Catalytic asymmetric phase-transfer reactions using tartrate-derived asymmetric two-center organocatalysts

A new highly versatile asymmetric two-center catalyst, tartrate-derived diammonium salt (TaDiAS), was designed and a catalyst library containing more than 70 new two-center catalysts was constructed. A variety of (S,S)- and (R,R)-TaDiAS were easily synthesized from diethyl l- and d-tartrate, respectively, using common and inexpensive reagents under operationally simple reaction conditions. TaDiAS was used in phase-transfer alkylations and Michael additions to afford various optically active α-amino acid equivalents in up to 93% yield. Moreover, dramatic counter anion effects were observed in phase-transfer catalysis (PTC) for the first time, making it possible to further improve reactivity and selectivity. These findings validate the usefulness of three-dimensional fine-tuning of the catalyst (acetal, Ar, and counter anion) for optimization. Recovery and reuse of the catalyst was also possible using simple procedures. The present asymmetric PTC was successfully applied to enantioselective syntheses of serine protease inhibitor aeruginosin 298-A and its analogues.     

An efficient and economical synthesis of 5-substituted 1H-tetrazoles via Pb(II) salt catalyzed [3+2] cycloaddition of nitriles and sodium azide

A simple, mild and efficient method is developed for the synthesis of 5-substituted 1H-tetrazoles. Out of three used Pb(II) catalysts, lead chloride (PbCl₂) has been found to be an efficient catalyst for [3+2] cycloaddition of NaN₃ with aromatic and aliphatic nitriles to afford 5-substituted 1H-tetrazoles. The catalyst is reusable up to four cycles with consistent activity. The cost effectiveness and easy availability of the catalyst, simple methodology, excellent yield and easy work-up are the additional advantages.     

Amino alcohol catalyzed direct asymmetric aldol reactions: enantioselective synthesis of anti-α-fluoro-β-hydroxy ketones

Prolinol but not proline-(a recently established catalyst of simple intermolecular aldol reactions) was found to be an efficient catalyst for fluoroaldol reactions providing anti-α-fluoro-β-hydroxy ketones with good regio-, diasterio-, and enantioselectivities.     

Poly(basic ionic liquid) coated magnetic nanoparticles: High-loaded supported basic ionic liquid catalyst

A novel poly(ionic liquid) (PIL) coated magnetic nanoparticle was synthesized by distillation-precipitation-polymerization of 1-vinyl-3- ethyl imidazolium in the presence of surface modified magnetic nanoparticles. The resulting catalyst was used as magnetic heterogeneous base catalyst for the synthesis of 4H-benzo[b]pyrans in water. The separation of the catalyst from the reaction mixture was readily achieved by simple magnetic decantation and the catalyst could be easily recycled without appreciable loss of catalytic activity. Because of polymer layers coated the surface of the magnetic nanoparticles, the catalyst has a high loading level of ionic liquid.     

Metalloporphyrin Cr(TPP)Cl-catalyzed Claisen rearrangement of simple aliphatic allyl vinyl ethers and its unique stereoselectivity

The catalytic Z-selective Claisen rearrangement of simple aliphatic allyl vinyl ethers can be achieved using a chromium(III) porphyrin complex, Cr(TPP)Cl, as a catalyst: Cr(TPP)Cl significantly enhances reversal of E-Z selectivity in the thermal Claisen rearrangement of allyl vinyl ethers, especially, 4,5- and 4,6-disubstituted derivatives, at low catalyst loading.     

Revisit to the Biginelli reaction: a novel and recyclable bioglycerol-based sulfonic acid functionalized carbon catalyst for one-pot synthesis of substituted 3,4-dihydropyrimidin-2-(1H)-ones

A simple and efficient synthetic protocol has been developed for the synthesis of 3,4-dihydropyrimidin-2-(1H)-ones by using a novel bioglycerol-based sulfonic acid functionalized carbon catalyst, devoid of moisture sensitive metal catalysts and corrosive acidic reagents. The developed method has the advantages of good to excellent yields, short reaction times, operational simplicity, and a recyclable catalyst. The catalyst can be prepared by a simple procedure from inexpensive and readily available glycerol and has been shown to be recoverable and reusable up to four cycles without any loss of activity.     

