Asymmetric Phase-transfer Mediated Epoxidation of α, β-Enones Using Dendritic Catalysts Derived from Cinchona Alkaloids

Chiral phase-transfer catalysts, derived from cinchona alkaloids and Fréchet dendritic wedges up to generation two, have been synthesized. These chiral dendritic molecules have been used as PTCs in the epoxidation of α, β-enones, showing a moderate level of asymmetric induction.

Progresses and Prospects of Asymmetrically Coordinated Single Atom Catalysts for Lithium-Sulfur Batteries

Lithium-sulfur batteries(LSBs)are widely regarded as promising next-generation batteries due to their high theoretical specific capacity and low material cost.However,the practical applications of LSBs are limited by the shuttle effect of lithium polysulfides(LiPSs),electronic insulation of charge and discharge products,and slow LiPSs conversion reaction kinetics.Accordingly,the introduction of catalysts into LSBs is one of the effective strategy to solve the issues of the sluggished LiPS conversion.Because of their nearly 100%atom utilization and high electrocatalytic activity,single-atom catalysts(SACs)have been widely used as reaction mediators for LSBs’reactions.Excitingly,the SACs with asymmetric coordination structures have exhibited intriguing electronic structures and superior catalytic activities when compared to the traditional M-N_(4)active sites.In this review,we systematically describe the recent advancements in the installation of asymmetrically coordinated single-atom structure as reactions catalysts in LSBs,including asymmetrically nitrogen coordinated SACs,heteroatom coordinated SACs,support effective asymmetrically coordinated SACs,and bimetallic coordinated SACs.Particularly noteworthy is the discussion of the catalytic conversion mechanism of LiPSs spanning asymmetrically coordinated SACs.Finally,a perspective on the future developments of asymmetrically coordinated SACs in LSB applications is provided.

Chalcogen heteroatoms doped nickel-nitrogen-carbon single-atom catalysts with asymmetric coordination for efficient electrochemical CO_(2) reduction

The electronic configuration of central metal atoms in single-atom catalysts(SACs)is pivotal in electrochemical CO_(2) reduction reaction(eCO_(2)RR).Herein,chalcogen heteroatoms(e.g.,S,Se,and Te)were incorporated into the symmetric nickel-nitrogen-carbon(Ni-N_(4)-C)configuration to obtain Ni-X-N_(3)-C(X:S,Se,and Te)SACs with asymmetric coordination presented for central Ni atoms.Among these obtained Ni-X-N_(3)-C(X:S,Se,and Te)SACs,Ni-Se-N_(3)-C exhibited superior eCO_(2)RR activity,with CO selectivity reaching~98% at-0.70 V versus reversible hydrogen electrode(RHE).The Zn-CO_(2) battery integrated with Ni-Se-N_(3)-C as cathode and Zn foil as anode achieved a peak power density of 1.82 mW cm^(-2) and maintained remarkable rechargeable stability over 20 h.In-situ spectral investigations and theoretical calculations demonstrated that the chalcogen heteroatoms doped into the Ni-N_(4)-C configuration would break coordination symmetry and trigger charge redistribution,and then regulate the intermediate behaviors and thermodynamic reaction pathways for eCO_(2)RR.Especially,for Ni-Se-N_(3)-C,the introduced Se atoms could significantly raise the d-band center of central Ni atoms and thus remarkably lower the energy barrier for the rate-determining step of ^(*)COOH formation,contributing to the promising eCO_(2)RR performance for high selectivity CO production by competing with hydrogen evolution reaction.

