- A New Synthesis of Cyclopentenones: Dihydrojasmone
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A new general olefin synthesis, via alkylation of an alpha-trifyl sulfone and subsequent Ramberg-Baecklund elimination of triflinate and SO2, is here applied to the synthesis of cyclopentenones, including dihydrojasmone and methylenomycin B.
- Hendrickson, James B.,Palumbo, Paul S.
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- Pheromone synthesis. Part 262: Determination of the absolute configuration of the female sex pheromone [(1S,2S)-(?)-(1,2-dimethyl-3-methylenecyclopentyl) acetaldehyde] of the pineapple mealybug (Dysmicoccus brevipes) by synthesis coupled with X-ray analysis
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The enantiomers of (anti-1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde, one of which is the female sex pheromone of the pineapple mealybug (Dysmicoccus brevipes), were synthesized. Chirality was introduced by means of lipase-catalyzed asymmetric acetylation of (±)-2,3-dimethyl-2-cyclopenten-l-ol. X-ray analysis of (?)-camphanate ester of (1S,2S)-(?)-2-(1,2-dimethyl-3-methylenecyclopentyl)ethanol confirmed its (1S,2S)-absolute configuration. The natural pheromone was identified with the (1S,2S)-aldehyde by comparing the specific rotation, enantioselective GC retention time and pheromone activity.
- Mori, Kenji,Tabata, Jun
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- Synthesis of substituted 2-cyclopenten-1-ones from oxodithioesters via a domino process
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Freshly prepared sulfines of δ-oxodithioesters underwent chemoselective addition of methyllithium to the electron poor sulfur atom of the thiocarbonyl moiety. Subsequent ring closure was effected by intramolecular addition of the carbanion, generated in situ, to the 8-carbonyl function leading to 2-cyclopenten-1-ones. While most described intramolecular procedures involve a base-catalysed cyclisation, our method is induced by an addition reaction. It is a new efficient synthesis of substituted 2- cyclopenten-1-ones via a domino process.
- Corbin, Florence,Alayrac, Carole,Metzner, Patrick
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- Pheromone synthesis. Part 260: Synthesis of (±)-(anti-1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde, the racemate of the female-produced sex pheromone of the pineapple mealybug (Dysmicoccus brevipes), and its syn-isomer
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(±)-(anti-1,2-Dimethyl-3-methylenecyclopentyl)acetaldehyde, the racemate of the female-produced sex pheromone of the pineapple mealybug, was synthesized in four different ways. Ireland–Claisen rearrangement or conjugate addition was employed for the const
- Mori, Kenji
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- SYNTHESIS OF CYCLOPENTANOID NATURAL PRODUCTS VIA VINYL PHOSPHONIUM SALTS
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Cyclopentenones obtained from cyclisations involving phosphonium salts are converted to dihydrojasmone, dihydrojasmolone and known precursors of methylenomycins A and B.
- Cameron, Andrew G.,Hewson, Alan T.,Osammor, Matthew I.
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- SYNTHESIS OF MONO- AND 1,4-DICARBONYL COMPOUNDS BASED ON THE OXYGENATION OF PHOSPHONATE CARBANIONS. SYNTHESIS OF DIHYDROJASMONE, ALLETHRONE AND METHYLENOMYCIN B
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Oxidation of the α-alkylthio-substituted phosphonate carbanions was found to give the corresponding carbonyl compounds.A new synthesis of 1,4-dicarbonyl systems involving the oxygenation of phosphonate carbanions as a key step is described.Total synthesis of dihydrojasmone and allethrone and formal synthesis of methylenomycin B is reported.
- Mikolajczyk, Marian,Midura, Wanda,Grzejszczak, Slawomir
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- Cyclopentenones from the Acid-induced Ring Expansion of 1-Alkenylcyclopropanol Derivatives
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1-Alkenylcyclopropanols (4a,b) and (5a,b) underwent acid-induced ring expansion into cyclopentenones (7), via 2-alkenylcyclobutanones (6); the 2-methylcyclopropanols (15a,b) are also synthesised using the same method.
