Showing papers on "Methyl vinyl ketone published in 1998"

Measurement of OH radical formation from the reaction of ozone with several biogenic alkenes

Abstract: OH radical formation from the ozone reaction with isoprene, α-pinene, and methyl vinyl ketone were measured using the recently developed small-ratio relative-rate technique. This method uses small amounts of fast-reacting aromatics and aliphatic ethers to trace OH formation. Measured OH yields were 0.25±0.06, 0.70±0.17, and 0.16±0.05 for isoprene, α-pinene, and methyl vinyl ketone, respectively. The levels of biogenic alkenes necessary to contribute a non-negligible fraction of new OH, HO2, and RO2 radicals are briefly discussed.

Ultraviolet absorption spectrum and cross-sections of vinyl (C2H3) radical in the 225–238 nm region

Abstract: The room-temperature gas-phase ultraviolet absorption spectrum and cross-sections of vinyl (C 2 H 3 ) radicals have been determined in the spectral range 225–238 nm, employing cavity ring-down absorption spectroscopy. Vinyl radicals in these experiments were produced from the 193 nm excimer laser photolysis of methyl vinyl ketone (CH 3 COC 2 H 3 ) and vinyl bromide (C 2 H 3 Br). The spectra obtained from the two systems were nearly identical. The observed spectrum exhibits a relatively broad and featureless absorption with a cross-section of 5.3×10 −18 cm 2 molecule −1 at 230 nm. A combined uncertainty of ∼25% for cross-section values has been assessed. The electronic transitions in the vinyl radical have been calculated by ab initio quantum chemical methods at the CIS, EOM-CCSD, CASSCF and CASPT2 levels of theories which assign the new observed band to the highly allowed and `in plane' π * (2a″) ← π(1a″) transition.

Ultraviolet Absorption Spectrum and Cross Sections of Vinyl [C2H3] Radical in the 225-238 nm Region

Abstract: The room-temperature gas-phase ultraviolet absorption spectrum and cross-sections of vinyl (C 2 H 3 ) radicals have been determined in the spectral range 225–238 nm, employing cavity ring-down absorption spectroscopy. Vinyl radicals in these experiments were produced from the 193 nm excimer laser photolysis of methyl vinyl ketone (CH 3 COC 2 H 3 ) and vinyl bromide (C 2 H 3 Br). The spectra obtained from the two systems were nearly identical. The observed spectrum exhibits a relatively broad and featureless absorption with a cross-section of 5.3×10 −18 cm 2 molecule −1 at 230 nm. A combined uncertainty of ∼25% for cross-section values has been assessed. The electronic transitions in the vinyl radical have been calculated by ab initio quantum chemical methods at the CIS, EOM-CCSD, CASSCF and CASPT2 levels of theories which assign the new observed band to the highly allowed and `in plane' π * (2a″) ← π(1a″) transition.

Rhodium(I)-catalysed alkylation of 2-vinylpyridines with alkenes as a result of C–H bond activation

Abstract: 2-Vinylpyridines undergo regioselective β-alkylation with alkenes in the presence of a rhodium(I) complex as a catalyst to give products resulting from an anti-Markownikoff reaction. These results show the feasibility of alkylation of an alkenic position as a result of C–H bond activation. 2-(Prop-1-en-2-yl)pyridine 1 and 1-phenyl-1-(2-pyridyl)ethylene 15 react with linear terminal alkenes to give the corresponding alkylated products in high yields. Cyclic alkenes, allyl alcohol, but-3-en-1-ol and methyl vinyl ketone, however, fail to react with 1. Pent-2-ene gives the linear alkylated product in low yield. 6-Methyl-2-vinylpyridine 24 and 2-vinylpyridine 32 give the alkylated products in low yield together with their dimeric products. The alkenic C–H bond of 2-(cyclohex-1-enyl)pyridine 36 has been regioselectively alkylated. 2-(Cyclohex-1-enyl)pyridine 36 with alkenes in the presence of the RhI catalyst undergoes regiospecific alkylation at the alkenic position.