Nuclephilic ring opening of epoxides promoted by multi-site phase-transfer catalyst:An efficient and eco-friendly route to synthesis of β-hydroxythiocyanate

A highly effective and mild protocol for ring opening of epoxides with NH4SCN in the presence of catalytic amount of a multi- site phase-transfer catalyst, α,α＇,α＂-N-hexakis（triethylammoniummethylene chloride）-melamine, is developed. A variety of ^-hydroxy thiocyanates as important intermediates in agricultural and pharmaceutical chemistry were obtained in high yields with excellent regioselectivity and in short reaction times. 2009 Ali Reza Kiasat. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

A New Reaction-controlled Phase-transfer Catalyst System

A new reaction-controlled phase-transfer catalyst system was designed and synthesized. In this system, heteropolytungstate [C7H7N(CH3)3]9PW9O34 was used for catalytic epoxidation of cyclohexene with H2O2 as the oxidant. The conversion of H2O2 was 100% and the yield of cyclohexene oxide was 87.1% based on cyclohexene. Infrared spectra showed that both fresh catalyst and the recovered catalyst do have completely same absorption peak, indicating the structure of catalyst is very stability and can be recycled.

A Convenient Synthesis of Aromatic Fluoride by Thermal Stable Pyridinium Phase-transfer Catalyst

Using 4-Dialkylaminopyridinium salt as a thermal stable phase-transfer catalyst (PTC), the excellent results were obtained in the halogen-exchange fluorination.

Asymmetric Reduction of Aromatic Ketone withSufonylamide Catalysts

The asymmetric borane reduction of carbonyl compounds using chiral catalysts is one of the most active research. Among them,Oxazaborolidines developed by Corey are most significant- Herein. we report the use of sufonylamides as chiral catalysts to reduce aromatic ketone in high yield and with e.e. of up to 91 %. Scheme:

THE ASYMMETRIC SYNTHESIS OF AMINO ACIDS UNDER POLYMER-SUPPORTED PHASE TRANSFER CATALYTIC CONDITION

The optical alpha-amino acids were synthesized under room temperature by alkylation of N-(diphenyl methylene) glycine t-butyl ester under polymer-supported phase transfer conditions using polymer-supported cinchonine (or quinine) alkaloids as chiral phase transfer catalysts and dichloromethane as solvent, followed by hydrolysis of the above intermediates introduced to the final products-optical alpha-amino acids. This is a new method for the asymmetric synthesis of alpha-amino acids. The influences of catalyst, temperature, substrates, and organic solvents on the chemical yield and optical purities of products were studied.

Design and synthesis of chiral Ti-1,1′-bi-2-naphthol coordination polymers for heterogeneous catalytic asymmetric oxidation of sulfides

Polymer-immobilized catalysis has many advantages such as easy recovery and reuse of catalyst. We prepared three novel chiral 1,1＇-bi-2-naphthol-Ti coordination polymers with properly designed ligands and Ti（O^ipr）4 under mild conditions. The prepared polymers exhibited good activity and excellent enantioselectivity （over 99%ee） in catalyzing the asymmetric oxidation of sulfides. The bridge linker in the polymer and the reaction solvent noticeably affected the enantioseleetivity. The chiral coordination polymer was very stable and easy to separate from catalyzed reaction systems, with no significant loss of activity or enantioselectivity after reuse for at least ten times. These findings suggest a promising type of catalysts for synthesizing the widely used sulfoxides by asymmetrically oxidizing sulfides.

Synthesis of chiral spirocyclo-quaternary ammonium salts from L-proline and their application as phase-transfer catalysts in asymmetric alkylation

A new series of chiral phase-transfer catalysts 7a-7h were designed and synthesized from L-proline with moderate to good yields.＇The catalytic activity of 7a-Th for the asymmetric alkylation of glycine Schiff bases was evaluated, and some interesting relationships between structure and catalytic activity were revealed.

pH敏感型催化剂在不对称Aldol反应中的可控催化研究

以介孔二氧化硅材料为核,聚丙烯酸为壳,手性联吡啶脯氨酸衍生物作为活性物种制备出具有pH智能响应性的催化剂(P-Z@BMMs)。将该催化剂应用于不对称Aldol反应进一步研究其可控催化性能,并采用HPLC分析手段对其催化性能进行表征。催化结果表明:P-Z@BMMs催化剂在不同pH值的复合有机溶剂中表现出良好的“智能开关”作用。

Asymmetric Nucleophilic Additions Promoted by Quaternary Phosphonium Ion-Pair Catalysts

