Asymmetric cyanosilylation of ketones catalyzed by recyclable polymer-supported copper(II) salen complexes

Various ketones have undergone asymmetric trimethylsilylcyanation at room temperature with (CH₃)₃SiCN (TMSCN) in the presence of a chiral-supported Cu(salen) complex and Ph₃PO as the catalyst. Aromatic, aliphatic, and heterocyclic ketones have been converted into the corresponding cyanohydrin trimethylsilyl ethers in 83?96% yields with 52?84% ee. Several factors concerning the reactivity and enantioselectivity have been discussed. A double activation where Cu(salen) plays the role of Lewis acid and Ph₃PO acts as a Lewis base is reported. Poly(ethylene glycol) monomethyl ether (MeO-PEG) has been used as a soluble support while JandaJel (JJ) and Merrifield (MF) resins served as insoluble supports. Each polymer is linked to the salen catalyst through a glutarate spacer. The soluble catalysts were recovered by precipitation with a suitable solvent while the insoluble catalysts were simply filtered from the reaction mixture. The JandaJel-attached Cu(salen) catalyst could be used for five cycles with the retention of efficiency and the Merrifield-bound Cu(salen) catalyst was found to loose activity with each use.     

Laser fluorescence studies of HF rotational relaxation

Rotation relaxation of HF in HF-Ar mixtures was observed using a laser infrared fluorescence technique. A specific vibrational-rotational state of HF was excited, and the fluorescence from HF was monitored. Total rotational energy-transfer rates, and individual state-to-state transition probabilities were obtained for υ = 1, J = 3 (ΔJ = ± 1, ±2) and υ = 1, J = 5; (ΔJ= ±1, ?2, ?3). The transition probabilities decreased with increasing ΔE_J,J, the energy transferred from R → T (rotation to translation). The data were fitted to a simple exponential model k_JJ, α exp(-ClΔE_J,J'l). C was estimated to be 1.55 ± 0.25 kcal^?1 mole.     

Preparation of two kinds of chloromethylated polystyrene particle using 1,4-bis (chloromethoxy) butane as chloromethylation reagent

By adopting “grafting from” manner, polystyrene was grafted onto the surface of silica gel particles with an average size of 125 μm in a solution polymerization system, and grafted particle PSt/SiO₂ was prepared. Using 1,4-bis (chloromethoxy) butane (BCMB, it is nontoxic.) as chloromethylation reagent, chloromethylation reaction for the grafted particle PSt/SiO₂ was performed in the presence of Lewis acid catalyst SnCl₄. At the same time, cross-linked styrene-divinylbenzene copolymer (CPS) microsphere also was chloromethylated with the same reagent as PSt/SiO₂, so that two kinds of chloromethylated polystyrene particles were obtained, and they are chloromethylated grafted particle (CMPS/SiO₂) and chloromethylated cross-linked polystyrene (CMCPS) microsphere, respectively. The chemical structures and compositions of the two particles were characterized using Fourier transform infrared and Volhard method. The effects of various factors on the chloromethylation reactions were mainly investigated. The experimental results show that the process to prepare the two kinds of chloromethylated polystyrene particles not only has the character of environment friendness and low cost but also is convenient to control via adjusting various reaction conditions. The main reaction conditions affecting the chloromethylation reactions are reaction time, the added amount of BCMB, and the used amount of solvent and catalyst. They influence the reaction in two respects: (1) the chloromethylation degrees of polystyrene are different under different conditions; (2) Friedel–Crafts cross-linking reaction between polystyrene macromolecules is accelerated or inhibited under different conditions (for CPS microsphere, this cross-linking reaction also is called the additional cross-linking). Under suitable conditions, the two kinds of chloromethylated polystyrene particles with a high chlorine content (about 17%, this chlorine content was calculated based on polystyrene weight) can be gained using SnCl₄ as catalyst and CH₂Cl₂ as solvent at room temperature for 10 h and basically without cross-linking or additional cross-linking.     

Development of sequential type iron salt-catalyzed Nazarov/Michael reaction in an ionic liquid solvent system

Sequential type one pot Nazarov/Michael reaction of pyrrole derivatives has been demonstrated using 5 mol% Fe(ClO4)3·Al2O as catalyst in an ionic liquid as solvent. We succeeded in obtaining 4,5-dihydrocyclopenta[b]pyrrol-6(1H)-one derivative in good yield for five repetitions of the reactions without any addition of the catalyst using an ionic liquid, [bmim][NTf2], as solvent system.     

