinatorial design approach has been developed. Chiral high-performance organocatalysts, thus obtained, have been successfully applied to the highly practical asymmetric synthesis of various amino acid derivatives, including α-alkyl and α,α-dialkyl-α-amino acids in addition to alkaloids. Furthermore, several chiral bifunctional phase-transfer catalysts have been designed and synthesized for effecting base-free phase-transfer reactions under essentially neutral conditions in order to realize green sustainable chemistry.

ChemInform Abstract: Phase‐Transfer‐Catalyzed Asymmetric Synthesis of 1,1‐Disubstituted Tetrahydroisoquinolines.

A highly efficient catalytic asymmetric synthesis of 1,1-disubstituted tetrahydroisoquinolines has been achieved via asymmetric alkylation or Michael addition of 1-cyanotetrahydroisoquinolines using binaphthyl-modified N-spiro-type chiral phase-transfer catalysts.

Design, synthesis, and application of tartaric acid derived N-spiroquaternary ammonium salts as chiral phase-transfer catalysts

A novel class of tartaric acid-derived N-spiro quaternary ammonium salts was synthesised starting from known TADDOLs. These compounds were found to catalyse the asymmetric α-alkylation of glycine Schiff bases with high enantioselectivities and in good yields.

Chiral quaternary phosphonium salts: a new class of organocatalysts

Phase-transfer catalysis has widely been used as a prime synthetic tool for both laboratory and industrial processes. During the last twenty years, asymmetric phase-transfer catalysis using chiral organocatalysts has attracted widespread interest. However, the scope of chiral phase-transfer catalysis has been limited mostly to the quaternary ammonium salts. As an emerging area, the recent developments in the application of quaternary phosphonium salts as chiral phase-transfer catalysts are discussed in this article.