Chiral quaternary phosphonium ion-pair catalysis showcases a distinctive catalytic and stereoinductive mode arising from the synergy between ionic and noncovalent interactions.Over recent decades,this methodology has been widely adopted to facilitate enantioselective nucleophilic addition reactions,including conjugate addition,Henry reaction,Mannich reaction,Strecker reaction,and hydrophosphonylation.This strategy has been successfully applied to the synthesis of numerous structurally diverse and multifunctionalized molecules,featuring challenging stereogenic centers.This minireview specifically highlights the accomplishments in asymmetric nucleophilic addition facilitated by chiral quaternary phosphonium catalysts.Its purpose is to cultivate interest among researchers,encouraging more engagement in this field and establishing quaternary phosphonium ion-pair catalysis as a potent and dependable tool for synthetic and pharmaceutical chemists.

Asymmetric Fluorinative Dearomatization of Tryptophol Derivatives by Chiral Anion Phase-Transfer Catalysis

An asymmetric fluorinative dearomatization reaction of tryptophol derivatives was developed via chiral anion phase-transfer catalysis. Vari- ous fluorinated furoindolines were obtained in moderate to excellent yields and enantioselectivity in the presence of Selectfluor. The preliminary mecha- nistic studies suggested the existence of an in situ formed tryptophol boronic ester plays a critical role in determining the enantioselectivity. This method features the facile introduction of a fluorine atom in a highly enantioselective manner and construction of two contiguous quaternary stereogenic cen- ters.

One-pot synthesis of cyclic aldol tetramer and ?, β-unsaturated aldol from linear aldehydes using quaternary ammonium combined with sodium hydroxide as catalysts

One-pot synthesis of cyclic aldol tetramer and α, β-unsaturated aldol from C3-C8 linear aldehydes using phase-transfer catalyst（PTC）, quaternary ammonium, combined with sodium hydroxide as catalysts was investigated. Butanal was subjected for detail investigations to study the effect of parameters. It was found that the selectivity of cyclic aldol tetramer depends greatly on the operating conditions of the reaction, especially the PTC/butanal molar ratio. The average selectivity of 2-hydroxy-6-propyl-l, 3, 5-triethyl-3-cyclohexene-1-carboxaldehyde（HPTECHCA） was 54.41% using tetrabutylammonium chloride combined with 14%（mass fraction） Na OH as catalysts at 60 ℃for 2 h with a PTC-to-butanal molar ratio of 0.09：1. Pentanal was more likely to generate cyclic aldol tetramer compared with other aldehydes under the optimum experimental conditions. Recovery of the PTC through water washing followed by adding enough sodium hydroxide from the washings was also demonstrated.

Styrene epoxidation catalyzed by polyoxometalate/quaternary ammonium phase transfer catalysts: The effect of cation size and catalyst deactivation mechanism

Catalytic epoxidation of alkenes is an important type of organic reaction in chemical industry,and the deep insight into catalyst deactivation will help to develop new epoxidation process.In this work,series of quaternary ammoniums bearing different cationic sizes,i.e.MTOA+(methyltrioctylammonium,[(C_(8)H_(17))_(3)CH_(3)N]+),HTMA+(hexadecyltrimethylammonium,[(C_(16)H_(33))(CH_(3))_(3)N]+) and DMDOA+(dimethyldioctadecylammonium,[(C_(18)H_(37))_(2)(CH_(3))_(2)N]+) were incorporated with polyoxometalate (POM) anions to prepare phase transfer catalysts (PTCs),which were used in the styrene epoxidations.Among them,(MTOA)_(3)PW_(4)O_(24)exhibits the best catalytic performance judged from the highest styrene conversion rate(52%) and styrene oxide selectivity (93%),during which the styrene epoxidation conditions were optimized.Meanwhile,the deactivation mechanism of this kind of PTCs was proposed firstly,i.e.in the case of low H_(2)O_(2) content,the oxidant can only be used in the styrene epoxidation,in which the catalyst can transform into stable Keggin-type POM.But when the content of H_(2)O_(2) is higher,the excess H_(2)O_(2) can reactivate the Keggin-type POM into active (PW_(4)O_(24))_(3)-anions,which can trigger the ring-opening polymerization of styrene oxide.Consequently,the catalyst is deactivated by adhered poly(styrene oxide)irreversibly,which was determined by NMR spectra.In this situation,the active moiety{PO_(4)[WO(O_(2))_(2)]_(4)}_(3)-in phase-transfer catalytic system can break into some unidentified species with low W/P ratio with the presence of epoxides.This work will be beneficial for the design of new PTCs in alkene epoxidation in fine chemical industry.