A reusable polymer supported copper catalyst for the C–N and C–O bond cross-coupling reaction of aryl halides as well as arylboronic acids

A simple and industrially viable protocol for C–N and C–O coupling was reported here. The polymer supported heterogeneous copper catalyst was prepared from chloromethyl polystyrene using a simple procedure. O-Arylation of substituted phenols with various aryl halides was achieved using this copper catalyst in DMSO medium. This heterogeneous copper catalyst, also efficiently works for the N-arylation of N–H heterocycles with aryboronic acids in methanol. This catalyst was also effective in amination reaction of primary amines with aryl halides as well as arylboronic acids in DMSO medium. The effects of solvent, base and temperature for the O-Arylation and amination reactions were reported. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused up to several times without sufficient loss of its catalytic activity.     

Development of a New Production Process for N-Vinyl-2-Pyrrolidone

The New Production Process for N-vinyl-2-pyrrolidone (NVP) consists of two stages: the synthesis of N-(2-hydroxyethyl)-2-pyrrolidone (HEP) from γ-butyrolactone (GBL) and monoethanolamine (MEA), and the vapor-phase dehydration of HEP to NVP. The key features of this technology are the dehydration catalyst and the vapor-phase reaction system. The catalyst is of very simple composition, being alkali (or alkaline earth) metal oxides–SiO₂. Though its acid and base strengths are very weak, its catalytic performance is high. An IR spectroscopic study of the HEP-adsorbed catalyst indicated that the isolated silanol of the catalyst surface plays an important role.     

Chitosan-g-mPEG-supported palladium (0) catalyst for Suzuki cross-coupling reaction in water

A chitosan-g-mTEG (methoxy triethylene glycol)- or mPEG (methoxy polyethylene glycol)-supported palladium (0) catalyst was prepared for the Suzuki cross-coupling reaction in water. The catalyst showed excellent catalytic activity in the Suzuki cross-coupling reaction without additional phase transfer reagents due to the enhanced solubility of the organic substrate by PEG grafting. In addition, the catalyst could be reused up to five times with the catalytic activity being recovered easily after simple manipulations.     

A reusable polymer supported copper catalyst for the C–N and C–O bond cross-coupling reaction of aryl halides as well as arylboronic acids

A simple and industrially viable protocol for C–N and C–O coupling was reported here. The polymer supported heterogeneous copper catalyst was prepared from chloromethyl polystyrene using a simple procedure. O-Arylation of substituted phenols with various aryl halides was achieved using this copper catalyst in DMSO medium. This heterogeneous copper catalyst, also efficiently works for the N-arylation of N–H heterocycles with aryboronic acids in methanol. This catalyst was also effective in amination reaction of primary amines with aryl halides as well as arylboronic acids in DMSO medium. The effects of solvent, base and temperature for the O-Arylation and amination reactions were reported. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused up to several times without sufficient loss of its catalytic activity.     

Distereoselective one-pot synthesis of pyrimidopyrimidines using sulfated tin oxide as a reusable catalyst： An extension of Biginelli-type reaction

The Biginelli-type compounds 4,5,8a-triarylhexahydropyrimido[4,5-d]pyrimidine-2,7（1H,3H）-diones were synthesized by a one-pot three-component reaction using sulfated tin oxide as a reusable catalyst. This method has the advantages of high yields, short reaction time, simple starting materials and reusability of catalyst for several times.     

An efficient synthesis of (E)-nitroalkenes catalyzed by recoverable diamino-functionalized mesostructured polymers

A clean, efficient, and simple method has been developed for synthesis of (E)-nitroalkenes using FDU-ED as an efficient catalyst. The reactions proceeded with moderate to high yields (60-96%) under mild conditions. The catalyst FDU-ED is recyclable and can be reused more than seven times without significant loss of activity and selectivity.     

Polymeric tertiaryphosphine as a green and recyclable organocatalyst for stereoselective isomerization reaction

A green, simple and effective polymeric organocatalytic system, polymer-supported triphenylphosphine (PS-TPP), for the stereoselective isomerization of α,β-ynones to (E,E)-α,β-γ,δ-dienones is reported here. The catalyst, PS-TPP could be recovered by simple filtration and reused several times with high activity.     