Activation of Benzylic Carbons in η2-Arene Complexes: A Novel and Efficient Synthesis of Functionalized Decalins

Abstract: 3-Alkylated anisole complexes of pentaammineosmium(II) are treated with methyl vinyl ketone and triflic acid to form 4H-anisolium Michael adducts. These compounds deprotonate regioselectively at the benzylic position adjacent to C3 and then undergo an aldol cyclization with the pendant carbonyl to form the decalin core. Reduction of the dienonium product can be directed in a 1,4 fashion to generate a trans decalin or in a 1,2 fashion to provide a methoxydiene complex that serves as a precursor to other functionalized decalins.

Syntheses and properties of photodegradable polystyrene-containing carbonyl group

Abstract: The copolymerizations of styrene (St) and methyl vinyl ketone (MVK) or phenyl vinyl ketone (PVK) were carried out in benzene by using azobisisobutylonitrile (AIBN). The synthesized copolymers, poly(St-co-MVK) and poly(St-co-PVK), were identified by infrared (IR) spectroscopy. Under the presence of oxygen, the copolymers containing carbonyl group after UV irradiation showed photodegradable properties that caused by Norrish Type II reaction. The new IR characteristic peaks, such as carbonyl and vinyl groups of the photooxidized copolymers, increased by increasing UV irradiation time. In the photodegradation property, the color differences of the synthesized copolymers were higher than those of polystyrene with increasing UV irradiation time, which was caused by the inherent photodegradable property of carbonyl unit in copolymers. The average molecular weights of samples after UV irradiation for 300 h decreased, as compared with polymers before irradiation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1237–1242, 1998

C‐Alkylation of Peptides Containing Aminomalonate and (Amino)(cyano)acetate Residues

Abstract: N-Acetyl-, N-[(tert-butoxy)carbonyl](Boc)-, and N-[(benzyloxy)carbonyl](Z)-protected tri-, penta-, and heptapeptide methyl esters, 1 – 8, with a central aminomalonate (Ama) (allyl, methyl, benzyl, or tert-butyl) or (amino)(cyano)acetate (Aca) residue have been prepared by conventional techniques (Schemes 4 – 6). The new peptides with acidic backbone-bound CH groups can be C-alkylated with primary alkyl, allyl, and benzyl halides, under mildly basic conditions (1 equiv. MeONa or t-BuOK in THF); also, they can be added to Michael acceptors such as acrylates, acrylonitrile, methyl vinyl ketone, or nitrostyrene (catalytic amounts of alkoxide bases in THF) (Schemes 7 – 16). In most cases, the products, 48 – 100, are formed in excellent yields (average of 77%); one of the epimeric products prevails (2 : 1 to > 20 : 1), and the epimers have been separated, isolated in pure form, and fully characterized (without configurational assignments); addition of the co-solvent 3,4,5,6-tetrahydro-1,3-dimethylpyrimidin-2(1H)-one (DMPU) or of LiBr may improve or even reverse the ratio of epimeric products formed; the heptapeptide derivative 8 had to be solubilized for alkylations in THF by the addition of 30 equiv. of LiBr. Cleavage of the Ama groups (benzyl with H2/Pd-C, t-Bu with HCl/Et2O) gave carboxylate derivatives which are actually peptides containing the alkylated aminomalonic acid, the lower homolog of aspartic acid, as residue in the central position. These acids are quite resistant to decarboxylation which had to be achieved by heating at reflux in THF in the presence of 2 equiv. of LiBr and of catalytic amounts of pyridine (Schemes 17 and 18). A one-step removal of the allyl aminomalonate group is possible with Pd/PPh3/formate (Scheme 19). The resulting peptides, 101 – 115, were formed as separable 1 : 1 mixtures of two epimers. The CN group of the alkylated Aca residue can be removed reductively (Na/NH3; Scheme 20). The value of the new method is compared with that of existing methods of peptide-backbone modification.

