Modified Hantzsch reaction in the presence of chiral organic catalysts

Modified Hantzsch reaction in three- and four-component system in the presence of new chiral organic catalysts was investigated and the advantages of this reaction in three-component system compared to four-component one were demonstrated, the influence of catalysts on the dynamics and stereochemistry of the reaction was elucidated. The enantiomeric excess of the main reaction product was evaluated with HPLC, its structure was proved by X-ray diffraction analysis.     

Two novel chiral rhodium complexes as catalysts for the enantioselective allylation of arylaldehydes

Two novel chiral rhodium complexes were successfully synthesized from the reaction of a new class of bidentate nitrogen ligands with RhCl₃·3H₂O in ethanol under reflux. The crystal structure of 4a was unambiguously established by X-ray analysis. Their corresponding cationic metal complexes prepared in situ from the reaction of 4a or 4b with AgBF₄ catalyze the enantioselective allylation of arylaldehydes with allylstannane in 5–50% ee.     

Asymmetric Michael reaction promoted by new chiral phase-transfer catalysts

A catalytic asymmetric Michael reaction promoted by new chiral quaternary ammonium salts is described. The products are obtained with moderate ee (up to 75% ee), and the enantioselectivity is strongly dependent on both the substituents on the aromatic rings and the ammonium moiety in the catalysts.     

A novel and efficient chiral palladium-phosphinooxazolidine catalyst for the enantioselective Diels-Alder reaction

An efficient ruthenium-catalyzed transfer dehydrogenation of amines to imines was acheived under mild conditions using 2,6-dimethoxy benzoquinone (2) or cat. 2/MnO2 as oxidant.     

Nmp-based ionic liquids: Recyclable catalysts for both hetero-Michael addition and Knoevenagel condensation in water

A series of novel N-methyl piperidine (Nmp)-based ionic liquids with 1,2-propanediol group are synthesized and used as catalysts for both hetero-Michael addition of α,β-unsaturated amides and Knoevenagel condensation at room temperature in water; and all the examined substrates could be transformed into corresponding products in good to excellent yields. Meanwhile IL-catalyzed hetero-Michael addition of α,β-unsaturated amides in water has not been reported in the previous literatures. Additionally, the catalyst is recyclable for the two reactions. This finding provides a green catalyst for both hetero-Michael addition of α,β-unsaturated amides and Knoevenagel condensation in water.     

Asymmetric Diels-Alder reaction between acrylates and cyclopentadiene in the presence of chiral catalysts

Asymmetric Diels-Alder reaction between cyclopentadiene and alkyl and cycloalkyl acrylates in the presence of new chiral catalysts, BBr₃·MentOEt, AlCl₂OMent, BBr₂OMent, and BBr(OMent)₂, was studied. Optically active bicyclo[2.2.1]hept-2-ene-5-carboxylates were synthesized. The influence of the reaction conditions on the total and optical yields and on the stereoselectivity of the adducts synthesized was examined.     

The ionic liquid ethyltri-n-butylphosphonium tosylate as solvent for the acid-catalysed hetero-Michael reaction

A new and convenient method for the acid-catalysed Michael addition reactions of alcohols, thiols and amines to methyl vinyl ketone has been developed using the ionic liquid ethyltri-n-butylphosphonium tosylate. The reaction conditions are mild and obviate the need for toxic and expensive Lewis acid catalysts, offering advantages over more commonly used systems.     

Asymmetric catalytic aza-Morita-Baylis-Hillman reaction using chiral bifunctional phosphine amides as catalysts

The asymmetric catalytic aza-Morita-Baylis-Hillman reaction of N-sulfonated imines with α,β-unsaturated ketones has been successfully conducted by using chiral bifunctional phosphine amides as catalysts. A series of new chiral bifunctional phosphine amides were designed, synthesized, and systematically studied for this asymmetric reaction. The corresponding aza-MBH adducts were obtained in good yields (75-99%) and up to very good enantiomeric excesses (51-95% ee) under mild conditions.     

Asymmetric Michael reaction using macrocyclic lactose derivatives as chiral catalysts.

Macrocyclic lactose derivatives complexed to potassium bases catalysed the Michael addition of phenyl- and naphthylacetic esters to methyl acrylate to give the corresponding adducts in enantiomeric excess ranging from 20 to 70%.     

Design,synthesis, and application of chiral electron-poor guanidines as hydrogen-bonding catalysts for the Michael reaction

The first chiral electron-poor guanidine organocatalysts were synthesized. The presence of a tunable electron-withdrawing group on the guanidine moiety allows for the modulation of the catalysts’ activity. The application of this new class of organocatalysts to the Michael reaction is demonstrated.     