Fluoride ion catalyzed multicomponent reactions for efficient synthesis of 4H-chromene and N-arylquinoline derivatives in aqueous media

4H-Chromene and N-arylquinoline derivatives are obtained in good to excellent yields by proceeding through a simple, mild, and efficient procedure utilizing tetrabutylammonium fluoride (TBAF) as catalyst.     

Bis[(L)prolinato-N,O]Zn–water: A green catalytic system for the synthesis of 3,4-dihydropyrimidin-2 (1H)-ones via the Biginelli reaction

A novel, greener approach was adopted for the synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives (4a–i) using bis[(L)prolinato-N,O]Zn as an inexpensive, efficient and mild Lewis acid catalyst in water. The methodology offers several advantages such as short reaction time, high yields, clean process, low loading of catalyst and simple operational procedure. The catalyst was active up to five cycles and was identified by SEM-EDX analysis.     

Poly(vinylpyrrolidonium) perchlorate catalyzed one-pot synthesis of tricyclic dihydropyrimidine derivatives

A simple and efficient procedure for the synthesis of benzo[4,5]imidazo[1,2-α]pyrimidine and 2-amino-4-substituted-1,4-dihydrobenzo[4,5]imidazolo[1,2-α]pyrimidine-3-carbonitrile derivatives using poly(vinylpyrrolidonium) perchlorate {[PVPH]ClO₄} as a newly reported, modified polymeric catalyst is reported. Some of the advantages of this novel synthetic method are: easy preparation of the catalyst, simple and easy work-up procedure, short reaction times, high to excellent yields of the products and reusability of the catalyst.     

Rapid,efficient and solvent-free synthesis of (un)symmetrical xanthenes catalyzed by recyclable sulfated polyborate

The present study describes a rapid, simple and straightforward approach to the synthesis of 1,8-dioxo-octahydroxanthenes, 14-phenyl-14H-dibenzo[a,j]xanthene and tetrahydrobenzoxanthene-11-ones under solvent-free conditions using sulfated polyborate as a highly efficient catalyst. The procedure offers several advantages including cleaner reaction profile, mild reaction condition, economic, recyclable and environmentally benign catalyst, high yields, simple experimental and workup procedures. While non-extractive work up/purification, along with reusability of catalyst make this method economically affordable for large scale.     

Polyvinylpolypyrrolidone-supported triflic acid (PVPP·OTf) as a new,efficient, and recyclable heterogeneous catalyst for the synthesis of bis-indolyl methane derivatives

A simple, inexpensive, environmentally friendly and efficient route for the synthesis of bis-indolyl methane derivatives by the reaction of indole or N-methyl indole with aldehydes using polyvinylpolypyrrolidone-supported triflic acid (PVPP·OTf) as a catalyst is described. PVPP·OTf catalyst is air-stable, heterogeneous, cost-effective, easy to handle, and easily removed from the reaction mixtures.     

Imidazolium-modified poly(l-leucine) catalyst: an efficient and recoverable catalyst for Juliá-Colonna reactions

A novel, easily recyclable imidazolium-modified poly(amino acid) catalyst was prepared. This catalyst exhibits high activity for the asymmetric epoxidation of α,β-unsaturated ketones without any pre-activation. The enantioselectivity was up to 99% ee for epoxidation of p-methoxychalcone. Compared to classical Juliá-Colonna catalysts, this insoluble, powdery catalyst can dramatically reduce the reaction time and can be easily recycled by a simple filtration after the reaction. More importantly, the recycled catalyst has been successfully reused for seven cycles without deterioration in catalytic efficiency.     

Environmentally friendly synthesis of 2-aryl-2,3-dihydroquinazolin-4(1H)-ones by novel Co-CNTs as recoverable catalysts

The objective of this study is to investigate the possibility of using Co-CNTs as a green reaction medium and a catalyst for the cyclo-condensation of o-aminobenzamide with various aldehydes. This inexpensive, non-toxic, and readily available catalyst efficiently catalyzes the above condensation for the synthesis of 2-aryl-2,3-dihydroquinazolin-4(1H)-ones. Compared to the classical reaction, this is a simple, highly yielding, time saving, and environmentally friendly method.