Showing papers on "Methyl vinyl ketone published in 1994"

Enhanced Hydrogen Bonding of Water to Diels-Alder Transition States. Ab Initio Evidence

Abstract: Ab initio molecular orbital calculations reveal enhanced hydrogen bonding of a water molecule to the transition states for the Diels-Alder reactions of cyclopentadiene with methyl vinyl ketone (MVK) and acrylonitrile. The optimal interaction energies are found to be 1.5-2.0 kcal/mol more favorable for hydrogen bonding to the oxygen or nitrogen in the transition states than for the dienophiles. This support the assertion from a prior simulation study that the observed rate accelerations for Diels-Alder reactions in aqueous solution arise from this hydrogen-bonding effect in addition to a relatively constant hydrophobic term

Diels-Alder Reactions in Water. Effects of Hydrophobicity and Hydrogen Bonding

Abstract: In order to check whether the activated complex for the Diels-Alder reactions of 5-substituted 1,4-naphthoquinones with cyclopentadiene is more polar in water than in other solvents, we have determined the substituent effects in seven different solvents. The substituent effects gradually decrease with increasing rate of the reaction in a specific solvent, indicating that the charge separation in the activated complex in water is not much different from that in the other solvents. We also compared solvent effects on the Diels-Alder reaction of methyl vinyl ketone with cyclopentadiene with effects on the corresponding reaction of methyl vinyl sulfone. The medium effects were separated into effects on initial state and activated complex. The destabilization of the initial state by water and the stabilization of the activated complex by 2,2,2-trifluoroethanol were less pronounced for the sulfone than for the ketone. These results further underline the importance of enforced hydrophobic interactions and changes in hydrogen bonding during the activation process in explaining the acceleration of Diels-Alder reactions in water.

Formation yields of methyl vinyl ketone and methacrolein from the gas-phase reaction of o3 with isoprene.

Abstract: The formation yields of methyl vinyl ketone and methacrolein from the gas-phase reaction of O 3 with isoprene were determined at 296±2 K and 740 Torr total pressure of air. Sufficient cycloherane was added to the reactant mixture to scavenge >97% of the OH radicals formed in the O 3 -isoprene reaction, and secondary reactions of O 3 with methyl vinyl ketone and methacrolein were taken into account. The formation yields obtained were 0.159±0.013 for methyl vinyl ketone and 0.387±0.030 for methacrolein. Experiments were also carried out in the absence of added cycloherane, and the methyl vinyl ketone and methacrolein data were consistent with formation from both the OH radical and O 3 reactions with isoprene

Investigation of solvent effects on pericyclic reactions by computer simulations

Abstract: A combination of quantum and statistical mechanics is being used to probe the origins of solvent effects on the kinetics of organic reactions. Ab initio molecular orbital calculations provide gas-phase reaction paths and partial charges for the reacting systems. The reaction paths are then followed by Monte Carlo simulations in periodic cells containing hundreds of solvent molecules, and the changes in Gibbs free energies of solvation are obtained. Results are provided for several prototypical pericyclic reactions : Diels–Alder cycloadditions for methyl vinyl ketone with cyclopentadiene and the dimerization of cyclopentadiene, the Claisen rearrangement of allyl vinyl ether, and the electrocyclic ring opening of cyclopropanones to oxyallyls. Detailed insights are obtained on issues such as the acceleration of the Diels–Alder reactions and Claisen rearrangement in water, and the electronic nature of oxyallyls.

Solvent effects on endo/exo- and regio-selectivities of Diels–Alder reactions of carbonyl-containing dienophiles

Abstract: The selectivity of Diels–Alder reactions of methyl vinyl ketone and methyl acrylate, with cyclopentadiene and isoprene, have been studied in 18 pure solvents and aqueous mixtures. The results obtained have been analysed by means of regression models, using empirical solvent parameters. The endo/exo selectivity mainly depends on the solvophobic (Sp) and hydrogen bond donor (α) properties of the solvent. The influence of the dipolarity (π*) is only observed in the reactions with methyl acrylate. Regioselectivity almost exclusively depends on the hydrogen bond donor ability of the solvent. The double coordination observed with highly hydrogen bond donating solvents in the case of methyl vinyl ketone greatly increases the para/meta isomer ratio.

