- Exceptionally Stable Ozonides. Influence of Methyl Substituents on the Course of Cyclopentene Ozonolyses and on the Reactivities of Ozonides
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Ozonolyses of 1,2,3,3,4,4,5,5-octamethyl- (1a), 1,2,3,3,4,4,5-heptamethyl- (1b), and 1,2,3,3,4,4-Hexamethyl cyclopentenes (1c) in methanol did not yield the ordinary hemiperacetals but gave the corresponding ozonides 6a-c instead.The ozonides 6a,b were extremely stable and remained intact even when refluxed with triphenylphosphine in tetrahydrofuran.Cycloreversion of the primary ozonides from unsymmetrically substituted 1,2,3,3-tetramethylcyclopentene (1d) and 1,5,5-trimethylcyclopentene (1f) was highly regioselective to yield intermediate ω-oxo carbonyl oxides with the geminal methyl groups remote from the carbonyl oxide groups.
- Mayr, Herbert,Baran, Janusz,Will, Elfriede,Yamakoshi, Hideyuki,Teshima, Koichi,Nojima, Masatomo
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Read Online
- Stereoselective synthesis of rac-(8R,13S,14S)-7-oxa-estra-4,9-diene-3,17-dione
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The first synthesis of a novel oxa-steroid, rac-(8R,13S,14S)-7-oxa-estra-4,9-diene-3,17-dione has been achieved via stereoselective catalytic hydrogenation of the tetra-substituted indene intermediate, whose structure was confirmed by X-ray crystallography. In contrast to the previous reports of similar indene systems, it was found that catalytic hydrogenation of indenes with a large substituent at the C-2 position and a bulky β-oriented protective group at the C-6 position resulted in cis-indanes instead of trans-indanes.
- Kang, Fu-An,Jain, Nareshkumar,Sui, Zhihua
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Read Online
- Synthesis of Diketones, Ketoesters, and Tetraketones by Electrochemical Oxidative Decarboxylation of Malonic Acid Derivatives: Application to the Synthesis of cis-Jasmone
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Disubstituted malonic acid derivatives are smoothly converted into diketones and ketoesters in good to excellent yield (68% to 91%) under electrochemical conditions. The scope can be extended to transform trisubstituted bis-malonic acids into tetraketones in 77% to 86% yield. The new method was applied to the total synthesis of cis-jasmone.
- Ma, Xiaofeng,Dewez, Damien F.,Du, Le,Luo, Xiya,Markó, István E.,Lam, Kevin
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Read Online
- Dynamic Kinetic Sensitization of β-Dicarbonyl Compounds—Access to Medium-Sized Rings by De Mayo-Type Ring Expansion
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Herein, we present a photocatalyzed two-carbon ring expansion of β-dicarbonyl compounds with unactivated olefins that provides facile access to medium-sized rings. Selective sensitization of the substoichiometric enol tautomer enables reactivity of substr
- Glorius, Frank,Guldi, Dirk M.,Henkel, Christian,James, Michael J.,Mai, Lukas A.,Paulisch, Tiffany O.,Strieth-Kalthoff, Felix
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supporting information
(2021/12/27)
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- METHODS AND COMPOSITIONS FOR MODULATING SPLICING
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Described herein are small molecule splicing modulator compounds that modulate splicing of mRNA, such as pre-mRNA, encoded by genes, and methods of use of the small molecule splicing modulator compounds for modulating splicing and treating diseases and conditions.
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Paragraph 0890-0891; 0934-0935
(2019/11/29)
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- Synthesis of Diketones, Ketoesters, and Tetraketones by Electrochemical Oxidative Decarboxylation of Malonic Acid Derivatives: Application to the Synthesis of cis-Jasmone
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Disubstituted malonic acid derivatives are smoothly converted into diketones and ketoesters in good to excellent yield (68% to 91%) under electrochemical conditions. The scope can be extended to transform trisubstituted bis-malonic acids into tetraketones in 77% to 86% yield. The new method was applied to the total synthesis of cis-jasmone.