Nitrogen containing heterocycles from aldoximes; a one-pot route to isoxazolobenzodiazepinones, N-substituted and N-unsubstituted isoxazoloquinolinones

Abstract: The aldoximes 1 in the presence of electron poor olefins react to form either the 5,6,7-tricyclic isoxazolobenzodiazepinone 3 or the 5,6,6-tricyclic isoxazoloquinolinone 5 ring skeleton. In each case the ring system formed depends on the relative electrophilicity of the added and internal olefin. The oximes 1a,b,c react with N-methylmaleimide, methyl acrylate or phenyl vinyl sulfone to afford the corresponding regioisomeric isoxazolobenzodiazepinones by a tandem intramolecular dipole formation–intermolecular cycloaddition sequence. With the more electrophilic olefin, methyl vinyl ketone, intermolecular nitrone generation precedes intramolecular cycloaddition and the isoxazoloquinolinone skeleton results and for each oxime reaction proceeds smoothly in a regio- and stereo-specific manner. Steric control of chemoreactivity is observed with the ring or chain substituted aldoximes 1d,e,f. These oximes react in the presence of phenyl vinyl sulfone to give the isoxazolobenzodiazepines 15 and 16 together with varying quantities of the N-unsubstituted isoxazoloquinolines 14. The latter arise via an oxime–nitrone-cycloaddition sequence, in each case the cycloaddition proceeds in a regio- and stereo-specific manner. The oximes 1d,e,f react with methyl vinyl ketone to give single regio- and stereo-isomers of the N-unsubstituted and -substituted isoxazoloquinolinones 14 and 17. The high degree of chemo-, regio- and stereo-selectivity with which the one-pot reaction of the oximes 1 with electron poor olefins proceeds represents a convenient method for the construction of the title tricyclic molecular frameworks.

Diels–Alder reactions of carbonyl-containing dienophiles catalyzed by tungstophosphoric acid supported on silica gel

Abstract: Tungstophosphoric acid (H3PW12O40) supported on silica gel proved to be an active heterogeneous catalyst for Diels–Alder reactions of enones with various dienes. The Diels–Alder adducts were formed in high regio- and/or stereoselectivity. In some cases the Diels–Alder reactions were accompanied by competing polymerization of the starting compounds. We also found that trifluoromethanesulfonic acid (triflic acid) is an effective homogeneous catalyst for the reaction of unprotected but-3-en-2-one (methyl vinyl ketone) with 1,3-cyclohexadiene, albeit with a lower activity than tungstophosphoric acid.

Reactivity of hexahydrocarbazol-4-ones in Michael reactions: stereocontrolled formation of decahydropyrido[2,3-d]carbazoles

Abstract: The reactivity of hexahydrocarbazolones 3 and 7 in Michael reactions has been studied with several reagents: treatment with acrylonitrile, methyl acrylate and the Mannich base of methyl vinyl ketone leads to 4a-substituted compounds 13–16 in good yields (65–93%), as previously observed with nitroethylene. In contrast, unexpected tetracyclic carbazoles 17 and 18 are obtained with methyl vinyl ketone itself. Reductive cyclisation (H2, PtO2) of 4a-cyanoethylhexahydrocarbazolones 13 and 15 affords decahydropyrido[2,3-d]carbazoles 20 and 21, potential intermediates in the synthesis of E-homo Aspidosperma alkaloids. Compounds 20 and 21 are isolated as single diastereoisomers with a C/E trans ring junction.†

Pressure Effect on Hydrogen Bonding in Aqueous Diels-Alder Reactions

Abstract: The kinetic pressure effect on Diels-Alder reactions involving methyl vinyl ketone and conjugated dienes is investigated in organic and water solution with and without a H-bond generator (paranitrophenol) respectively. Whereas the difference in activation volumes is zero in organic solution, it amounts 3 - 4 cm3. mol-1 in water. Such result points to an increased polarization of the keto group in aqueous solution ascribed to enhanced hydrogen bonding. It is suggested that hydrogen bond effects contributes to the kinetic effect in aqueous Diels-Alder reactions.

Kinetic Analysis of the Gas-Phase Reactions of Methyl Vinyl Ketone with the OH Radical in the Presence of NOx

Abstract: An explicit chemical mechanism for the reaction of methyl vinyl ketone (MVK) with OH radicals in NOx-air systems, was simulated by solving the corresponding ordinary differential equations using Runge-Kutta-4-semi-implicit method. The simulated results are consistent with the published experimental data and the model accounts for all the major pathways by which MVK reacts in NOx-air systems. An eigenvalue-eigenvector analysis is used to extract meaningful kinetic information from linear sensitivity coefficients computed for all species of the chemical mechanism at several time points. This method is used to get an objective condition for constructing a minimal reaction set. Also, a classic method called rate of production analysis (ROPA) was used for the study of the reactions relevance. Using the principal component information as well as the rate of production analysis the main paths of reaction are identified and discussed.