An efficient polymer-supported copper(II) catalyst for the <Emphasis Type="Italic">N</Emphasis>-arylation reaction of N(H)-heterocycles with aryl halides as well as arylboronic acids

Immobilization of copper onto polystyrene provided a polymer-supported copper(II) catalyst, which was effective in cross-coupling reactions between N-containing substrates and arylboronic acids using methanol as a solvent in air under base-free conditions. This catalyst was also effective in N-arylation of imidazole with aryl halides in DMSO using K₂CO₃ as a base under nitrogen atmosphere. The catalyst was characterized by physico-chemical and spectroscopic techniques. The product N-arylimidazoles and N-arylbenzimidazoles were isolated in good to excellent yields. This copper catalyst was air stable and could be recycled with minimal loss of activity.     

A solid-phase iridium-based ortho-exchange catalyst for the one-step labelling of aromatic substrates with deuterium

A wide range of aromatic compounds containing suitable directing groups can be labelled efficiently with deuterium using isotopic exchange catalysed by an easily prepared polystyrene based ortho-exchange catalyst. The labelling reactions can be carried out efficiently at ambient temperature by simple stirring of the substrate and catalyst under a deuterium atmosphere for a few hours. Isolation consists of a simple filtration and evaporation of the solvent. Deuterium is incorporated with ortho-regiospecificity.     

Realizing porphyrin‐functionalization of crosslinked polystyrene microspheres via two special polymer reactions

A novel route to make crosslinked polystyrene (CPS) microspheres to be porphyrin‐functionalized via two special polymer reactions, Kornblum reaction and Adler reaction, was designed and founded. The chloromethyl groups of chloromethylated crosslinked polystyrene (CMCPS) microspheres were first oxidized to aldehyde groups by dimethyl sulfoxide as oxidant via Kornblum oxidation reaction, obtaining aldehyde group‐modified microspheres, ALCPS microspheres, in which, a great quantity of benzaldehyde groups suspend from the main chain, and the effects of the main factors including the reaction temperature, the addition of KI as catalyst and the used amount of NaHCO₃ as acid acceptor on the oxidation reaction were examined. Subsequently, the synchronic synthesizing and immobilizing of porphyrins on CPS microspheres were carried out via the Adler reaction between solid and liquid phases, in which, ALCPS microspheres, pyrrole and benzaldehyde or benzaldehyde analog in a solution were used as co‐reactants, resulting in porphyrin‐functionalized microspheres, and the influence of diverse factors including the acidity of the protonic acid catalyst, the substituent structure of benzaldehyde analog, and the polarity of the solvent as well as the swelling property of the solvent for CPS microspheres on the process of synchronously synthesizing and immobilizing porphyrins on CPS microspheres were investigated in depth. The experimental results indicate that via the designed route, the porphyrin‐functionalization of CPS microspheres can successfully be realized. For the Kornblum oxidation reaction, under the optimal reaction conditions, the conversion of chloromethyl groups can reach 90%. For the Adler reaction between solid and liquid phases, the fitting protonic acid catalyst is lactic acid, appropriate solvent is a mixture of dimethyl sulfoxide and xylene, and using 4‐chlorobenzaldehyde as a benzaldehyde analog reactant in the solution is in favor of the porphyrin‐functionalization of CPS microspheres. Under these specific conditions, the immobilized amount of porphyrin can get up to 23.33 mmol/100 g. Copyright © 2011 John Wiley & Sons, Ltd.     

The rotational spectra of the ground and first excited bending states of deuterium isocyanide,DNC, up to 2 THz

The pure rotational spectrum of deuterium isocyanide (DNC) was recorded in the frequency range from approximately 680 to 1985 GHz. Twenty-one new transitions in the vibrational ground and first excited bending states (01^e,f 0) have been assigned, namely R-branch transitions from J=9←8 to 25←24. In a least squares analysis of these new transition frequencies together with previously reported millimeter-wave data, spectroscopic parameters up to sextic order could be derived with high precision for both states. Furthermore, the ℓ-type doubling constant q and its centrifugal distortion terms q_J and q_JJ were obtained for the first excited bending state.     

Copper-based reverse ATRP process of styrene in mixed solvents

Xylene/N,N-dimethylformamide (DMF) and xylene/ethanol were employed as mixed solvents, respectively, for the reverse atom transfer radical polymerization (R-ATRP) of styrene with the azobisisobutyronitrile (AIBN)/CuBr₂/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) initiating system. With a limited amount of DMF added in, CuBr₂/PMDETA complex could dissolve well in the reaction system, so the control of polymerization was enhanced compared with the one in which simplex xylene was used as solvent. But the polarity of DMF leaded kinetics to deviation from first order. Ethanol could also improve the solubility of catalyst and be scavenged quickly by argon at 110°, therefore the impact of polarity of solvent on kinetics was negligible. Induction periods were not observed here indicating rapidly establishment of equilibrium between Cu(I) and Cu(II). This method that adding a little amount of polar solvent with low boiling point into non-polar solvent gives a new way to solve the problem of poor solubility of the catalyst in R-ATRP.     