Diels–Alder reactions catalysed by cation-exchanged clay minerals

Abstract: Catalysis of Diels–Alder reactions by various clay minerals exchanged with a variety of transition metal cations was shown to occur readily at ambient temperatures in a variety of solvents. Nontransition and lanthanide cation-exchanged clays were found to be ineffective. α,β-Unsaturated carbonyl compounds (such as methyl vinyl ketone, methyl acrylate and methyl methacrylate) were used as dienophile. Cyclopentadiene, furan, pyrrole, isoprene and cyclohexa-1,3-diene were successfully employed as the diene, whilst thiophene was unreactive. Such reactions (except that with isoprene which produces a mixture of 1,3- and 1,4-isomers) produced a mixture of endo- and exo-isomers, the ratios of which could be altered by manipulation of the inter-layer reaction space of the clay catalyst. Choosing a clay with a higher layer charge, and hence lower basal spacing, Δd, gave increased selection for the kinetically less favoured, but less bulky isomer.

Vapour-phase reaction of methanol with acetone over alkali containing zeolites

Abstract: Three types of reactions were observed on alkali exchanged A, X and Y zeolites during the vapour phase reaction of methanoi with acetone: the methylation of acetone followed by dehydrogenation to form methyl vinyl ketone ( MVK) ; the Meerwein-Ponndorf-Verley ( MPV ) reaction between acetone and methanol, coupled with the further dehydration to form propene and formaldehyde; and the condensation of acetone followed by further decomposition to form isobutene. The last two kinds of reactions are the main reactions on LiX and NaX, which possess a relatively strong Lewis acidity. When Lewis basicity increases and Lewis acidity decreases, these two reactions are dramatically depressed, which results in an increase in selectivity to MVK. After high energy milling the zeolite becomes amorphous with no change in chemical composition. The catalytic results over these materials also revealed an increase in the production of MVK and the depressing of the other two reactions. This change is attributed to the crush of the zeolite pore structure, which is another factor affecting the product distribution.

Stereoselectivity in the homo-Diels–Alder reaction: effect of a remote 7-substituent on nickel-catalysed cycloadditions

Abstract: 7-Substituted norbornadienes have been shown to undergo highly stereoselective homo-Diels–Alder reactions with a variety of dienophiles. Excellent exo/endo selectivity (always > 97:3) was observed when methyl vinyl ketone was used as dienophile. Increasing anti/syn selectivity (up to 95:5 when Y = OBut) was observed as the electronegativity of the 7-substituent increased.

Syntheses of 1,2-Thiaphospholes and Their Thermal and Lewis Acid-Promoted Addition Reactions

Abstract: 3,5-Di-substituted 1,2-thiaphospholes were efficiently prepared by treating 2,9-dithia-1-phosphabicyclo[4.3.0]nona-3,7-diene 1-sulfides with n-Bu3P. The thiaphospholes reacted thermally with norbornadiene, norbornene or diethyl azodicarboxylate to produce the 1 : 2 double Diels–Alder cycloadducts. With a mixture of norbornadiene and methyl acrylate or acrylonitrile, the crossed double Diels–Alder cycloadducts were obtained. In the presence of a Lewis acid, the thiaphospholes underwent, at the initial step, the Diels–Alder reaction with acrylic esters, methyl vinyl ketone or acrylonitrile, followed in tandem by the Michael addition of the 1 : 1 cycloadducts to another molecule of the reactant.

Multifunktionellebis-(trifluormethyl)-substituierte Synthesezwischenstufen aus 4,4-Bis-(trifluormethyl)-1-oxa-3-azabuta-1,3-dienen viaBaylis-Hillman Reaktion

Abstract: TheBaylis-Hillman reaction of 4,4-bis-(trifluoromethyl)-1-oxa-3-azabuta-1,3-dienes with acrolein, methyl vinyl ketone, ethyl vinyl ketone, acrylonitrile, ethyl acrylate, andn-butyl acrylate provides useful multifunctional partial fluorinated building blocks in one step.

Lewis acid catalyzed Diels–Alder reactions of two useful dienyl phosphate esters

Abstract: The Lewis acid catalyzed Diels–Alder reactions of dienyl phosphate esters 1 and 2 were examined. 2-Diethylphosphoryloxy-1,3-butadiene (1) was found to react with a variety of α,β-unsaturated carbonyl compounds under Lewis acid catalysis with excellent regioselectivity to give synthetically useful cyclohexene derivatives. The adducts were produced in accordance with the normal rules governing the Diels–Alder addition. In the presence of stannic chloride acyclic α,β-unsaturated ketones such as ethyl vinyl ketone and methyl vinyl ketone reacted rapidly with diene phosphate 1 to give exclusively the para-addition products 8 and 9 in excellent yields. When diene 1 was treated with the complex cyclic enone ester 14 in the presence of ferric chloride the single para-rule adduct 15 was obtained in good yield. The stannic chloride catalyzed Diels–Alder reactions of trans-2-diethylphosphoryloxy-1,3-pentadiene (2) were also studied. Diene phosphate 2 reacted efficiently with a number of acyclic α,β-unsaturated keton...

