Showing papers on "Methyl vinyl ketone published in 2009"

aza-Baylis−Hillman Reaction

Abstract: 2.3.3. Fluorinated Imines 7 2.3.4. Arylimino Acetates 8 2.3.5. In Situ Generated Iminium Ions 8 2.4. -Substituted Michael Acceptors 8 2.5. Formation of Unexpected Products 10 2.5.1. Reaction with Cyclic Enones 11 2.5.2. Reaction with Vinyl Ketones 11 2.5.3. Reaction with Acrolein 12 2.5.4. Reaction with Activated Allenes and Alkynes 12 2.5.5. Reaction of Salicyl N-Tosylimines 12 3. Stereoselective Synthesis 13 3.1. Use of Chiral Aldehydes 13 3.2. Use of Chiral Bases 13 3.3. Use of Chiral Phosphines 16 3.4. Use of a Chiral Sulfide 18 3.5. Use of an Organocatalyst Derived from BINOL 18 3.6. Use of a Chiral Ligand Derived from Thiourea 18 3.7. Use of Chiral Ionic Liquids 18 4. Alternative Access Pathways to -Aminocarbonyl Compounds 18

Solvent-Promoted and -Controlled Aza-Michael Reaction with Aromatic Amines

Abstract: 1,4-Addition of anilines onto Michael acceptors proceeds easily in specific polar protic solvents, without any promoting agent. According to the solvent and to the electrophile, the selectivity of the reaction can be finely tuned. With methyl acrylate as electrophile, only monoaddition takes place in water, while the diadduct is yielded in hexafluoroisopropyl alcohol (HFIP). The use of methyl vinyl ketone as a partner affords the monoadduct in water, the diadduct in trifluoroethanol (TFE), and the quinoline in HFIP.

The formation of secondary organic aerosol from the isoprene + OH reaction in the absence of NO x

Abstract: . The reaction of isoprene (C5H8) with hydroxyl radicals has been studied in the absence of nitrogen oxides (NOx) to determine physical and chemical characteristics of the secondary organic aerosol formed. Experiments were conducted using a smog chamber operated in a steady-state mode permitting measurements of moderately low aerosol levels. GC-MS analysis was conducted to measure methyl butenediols in the gas phase and polyols in the aerosol phase. Analyses were made to obtain several bulk aerosol parameters from the reaction including values for the organic mass to organic carbon ratio, the effective enthalpy of vaporization (ΔHvapeff), organic peroxide fraction, and the aerosol yield. The gas phase analysis showed the presence of methacrolein, methyl vinyl ketone, and four isomers of the methyl butenediols. These gas-phase compounds may serve as precursors for one or more of several compounds detected in the aerosol phase including 2-methylglyceric acid, three 2-methyl alkenetriols, and two 2-methyl tetrols. In contrast to most previous studies, the 2-methyl tetrols (and the 2-methyl alkenetriols) were found to form in the absence of acidic sulfate aerosol. However, reaction conditions did not favor the production of HO2 radicals, thus allowing RO2+RO2 reactions to proceed more readily than if higher HO2 levels had been generated. SOA/SOC (i.e. OM/OC) was found to average 1.9 in the absence of NOx. The effective enthalpy of vaporization was measured as 38.6 kJ mol−1, consistent with values used previously in modeling studies. The yields in this work (using an independent technique than used previously) are lower than those of Kroll et al. (2006) for similar aerosol masses. SOC yields reported in this work range from 0.5–1.4% for carbon masses between 17 and 49 μgC m−3.

Methyl ethyl ketone combustion over La-transition metal (Cr, Co, Ni, Mn) perovskites

Abstract: A series of LaBO3 (B = Cr, Co, Ni, Mn) and La0.9K0.1MnO3+δ perovskites have been prepared and tested as catalysts in the combustion of methyl ethyl ketone (MEK) at two concentration levels in air. Complete MEK conversion can be achieved for the most concentrated stream (1250 ppmv, WHSV = 425 h−1) at temperatures between 270 °C (manganite) and 345 °C (chromite). Activity is governed by the nature of the cation in position B and related to reducibility, being comparable for manganite activity with that of the much more expensive Pt-supported catalysts. Doping with K of lanthanum manganite produces an increase in surface area, as well as the formation of non-stoichiometric oxygen and a greater proportion of Mn4+ on the surface. All these factors may have a role in increasing its activity for catalytic combustion. Catalytic results suggest a marked influence of MEK concentration on the combustion rate. MEK oxidation to CO2 goes through acetaldehyde as intermediate product; methyl vinyl ketone and diacetyl (2,3-butanedione) were also formed, albeit in very low amounts. Nevertheless, acetaldehyde yield is zero at complete conversion, so the combustion of MEK can be carried out over these perovskite systems with 100% selectivity for CO2.