- Barnier, Jean-Pierre,Karkour, Belkacem,Salauen, Jacques
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- Polymer-mediated reactions. A Nazarov-like cyclization
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The polymer PEDOT+ mediates a Nazarov-like cyclization of dienones, in an heterogeneous system and in hydrocarbon solvents. The polymer-mediated reactions show clear differences in product formation when compared to the same reaction with tosic acid, or when compared to reports in the literature. Comparable or improved yields are observed, as well as the ability to give a -Nazarov product in cases where treatment with acid fails to give cyclization, or leads to an undesirable rearrangement. In addition, the ability to recycle the polymer makes this a potentially useful protocol for an important organic chemical reaction. Georg Thieme Verlag Stuttgart · New York.
- Pavlik, Christopher,Morton, Martha D.,Invernale, Michael A.,Berghorn, Ian D.,Sotzing, Gregory A.,Smith, Michael B.
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- A new synthetic route to methylenomycin B via Rhodium(II)-mediated decomposition of α,β-unsaturated α'-diazoketones
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A new synthesis of methylenomycin B, involving Rh(II)-catalyzed, intramolecular carbon-hydrogen insertion of diazoketone 2c, derived from 2,3-dimethyl-2-butenoic acid 2b, is reported.
- Ceccherelli,Curini,Marcotullio,Rosati
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- Acyclic O- and N-substituted Pentadienyl Cations: Structural Characterisation, Cyclisation and Computational Results
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A number of 1- and 3-hydroxy and 1-amino substituted acyclic pentadienyl cations have been characterised by NMR spectroscopy in situ at low temperature.Some of the 3-hydroxy cations undergo cyclisation to give 1-hydroxycyclopentenyl cations which on deprotonation give substituted cyclopentenones.
- Howell, James A. S.,O'Leary, Paula J.,Yates, Paul C.,Goldschmidt, Zeev,Gottlieb, Hugo E.,Hezroni-Langerman, Daphna
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- METHOD OF PRODUCING 2,3-DIMETHYL-2-CYCLOPENTENONE
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PROBLEM TO BE SOLVED: To provide a method of industrially producing 2,3-dimethyl-2-cyclopentenone. SOLUTION: In a first step, a compound represented by formula (1) and acetone are reacted in the presence of a base to obtain a compound represented by formula (2). Then, the compound represented by formula (2) is subjected to second, third and fourth steps to obtain a compound represented by formula (6), which is further reacted in the presence of an acid or base to produce 2,3-dimethyl-2-cyclopentenone represented by formula (7). SELECTED DRAWING: None COPYRIGHT: (C)2020,JPO&INPIT
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Paragraph 0008; 0035-0040
(2020/04/09)
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- Coupling of Methanol and Carbon Monoxide over H-ZSM-5 to Form Aromatics
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The conversion of methanol into aromatics over unmodified H-ZSM-5 zeolite is generally not high because the hydrogen transfer reaction results in alkane formation. Now circa 80 % aromatics selectivity for the coupling reaction of methanol and carbon monoxide over H-ZSM-5 is reported. Carbonyl compounds and methyl-2-cyclopenten-1-ones (MCPOs), which were detected in the products and catalysts, respectively, are considered as intermediates. The latter species can be synthesized from the former species and olefins. 13C isotope tracing and 13C liquid-state NMR results confirmed that the carbon atoms of CO molecules were incorporated into MCPOs and aromatic rings. A new aromatization mechanism that involves the formation of the above intermediates and co-occurs with a dramatically decreased hydrogen transfer reaction is proposed. A portion of the carbons in CO molecules are incorporated into aromatic, which is of great significance for industrial applications.
- Chen, Zhiyang,Ni, Youming,Zhi, Yuchun,Wen, Fuli,Zhou, Ziqiao,Wei, Yingxu,Zhu, Wenliang,Liu, Zhongmin
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supporting information
p. 12549 - 12553
(2018/09/11)
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- Reaction routes in catalytic reforming of poly(3-hydroxybutyrate) into renewable hydrocarbon oil
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Poly(3-hydroxybutyrate) or PHB is an energy storage material of microbial organisms and can be reformed into hydrocarbon oils rich with aromatic compounds. This work investigated the main reaction routes from PHB to the key intermediates and final hydrocarbons. The main sequential reactions under catalysis of phosphoric acid at moderate temperatures (200-230 °C) consist of: (1) decomposition of PHB into crotonic acid, a major monomeric intermediate, (2) deoxygenation of crotonic acid, and (3) combination of the deoxygenated molecules. The oxygen in PHB is removed as CO2 and H2O in stage (2), involving decarboxylation and ketonization of crotonic acid. The main aromatic compounds are formed in stage (3) from propylene and 2,3-dimethyl-2-cyclopenten-1-one as two key intermediates, the former from decarboxylation and the latter from ketonization of crotonic acid. The reaction routes reveal that the formation of aromatics is affected to a great extent by the concentrations of phosphoric acid and water in the reaction, which can be used to control the composition of hydrocarbon oil.