Development of new methods toward efficient immobilization of chiral catalysts

BINOL moieties are efficiently immobilized onto the surface of a micelle-derived spherical polymer and a monolayer-protected Au cluster (Au-MPC). Ti-BINOLate complexes generated from the BINOL immobilized polymer and Au-MPC are found to promote catalytic asymmetric alkylation of benzaldehyde with Et₂Zn to afford the adduct in up to 84% ee and 86% ee, respectively. Au-MPC-supported multicomponent asymmetric catalyst was prepared and used in the Michael reaction of 2-cyclohexen-1-one with dibenzyl malonate affording the adduct in up to 67% yield and 98% ee.     

Development of chromium-free iron-based catalysts for high-temperature water-gas shift reaction

Chromium-free iron-based catalysts were prepared and studied in regard to their performance in the high-temperature water-gas shift reaction (HTS). The effects of various catalyst preparation variables (i.e., Fe/promoter ratio, pH of precipitation medium, calcination and reduction temperatures) and preparation methods were investigated. Aluminum is a potential chromium replacement in HTS catalysts. Further improvement in WGS activity of Fe–Al catalysts can be achieved by the addition of small amounts of copper or cobalt. Catalysts were characterized using BET surface area measurements, temperature-programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). As a textural promoter, aluminum and chromium prevent the sintering of iron oxides and stabilize magnetite phase by retarding its further reduction to FeO and metallic Fe. The promotional effect of Cu is found to be strongly dependent on the preparation method.     

Universal strategy for the immobilization of chiral dirhodium catalysts

[reaction: see text] Chiral rhodium(II) catalysts used in asymmetric carbenoid chemistry can be efficiently heterogenized using a novel immobilization strategy. The immobilized catalysts display similar reactivity and stereoselectivity to their homogeneous counterparts and can be effectively recycled with limited loss in stereoselectivity.     

Evidence that protons can be the active catalysts in Lewis acid mediated hetero-Michael addition reactions

The mechanism of Lewis acid catalysed hetero‐Michael addition reactions of weakly basic nucleophiles to α,β‐unsaturated ketones was investigated. Protons, rather than metal ions, were identified as the active catalysts. Other mechanisms have been ruled out by analyses of side products and of stoichiometric enone–catalyst mixtures and by the use of radical inhibitors. No evidence for the involvement of π‐olefin–metal complexes or for carbonyl–metal‐ion interactions was obtained. The reactions did not proceed in the presence of the non‐coordinating base 2,6‐di‐tert‐butylpyridine. An excellent correlation of catalytic activities with cation hydrolysis constants was obtained. Different reactivities of mono‐ and dicarbonyl substrates have been rationalised. A ¹H NMR probe for the assessment of proton generation was established and Lewis acids have been classified according to their propensity to hydrolyse in organic solvents. Brønsted acid‐catalysed conjugate addition reactions of nitrogen, oxygen, sulfur and carbon nucleophiles are developed and implications for asymmetric Lewis acid catalysis are discussed.     

Novel polymer-supported chiral catalysts for asymmetric synthesis

Hydroxy amino acid monomers 3, 5 and amino acid monomers 10, 11 were prepared. Suspension polymerization of these chiral monomers with styrene and crosslinking agent afforded insoluble chiral polymers which were used as chiral ligands of the enantioselective Diels-Alder reaction catalysts. A continuous flow system using polymeric catalyst was also successfully achieved in the same reaction.     

Self-supported chiral catalysts for heterogeneous enantioselective reactions

The development of heterogeneous chiral catalysts for enantioselective reactions is highly desirable in order to overcome some drawbacks of homogeneous catalysts. Different from the conventional approaches by using various types of supports or biphasic systems for the recovery and reuse of homogeneous catalysts, a conceptually new strategy for heterogenization of homogeneous chiral catalysts, that is, a "self-supporting" approach, has been developed to use homochiral metal-organic coordination polymers generated by the self-assembly of chiral multitopic ligands with metal ions, and thus obviates the use of any support. In this concept article, the success of this "self-supporting" strategy will be exemplified in heterogeneous catalysis of asymmetric carbonyl-ene, sulfoxidation, epoxidation, and asymmetric hydrogenation reactions.     

喹啉及其衍生物的多相不对称氢转移反应

喹啉及其衍生物的多相不对称氢转移是制备杂环手性化合物的理想策略.多相手性催化体系具有催化剂可循环利用及产物分离提纯容易等优势.然而,喹啉及其衍生物的多相手性高效催化体系鲜有报道.这主要是由于多相手性氢转移为水-油-固三相反应,在反应的过程中,传质问题极大影响固体催化剂的催化性能.因此,发展具有相转移功能的手性催化材料,...     

Enantioselective direct aldol reaction "on water" promoted by chiral organic catalysts

[structure: see text]. 1,1'-Binaphthyl-2,2'-diamine-based (S)-prolinamides in the presence of stearic acid were able to promote the direct aldol condensation of cyclohexanone and other ketones with different aldehydes in the presence of a massive amount of water in very good yields, high diastereoselectivity, and up to 99% ee. The behavior of both C2- and C1-symmetric catalysts in combination with different additives was investigated, and a preliminary experiment of recovering and recycling of the catalytic system was also attempted.