Dendritic Chiral Phosphine Lewis Bases‐Catalyzed Asymmetric Aza‐Morita–Baylis–Hillman Reaction of N‐Sulfonated Imines with Activated Olefins

A series of polyether dendritic chiral phosphine Lewis bases was synthesized, and successfully applied to the asymmetric aza‐Morita–Baylis–Hillman reaction of N‐sulfonated imines (N‐arylmethylidene‐4‐methylbenzenesulfonamides) with methyl vinyl ketone (MVK), ethyl vinyl ketone (EVK), and acrolein to give the adducts in good to excellent yields along with up to 97 % ee, which are more effective than our previously reported original chiral phosphine Lewis bases. In addition, the dendrimer‐supported chiral phosphine Lewis bases can be easily recovered and reused.     

A New Type of Stereoselectivity in Baeyer–Villiger Reactions: Access to E‐ and Z‐Olefins

A new concept for accessing configurationally defined trisubstituted olefins has been developed. Starting from a common ketone precursor of the type 4‐ethylidenecyclohexanone, Baeyer–Villiger monooxygenases are employed as catalysts in diastereoselective Baeyer–Villiger reactions leading to the corresponding E‐ or Z‐configurated lactones. Wild‐type cyclohexanone monooxygenase (CHMO) as catalyst delivers the E‐isomers and a directed evolution mutant the opposite Z‐isomers. Subsequent transition metal‐catalyzed chemical transformations of a key product containing a vinyl bromide moiety provide a variety of different trisubstituted E‐ or Z‐olefins. A model based on QM/MM sheds light on the origin of this unusual type of diastereoselectivity. In contrast to this biocatalytic approach, traditional Baeyer–Villiger reagents such as m‐CPBA fail to show any selectivity, 1:1 mixtures of E‐ and Z‐olefins being formed.     

Efficient Asymmetric Synthesis of 2,6‐Disubstituted 2H‐Dihydropyrans via a Catalytic Hetero‐Diels–Alder/Allylboration Sequence

[4+2] Cycloaddition of (E)‐3‐borylacrolein 1 with ethyl vinyl ether, catalysed by chromium complex (1R,2S) or (1S,2R) 2 , led to the corresponding cycloadducts with high diastereo‐ and enantioselectivities. Further reaction with aldehydes offers an attractive asymmetric route to synthetically useful substituted 3,4‐dihydro‐2H‐pyrans.     

Asymmetric Aza‐Morita–Baylis–Hillman‐Type Reactions: The Highly Enantioselective Reaction between Unmodified α,β‐ Unsaturated Aldehydes and N‐Acylimines by Organo‐co‐catalysis

The highly enantioselective organo‐co‐catalytic aza‐Morita–Baylis–Hillman (MBH)‐type reaction between N‐carbamate‐protected imines and α,β‐unsaturated aldehydes has been developed. The organic co‐catalytic system of proline and 1,4‐diazabicyclo[2.2.2]octane (DABCO) enables the asymmetric synthesis of the corresponding N‐Boc‐ and N‐Cbz‐protected β‐amino‐α‐alkylidene‐aldehydes in good to high yields and up to 99% ee. In the case of aza‐MBH‐type addition of enals to phenylprop‐2‐ene‐1‐imines, the co‐catalytic reaction exhibits excellent 1,2‐selectivity. The organo‐co‐catalytic aza‐MBH‐type reaction can also be performed by the direct highly enantioselective addition of α,β‐unsaturated aldehydes to bench‐stable N‐carbamate‐protected α‐amidosulfones to give the corresponding β‐amino‐α‐alkylidene‐aldehydes with up to 99% ee. The organo‐co‐catalytic aza‐MBH‐type reaction is also an expeditious entry to nearly enantiomerically pure β‐amino‐α‐alkylidene‐amino acids and β‐amino‐α‐alkylidene‐lactams (99% ee). The mechanism and stereochemistry of the chiral amine and DABCO co‐catalyzed aza‐MBH‐type reaction are also discussed.     

Palladium‐Catalyzed Carbonylative Synthesis of 2,3‐Disubstituted Chromones

An unexpected palladium‐catalyzed carbonylative synthesis of 2,3‐disubstituted chromones has been developed. Starting from 2‐bromofluorobenzenes and ketones, the corresponding chromones were produced in good yields. By control experiments, this transformation was found to proceed through a sequential carbonylation/Claisen–Hasse rearrangement/intramolecular nucleophilic aromatic substitution approach (S_NAr). More specifically, the reaction sequence started with a palladium‐catalyzed carbonylation of the ketone with o‐bromofluorobenzene to give the vinyl benzoates, which subsequently transformed into 1,3‐diketones via a Claisen–Hasse rearrangement. The final products were produced after an intramolecular S_NAr reaction of the in situ formed 1,3‐diketone.