- Kang, Shimin,Yu, Jian
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p. 30005 - 30013
(2015/05/13)
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- The scent of bacteria: Headspace analysis for the discovery of natural products
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Volatile compounds released by 50 bacterial strains, 45 of them actinobacteria in addition to three chloroflexi and two myxobacteria, have been collected by use of a closed-loop stripping apparatus, and the obtained headspace extracts have been analyzed by GC-MS. Excluding terpenes that have recently been published elsewhere, 254 compounds from all kinds of compound classes have been identified. For unambiguous compound identification several reference compounds have been synthesized. Among the detected volatiles 12 new natural products have been found, in addition to mellein, which was released by Saccharopolyspora erythraea. The iterative PKS for this compound has recently been identified by in vitro experiments, but mellein production in S. erythraea has never been reported before. These examples demonstrate that headspace analysis is an important tool for the discovery of natural products that may be overlooked using conventional techniques. The method is also useful for feeding experiments with isotopically labeled precursors and was applied to investigate the biosynthesis of the unusual nitrogen compound 1-nitro-2-methylpropane, which arises from valine. Furthermore, several streptomycetes emitted compounds that were previously recognized as insect pheromones, thus questioning if bacterial symbionts are involved in insect communication.
- Citron, Christian A.,Rabe, Patrick,Dickschat, Jeroen S.
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supporting information
p. 1765 - 1776
(2013/01/15)
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- Lewis acid-catalyzed oxidative rearrangement of tertiary allylic alcohols mediated by TEMPO
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Two methods for the oxidative rearrangement of tertiary allylic alcohols have been developed. Most of tertiary allylic alcohols studied were oxidized to their corresponding transposed carbonyl derivatives in excellent to fair yields by reaction with TEMPO in combination with PhIO and Bi(OTf)3 or copper (II) chloride in the presence or not of oxygen. Other primary oxidants of TEMPO such as PhI(OAc)2, mCPBA, and Oxone were unsatisfactory giving the enone in modest to low yields.
- Vatèle, Jean-Michel
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experimental part
p. 904 - 912
(2010/03/24)
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- Lewis acid promoted oxidative rearrangement of tertiary allylic alcohols with the PhIO/TEMPO system
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A mild and environmentally friendly method for Lewis acid catalyzed oxidative rearrangement of tertiary allylic alcohols to β-disubstituted enones by the TEMPO/PhIO system is described. Bismuth triflate was found to be the most efficient catalyst for the majority of the substrates tested except for tertiary vinyl carbinols which could be transformed to enals in fair yields only when Re2O7 was used as catalyst. A plausible mechanism for this oxidative rearrangement is discussed. Georg Thieme Verlag Stuttgart.
- Vatèle, Jean-Michel
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experimental part
p. 1785 - 1788
(2009/04/07)
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- Synthesis and cyclic voltammetry of 1,2,3-trisubstituted bis(cyclopentadienyl)zirconium dichlorides
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The synthesis of the 1,2,3-trisubstituted cyclopentadienes 3-10 and their corresponding zirconocene dichlorides 11-18 from commercially available internal alkynes is presented. The solid state structures of the differently substituted zirconocenes 11-13 and 15-17 were examined by means of X-ray analysis. The bite angles have shown not to be dependent on the substitution pattern of the cyclopentadienyl ligand. Cyclic voltammetry was used to measure the effect of introducing electron withdrawing and donating groups at the five membered ligand on the Lewis acidity of the zirconium central atom.
- Rausch, Bernhard J,Gleiter, Rolf,Rominger, Frank
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p. 242 - 250
(2007/10/03)
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- New route to herbertanes via a Suzuki cross-coupling reaction: Synthesis of herbertenediol
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The synthesis of herbertenediol, a relevant member of the herbertane-type sesquiterpene family, is described. The synthesis is based on a new general approach to this group of sesquiterpenes where the herbertane skeleton is constructed using a Suzuki cross-coupling reaction and a [2,3]-sigmatropic Still-Wittig rearrangement as key synthetic steps.