Enantioselective Trifunctional Organocatalysts for Rate-Enhanced Aza-Morita-Baylis-Hillman Reactions at Room Temperature

Abstract: A Bronsted acid-activated trifunctional organocatalyst, based on the BINAP scaffold, was used for the first time to catalyze aza-Morita-Baylis-Hillman reactions between N-tosylimines and methyl vinyl ketone with fast reaction rates and good enantioselectivity at room temperature. This trifunctional catalyst, containing a Lewis base, a Bronsted base, and a Bronsted acid, required acid activation to confer its enantioselectivity and rate improvement for both electron-rich and electron-deficient imine substrates. The role of the amino Lewis base of la was investigated and found to be the activity switch in response to an acid additive. The counterion of the acid additive was found to influence not only the excess ratio but also the sense of asymmetric induction.

Trifunctional organocatalyst-promoted counterion catalysis for fast and enantioselective aza-Morita–Baylis–Hillman reactions at ambient temperature

Abstract: Fast and enantioselective aza-Morita–Baylis–Hillman reactions between electron-deficient or electron-rich aromatic N-tosyl imines and methyl vinyl ketone were achieved at ambient temperature using asymmetric counterion-directed catalysis promoted by trifunctional organocatalysts with a Bronsted base as the activity switch after protonation with benzoic acid.

Bifunctional heterogeneous catalysis of silica-alumina-supported tertiary amines with controlled acid-base interactions for efficient 1,4-addition reactions.

Abstract: We report the first tunable bifunctional surface of silica-alumina-supported tertiary amines (SA-NEt 2 ) active for catalytic 1,4-addition reactions of nitroalkanes and thiols to electron-deficient alkenes. The 1,4-addition reaction of nitroalkanes to electron-deficient alkenes is one of the most useful carbon-carbon bond-forming reactions and applicable toward a wide range of organic syntheses. The reaction between nitroethane and methyl vinyl ketone scarcely proceeded with either SA or homogeneous amines, and a mixture of SA and amines showed very low catalytic activity. In addition, undesirable side reactions occurred in the case of a strong base like sodium ethoxide employed as a catalytic reagent. Only the present SA-supported amine (SA-NEt 2 ) catalyst enabled selective formation of a double-alkylated product without promotions of side reactions such as an intramolecular cyclization reaction. The heterogeneous SA-NEt 2 catalyst was easily recovered from the reaction mixture by simple filtration and reusable with retention of its catalytic activity and selectivity. Furthermore, the SA-NEt 2 catalyst system was applicable to the addition reaction of other nitroalkanes and thiols to various electron-deficient alkenes. The solid-state magic-angle spinning (MAS) NMR spectroscopic analyses, including variable-contact-time 13 C cross-polarization (CP)/MAS NMR spectroscopy, revealed that acid-base interactions between surface acid sites and immobilized amines can be controlled by pretreatment of SA at different temperatures. The catalytic activities for these addition reactions were strongly affected by the surface acid-base interactions.

Development of DNPH/HPLC method for the measurement of carbonyl compounds in the aqueous phase: applications to laboratory simulation and field measurement

Abstract: Environmental context. Carbonyl compounds, a class of oxygenated organic matter, are crucial participants in atmospheric processes. Recently, studies have shown that the aqueous-phase processes of carbonyls have an important contribution to the formation of secondary organic aerosol (SOA), which is considered to have a significant impact on global climate change and human health. We developed the classical DNPH/HPLC method to characterise the aqueous-phase carbonyls, especially methacrolein, methyl vinyl ketone, glyoxal, and methylglyoxal, which are important precursors of SOA, in order to better understand the pathways of SOA formation in the atmosphere. Abstract. The DNPH/HPLC method for characterising monocarbonyls and dicarbonyls in the aqueous phase has been developed. A series of experiments have been carried out using eight atmospheric ubiquitous carbonyl compounds as model dissolved compounds in both acetonitrile and water solution to obtain the optimal derivatisation and analysis qualifications. Compared with the analysis of carbonyls dissolved in acetonitrile, the influence of acidity on the derivatisation efficiency should be carefully considered in determining carbonyls in water and the optimal acidity is pH 2.0. We find that methyl vinyl ketone (MVK) transforms to crotonaldehyde during the derivatisation reaction. This transformation can be controlled to a minor degree by increasing the mixing ratio of DNPH to MVK up to 100 : 1. This improved method has been satisfactorily applied to laboratory simulations and field measurements for better understanding the carbonyl chemistry in the atmosphere.