     

Synthesis of chitosan‐graft‐poly[2‐cyano‐1‐(pyridin‐3‐yl)allyl acrylate] copolymer from a novel monomer,prepared using a Morita–Baylis–Hillman reaction,and characterization of its antimicrobial activity

A novel method has been developed to modify the natural polymer chitosan. The process utilizes a monomer prepared by employing a Morita–Baylis–Hillman (MBH) reaction. Specifically, the vinyl monomer 2‐[hydroxy(pyridin‐3‐yl)methyl]acrylonitrile (HPA) was synthesized using a high‐yielding MBH reaction of acrylonitrile with pyridine‐3‐carboxaldehyde in the presence of 1,4‐diazabicyclo[2.2.2]octane. Conversion of HPA to 2‐cyano‐1‐(pyridin‐3‐yl)allyl acrylate (CPA) was then carried out by reaction of acryloyl chloride. The highly functionalized monomer CPA was grafted onto chitosan through a reaction in 2% acetic acid containing a persulfate and a sulfite (K₂S₂O₈/Na₂SO₃) as redox promoter. An optimal grafting percentage of 123% is obtained when the grafting process is conducted at 60 °C for 4 h employing a 1:0.5 ratio of K₂S₂O₈ and Na₂SO₃ at a concentration of 2.5 × 10^?3 mol L^?1. Chitosan‐graft‐poly[2‐cyano‐1‐(pyridin‐3‐yl)allyl acrylate] graft copolymers, having various grafting percentages, were characterized using Fourier transform infrared, ¹H NMR and ¹³C NMR spectroscopies, X‐ray diffraction, thermogravimetric analysis and scanning electron microscopy. Finally, the results of studies probing the antimicrobial activities of the polymers against selected microorganisms show that the graft copolymers display higher growth inhibition activities against bacteria and fungi than does chitosan. © 2014 Society of Chemical Industry     

Synthesis of polar vinyl monomer–olefin copolymers by α‐diimine nickel catalyst

Vinyl acetate, methyl methacrylate, acrylonitrile and methyl vinyl ketone were investigated for co‐ and terpolymerization with ethylene and ethylene–propylene. Precursor [bis(N,N ′‐dimesitylimino)acenaphthene]dibromonickel, activated by methylaluminoxane was used as a catalyst system and trialkylaluminium was employed to block the polar groups for these polymerizations. Polymerization activities of the order of magnitude of 10⁶ in the case of vinyl acetate and methyl methacrylate, and 10⁵ in the case of acrylonitrile were achieved. Microanalysis and GPC of acrylonitrile copolymers found about 17 units of acrylonitrile per polymer chain. Copolymers with very different properties from the parent homopolymers were obtained in all cases except that of methyl vinyl ketone. © 2001 Society of Chemical Industry     

Polystyrene nanocomposite materials by in situ polymerization into montmorillonite–vinyl monomer interlayers

A different series of new polystyrene–clay nanocomposites have been prepared by grafting polymerization of styrene with vinyl‐montmorillonite (MMT) clay. The synthesis was achieved through two steps. The first step is the modification of clay with the vinyl monomers, such as N,N‐dimethyl‐n‐octadecyl‐4‐vinylbenzyl‐ammonium chloride, n‐octadecyl‐4‐vinylbenzyl‐ammonium chloride, triphenyl‐4‐vinylbenzyl‐phosphonium chloride, and tri‐n‐butyl‐4‐vinylbenzyl‐phosphonium chloride. The second step is the polymerization of styrene with different ratios of vinyl‐MMT clay. The materials produced were characterized by different physical and chemical methods: (1) IR spectra, confirming the intercalation of the vinyl‐cation within the clay interlayers; (2) thermogravimetric analysis (TGA), showing higher thermal stability for PS–nanocomposites than polystyrene (PS) and higher thermal stability of nanocomposites with of phosphonium moieties than nanocomposites with ammonium moieties; (3) swelling measurements in different organic solvents, showing that the swelling degree in hydrophobic solvents increases as the clay ratio decreases; (4) X‐ray diffraction (XRD), illustrating that the nanocomposites were exfoliated at up to a 25 wt % of organoclay content; and (5) scanning electron microscopy (SEM), showing a complete dispersion of PS into clay galleries. Also, transmission electron microscopy (TEM) showed nanosize spherical particles of ～ 150–400 nm appearing in the images. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3739–3750, 2007     