- Abad, Antonio,Agulló, Consuelo,Cu?at, Ana C,Jiménez, Diego,Perni, Remedios H
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p. 9727 - 9735
(2007/10/03)
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- The utility of vinyl ethers and vinyl esters in the Khand reaction. The value of vinyl esters as ethylene equivalents and a modified synthesis of (+)-taylorione as an example
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The behaviour of various oxygenated alkenes in the Khand cyclisation reaction has been studied. Although several vinyl ethers reacted to give the expected oxygenated cyclopentenone products, usually with good levels of regioselectivity, the use of vinyl esters was found to afford, as the major products, reduced cyclopentenones in which the carbon-oxygen bond had been cleaved. This unexpected reaction was developed into an alternative procedure to using ethylene gas in the Khand reaction and was found to be applicable with a variety of alkyne substrates. The method was then extended to form the key step in the synthesis of the natural product (+)-taylorione (and (+)-nortaylorione).
- Kerr, William J.,McLaughlin, Mark,Pauson, Peter L.,Robertson, Sarah M.
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p. 104 - 117
(2007/10/03)
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- Reaction of cyclic α-hydroxy epoxides with a strong base: A new 1,2-rearrangement, evidence for a carbenoid pathway
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Several substituted five- and six-membered cyclic α,β-unsaturated ketones are readily available by treatment of the corresponding α-hydroxy epoxides with an organolithium reagent. The reaction involves a new carbenoid 1,2-alkyl rearrangement. Evidence for the carbenoid intermediate has been obtained by an intramolecular trapping of the highly reactive species.
- Doris, Eric,Dechoux, Luc,Mioskowski, Charles
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p. 12700 - 12704
(2007/10/03)
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- New synthetic applications of organotin compounds: Synthesis of stereodefined 2-iodo-2-alkenones, 2-substituted (E)-2-alkenones and 2-methyl-2-cycloalkenones
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Stereoisomeric mixtures of 3-iodo-3-nonen-2-one, 8a, 2-iodo-1-phenyl-2-octen-1-one, 8b, 2-iodo-1,3-diphenyl-2-propen-1-one, 8c, as well as (Z)-3-iodo-4-phenyl-3-buten-2-one, 8d, have been efficiently synthesized by a reaction sequence involving a Pd-catalyzed reaction between the corresponding 1-alkynyl ketones, 10, and Bu3SnH followed by iododestannylation. Stereomutation experiments carried out in the presence of daylight and using catalytic amounts of I2 showed that the Z stereoisomers of 8a, 8b and 8c, which could be separated by MPLC on silica gel from the corresponding E stereoisomers, as well as compound (Z)-8d were more stable than their E stereoisomers. Compounds 8a-d underwent Pd-catalyzed cross-coupling reactions with C6H5SnMe3, CH2=CH-SnBu3 and SnMe4 providing an efficient route to the corresponding 2-substituted 2-alkenones, 13. However, the Pd-catalyzed reaction between (Z)-8c and PhSnMe3 afforded a mixture of the expected cross-coupled product, (E)-13f with the compound derived from methyl transfer, (E)-13e. The couplings involving (Z)-8a, (Z)-8b, (Z)-8c and (Z)-8d proceeded with clean retention of stereochemistry, but the Pd-catalyzed reaction between (E)-8c and SnMe4 afforded a stereoisomeric mixture of 13e. On the contrary, the coupling between (E)/(Z)-8b and SnMe4 produced stereoisomerically pure (E)-13c. Two 2-iodo-2-cycloalkenones, i.e. compounds 18a and 18b, also reacted with SnMe4, in the presence of a Pd catalyst, to give the corresponding 2-methyl-2-cycloalkenones, 19a and 19b, respectively, in satisfactory yields. Compound 19b represents a very useful precursor to methylenomycin B, 9.
- Bellina, Fabio,Carpita, Adriano,Ciucci, Donatella,De Santis, Massimo,Rossi, Renzo
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p. 4677 - 4698
(2007/10/02)
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- A SIMPLE ROUTE TO 2-METHYL-2-CYCLOPENTENONES
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Reaction of carboxylate esters with ethylmagnesium bromide in the presence of tetraisopropoxytitanium has given 1-(3-oxobutyl)cyclopropanol, 1-cyclopropanol, and bis-1,2-(1-hydroxy-1-cyclopropyl)ethane.Treatment of these compounds with sodium hydroxide in aqueous ethanol affords 81-83 percent yields of the 3-substituted-2-methyl-2-cyclopentenones by cleavage of the three-carbon ring followed by cyclization of the intermediate ethyl ketones.