- Ma, Xiaofeng,Du, Le,Luo, Xiya,Markó, István E.,Dewez, Damien F.,Lam, Kevin
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p. 12044 - 12055
(2019/03/01)
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- Palladium-Catalyzed Long-Range Deconjugative Isomerization of Highly Substituted α,β-Unsaturated Carbonyl Compounds
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The long-range deconjugative isomerization of a broad range of α,β-unsaturated amides, esters, and ketones by an in situ generated palladium hydride catalyst is described. This redox-economical process is triggered by a hydrometalation event and is thermodynamically driven by the refunctionalization of a primary or a secondary alcohol into an aldehyde or a ketone. Di-, tri-, and tetrasubstituted carbon-carbon double bonds react with similar efficiency; the system is tolerant toward a variety of functional groups, and olefin migration can be sustained over 30 carbon atoms. The refunctionalized products are usually isolated in good to excellent yield. Mechanistic investigations are in support of a chain-walking process consisting of repeated migratory insertions and β-H eliminations. The bidirectionality of the isomerization reaction was established by isotopic labeling experiments using a substrate with a double bond isolated from both terminal functions. The palladium hydride was also found to be directly involved in the product-forming tautomerization step. The ambiphilic character of the in situ generated [Pd-H] was demonstrated using isomeric trisubstituted α,β-unsaturated esters. Finally, the high levels of enantioselectivity obtained in the isomerization of a small set of α-substituted α,β-unsaturated ketones augur well for the successful development of an enantioselective version of this unconventional isomerization.
- Lin, Luqing,Romano, Ciro,Mazet, Clément
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supporting information
p. 10344 - 10350
(2016/08/31)
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- Ligand Effects in the Gold Catalyzed Hydration of Alkynes
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In the gold(I) (e. g. L-Au-OTf) catalyzed hydration of alkynes, the steric hindrance of ligands has a significant influence on the kinetics of the reaction, whereas their electronic effects are less influential. Very low loadings (ppm levels) of a gold catalyst containing a highly sterically hindered phosphine ligand (e. g. L4-Au-OTf) (L4=Me3(OMe)tBuXPhos) is able to catalyze the hydration of a wide range of alkyne substrates in good yields, at relatively low temperature.
- Ebule, Rene E.,Malhotra, Deepika,Hammond, Gerald B.,Xu, Bo
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supporting information
p. 1478 - 1481
(2016/05/19)
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- Development of an azanoradamantane-type nitroxyl radical catalyst for class-selective oxidation of alcohols
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The development of 1,5-dimethyl-9-azanoradamantane N-oxyl (DMN-AZADO; 1,5-dimethyl-Nor-AZADO, 2) as an efficient catalyst for the selective oxidation of primary alcohols in the presence of secondary alcohols is described. The compact and rigid structure of the azanoradamantane nucleus confers potent catalytic ability to DMN-AZADO (2). A variety of hindered primary alcohols such as neopentyl primary alcohols were efficiently oxidized by DMN-AZADO (2) to the corresponding aldehydes, whereas secondary alcohols remained intact. DMN-AZADO (2) also has high catalytic efficiency for one-pot oxidation from primary alcohols to the corresponding carboxylic acids in the presence of secondary alcohols and for oxidative lactonization from diols.
- Doi, Ryusuke,Shibuya, Masatoshi,Murayama, Tsukasa,Yamamoto, Yoshihiko,Iwabuchi, Yoshiharu
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p. 401 - 413
(2016/10/12)
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- Hydration of alkynes at room temperature catalyzed by gold(I) isocyanide compounds
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An effective method using gold(I) isocyanide complexes as catalysts for the transformation of various alkynes to the corresponding ketones is successfully developed. The hydration process proceeds smoothly at room temperature with quite high yield (up to 99%). The catalytic center is the isocyanide-Au(I)+ cation. Further theoretical research reveals a direct hydration mechanism by H2O, and the rate-determining step has an energy barrier of 23.7 kcal mol?1. These results show a good example to reduce unnecessary steps and achieve milder reaction conditions at the same time for the hydration of alkynes.