Rhodium nanoparticles as catalysts in the hydroformylation of 1-dodecene and their recycling in thermomorphic solvent systems

Rhodium nanoparticles of about 3 nm in size were provided in stabilizing polar solvents. These nanoparticles were used in hydroformylation reactions of higher alkenes; 1-dodecene was used as a model substance. With a metal/substrate ratio of 1:1000, a 97% yield of aldehydes was achieved and an n/iso ratio of 72:28 was obtained. The addition of the ligand biphephos decelerated the reaction, but high n/iso ratios of up to 96:4 were achieved.For the first time, an effective catalyst recycling of these long-term stable nanoparticles in a thermomorphic multicomponent solvent (TMS) system was performed. The catalyst phase was recycled for three runs without any evident loss in activity. TEM images proved that after the recycling runs rhodium nanoparticles were still the active catalyst.     

Catalytic oxidation of primary aromatic amines with sodium periodate catalyzed by Mn(III)salophen complex supported on polystyrene-bound imidazole

The catalytic activity of Mn(III)salophen complex supported on polystyrene-bound imidazole, [Mn(salophen)Cl-PSI], was studied in the oxidation of primary aromatic amines in acetonitrile/water, using sodium periodate as an oxygen source. Amines were oxidized efficiently to their corresponding azo derivatives in the presence of this catalyst. The heterogeneous catalyst showed high stability and reusability in the oxidation reactions and could be reused several times without loss of its activity. The effect of different solvents was studied in the oxidation of p-toluidine and CH₃CN/H₂O was chosen as the solvent.     

Fast dye salts provide fast access to azidoarene synthons in multi-step one-pot tandem click transformations

This study examined whether commercially available diazonium salts could be used as efficient aromatic azide precursors in one-pot multi-step click transformations. Seven different diazonium salts, including Fast Red RC, Fast Blue B, Fast Corinth V and Variamine Blue B were surveyed under aqueous click reaction conditions of CuSO₄/Na ascorbate catalyst with 1:1 t-BuOH/H₂O solvent. Two-step tandem reactions with terminal alkyne and diyne co-reactants led to 1,2,3-triazole products in 66-88% yields, while three-step tandem reactions with trimethylsilyl-protected alkyne and diyne co-reactants led to 1,2,3-triazole products in 61-78% yields.     

Convenient One‐Pot Protocol for an Exclusive Synthesis of 4‐Cyano/ethoxycarbonyl‐2,2‐dimethyl‐2H‐chromene and/or 3‐Cyano/ethoxycarbonyl‐2‐isopropyl‐benzo[b]furan from a Single Oxo‐ylide

[{2‐(Fluoroaryloxy)‐2‐methyl‐propanoyl}‐(cyano/ethoxycarbonyl) methylene]triphenylphosphoranes underwent microwave‐assisted tandem intramolecular Wittig and Claisen rearrangement and internal cyclization reactions to afford fluoro‐substituted 2,2‐dimethyl‐2H‐chromenes and/or 2‐isopropyl‐benzo[b]furans in good yield. Upon controlled microwave irradiation in the presence of Nafion H catalyst in xylene, the oxo‐ylides selectively formed 4‐cyano/ethoxycarbonyl‐2,2‐dimethyl‐2H‐chromenes. Microwave irradiation of the same oxo‐ylide in the presence of K₂CO₃ as catalyst or in a polar solvent–like sulfolane resulted in the exclusive formation of the corresponding fluoro‐substituted 3‐cyano/ethoxycarbonyl‐2‐isopropyl‐benzo[b]furans.     

Microstructure analysis of ethylene/1-hexene co-polymers with embeddedrac-Et[Ind]2ZrCl2 metallocene catalyst

Co-polymerization of ethylene and 1-hexene usingrac-Et[Ind]₂ZrCl₂/MAO catalyst embedded in polystyrene in liquid slurry process was examined. The embedded catalyst was prepared by polymerizing a small amount of styrene. The specific activities and bulk densities of the copolymers produced by the embedded catalyst were higher than those of the homogeneous catalyst. The produced co-polymer with embedded catalyst had more random distribution of 1-hexene at the similar co-monomer content than that with homogeneous catalyst.     