- Vasilevskii, D. A.,Sviridov, S. V.,Kulinkovich, O. G.
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p. 1885 - 1887
(2007/10/02)
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- Base-Induced Cyclization of α-Chloro- β,γ-Unsatured Ketones. Facile Synthesis of Tri- and Tetrasubstituted 2-Cyclopenten-1-ones
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Base-induced cyclization of fully substituted α-chloro β,γ-unsatured ketones results in substituted cyclopentenones.Potassium tert-butoxyde, lithium diisopropylamide, sodium hydroxide, and ammonium hydroxide can be used as the base for this process.In the case of ammonium hydroxide , it is proposed that initial formation of an enamine is followed by an intramolecular SN2'reaction of the enamine carbon.For all other bases, the reaction most likely proceeds through a ketone enolate.Application of this novel cyclization has been extended to the synthesis of several 2,3-substituted, 2,3,5-trisubstituted, and 2,3,5,5-tetrasubstituted 2-cyclopenten-1-ones.
- Mathew, Jacob
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p. 713 - 716
(2007/10/02)
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- Synthesis of 2,3,5-trisubstituted-2-cyclopentenones via base induced cyclization of alpha-chloro unsaturated ketones
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2,3,5-trisubstituted-2-cyclopentenones or 2,3-disubstituted-2-cyclopentenones (such as cis-jasmone) are prepared by contacting a 3-chloro-3,4-disubstituted-4-pentene-2-one with a strong base. Methods of preparing the reactants are also disclosed.
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- Hydrocarbonylating Cyclization of Dienes, 8. - Cyclization of 1,4-Dienes with Functional Groups in 3-Position
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1,4-Dienes 1a-i with functional groups at C-3 were synthesized and treated under the conditions of metal-cytalyzed hydrocarbonylating cyclization.Under the usual conditions no cyclization products could be isolated.Modifications of the reaction conditions did not lead to the expected cyclopentanones of type 2 or 3 either.Instead, the original functional groups are slit off.Depending on the reaction conditions, either the non-functionalized 2-cyclopentenones 5, the cyclopentanones 6, or the 2-cyclopentenones 7 with a functional group introduced from the solvent into the 2-methyl group are obtained.These unexpected products of type 7 at least formally correspond to allylic rearrangement products of the expected but not observed type-3 exo-methylenecyclopentanones.The mechanism of the formation of these products is discussed.
- Eilbracht, Peter,Huettmann, Gerd-Erich,Deussen, Rainer
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p. 1063 - 1070
(2007/10/02)
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- Synthesis and Reactions of α-Chloro-β,γ-unsaturated Esters. 1
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Four new α-chloro-β,γ-unsaturated esters were prepared in good yield by the reaction of hypochlorous acid with substituted ethyl 2-butenoates.Reaction of these substituted allylic chlorides with several nucleophiles has been investigated.Thiophenol in the presence of aqueous sodium hydroxide react with ethyl 2-chloro-3-methyl-3-butenoate (2) to give 6, whereas ethyl 2-chloro-2,3-dimethyl-3-butenoate (1) is unreactive.Tertiary allylic chlorides 1, 3 and 4 react with secondary amines to give exclusive abnormal SN2 reaction products.With benzylamine abnormal SN2 substitution is followed by cyclization to give 1-benzyl-3-pyrrolin-2-ones.While ethyl lithioacetate reacts with 1 to give acylation product 18, sodium diphenylmethide in liquid ammonia undergoes alkylation on the tertiary carbon possibly by an electron-transfer reaction pathway.Lithio-1,3-dithiane reacts with 1 to give 2,3-dimethyl-6,10-dithiaspirodec-2-en-1-one (20) via a two-step process, viz., acylation followed by anovel variation of the intramolecular abnormal SN2 reaction.Raney nickel desulfurization of 20 gave 2,3-dimethyl-2-cyclopenten-1-one.Synthetic and mechanistic implications of these results are discussed.