- Xu, Yun,Hu, Xingbang,Shao, Jing,Yang, Guoqiang,Wu, Youting,Zhang, Zhibing
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supporting information
p. 532 - 537
(2018/04/16)
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- 9-azanoradamantane N—oxyl compound and method for producing same, and organic oxidation catalyst and method for oxidizing alcohols using 9-azanoradamantane N—oxyl compound
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An organocatalyst for oxidizing alcohols in which a primary alcohol is selectively oxidized in a polyol substrate having a plurality of alcohols under environmentally-friendly conditions. The organic oxidation catalyst has an oxygen atom bonded to a nitrogen atom of an azanoradamantane skeleton and at least one alkyl group at positions 1 and 5. The oxidation catalyst has higher activity than TEMPO, which is an existing oxidation catalyst, in the selective oxidation reaction of primary alcohols, and better selectivity than AZADO and 1-Me-AZADO. This DMN-AZADO can be applied to the selective oxidation reaction of primary alcohols that contributes to shortening the synthesizing process for pharmaceuticals, pharmaceutical raw materials, agricultural chemicals, cosmetics, organic materials, and other such high value-added organic compounds.
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- Cp* iridium precatalysts for selective C-h oxidation with sodium periodate as the terminal oxidant
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Sodium periodate (NaIO4) is shown to be a milder and more efficient terminal oxidant for C-H oxidation with CpIr (Cp* = C 5Me5) precatalysts than ceric(IV) ammonium nitrate. Synthetically useful yields, regioselectivities, and functional group tolerance were found for methylene oxidation of substrates bearing a phenyl, ketone, ester, or sulfonate group. Oxidation of the natural products (-)-ambroxide and sclareolide proceeded selectively, and retention of configuration was seen in cis-decalin hydroxylation. At 60 C, even primary C-H bonds can be activated: whereas methane was overoxidized to CO2 in 39% yield without giving partially oxidized products, ethane was transformed into acetic acid in 25% yield based on total NaIO4. 18O labeling was demonstrated in cis-decalin hydroxylation with 18OH2 and NaIO 4. A kinetic isotope effect of 3.0 ± 0.1 was found in cyclohexane oxidation at 23 C, suggesting C-H bond cleavage as the rate-limiting step. Competition experiments between C-H and water oxidation show that C-H oxidation of sodium 4-ethylbenzene sulfonate is favored by 4 orders of magnitude. In operando time-resolved dynamic light scattering and kinetic analysis exclude the involvement of metal oxide nanoparticles and support our previously suggested homogeneous pathway.
- Zhou, Meng,Hintermair, Ulrich,Hashiguchi, Brian G.,Parent, Alexander R.,Hashmi, Sara M.,Elimelech, Menachem,Periana, Roy A.,Brudvig, Gary W.,Crabtree, Robert H.
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supporting information
p. 957 - 965
(2013/04/23)
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- Silica-supported HgSO4/H2SO4: A convenient reagent for the hydration of alkynes under mild conditions
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The silica-supported aqueous-phase catalyst (SAPC) approach has proven convenient for efficiently performing the hydration of alkynes with HgSO 4/H2SO4 to give the corresponding carbonyl compounds in dichloromethane under mild conditions. The use of this solid reagent significantly improves the reaction work-up as it merely involves filtering and evaporating the solvent.
- Mello, Rossella,Alcalde-Aragonés, Ana,González-Nú?ez, María Elena
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scheme or table
p. 4281 - 4283
(2010/09/07)
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- Cobalt-Catalyzed Oxidations in Volumetrically Expanded Liquids by Compressed Gases
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Oxidations of hydrocarbons, cycloalkanes and alkenes, arylalkanes, and a variety of other organic substrates are accomplished by cobalt-N-hydroxysuccinimide co-catalyzed reactions with dioxygen under unusually mild, near ambient conditions of temperature and pressure. The improved safety of the oxidation method and the high yields of product obtained make use of a unique combination of cobalt (II) complexes with N-hydroxysuccinimide. These autoxidation reactions do not have prolonged initiation times. Many of these reactions can be safely performed under normal chemical laboratory conditions and do not require specialized equipment or reagents.