Regio- and Stereoselectivity in the Decatungstate Photocatalyzed Alkylation of Alkenes by Alkylcyclohexanes

Abstract: Tetrabutylammonium decatungstate (WO) photocatalyzes radical alkylation reactions starting directly from alkanes. When using tert-butylcyclohexane and methylcyclohexane as the radical precursors, the addition to electrophilic alkenes (beta,beta-dialkylmethylenemalononitriles, acrylonitrile, methyl acrylate, methyl vinyl ketone) is regioselective and exclusively gives 3- and 4-substituted cyclohexyl adducts, with no significant functionalization of the other positions. Furthermore, when a beta,beta-disubstituted alkene is used, the reaction is stereoselective (cis stereochemistry for the 1,3-cyclohexane derivatives and trans for the 1,4 isomers). Some of the reactions have also been carried out by using benzophenone as the photocatalyst, giving the same product distribution. However, the decatungstate anion is a superior catalyst from a preparative point of view, because it is efficient at low concentrations (0.002 m, 2 mol %) and allows for a simple work up. From a mechanistic point of view, the role of both the alkyl radicals and the radical adducts has been assessed by trapping experiments in the presence of suitable additives (alpha-phenyl-N-tert-butylnitrone, PBN, and 2-methyl-2-nitrosopropane, MNP) and by EPR spectroscopic detection of the resulting nitroxides in solution. Furthermore, trapping by the nitroxide TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine N-oxide) gives O-(tert-butylcyclohexyl)hydroxylamines, again as only the 3- and the 4-substituted isomers. We conclude that the observed regioselective activation originates from the initial hydrogen abstraction step (the statistically corrected ratio for positions 3 and 4 ranges from 1.1 to 1.35 for all of the trapping products). The selectivity is mainly due to steric hinderence.

Highly diastereoselective addition of allyltitanocenes to ketones.

Abstract: A route with less congestion: A practical method for the highly diastereoselective preparation of anti tertiary homoallylic alcohols has been developed. The reaction of allyltitanocenes, generated by the reductive titanation of various allylic substrates with a titanocene(II) species, with a variety of ketones produced the anti tertiary homoallylic alcohols in good diastereoselectivity, even when using sterically less congested ketones (see scheme; Cp: cyclopentadienyl; Piv: pivaloyl). The reaction of allyltitanocenes, generated by the reductive titanation of allylic sulfides or allylic alcohol derivatives with a titanocene(II) species, with phenyl and sterically hindered alkyl methyl ketones produced anti tertiary homoallylic alcohols with complete diastereoselectivity. Even when sterically less congested methyl ethyl ketone and methyl vinyl ketone were employed, the anti homoallylic alcohols were obtained with unprecedented high diastereoselectivity. The observed anti selectivity suggests that the reaction proceeds by the addition of primary (E)-σ-allyltitanocenes to ketones through chairlike cyclic transition states.

On the relative preference of enamine/iminium pathways in an organocatalytic Michael addition reaction.

Abstract: The mechanism of the organocatalyzed Michael addition between propanal and methyl vinyl ketone is investigated using the density functional and ab intio methods. Different modes of substrate activation offered by a secondary amine (pyrrolidine) organocatalyst are reported. The electrophilic activation of enone (P-I) through the formation of an iminium ion, and nucleophilic activation of propanal (P-II) in the form of enamine have been examined by identifying the corresponding transition states. The kinetic preference for the formation of key intermediates is established in an effort to identify the competing pathways associated with the title reaction. A comparison of barriers associated with different pathways as well as intermediate formation allows us to provide a suitable mechanistic rationale for Michael addition reactions catalyzed by a secondary amine. The overall barriers for the C-C bond formation pathways involving enol or iminium intermediates are identified as higher than the enamine pathway. Additionally, the generation of iminium is found to be less favored as compared to enamine formation. The effect of co-catalyst/protic solvent on the energetics of the overall reaction is also studied using the cluster continuum approach. Significant reduction in the activation energies for each step of the reaction is predicted for the solvent-assisted models. The co-catalyst assisted addition of propanal-enamine to methyl vinyl ketone is identified as the most preferred pathway (P-IV) for the Michael addition reaction. The results are in concurrence with the available experimental reports on the rate acceleration by the use of a co-catalyst in this reaction.

A catalytic method for the preparation of polysubstituted cyclopentanes: [3+2] cycloaddition of vinylidenecyclopropanes with activated olefins catalyzed by triflic imide.