Synthesis and photodegradable properties of methyl vinyl ketone–EPDM–styrene graft terpolymer

Abstract: The graft terpolymerization of methyl vinyl ketone (MVK) and styrene (St) onto ethylene–propylene–diene terpolymer (EPDM) was carried out under various polymerization conditions. The synthesized graft terpolymer, MVK–EPDM–St (MVES), was identified by infrared (IR) spectroscopy. The effects of monomer concentration, mole ratio of MVK to St, reaction time, reaction temperature, and initiator concentration on the graft terpolymerization were examined. Upon UV irradiation in the presence of oxygen, the MVES-containing carbonyl group showed photodegradable properties caused by Norrish type II reaction. The new IR characteristic peaks, such as carbonyl, vinyl, and hydroxy groups of the photodegraded MVES, increased with increasing UV irradiation time. The tensile strength and elongation at break of MVES after UV irradiation were lower than those of before UV irradiation. The color difference of the irradiated MVES was higher than that of EPDM. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1721–1727, 1998

1,1-Dialkyl-2-acyl-3-hydroxypyrazolidinium and 2,2-dialkyl-5-hydroxyisoxazolidinium salts

Abstract: Salts of 1,1-dimethyl-2-acylhydrazines and 1,1-dialkylhydroxylamines add quantitatively to the double bond of oxo compounds with an unsubstituted vinyl substituent. The structure of the products depends on the nature of the substituent at the carbonyl group.1H and13C NMR spectroscopy indicated that acrolein derivatives have the cyclic structure of 1,1-dialkyl-2-acyl-3-hydroxypyrazolidinium and 2,2-dialkyl-5-hydroxyisoxazolidinium salts, while derivatives of phenyl vinyl ketone and hydrazide salts are the corresponding linear, hydrazinium salts. Ring-chain tautomerism was found for several derivatives of methyl vinyl ketone in solution.

Total Synthesis of (.+-.)-Phosphonothrixin

Abstract: Synthesis of the novel natural product Phosphonothrixin has been accomplished in 6 steps and 24% overall yield from the commercially available Baylis-Hillman adduct derived from acetaldehyde and methyl vinyl ketone. The synthesis features use of a trisubstituted olefin as a latent a-hydroxyketone, which formally reverses the oxidation states of the hydroxyl and carbonyl functionalities. This alleviates some of the difficulties encountered in alternative syntheses which proceed through metastable intermediates.

Behavior of acrylamide in the presence of cyclohexanone and methyl ethyl ketone

Abstract: Reactions of acrylamide(AAm)were carried out in the presence of cyclohexanone, methyl ethyl ketone and its derivatives in tetrahydorafuran at various reaction temperatures. Interactions between the carbonyl oxygen of ketones and the amide group were found to enhance the reactivity of AAm. No reactions of AAm occurred in the absence of the ketones under the same condition. Interactions of carbonyl group in the ketone with AAm could be examined directly using the 13 C NMR spectra of a mixture of AAm and t-butyl methyl ketone or poly (methyl vinyl ketone).

Ethyl-(R,S)-5-acetyl-4,5-dihydro-3-isoxazole Acetate

Abstract: The isoxazoline 3 was prepared by the [3+2] cycloaddition of the nitroderivative 1 [1] with methyl vinyl ketone 2 under Mukaiyama conditions [2].[...]

Nitrogen Containing Heterocycles from Aldoximes; a One-Pot Route to Isoxazolobenzodiazepinones, N-Substituted and N-Unsubstituted Isoxazoloquinolinones.