Kinetics for phenolysis of ethyl 2‐bromoisobutyrate via phase‐transfer catalysis in a solid–liquid system

The kinetics of phase‐transfer catalyzed etherification of sodium phenoxide with ethyl 2‐bromoisobutyrate to produce ethyl 2‐phenoxyisobutyrate in a solid–liquid system has been investigated. Being catalyzed by the quaternary ‘onium salts, the reaction was carried out in a stirred batch reactor to explore the effects of various operating variables. At a temperature of 80 °C and a molar ratio of tetra‐n‐butylammonium bromide to sodium phenoxide equal to 0.372, 94% conversion was obtained after 4 h, and no other side products were observed. A kinetic model of pseudo‐first‐order reaction accompanied by catalyst deactivation was proposed to describe the overall reaction. A deactivation function was employed to evaluate the kinetic parameters. The decay of catalytic activity was mainly caused by the deposition of the salts produced on the surface of solid particles. The results show that the initial reaction rate was not influenced by the agitation rate when exceeding 350 rpm, but the deactivation rate increased with increasing stirring speed and the amount of catalyst used. The intrinsic organic reaction was conducted by the phase‐transfer catalytic intermediate. The order of reactivity for different phase‐transfer catalysts was determined as tetra‐n‐butylphosphonium bromide > tetra‐n‐butylammonium bromide > tetra‐n‐butylammonium iodide ≈ tetra‐n‐butylammonium hydrogen sulfate ≈ Aliquat 336. The apparent activation energy for tetra‐n‐butylammonium bromide was estimated as 51.4 kJ mol⁻¹. This work provides an improved method for synthesizing phenolic substances in solid–liquid phases and preventing unfavorable side reactions. © 2000 Society of Chemical Industry     

Organoselenium‐Catalyzed Baeyer–Villiger Oxidation of α,β‐Unsaturated Ketones by Hydrogen Peroxide to Access Vinyl Esters

By carefully screening the organoselenium pre‐catalysts and optimizing the reaction conditions, simple dibenzyl diselenide was found to be the best pre‐catalyst for Baeyer–Villiger oxidation of (E)‐α,β‐unsaturated ketones with the green oxidant hydrogen peroxide at room temperature. The organoselenium catalyst used in this reaction could be recycled and reused several times. This new method was suitable not only for methyl unsaturated ketones, but also for alkyl and aryl unsaturated ketones. Therefore, it provided a direct, mild, practical, highly functional group‐tolerant process for the chemoselective preparation of the versatile (E)‐vinyl esters from the readily available (E)‐α,β‐unsaturated ketones. A possible mechanism was also proposed to rationalize the activity of the organoselenium catalyst in the presence of hydrogen peroxide in this Baeyer–Villiger oxidation reaction.

     

Tunable Bifunctional Phosphine–Squaramide Promoted Morita–Baylis–Hillman Reaction of N‐Alkyl Isatins with Acrylates

A series of highly tunable bifunctional phosphine‐squaramide H‐bond donor organocatalysts 6 has been synthesized from inexpensive and commercially available β‐amino alcohols in moderate yields. Catalyst 6 f can efficiently promote the asymmetric Morita–Baylis–Hillman (MBH) reaction of N‐alkyl isatins with acrylate esters providing the chiral 3‐substituted 3‐hydroxy‐2‐oxindoles in good yields and enantioselectivities (up to 93 % yield and 95 % ee), in which the challenging substrate tert‐butyl acrylate 9 d , provided the best ee value to date. Moreover, this methodology was applied successfully in the synthesis of chiral cyclic spiropyrrolizidineoxindole and γ‐butyrolactone derivatives without enantioselectivity deterioration. The possible mechanism of this MBH reaction was also investigated by ³¹P NMR, ESI‐MS and KIE studies. The KIE experiments show that the electrophilic addition of N‐methyl isatin to the complex of acrylate ester and phophine‐squaramide is the rate‐determing step of the asymmetric MBH reaction.