Intramolecular competitive addition of vinyl radicals to keto and alkenyl groups in Wieland–Miescher ketones—synthesis of carbocycles and propellanes

Abstract: Wieland–Miescher ketone analogues are prepared by monoalkylation of cyclohexane-1,3-dione with bromomethylcycloalkenyl bromides followed by annulation with methyl vinyl ketone; they undergo 5-exo-trig competitive intramolecular radical addition to the keto and enone olefins to give angularly rused carbocycles and propellanes, respectively.

Thermal Rearrangements, XXII. The Propargyl-Cope Rearrangement of meso- and d,l-3,4-Dimethyl-1,5-hexadiyne-3,4-diol

Abstract: The thermal behavior of meso- and d,l-3,4-dimethyl-1,5-hexadiyne-3,4-diol (meso- and d,l-4) has been studied at 400 o C in the gas phase. In a tandem reaction the diols isomerize via the bisallenes 5 first to cis- and trans-3,4-diacetylcyclobutene (cis- and trans-8) which have been detected as intermediates by 13 C-NMR spectroscopy as well as catalytic hydrogenation to 1,2-diacetylcyclobutane (9). Subsequently, 8 stabilizes itself by ring opening to (E,Z)- and (E,E)-3,5-octadien-2,7-dione [(E,Z)- and (E,E)-6]. As a side reaction retroene cleavage of 4 to 2-butynone (10) and methyl vinyl ketone (12) is observed. By pyrolysis of the pure diastereomers 4 it is shown that the retro-ene process is more pronounced in the d,l than in the meso series

Utilization of selenium-directed [2 + 2] cycloadditions: concise synthesis of (±)-fragranol

Abstract: The reaction of 2-(phenylseleno)prop-1ene 1 and methyl vinyl ketone 2 in the presence of EtAlCl2 gave the [2 + 2] cycloadducts 3a and 3b. A radical substitution of the adducts 3a and 3b with allytributyltin gave the allylated cyclobutane product, which was transformed into the cyclobutane natural product, (±)-fragranol. Stereoselective radical substitution using the ethylene glycol ketals of compounds 3a and 3b was also achieved.

Diacetyl synthesis by the direct partial oxidation of methyl ethyl ketone over vanadium oxide catalysts

Abstract: The selective oxidation of butan-2-one to diacetyl has been studied in the temperature range 200-380°C over vanadium oxide and vanadium-phosphorus oxide catalysts. In addition to diacetyl, the principal reaction products detected were acetic acid, acetaldehyde, methyl vinyl ketone, propionaldehyde and carbon dioxide. Detailed steady state and transient kinetic analysis indicate that there are three distinct reaction pathways which lead to the observed product distribution. In the first of these diacetyl and methyl vinyl ketone are formed via a common intermediate, namely acetoin: Evidence for this reaction route include the fact that acetoin was detected as a reaction intermediate in Temporal Analysis of Products (TAP) and when acetoin was fed to the reactor it was converted into diacetyl and methyl vinyl ketone. The second reaction pathway observed involved the oxidation of the enol form of methyl ethyl ketone with the formation of acetic acid and acetaldehyde This reaction predominated at high oxygenpartial pressures and represented a significant route away from diacetyl formation in these conditions. The third reaction pathway observed was the decomposition of methyl ethyl ketone to two molecules of acetaldehyde via a diol intermediate: Evidence that a second pathway was involved in the formation of acetaldehyde emerged from the fact that the molar ratio of acetaldehyde to acetic acid was always greater than unity in spite ofthe fact that acetic acid was more stable than acetaldehyde in our reaction conditions. The second pathway was confirmed when propiophenone was fed to the reactor. Cleavage of the enol form of propiophenone should lead only to the formation of benzoic acid and never benzaldehyde. In our reaction conditions benzaldehyde was in fact observed in the reaction products, confirming that a molecule bearing the aldehyde functional group could form on the carbonyl side of the substrate.

S-(+)-carvone as starting material in the enantioselective synthesis of natural products.