A New Quaternary Ammonium Heteropolyoxotungstate Catalyst for Propylene Epoxidation to Propylene Oxide

A new quatemary ammonium heteropolyoxotungstant (cat.C) is prepared andcharacterized. And the cat.C also is an reaction-controlled phase-transfer catalyst The catalyticsystem of O_2/EAHQ (2-ethylanthrahydroquinone)/cat.c is used for the epoxidation of propylene.Under the optimal conditions, the yield of propylene oxide based on EAHQ is 84.1%, theselectivity for propylene oxide based on propylene is 99.8% and the conversion of propylene basedon EAHQ is 84.3%. The cat.c precipitates after the epoxidation reaction for easy separation.The cat C is stable enough to be recycled three times without any loss in selectivity.

人工Cu-TM1459金属酶催化不对称迈克尔加成反应

不对称迈克尔加成反应是合成手性化合物的重要反应,手性的构建一般由传统手性金属络合物催化完成,催化剂结构复杂,制备困难。人工金属酶可以利用生物大分子替代过渡金属手性催化剂,成为研究的热点。使用TM1459蛋白质支架,在原有的金属结合基序上理性引入两个组氨酸和一个羧酸盐面部三联基序,配位Cu2+,制备了人工Cu-TM1459金属酶。将其用于催化不对称迈克尔加成反应研究,Cu-H52A/H58E变体金属酶具有中等反应活性和较高对映选择性(e.e.值达58%)。进一步通过分子对接和催化机理研究对金属结合位点附近关键残基进行定点突变,I108A/C106V/K24E突变体催化该反应,产率99%,e.e.值93%。

Novel Chiral Ferrocenyl Aziridino Alcohol Catalysts Promoting Asymmetric Addition of Diethylzinc to Aldehydes

Optically active aziridino alcohols containing ferrocenyl groups were prepared from commercially available L-threonine in excellent yields and used as catalysts to promote the asymmetric addition of diethylzinc to aryalde-hydes to afford 1-arylpropanol in up to 84% enantiomeric excesses with moderate to good yields.

Lacunary Keggin Polyoxotungstate as Reaction-controlled Phase-transfer Catalyst for Catalytic Epoxidation of Olefins

A new reaction-controlled phase-transfer catalyst system, lacunary Keggin polyoxotungstate [C7H7N(CH3)3]9PW9O34 has been synthesized and used for catalytic epoxidation of olefins with H2O2 as the oxidant. Infrared spectra were used to analyze the behavior of the phase transfer of catalyst. In this system, the catalyst not only can act as homogeneous catalyst but also as heterogeneous catalyst to be easily filtered and reused. The epoxi- dation reaction is clean and exhibits high conversion and selectivity as well as excellent catalyst stability.

2-甲酰基-1,1′-联萘手性醛催化剂的合成

目前报道的手性醛催化剂(3)的合成路线总收率较低,不适用于大量合成。通过对3的合成路线进行改进,以(S)-1,1′-联二萘酚((S)-BINOL)为原料,经磺酰化、插羰反应、偶联反应、硼化、氧化、甲氧基甲基保护、还原、氧化、脱除甲氧基甲基以及溴化10步反应合成了手性醛催化剂(3a~3i),其中大部分化合物的总收率大于20%。该合成路线可放大到10 mmol规模来进行,具有一定的应用前景。