     

Interfacially initiated microemulsion copolymerization: One‐stage preparation of poly(n‐butyl methacrylate)–poly(N‐vinyl pyrrolidone) core–shell nanoparticles

Interfacially initiated microemulsion copolymerizations of n‐butyl methacrylate (BMA) and N‐vinyl pyrrolidone (NVP) by the redox initiation couple of benzoyl peroxide and ferrous sulfate were carried out with Tween 80 and n‐butanol as the surfactant and cosurfactant, respectively. Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy were recorded to analyze the chemical composition of the latex particles. Transmission electron microscopy was used to observe the particle morphology and dynamic light scattering to determine the particle size. The results demonstrated that interfacially initiated microemulsion polymerization prompted the copolymerization of the water‐soluble NVP monomer with the oil‐soluble BMA monomer to form core–shell nanoparticles. The influence of the surfactant concentration, BMA amount, and temperature on the particle size and polymerization rate was investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3751–3757, 2006     

Highly active and selective Co‐based Fischer–Tropsch catalysts derived from metal–organic frameworks

The design of supported Co‐based Fischer–Tropsch (F–T) catalysts with suitable reducibility, dispersion, loading, and nanoparticle structure is necessary so that high catalytic activity and selectivity for C₅₊ hydrocarbons can be achieved. Herein, we report that pyrolyzing a Co‐metal–organic framework‐71 precursor can provide porous carbon‐supported Co catalysts with completely reduced, well‐dispersed face‐centered cubic (FCC) Co nanoparticles (～10 nm in average size). The catalysts can be further tailored dimensionally by doping with Si species, and the FCC Co nanoparticles can be partially transformed into hexagonal close‐packed Co via a Co₂C intermediate. All the as‐prepared catalysts had extremely high Co site density (>3.5 × 10^?4 mol/g‐cat.) because they had a high number of Co active sites and low mass. Aside from having high F–T activity and C₅₊ selectivity, with diesel fuels being the main constituents, they showed unprecedentedly high C₅₊ space time yields (up to 1.45 g/(g‐cat. h)) as compared to conventional Co catalysts. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2935–2944, 2017     

Rhodium‐Catalyzed Asymmetric Pauson–Khand Reaction Using Monophosphoramidite Ligand SIPHOS

A novel rhodium‐catalyzed asymmetric intramolecular Pauson–Khand reaction using a chiral monophosphoramidite ligands is described. In this reaction, an in situ generated catalyst from [Rh(CO)₂Cl]₂, the spiro‐monophosphoramidite ligand SIPHOS and AgSbF₆ was found to be effective for a series of 1,6‐enynes, providing the co‐cyclization products in good enantioselectivities (84% ee).     

Preparation of sorbitol from D‐glucose hydrogenation in gas–liquid–solid three‐phase flow airlift loop reactor

A new process for D ‐glucose hydrogenation in 50 wt% aqueous solution, into sorbitol in a 1.5 m³ gas–liquid–solid three‐phase flow airlift loop reactor (ALR) over Raney Nickel catalysts has been developed. Five main factors affecting the reaction time and molar yield to sorbitol, including reaction temperature (T_R), reaction pressure (P_R), pH, hydrogen gas flowrate (Q_g) and content of active hydrogen, were investigated and optimized. The average reaction time and molar yield were 70 min and 98.6% under the optimum operating conditions, respectively. The efficiencies of preparation of sorbitol between the gas–liquid–solid three‐phase flow ALR and stirred tank reactor (STR) under the same operating conditions were compared. Copyright © 2004 Society of Chemical Industry     

Graphite Oxide as an Auto‐Tandem Oxidation–Hydration–Aldol Coupling Catalyst

Graphite oxide (GO) was found to function as an auto‐tandem oxidation–hydration–aldol coupling catalyst for the formation of chalcones in a single reaction vessel. Various alkynes or alcohols were hydrated or oxidized in situ to their corresponding methyl ketones or aldehydes, respectively, which underwent a subsequent Claisen–Schmidt condensation. Each of the aforementioned reactions proceeded in the absence of metals (confirmed by inductively coupled plasma mass spectrometry, ICP‐MS) and afforded a range of chalcone products in good to excellent yields from commercially available starting materials.     