Abstract: [3+2] Cycloadditions of vinylidenecyclopropanes (VDCPs) with electron-deficient olefins, such as methyl vinyl ketone (MVK) and acrylaldehyde, proceed smoothly in the presence of a catalytic amount of triflic imide (Tf2NH) to give the corresponding functionalized cyclopentanes in good to high yields.

Vibrational modes of the vinyl and deuterated vinyl radicals.

Abstract: Following the initial report of the detection of fundamental transitions of all nine vibrational modes of the vinyl radical [Letendre, L.; Liu, D.-K.; Pibel, C. D.; Halpern, J. B.; Dai, H.-L. J. Chem. Phys. 2000, 112, 9209] by time-resolved IR emission spectroscopy, we have re-examined the assignments of the vibrational modes through isotope substitution. Precursor molecules vinyl chloride-d3, vinyl bromide-d3, and 1,3-butadiene-d6 are used for generating vibrationally excited vinyl-d3 through 193 nm photolysis. The nondeuterated versions of these molecules along with vinyl iodide and methyl vinyl ketone are used as precursors for the production of vinyl-h3. IR emission following the 193 nm photolysis laser pulse is recorded with nanosecond time and ∼8 cm−1 frequency resolution. A room-temperature acetylene gas cell is used as a filter to remove the fundamental transitions of acetylene, a photolysis product, in order to reduce the complexity of the emission spectra. Two-dimensional cross-spectra correlati...

Nitropyrazoles 16. The use of methoxymethyl group as a protecting group for the synthesis of 4-methyl-3-nitro-5-R-pyrazoles

Abstract: 4-Methyl-3,5-dinitropyrazole prepared by nitration of 1,4-dimethylpyrazole readily reacts with methoxymethyl chloride and methyl vinyl ketone in acetonitrile in the presence of a base giving 1-methoxymethyl-4-methyl-3,5-dinitropyrazole and 4-methyl-3,5-dinitro-1-(3-oxobutyl)pyrazole, respectively. The action of the thioglycolanilide anion on 4-methyl-3,5-dinitro-1-(3-oxobutyl)pyrazole results only in the removal of 1-protecting group and the formation of 2-[(3-oxobutyl)thio]acetanilide, while the action of anionic S-nucleophiles on 1-methoxymethyl-4-methyl-3,5-dinitropyrazole leads to the substitution products of the 5-NO2 group in which the methoxymethyl group can be removed by acid hydrolysis.

Kinetics of reactions between arylnitroso oxides and methyl vinyl ketone

Abstract: The kinetics of the reactions of phenylnitroso oxide, (4-methylphenyl)nitroso oxide, (4-methoxyphenyl) nitroso oxide, 4-(N, N -dimethylamino)phenylnitroso oxide, (4-chlorophenyl)nitroso oxide, (4-bromophenyl) nitroso oxide, and (4-nitropenyl)nitroso oxide with methyl vinyl ketone in acetonitrile at 295 K was studied. With the use of 4-CH3O-C6H4-NOO as an example, it was found that only the trans isomers of nitroso oxides entered into the reaction. The rate constants of the reactions of the trans isomers of nitroso oxides with methyl vinyl ketone were measured. A linear correlation between the logarithms of reaction rate constants and the electronic properties of substituents in the aromatic rings of nitroso oxides on the Hammett scale was established: ρ = 1.11 ± 0.08; r = 0.990.

Novel Oxidation of CyclosporinA: Preparation of Cyclosporin Methyl Vinyl Ketone (Cs-MVK)

Abstract: Cyclosporin A (CsA) was converted into cyclosporin methyl vinyl ketone (Cs-MVK) by either a biocatalytic method utilizing 1-hydroxybenzotriazole-mediated laccase oxidation or by a chemical oxidation using t-butyl hydroperoxide and potassium periodate as co-oxidants. Cs-MVK is a novel, versatile synthetic intermediate that can be used for the preparation of many novel cyclosporin analogues possessing therapeutic potential as immunosuppressive agents.

Catalysis of Diels–Alder Reactions in Water and in Hydrogen‐Bonding Environments

Abstract: 1 Introduction 2 Aspects of Catalysis 3 Reactions in Water 4 Conclusions 5 Acknowledgements Keywords: catalysis of Diels–Alder reactions in water; ‘Organic Chemistry in Water’ - active field of research; reactivity and selectivity of Diels–Alder reaction; uncatalysed Diels–Alder reactions; hydrogen bonding; hydrophobicity; reactions in water; minimum energy reaction path (MERP) and Diels–Alder reaction of methyl vinyl ketone

Chromone Studies. Part 17. Tricyclic Scaffolds from Reactions of chromone-3-carbaldehydes and methyl vinyl ketone under Baylis–Hillman conditions:

Abstract: Reaction of a series of chromone-3-carbaldehydes with methyl vinyl ketone under Baylis–Hillman conditions, using 3-hydroxyquinuclidine in chloroform or DABCO in 1-methyl-2-pyrrolidinone, affords un...