Abstract: In this thesis the applicability of S-(+)-carvone as chiral starting material in the synthesis of biologically active compounds is examined. S-(+)-carvone is the major compound of caraway essential oil. The essential oil content of caraway seed may vary from 2-7% and it contains about 50-60% of S-(+)-carvoneS-(+)-carvone exhibits a number of interesting biological activities, eg., antifungal, insecticidal and plant growth regulatory activities. Especially the inhibiting effect of S-(+)-carvone on the sprouting of potatoes attracted a lot of attention, and this was important for the start of a national caraway research program in the Netherlands. Within the framework of this "National Caraway Research Program" the potential of caraway for the production of non-food products was investigated. The outlines of this research are sketched in chapter 1. An overview of the application of S-(+)-carvone and R-(-)-carvone as chiral starting material in the synthesis of natural products is also given in chapter 1.The Lewis acid catalyzed Diels-Alder reaction of S-(+)-carvone with some silyloxy dienes is described in chapter 2. The anti -addition products 94 , with the angular methyl group and the isopropenyl group in a cis -position, are formed in high yields. The synthetic utility of these Diels-Alder adducts was demonstrated by the total synthesis of (+)-α-cyperone (95) from diketone 94b . (+)-α-Cyperone ( 95 ), that can be isolated from the tubers of Cuperus rotundus L., exhibits an interesting in vitro activity against Plasmodium flaciparum K1, a multidrug resistant malaria parasite (scheme 8.1). In chapter 3, the Robinson annulation products 33 and 96 were transformed into interesting chiral intermediates for organic synthesis and also into some biologically active compounds. The decalones 111 and 112 , were formed from 33 . Decalone 111 is a famous molecule in perfumery and 112 is an important intermediate in the synthesis of several drimanes and drimane-related natural products. Compound 33 was also converted into decalol 113 , a potent inhibitor of the cholesterol biosynthesis.(+)-Geosmin ( 97 ), an interesting olfactive compound was synthesized from decalone 96 (scheme 8.2). In chapter 4, the syntheses of the more functionalized decalones 98 , 99 , 131 and 132 from S-(+)-carvone via two different conjugate addition annulation methodologies are presented (scheme 8.3). The conjugate addition of potassium cyanide to S-(+)-carvone gave cyano ketone 135 in high yield. The base catalyzed Robinson annulation of 135 with methyl vinyl ketone followed by dehydration gave decalone 98 stereoselectively and also in high yield. The copper catalyzed conjugate addition of Grignard reagents gave alkyl substituted dihydrocarvones, which were annulated via their silyl enol ethers 127 . A Lewis acid catalyzed Michael addition of the silyl enol ether 129 to methyl vinyl ketone gave the intermediate diketones 130 in good yield. The diketones were cyclized to the substituted decalones 99 , 131 and 132 under basic conditions.Decalone 98 was used for a new chiral approach to 3-oxygenated drimanes as is described in chapter 5. Hydroxyketone 153 was formed via an ozonolysis/Criegee rearrangement procedure of the isopropenyl substituent (scheme 8.4). Hydroxyketone 153 was by total synthesis further transformed into (-)-3-β-acetoxydrimenin ( 100 ), that can be isolated from the leaves of Drimys winteri,. In chapter 6 the total synthesis of (-)-Ambrox ® ( 101 ), a commercially interesting olfactive compound, from both the allyl substituted decalone 99 and the nitrile substituted decalone 98 is presented (scheme 8.5). In both synthetic sequences, alcohol 159 was formed as the key intermediate. (-)-Ambrox ® ( 101 ), was synthesized by simple cyclization of alcohol 159 at room temperature under acidic conditions.

1.4 Methanol-Based Synthetic Reactions over Solid-Base Catalysts

Abstract: Novel methods for catalytically synthesizing α,β-unsaturated compounds and higher alcohols were developed, where methanol was used as a key reagent for C-C bond formation. Reactants were saturated ketones, esters, nitriles, or alcohols besides methanol, and CH2= or CH3- group is introduced into their methyl or methylene carbons by the addition of methanol. For the catalytic synthesis of α,β-unsaturated compounds, magnesium oxide activated by manganese ion or chromium ion has been found to give the most effective catalytic performance. The most promising application of this synthetic method is demonstrated by the selective synthesis of acrylonitrile from acetonitrile and methanol over Mn-MgO catalyst. The selectivity to acrylonitrile was more than 95% and no deactivation of the catalyst was observed. The method was also applied to the conversion of acetone to methyl vinyl ketone and methyl propionate to methyl methacrylate. Condensations of various primary alcohols(C2-C5) with methanol were carried out at atmospheric pressure over various metal oxides having a solid-base property. The reactions gave one or two carbon higher alcohol than the reacted primary alcohol. MgO catalyst was most active for the reaction and yielded the alcohol products in high selectivty(>80%). Based on the kinetic measurements, reaction mechanisms for both reactions are discussed.