Retro‐Diels–Alder Reactions of Masked Cyclopentadienones Catalyzed by Heterogeneous Brønsted Acids

The zeolite H‐Beta catalyzes the retro‐Diels–Alder reaction of a range of cyclopentadiene cyclo‐adducts at moderate temperatures and ambient pressure, in the presence of an active dienophile. The active catalyst was identified and optimum reaction conditions established after screening a range of zeolites in the retro‐Diels–Alder reaction of the cyclopentadiene adduct of cyclopentenone. Our results suggest that retro‐Diels–Alder reactions of tricyclodecadienones are catalyzed by Brønsted acids and the high catalytic performance of H‐Beta catalysts can be ascribed to the optimal balance between the number of acid sites and their strength as well as to the accessibility of these sites. The methodology was then applied to a series of alkyl derivatives of cyclopentadienylcyclopentenones to provide a viable alternative synthetic route to 4‐alkylcyclopentenones and the versatility of the approach was demonstrated by the successful cycloreversion of N‐cyclohexyl‐2‐azanorborn‐5‐ene.     

Synthesis of an Enantiocomplementary Catalyst of β‐Isocupreidine (β‐ICD) from Quinine

Compound 20 , a pseudoenantiomer of β‐isocupreidine (β‐ICD), was synthesized from quinine employing a Barton reaction of nitrosyl ester 13 and acid‐catalyzed cyclization of carbinol 18 as key steps. The Baylis–Hillman reaction of benzaldehyde, p‐nitrobenzaldehyde, and hydrocinnamaldehyde with 1,1,1,3,3,3‐hexafluoroisopropyl acrylate (HFIPA) using 20 as a chiral amine catalyst was found to give the corresponding S‐enriched adducts in high optical purity (>91% ee) in contrast to the β‐ICD‐catalyzed reaction which affords R‐enriched adducts. This result suggests that compound 20 can serve as an enantiocomplementary catalyst of β‐ICD in the asymmetric Baylis–Hillman reaction of aldehydes with HFIPA.     

Effect of the third acrylated vinyl comonomer on absorption and desorption properties of styrene–divinylbenzene–alkyl acrylate terpolymers,imbibing solvent on a water surface

A series of imbiber terpolymer beads was prepared by radical suspension copolymerization of styrene–divinylbenzene with varied contents of acrylated vinyl monomers, n‐butyl acrylate and 2‐ethyl hexyl acrylate, as the third comonomer. A DVB content of 6 wt % and a mixture of 60/40 wt % toluene/n‐heptane as the diluent were used throughout this study. The influence of acrylated vinyl comonomers on bead properties and swelling properties was investigated. The imbiber beads are capable of absorption and desorption of organic solvents having solubility parameters in the range of 14.9–20.9 (MPa)^1/2. Styrenic imbiber beads were swelled in a toluene/n‐heptane mixture of 50% by volume and the kinetics of absorption was studied. The imbiber beads could absorb the toluene/n‐heptane mixture completely within 20 min and yielded a maximum swelling ratio of 6.8. The diffusion coefficient values of these beads were in the range of 6.40 × 10⁻⁶ to 1.52 × 10⁻⁵ cm² s⁻¹. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 504–516, 2001     

Ethylene‐co‐vinyl acetate copolymer crosslinking through ester–alkoxysilane exchange reaction catalyzed by dibutyltin oxide: mechanistic aspects investigated through model compounds by multinuclear NMR spectroscopy

It was shown that the crosslinking of ethylene‐co‐vinyl acetate (EVA) copolymer by a tetraalkoxysilane in molten state, in the temperature range 100–250 °C, was obtained only in the presence of dibutyltin oxide. At this temperature EVA pendant ester groups readily react with dibutyltin oxide to give a dimeric 1‐alkoxy‐3‐acetoxytetrabutyldistannoxane distributed along the polymer chains. The exact role of this tin compound in the ester–alkoxysilane reaction was elucidated through reactions of the tetraalkoxysilane with parent tin compounds: tributylethoxytin, dimeric diacyloxydistannoxane and finally a dimeric 1‐alkoxy‐3‐acyloxydistannoxane, obtained by reaction of the dibutyltin oxide with a model ester instead of the EVA‐ester pendant group. Ligand exchanges on tin atoms characterized by multinuclear NMR spectroscopy (¹H, ¹³C and ¹¹⁹Sn) showed that substitutions were selective and concern only the exo‐cyclic tin ligand (OR or OCOR′) without alteration of the dimeric distannoxane structure. Furthermore, these ligand exchanges occurred at room temperature. This approach with model compounds gave evidence that the crosslinking occurred via an alkoxy‐Sn/alkoxy‐Si exchange on the exo‐cyclic sites of the distannoxane structure formed in situ. This distannoxane was shown to be an efficient catalyst of this transesterification. The temperature of formation of this catalytic species governed the temperature of the beginning of the crosslinking reaction. Copyright © 2004 Society of Chemical Industry