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Page/Page column 7
(2008/12/06)
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- Organocatalytic asymmetric reaction cascade to substituted cyclohexylamines
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We report a new strategy for organocatalytic cascade reactions. Accordingly, enamine catalysis, iminium catalysis, and Bronsted acid catalysis can work in concert in a highly enantioselective organocatalytic cascade sequence toward chiral cis-3-substituted cyclohexylamines. We found that an achiral amine in combination with a catalytic amount of a chiral Bronsted acid can accomplish an aldol addition-dehydration-conjugate reduction-reductive amination to provide potential intermediates of pharmaceutically active compounds in good yields and excellent enantioselectivities. Copyright
- Zhou, Jian,List, Benjamin
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p. 7498 - 7499
(2008/02/10)
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- Intramolecular 1,3-dipolar cycloadditions of dihydroimidazolium ylides: Synthesis of pyrrolo[1,2,3-de]quinoxalines and imidazo[1,2-a]indoles
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N-Alkylation of 4,5-dihydroimidazoles with alkene-containing bromomethyl ketones and treatment of the so-formed 4,5-dihydroimidazolium ions with DBU gives rise to an intramolecular 1,3-dipolar cycloaddition reaction that affords (via a reaction cascade involving eliminative ring-opening, recyclisation and prototropic tautomerism) unexpected hexahydropyrrolo[1,2,3-de]quinoxaline products. Steric bulk in both the dihydroimidazole and the dipolarophile allows isolation of an imidazo[1,2-a]indole, the initial product of cycloaddition. When the bromomethyl ketone contains no other functionality, or when cycloaddition is inhibited due to steric constraints, the dihydroimidazolium ion undergoes ring-opening hydrolysis followed by recyclization of the exposed amino ketone to afford either 3-alkyl-1-formylpiperazine-2-ones or 3-aryl-1-formyl-1,4,5,6- tetrahydropyrazines. The Royal Society of Chemistry 2006.
- Lory, Pedro M.J.,Jones, Raymond C.F.,Iley, James N.,Coles, Simon J.,Hursthouse, Michael B.
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p. 3155 - 3165
(2008/03/12)
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- Synthesis of Anthropomorphic Molecules: The NanoPutians
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Described here are the synthetic details en route to an array of 2-nm-tall anthropomorphic molecules in monomeric, dimeric, and polymeric form. These anthropomorphic figures are called, as a class, NanoPutians. Using tools of chemical synthesis, the ultimate in designed miniaturization can be attained while preparing the most widely recognized structures: those that resemble humans.
- Chanteau, Stephanie H.,Tour, James M.
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p. 8750 - 8766
(2007/10/03)
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- New ketone homoenolate anion equivalents derived from (alkenyl)pentamethyl phosphoric triamides
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Lithiated ambident anions derived from (1-alkyl-2-propenyl)- or (1-phenyl-2-propenyl)-pentamethyl phosphoric triamides undergo regioselectively γ-reaction with various alkylating reagents and isobutyraldehyde. Further hydrolysis of adducts releases the ketone under acid conditions. Number of synthetic applications clearly show the ketone homoenolate behaviour of these new carbanions.
- Grison, Claude,Thomas, Antoine,Coutrot, Frédéric,Coutrot, Philippe
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p. 2101 - 2123
(2007/10/03)
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- Selective Wacker-type oxidation of terminal alkenes and dienes using the Pd(II)/molybdovanadophosphate (NPMoV)/O2 system
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Selective Wacker-type oxidation of long-chain terminal alkenes to methylketones was successfully achieved by using Pd(OAc)2/molybdovanadophosphate (NPMoV)/O2 system. The selectivity of the reaction increased by slow addition of the alkenes to the catalytic solution. The oxidation of α,ω-dienes was also examined, and the selectivity of the oxidation was found to depend on the chain length of the dienes used.