Thiazole constrained analogues of the thevinones: synthesis and structure.

Abstract: A simple synthesis of ring-constrained endoethenomorphinans possessing 2′-substituted thiazole ring 4–6 has been achieved by regio- and stereoselective Diels–Alder reaction of thiazolomorphinandienes 1–3 and methyl vinyl ketone in high yield (72, 64 and 87%, respectively) The structure of cycloaddition products was determined by high resolution mass spectrometry (HRMS), IR, 1D and 2D NMR techniques Double-pulsed field gradient spin-echo–nOe and HMBC were found to be particularly powerful and indispensable tools in the exact structural elucidation of the presented new class of spatially constrained thevinones Copyright © 2009 John Wiley & Sons, Ltd

SYNTHESIS OF HETEROCYCLIC COMPOUNDS USING BASIC ZEOLITE Csβ

Abstract: The application of the basic zeolite Csβ as catalyst for the interaction of methyl vinyl ketone (MVK) with 5-methoxybenzimidazole-2-thiol leads to a Michael heteroreaction exclusively at the N-nucleophilic center with the formation of a fairly unusual product of di-addition of MVK to thiol. The reaction of 1,2,4-triazole-3-thiol with MVK in the presence of zeolite Csβ proceeds both at the S- and also at the N-nucleophilic center and leads to the formation of products of mono- and diaddition according to Michael, and also to the product of heterocyclization. On interacting crotonaldehyde with salicylaldehyde in the presence of Csβ 2-methyl-2H-chromene-3-carbaldehyde is formed.

New approaches for synthesis and analysis of adducts to N-terminal valine in hemoglobin from isocyanates, aldehydes, methyl vinyl ketone and diepoxybutane

Abstract: Human exposure to harmful compounds in the environment, from intake via food, occupational exposures or other sources, could have health implications Exposure to reactive compounds/metabolites can

Gold(III) Iminophosphorane Complexes as Catalysts in C—C and C—O Bond Formations.

Abstract: The reaction of K[AuCl4] with AgClO4 and iminophosphorane ligands (N,N-IM) Ph3P NR [R = CH2-2-NC5H4 (1), C(O)-2-NC5H4 (2)] or Ph2PyP NR [Py = -2-NC5H4; R = Ph (3), C(O)Ph (4)] (mol ratio 1:2.2:1) in acetonitrile affords complexes [AuCl2(N,N-IM)]ClO4 (5–8). These compounds are air- and moisture-stable and they have been evaluated in two types of catalytic processes. They have been found to be effective catalysts in the addition of 2-methylfuran or azulene to methyl vinyl ketone, as well as in the synthesis of 2,5-disubstituted oxazoles from N-propargylcarboxamides. The reactions proceed in mild conditions and with similar yields to those described for AuCl3. Using this method, oxazoles bearing a thiophene functional group 2-(2′-thienyl)-5-methylthiazole can be prepared in excellent yields. In all cases the intermediate 5-methylene-4,5-dihydroxazole can be observed by 1H NMR.

The photolysis of methyl vinyl ketone at 308 nm

Abstract: The photolysis of methyl vinyl ketone at small conversions has been studied at 308 nm and at temperatures from approximately 300 K to 475 K as a function of the partial pressures of methyl vinyl ketone, argon and oxygen. The main products of photolysis from 300 K to 435 K are propylene and carbon monoxide together with much smaller yields of methane. The absence of measurable yields of ethane, ethylene and 1,3-butadiene indicates that dissociation of methyl vinyl ketone to free radical products is unimportant under these conditions. At 475 K, small yields of ethane, ethylene and 1,3-butadiene were observed suggesting the increased importance of channels producing CH3 and C2H3 radicals which were not observable at the lower temperatures. The formation of propylene is quenched by methyl vinyl ketone, argon and oxygen. However, the yield of methane is increased by the addition of argon and oxygen but is reduced by increasing the pressure of methyl vinyl ketone. The maximum partial pressures of argon and oxygen used in these experiments were approximately 450 Torr. The maximum pressure of methyl vinyl ketone was limited by its vapour pressure to approximately 45 Torr. The markedly different variation in the yields of propylene and methane with changing pressure and with the addition of argon and oxygen suggests that propylene and methane are formed from different excited states of methyl vinyl ketone. These results are discussed within the context of the energetically accessible states of methyl vinyl ketone.