Synthesis and catalytic activity of binuclear Mn(III,III)–BINOL complexes for epoxidation of olefins

The novel binuclear complexes [Mn₂^{(III, III)}(BINOL)₃L₂]2H₂O, where, L = 2, 2′‐bipyridine (Bpy) or 1,10‐phenanthroline (Phen) and BINOL = 1, 1′‐bi‐2‐naphthol were synthesized and characterized by elemental analyses, magnetic susceptibility and various spectral methods. The catalytic activity of these complexes was studied for the epoxidation reaction of unfunctionalized olefins like styrene, 1‐hexene, 1‐octene and 1‐decene. The products thus obtained were analyzed by GC. The epoxidation reactions were carried out, in the presence of catalyst with different oxidants, to study the effect of the nature of the oxidant on the reactions. The different oxidants used were the peroxide oxygen donor (e.g. TBHP and H₂O₂), mono oxygen donor (e.g. PhIO) and dioxygen donor (e.g. molecular O₂). TBHP was found to be the best oxidant for the epoxidation reaction. To study the effect of the solvent on the epoxidation, the reactions were carried out in different media, such as a polar media (e.g. with CH₃OH as solvent), non‐polar media (e.g. with CH₂Cl₂ and C₆H₆ as solvents) and coordinating solvent (e.g. CH₃CN). The maximum epoxide formation was observed in CH₂Cl₂ medium. The epoxidation reactions with optically active BINOL catalysts under optimum established conditions were carried out to examine the enantioselectivity of the catalysts. The complexes were, however, found not to be enantioselective. Copyright © 2006 John Wiley & Sons, Ltd.     

Enantioselective Organocatalyzed Michael Addition of Isobutyraldehyde to Maleimides in Aqueous Media

Thiourea was introduced into (R,R)-1,2-diphenylethylenediamine as an organocatalyst to promote the reaction between isobutyraldehydes and maleimides. Enantioselective Michael addition reaction was carried out as an eco-friendly method using water as the solvent. As a result of the reaction between isobutyraldehyde and maleimide, ≥97% yield and 99% enantioselectivity were obtained at a low catalyst loading of 0.01 mol%. The solvent effect can be explained by theoretical calculations that indicate the participation of a transition state, in which the CF₃ substituent of the catalyst is a hydrogen bond activated by the surrounding water molecules. This discovery enabled the use of low catalyst loading in the organic reactions of chiral substances for pharmaceutical applications. Furthermore, a solvent effect for Michael reaction of the organocatalysts was proposed, and the organic reaction mechanisms were determined through quantum calculations.     

Cyanoesterification of norbornenes catalyzed by palladium: facile synthetic methodology to introduce cyano and ester functionalities via direct carbon-carbon bond cleavage of cyanoformates

Addition of cyanoformates (NC-COOR) to norbornene at 110 °C in the presence of Pd(PPh₃)₄ (10 mol %) as a catalyst affords with high selectivity the corresponding doubly functionalized polar norbornane derivatives bearing both cyano and ester groups. By using benzonorbornadiene and norbornadienes as the substrates, the reaction can be extended to synthesis of various functionalized norbornene derivatives in moderate to excellent yields. In most cases alkyl groups such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, tert-butyl, and benzyl in the ester functionalities are applicable to the reactions. Oxidative addition of cyanoformates to Pd(0), insertion of norbornenes, and reductive elimination of the corresponding adducts constitute the proposed catalysis pathway.     

Homogene katalytische hydrierung mit IrCl(CO)L2 bei mittleren aktivitäten bis 180 und umsatzzahlen bis 150 000

Homogeneous hydrogenation without solvent of unsaturated compounds with IrCl(CO)L₂ as catalyst was examined as a function of ligand L, temperature and mmol catalyst employed. Best results were found with the ligand P(C₆H₁₁)₃ in the temperature range 80 to 120°C and 10 atm H₂ pressure. Mean activities ā up to 180 and turnover numbers UZ up to 150.000 were found.     

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.     

Asymmetric conjugate addition of thioglycolate to a range of chalcones using tetrahydroisoquinoline (TIQ) N,N′-dioxide ligands

A series of novel TIQ based N,N′-oxide ligands were synthesised and screened for their catalytic activity in the enantioselective conjugate addition of thioglycolate to chalcones. Bulky groups on the side chain of the TIQ backbone provided the highest enantioselectivity of up to 88% with 10 mol % catalyst loading. It was also observed that these reactions proceeded optimally in the presence of dichloromethane as a solvent. Screening of various metals emphasized La(OTf)₃ as the ideal pre-catalyst for this particular reaction.