- Mathew, Jacob,Alink, Ben
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p. 3880 - 3886
(2007/10/02)
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- Process for preparing oxocyclopentene derivatives
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A process for preparing oxocyclopentenes of the formula: STR1 wherein R1 is hydrogen, lower alkyl or lower alkenyl and R2 is hydrogen, lower alkyl, lower alkenyl, lower alkynyl, substituted or unsubstituted aryl, ar(lower)alkyl, thienyl or cycloalkyl, which comprises subjecting a furan-carbinol of the formula: STR2 wherein R1 is as defined above and R3 is hydrogen, lower alkyl, lower alkenyl, lower alkynyl, substituted or unsubstituted aryl, ar(lower)alkyl, thienyl or cycloalkyl to rearrangement, subjecting the resultant hydroxycyclopentenone of the formula: STR3 wherein R1 and R3 are each as defined above to hydrogenation and subjecting the resulting hydroxycyclopentanone of the formula; STR4 wherein R1 and R2 are each as defined above to dehydration.
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- Reactions of Some Cyclic Ethers in Superacids
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The reactions of some epoxides and tetrahydrofuran derivatives in superacidic media have been studied.The tetrahydrofurans decompose only at 0 deg C or above, yielding, in some cases, unsaturated carbocations which react to give carbocyclic products, though many yield only tar.Cyclohexene oxides decompose more readily; unsubstituted, they slowly form an allylic ion; with one carbon at the epoxide link substituted they yield the ketone, and with both carbons substituted they give the ring-contracted aldehyde.Limonene 1,2-oxide behaves in a similar manner, though yielding small amounts of the ring-contracted protonated aldehyde (10).Reaction of geraniol 2,3-oxide is initially similar but the intermediate is intercepted intramolecularly to yield the hydroxy-iridoid ethers, 3,3,6β-trimethyl-cis-perhydrocyclopentafuran and 3,3,6α-trimethyl-cis-perhydrocyclopentafuran.Protonation of cyclohexene oxide or norbornene oxide yields onium salts, stable at -70 deg C, which show the addition to be either unsymmetrical (i.e. edge protonation) or to take place in two different positions.
- Baig, Mirza Azam,Banthorpe, Derek V.,Carr, Graham,Whittaker, David
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p. 1981 - 1986
(2007/10/02)
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- Nuclear Synthons: Mesyltriflone as an Olefin Polyanion Equivalent
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Mesyltriflone (CF3SO2CH2SO2CH3) is developed as a nuclear synthon reagent capable first of multiple constructions such as alkylations then of Ramberg-Baecklund elimination to a substituted olefin.The alkylations are clean and regiospecific, often amenable to one-pot operation, and in most cases the elimination is smooth.A variety of examples is presented to establish the scope of the method, and the mechanism and stereochemistry are discussed.
- Hendrickson, James B.,Boudreaux, Gerald J.,Palumbo, Paul S.
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p. 2358 - 2366
(2007/10/02)
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- SYNTHETIC APPLICATIONS OF 2-PHENYLSELENENYLENONES-III AN OVERVIEW
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2-Phenylselenenylenones are versatile species which can be selectively converted a number of different ketones and enones in high overall yields.
- Liotta, Dennis,Saindane, Manohar,Barnum, Christopher,Zima, George
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p. 4881 - 4890
(2007/10/02)
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- SYNTHESIS OF 1,4-DIEN-3-ONES AND 2-CYCLOPENTENONES
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Aluminium trichloride catalyzed reaction of trimethylvinylsilane with α,β-unsaturated acyl chlorides gives 1,4-dien-3-ones, from which 2-cyclopentenones may be prepared.
- Kjeldsen, Gunhild,Knudsen, Jes S.,Ravn-Petersen, Lise S.,Torssell, Kurt B. G.
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p. 2237 - 2240
(2007/10/02)
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- Specificities of the α-Alkynone Cyclization
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Die Regio- und Stereospezifitaeten der α-Alkinon-Cyclisierung, einer thermischen Umwandlung von Alkinyl-alkyl-ketonen, welche in β'-Stellung mindestens ein H-Atom tragen, zu 2-Cyclopentenonen wurden untersucht.Cyclisierung zum hoeher substituierten C(β')-Atom ist dabei bevorzugt, vorausgesetzt, dass die zur Insertion zur Verfuegung stehende C(β'),H-Bindung zur Propioloylseitenkette eine moeglichst synplanare Anordnung einnehmen kann.In Cyclisierungen zu β'-Methylen-C-Atomen, welche diastereotope H-Atome tragen, wird daher eines der moeglichen epimeren Produkte bevorzugt oder ausschliesslich gebildet.Die mechanistischen Konsequenzen der gefundenen Specifitaeten werden diskutiert.