Abstract: The aldoximes 1 in the presence of electron poor olefins react to form either the 5,6,7-tricyclic isoxazolobenzodiazepinone 3 or the 5,6,6-tricyclic isoxazoloquinolinone 5 ring skeleton. In each case the ring system formed depends on the relative electrophilicity of the added and internal olefin. The oximes 1a,b,c react with N-methylmaleimide, methyl acrylate or phenyl vinyl sulfone to afford the corresponding regioisomeric isoxazolobenzodiazepinones by a tandem intramolecular dipole formation–intermolecular cycloaddition sequence. With the more electrophilic olefin, methyl vinyl ketone, intermolecular nitrone generation precedes intramolecular cycloaddition and the isoxazoloquinolinone skeleton results and for each oxime reaction proceeds smoothly in a regio- and stereo-specific manner. Steric control of chemoreactivity is observed with the ring or chain substituted aldoximes 1d,e,f. These oximes react in the presence of phenyl vinyl sulfone to give the isoxazolobenzodiazepines 15 and 16 together with varying quantities of the N-unsubstituted isoxazoloquinolines 14. The latter arise via an oxime–nitrone-cycloaddition sequence, in each case the cycloaddition proceeds in a regio- and stereo-specific manner. The oximes 1d,e,f react with methyl vinyl ketone to give single regio- and stereo-isomers of the N-unsubstituted and -substituted isoxazoloquinolinones 14 and 17. The high degree of chemo-, regio- and stereo-selectivity with which the one-pot reaction of the oximes 1 with electron poor olefins proceeds represents a convenient method for the construction of the title tricyclic molecular frameworks.

C‐Alkylation of Peptides Containing Aminomalonate and (Amino)(cyano)acetate Residues

Abstract: N-Acetyl-, N-[(tert-butoxy)carbonyl](Boc)-, and N-[(benzyloxy)carbonyl](Z)-protected tri-, penta-, and heptapeptide methyl esters, 1 – 8, with a central aminomalonate (Ama) (allyl, methyl, benzyl, or tert-butyl) or (amino)(cyano)acetate (Aca) residue have been prepared by conventional techniques (Schemes 4 – 6). The new peptides with acidic backbone-bound CH groups can be C-alkylated with primary alkyl, allyl, and benzyl halides, under mildly basic conditions (1 equiv. MeONa or t-BuOK in THF); also, they can be added to Michael acceptors such as acrylates, acrylonitrile, methyl vinyl ketone, or nitrostyrene (catalytic amounts of alkoxide bases in THF) (Schemes 7 – 16). In most cases, the products, 48 – 100, are formed in excellent yields (average of 77%); one of the epimeric products prevails (2 : 1 to > 20 : 1), and the epimers have been separated, isolated in pure form, and fully characterized (without configurational assignments); addition of the co-solvent 3,4,5,6-tetrahydro-1,3-dimethylpyrimidin-2(1H)-one (DMPU) or of LiBr may improve or even reverse the ratio of epimeric products formed; the heptapeptide derivative 8 had to be solubilized for alkylations in THF by the addition of 30 equiv. of LiBr. Cleavage of the Ama groups (benzyl with H2/Pd-C, t-Bu with HCl/Et2O) gave carboxylate derivatives which are actually peptides containing the alkylated aminomalonic acid, the lower homolog of aspartic acid, as residue in the central position. These acids are quite resistant to decarboxylation which had to be achieved by heating at reflux in THF in the presence of 2 equiv. of LiBr and of catalytic amounts of pyridine (Schemes 17 and 18). A one-step removal of the allyl aminomalonate group is possible with Pd/PPh3/formate (Scheme 19). The resulting peptides, 101 – 115, were formed as separable 1 : 1 mixtures of two epimers. The CN group of the alkylated Aca residue can be removed reductively (Na/NH3; Scheme 20). The value of the new method is compared with that of existing methods of peptide-backbone modification.

Reactivity of Hexahydrocarbazol-4-ones in Michael Reactions: Stereocontrolled Formation of Decahydropyrido[2,3-d]carbazoles.

Abstract: The reactivity of hexahydrocarbazolones 3 and 7 in Michael reactions has been studied with several reagents: treatment with acrylonitrile, methyl acrylate and the Mannich base of methyl vinyl ketone leads to 4a-substituted compounds 13–16 in good yields (65–93%), as previously observed with nitroethylene. In contrast, unexpected tetracyclic carbazoles 17 and 18 are obtained with methyl vinyl ketone itself. Reductive cyclisation (H2, PtO2) of 4a-cyanoethylhexahydrocarbazolones 13 and 15 affords decahydropyrido[2,3-d]carbazoles 20 and 21, potential intermediates in the synthesis of E-homo Aspidosperma alkaloids. Compounds 20 and 21 are isolated as single diastereoisomers with a C/E trans ring junction.†