Utilization of Selenium-Directed (2 + 2) Cycloadditions: Concise Synthesis of (.+-.)-Fragranol.

Abstract: The reaction of 2-(phenylseleno)prop-1ene 1 and methyl vinyl ketone 2 in the presence of EtAlCl2 gave the [2 + 2] cycloadducts 3a and 3b. A radical substitution of the adducts 3a and 3b with allytributyltin gave the allylated cyclobutane product, which was transformed into the cyclobutane natural product, (±)-fragranol. Stereoselective radical substitution using the ethylene glycol ketals of compounds 3a and 3b was also achieved.

Process for solid-phase michael addition reaction

Abstract: PURPOSE:To obtain an optically active addition product in high chemical and asymmetric yields by carrying out Michael addition reaction of a conjugated ketone compound. CONSTITUTION:A clathrate complex crystal derived from a host compound [preferably an optically active host compound of formula ((n) is 0 or 1)] and a conjugated ketone (e.g. acrolein, methyl vinyl ketone or vinyl phenyl ketone) is made to react with a nucleophilic attacking agent precursor (e.g. an aromatic thiol, an aromatic diol having hetero atom on the aromatic ring, a beta- ketocarboxylic acid ester or a 1,3-diketone) in the presence of a base (preferably quaternary ammonium hydroxide) without using a solvent to obtain an addition product usable as a precursor for a biologically active compound. The compound of formula is e.g. trans-2,3-bis (hydroxydiphenyl)-1,4-dioxaspiro[4,4]nonane.

Synthesis and conformational studies of indolizines

Abstract: The present investigation has involved a kinetic and mechanistic study of the thermal cyclization of 3-acetoxy-3-(2-pyridyl)-2-methylenepropanoate esters and related compounds to 2-substituted indolizines. Substrates for the kinetic study were prepared via the Baylis-Hillmann reaction of pyridine-2-carboxaldehydes with acrylate esters, acrylonitrile and methyl vinyl ketone. The resulting hydroxy compounds were then acetylated to afford the acetoxy derivatives, thermal cyclization of which gave the corresponding 2-substituted indolizines. The cyclization reactions was followed using 'H NMR spectroscopy and were shown to follow firstorder kinetics. The influence of the various substituents on the observed first-order rate constants has been examined and variable temperature studies have permitted evaluation of activation parameters for the formation of methyl indolizine-2-carboxylate and ethyl indolizine-2-carboxylate. An alternative route to 2-substituted indolizines via halogenated derivatives was explored and several halogenated 2-pyridyl derivatives were synthesised and their thermal cyclization to indolizines was attempted. Novel 5-methylindolizine-2-carboxamides were prepared as part of this investigation and dynamic NMR spectroscopy was used to study internal rotation about the amide N-CO bond in these compounds.

Cyclization Reactions Leading to β-Hydroxyketo Esters.

Abstract: □ The purpose of the research was to synthesize β-diketo esters and to evaluate them for anticonvulsant activity. The reaction of methyl vinyl ketone with dimethyl malonate in the presence of potassium carbonate gave an uncyclized product that underwent a Clalsen condensation to yield methyl 2-hydroxy-4-oxocyclohex-2-en- 1-oate (5a). Similarly, other cyclized β-hydroxyketo esters were prepared, and their spectrometric data confirmed that the enol tautomers were preferred to the β-diketo tautomers. The synthetic work clarified the reaction pathway for the Michael addition of malonate esters to enones. Of the intermediates and products tested for anticonvulsant activity, dimethyl 2,2-bis-(3-oxobutyl)malonate (9a) was found to possess anticonvulsant property. However, it is emphasized that the β-hydroxyketo esters could be useful intermediates in the synthesis of enaminone anticonvulsants.

Intramolecular Competitive Addition of Vinyl Radicals to Keto and Alkenyl Groups in Wieland-Miescher Ketones - Synthesis of Carbocycles and Propellanes.

Abstract: Wieland–Miescher ketone analogues are prepared by monoalkylation of cyclohexane-1,3-dione with bromomethylcycloalkenyl bromides followed by annulation with methyl vinyl ketone; they undergo 5-exo-trig competitive intramolecular radical addition to the keto and enone olefins to give angularly rused carbocycles and propellanes, respectively.