- Karpf, Martin,Huguet, Joan,Dreiding, Andre S.
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- Reaction of β-halo α,β-unsaturated ketons with cuprate reagents. Efficient syntheses of β,β-dialkyl ketones and β-alkyl α,β-unsaturated ketones. A synthesis of (Z)-jasmone
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Treatment of the 3-halo-2-cyclohexen-1-ones 11-15 and 17 with an excess of lithium dimethylcuprate provided good to excellent yields of the corresponding 3,3-dimethylcyclohexanones 21-24.Similar reactions involving the β-bromo cyclopentenones 19 and 20 stopped at the monoaddition stage, producing the cyclopentenones 40 and 43.Reaction of the β-bromo cyclohexenones 12 and 15 with 1.1 equiv. of lithium dimethylcuprate did not effect clean conversion of these substrates into the corresponding 3-methyl-2-cyclohexen-1-ones.When a series of β-bromo enones 12, 14-19were allowed to react with the lithium (phenylthio)(alkyl)cuprates 44-47, the correspondig β-alkyl enones were, in general, produced cleanly and efficiently.However, reaction of 3-bromo-2-methyl-2-cyclopenten-1-one (19) with the cuprate reagent 44 gave mainly the β-phenylthio enone 49.This undesired result could be avoided by employing, in the place of 19, The β-iodo cyclopentenone 50, which reacted smoothly with 44 to give a high yield of 2,3-dimethyl-2-cyclopenten-1-one (40).Reaction of 3-bromo-2-cyclohexen-1-one (14) with 3 equiv. of the mixed vinylcuprate reagent 48 gave 3-(3-butenyl)-2-cyclohexen-1-one (32).Alkylation of 1,3-cyclopentanedione with (Z)-1-chloro-2-pentene afforded compound 51, which was converted into the β-bromo enone 52.Treatment of the latter substance with lithium dimethylcuprate provided (Z)-jasmone (53).
- Piers, Edward,Cheng, Kin Fai,Nagakura, Isao
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p. 1256 - 1263
(2007/10/02)
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- Nucleophilic substitution of 5,5-dimethyl-2-cyclopentenyl derivatives. Lack of SN2' reaction
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Treatment of tetramethyl-1,3-cyclobutadienone with two equivalents of allyl oxide anion at 140 deg C yields 2,2-dimethyl-4-pentenoic acid which is cyclized via the acid chloride whith aluminium chloride to 5,5-dimethyl-2-cyclopentenone 4.Reduction of 4 with aluminium hydride provides 5,5-dimethyl-2-cyclopentenol 1-OH which is pyrolyzed to 5,5-dimethyl-1,3-cyclopentadiene in dimethylsulfoxide.Reduction of 4 with tri-t-butoxyaluminium hydride at -70 deg C gives 2,2-dimethylcyclopentanone.The 2,6-dichlorobenzoate ester of 1-OH failed to yield SN2' products under a variety of conditions.The rate constants for solvolysis of the p-nitrobenzoate esters of 1-OH, 2-cyclopentenol and Z-2-methyl-4-hexene-3-ol in 80 percent ethanol at 80 deg C are 20.2, 523, and 0.63 x 1E-6s-1, respectively, and the main products of solvolysis are 5-ethoxy-3,3-dimethylcyclopentene, 3-ethoxycyclopentene, and E-2-ethoxy-5-methyl-3-hexene, respectively.There is steric hindrance to solvatation during ionization of the p-nitrobenzoate of 1-OH.
- Kopecky, Karl R.,Levine, Cyril
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p. 3273 - 3279
(2007/10/02)
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- Synthetic Applications of 2-Phenylselenenyl Enones. Selective Formation of Exocyclic or Endocyclic Enones from a Common Intermediate
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2-Phenylselenenyl enones are versatile species which can be selectively converted into a number of different ketones and enones (e.g.5, 6, 9, 10, or 11) in high overall yields.
- Zima, George,Barnum, Christopher,Liotta, Dennis
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p. 2736 - 2737
(2007/10/02)
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- Process for preparing cyclopentenone derivatives
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A novel and industrial process for preparing cyclopentenone derivatives by heating C5 ?C13 aliphatic acids having one substituent or intramolecular esters thereof in the presence of a solid acid catalyst in a good yield.
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