- Silicon in synthesis. C2-C3 annulation using vinyltrimethylsilane as an ethylene equivalent for bicyclo[n.3.0]enone synthesis
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Vinyltrimethylsilane reacts with cyclic α,β-unsaturated acid chlorides in the presence of stannic tetrachloride to give bicyclo[n.3.0]enones.
- Cooke, Frank,Schwindeman, James,Magnus, Philip
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- CYCLOPENTENONE AND CYCLOHEXENONE ANNULATIONS VIA ACID-CATALYSED 1,2- AND 1,3-ACYL MIGRATION OF 2-VINYLCYCLOBUTANONES. REARRANGEMENT ROUTE TO SPIRO- AND ANGULARLY SUBSTITUTED FUSED-CYCLOPENTENONES.
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In the presence of acid, 2-alkyl-2-vinylcyclobutanones rearrange mainly by a 1,2-acyl migration to give cyclopentenones while 2-vinylcyclobutanones lacking 2-alkyl substituents undergo a 1,3-acyl migration to produce cyclohexenenes: the former rearrangement can be used to produce angularly substituted fused bicyclic systems.
- Matz, James R.,Cohen, Theodore
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- Catalytic, asymmetric transannular aldolizations: Total synthesis of (+)-hirsutene
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We report an asymmetric, catalytic transannular aldolization that provides polycyclic products useful for natural product synthesis. We found that a proline-derivative catalyzes the transannular aldol reaction of 1,4-cyclooctanediones to the corresponding cyclic β-hydroxy ketones in good yields and with high enantioselectivities. The utility of our reaction has been demonstrated in a total synthesis of (+)-hirustene. Copyright
- Chandler, Carley L.,List, Benjamin
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p. 6737 - 6739
(2008/12/22)
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- Palladium-catalyzed intramolecular 5-endo-trig oxidative Heck cyclization: a facile pathway for the synthesis of some sesquiterpene precursors
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An efficient and convenient method for the construction of substituted cyclopentenones via palladium-catalyzed intramolecular 5-endo-trig oxidative cyclization has been introduced as a powerful new strategy for the synthesis of sesquiterpenes.
- Ray, Devalina,Paul, Sunanda,Brahma, Sulagna,Ray, Jayanta. K.
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p. 8005 - 8008
(2008/03/18)
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- Palladium-catalyzed carbonylative cyclization of unsaturated aryl iodides and dienyl triflates, iodides, and bromides to indanones and 2-cyclopentenones
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Indanones and 2-cyclopentenones have been successfully prepared in good to excellent yields by the palladium-catalyzed carbonylative cyclization of unsaturated aryl iodides and dienyl triflates, iodides, and bromides, respectively. The best results are obtained by employing 10 mol % of Pd(OAc)2, 2 equiv of pyridine, 1 equiv of n-Bu4NCl, 1 atm of CO, a reaction temperature of 100 °C, and DMF as the solvent. This carbonylative cyclization is particularly effective on substrates that contain a terminal olefin. The proposed mechanism for this annulation includes (1) Pd(OAc)2 reduction to the active palladium(0) catalyst, (2) oxidative addition of the organic halide or triflate to Pd(0), (3) coordination and insertion of carbon monoxide to produce an acylpalladium intermediate, (4) acylpalladation of the neighboring carbon-carbon double bond, (5) reversible palladium β-hydride elimination and re-addition to form a palladium enolate, and (6) protonation by H2O to produce the indanone or 2-cyclopentenone.
- Gagnier, Steve V.,Larock, Richard C.
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p. 4804 - 4807
(2007/10/03)
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- A Novel NO2/OH Exchange in α-Nitro Ketones: A Mechanistic Investigation
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The reaction of α-nitro ketones to the corresponding α-hydroxy ketones under basic aqueous conditions, a novel transformation, was studied. The investigation revealed that the reaction is only possible with α-nitro ketones that are CH-acidic in the α′-position and readily deprotonated under the reaction conditions. The NO2/OH exchange was established to proceed with retention of configuration at the stereogenic center, and labeling experiments have shown that the OH O-atom originates, to a great extent, from the solvent. In particular, the stereochemical course of the reaction and the incorporation of external nucleophiles led us to propose a mechanism that involves neighboring-group participation. The product formation is explained by a double SN2 reaction, which proceeds via a favorsii-like cyclopropanone intermediate.
- Yurdakul, Aycil,Gurtner, Christian,Jung, Elena-Silvia,Lorenzi-Riatsch, Annalaura,Linden, Anthony,Guggisberg, Armin,Bienz, Stefan,Hesse, Manfred
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p. 1373 - 1392
(2007/10/03)
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- Electroorganic Chemistry. 140. Electroreductively Intra- and Intermolecular Couplings of Ketones with Nitriles
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Electroreduction of γ- and δ-cyano ketones in i-PrOH with Sn cathode gave α-hydroxy ketones and their dehydroxylated ketones as the intramolecularly coupled products.Guaiazulene, (-)-valeranone, polyquinanes, dihydrojasmone, methyl dihydrojasmonate, and rosaprostol have been synthesized by utilizing this electroreductive intramolecular coupling of γ- and δ-cyano ketones in one of the key steps.Similarly, electroreduction of a mixture of ketone and nitrile gave the corresponding intermolecularly coupled product.The product obtained by the electroreductive intermolecular coupling of (+)-dihydrocarvone with acetonitrile has been found to be the precursor of an effective chiral ligand for the enantioselective addition of diethylzinc to aldehydes.
- Shono, Tatsuya,Kise, Naoki,Fujimoto, Taku,Tominaga, Naoto,Morita, Hiroshi
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p. 7175 - 7187
(2007/10/02)
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- STRATEGY FOR CYCLOPENTENONE ANNULATION OF OLEFINS: A GENERAL PROTOCOL FOR BICYCLOENONE SYNTHESIS
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Several bicyclic α-chloro enones obtained through Greene annulation of cyclic olefins are shown to undergo efficient, two step, enone transposition via Luche reduction and aq. formic acid treatment.Application of this methodology to the formal synthesis of exaltone and (+/-)-muscone is described.
- Mehta, Goverdhan,Rao, K. Srinivas
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p. 1839 - 1842
(2007/10/02)
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- Silanes in Organic Synthesis. 8. Preparation of Vinylsilanes from Ketones and Their Regiospecific Cyclopentenone Annulation
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A general method is described for the formation of vinylsilanes from ketones.Thus, conversion to the benzene- or p-toluenesulfonylhydrazone and sequential treatment with n-butyllithium and chlorotrimethylsilane in anhydrous tetramethylethylenediamine proceeds regiospecifically to afford the less substituted vinylsilane (in unsymmetrical cases).Friedel-Crafts acylation with acryloyl chlorides and aluminium chloride and subsequent Nazarov cyclization with Lewis acid catalysis results in cyclopentenone annulation.Numerous examples that reveal the scope of this processare described.Due to accompanying polymerization, annulation with acryloyl chloride itself is least efficient.This complication can, however, be averted through use of β-chloropropionyl chloride and dehydrochlorination with 1,5-diazabicycloundec-5-ene prior to ring closure.
- Paquette, Leo A.,Fristad, William E.,Dime, David S.,Bailey, Thomas R.
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p. 3017 - 3028
(2007/10/02)
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- Silicon in Synthesis. 8. Vinyltrimethylsilane, a Convenient Ethylene Equivalent for the Synthesis of Vinyl Aryl Sulfides, Vinyl Aryl Sulfoxides, Thiosilylketene Acetals, and Fused Cyclopentenones
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Vinyltrimethylsilane reacts with a variety of arylsulfenyl chlorides to give 2-chloro-1-(trimethylsilyl)ethyl aryl sulfide adducts 9-13.These adducts can be converted into vinyl aryl sulfides and vinyl aryl sulfoxides, and for the case of 2-chloro-1-(trimethylsilyl)ethyl phenyl sulfide (11), treatment with 1,5-diazabicyclonon-5-ene (DBN) gave 1-(trimethylsilyl)-1-(phenylthio)ethylene (24). α,β-Unsaturated acid chlorides react with vinyltrimethylsilane in the presence of stannic tetrachloride to give fused cyclopentenones.In all of the reaction described, vinyltrimethylsilane serves as a convenient ethylene equivalent.
- Cooke, Frank,Moerck, Rudi,Schwindeman, James,Magnus, Phillip
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p. 1046 - 1053
(2007/10/02)
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- Abnormal Nazarov Reaction. A New Synthetic Approach to 2,3-Disubstituted 2-Cyclopentenones
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Acid-catalyzed reaction of β,β'-disubstituted cross conjugated dienones or the corresponding ethylene acetals gives mainly 2,3-disubstituted 2-cyclopentenones in stead of the simple Nazarov cyclization products, 3,4-disubstituted 2-cyclopentenones.This transformation is explained in terms of electrocyclic ring-closure, addition of hydroxylic solvent(s), tautomerization of the resulting 2-hydroxycyclopentanone intermediates, followed by solvolysis and isomerization.Based on this working hypothesis a new route to jasmonoids is disclosed which involves acid-treatment of the acyloin disilyl ethers derived from substituted glutarates.
- Hirano, Shigeo,Takagi, Seiji,Hiyama, Tamejiro,Nozaki, Hitosi
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p. 169 - 173
(2007/10/02)
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- Cyclopentenone Synthesis from 1,1-Dichloroallyllithium-Ketone Adducts as Well as from Dichlorocarbene-Allyl Alcohol Adducts
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Treatment of (3,3-dialkyl-2,2-dichlorocyclopropyl)methanols with hydrobromic acid gives 2-cyclopentenones through postulated intermediates, 3-chlorocyclopentadienyl cations.Another method which should give the same cationic intermediates involves trifluoroacetic acid catalyzed reaction of 3,3-dichloro-1-alken-4-ols.This is found to be particularly useful for cyclopentenone annulation.
- Hiyama, Tamejiro,Shinoda, Masaki,Tsukanaka, Masao,Nozaki, Hitosi
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p. 1010 - 1014
(2007/10/02)
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- Vinylsilane mediated regiospecific cyclopentenone annulation of ketones
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The development of a new cyclopentenone annulation sequence of general scope which involves Friedel-Crafts acylation of a vinylsilane with an α,β-unsaturated acid chloride followed by Nazarov cyclization is reported.
- Fristad, William E.,Dime, David S.,Thomas R, Bailey,Leo A, Paquette
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p. 1999 - 2002
(2007/10/10)
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