- Yokota, Takahiro,Sakakura, Aki,Tani, Masayuki,Sakaguchi, Satoshi,Ishii, Yasutaka
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p. 8887 - 8891
(2007/10/03)
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- Reactions of Grignard reagents with bis- or mono-phosphonium ions in Situ generated from Bu3P and dicarboxylic acid dichlorides or ω-ethoxycarbonyl alkanoyl chlorides as a novel method to obtain diketones and ketoesters
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Reactions of Grignard reagents with bis-phosphonium or mono-phosphonium ions in situ generated from Bu3P and ClCO(CH2)(n)COCl (5) or ClCO(CH2)(n)CO2Et (13) as a tool for preparation of symmetrical diketones or ketoesters were examined. Addition of Bu3P (2.0 eq) to a THF solution of 5 (n=2) at -40°C followed by addition of n-BuMgCl (2.0 eq) gave the corresponding diketone in good yield. When a mixture of Bu3P and the Grignard reagent (2.0 eq each) was added to the dichloride solution at the same temperature, a better result was obtained. The latter method not with PhMgBr but with n-BuMgCl or MeMgBr was shown to be useful for preparation of symmetrical alkanediones and keto alkanoates from various 5 (n=2 - 6) and 13 (n=2 or 3), respectively. For synthesis of α-diketones or α-ketoesters, only PhMgBr entered the reaction, although the yields were not satisfactory. Addition of a mixture of Bu3P (2.0 eq), MeMgBr (1.0 eq) and BuMgCl (1.0 eq) to a THF solution of 5 (n=4) at -40°C afforded a mixture of 2,7-undecanedione and the corresponding two symmetrical diketones, with the yield of the unsymmetrical diketone being 36%.
- Maeda,Hino,Yamauchi,Ohmori
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p. 1196 - 1199
(2007/10/03)
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- A continuous Michael and aldol coupling of α,β-enones catalyzed by iridium complexes
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Ir[(COD)(PPh3)2]OTf activated by H2 molecule catalyzes Michael-type coupling of α,β-enones with enoxysilanes to give 1,5-dicarbonyl compounds after the subsequent protodesilylation. An identical catalyst system makes it possible to attain a continuous Michael and aldol modification toward α,β- enones in a one-pot operation. (C) 2000 Elsevier Science Ltd.
- Matsuda, Isamu,Makino, Tatsuya,Hasegawa, Yuki,Itoh, Kenji
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p. 1409 - 1412
(2007/10/03)
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- Gas-Phase Reactions of 1,2-Dimethylcyclopentene and of 2,6-Heptanedione with Ozone: Unprecedented Formation of an Ozonide by Ozone Treatment of a Diketone
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Gas-phase ozonizations of 1,2-dimethylcyclopentene (1) and of 2,6-heptanedione (5) afforded in each case dimethylcyclopentene ozonide (2) in low yields. In the ozonization of 1, diketone 5 was formed as the single major product, along with nine "abnormal" ozonolysis products which were formed by oxidative cleavage of carbon-carbon single bonds.
- Griesbaum, Karl,Miclaus, Vasile,Jung, Chan,Quinkert, Ralf-Olaf
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p. 627 - 629
(2007/10/03)
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- Intramolecular aldol condensations: Rate and equilibrium constants
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Rate and equilibrium constants have been determined for both the aldol addition and the elimination steps in the intramolecular condensation reactions of 2,5-hexanedione, 2,6-heptanedione, 1-phenyl-1,5-hexanedione, and 5-oxohexanal. The overall thermodynamics are similar for cyclization of 2,5-hexanedione and 2,6-heptanedione; conversion of 2,5-hexanedione to the corresponding enone is actually more favorable, but the cyclization of 2,5-hexanedione is 2400 times slower than that of 2,6-heptanedione. As expected on the basis of intermolecular analogs, the addition step is less favorable and slower for 1-phenyl-1,5-hexanedione, and the addition step for 5-oxohexanal is more favorable though similar in rate to that for heptanedione. Detailed analysis of the kinetics and equilibrium for all of these compounds, as well as 2-(2-oxopropyl)benzaldehyde, in terms of Marcus theory, leads to the same intrinsic barriers for the intramolecular reactions as were seen previously for the intermolecular reactions. This means that rate constants for intramolecular aldol reactions should be predictable from the energetics of the reactions and that the effective molarity can be calculated. Methods for estimating thermodynamic quantities for reactants and products of these reactions have been examined.
- Guthrie,Guo
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p. 11472 - 11487
(2007/10/03)
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- Photochemical nucleophile-olefin combination, aromatic substitution (photo-NOCAS) reaction. Part 9: methanol-2,6-dimethyl-1,6-heptadiene, and 1,4-dicyanobenzene
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The photochemical nucleophile-olefin combination, aromatic substitution (photo-NOCAS) reaction of methanol, 2,6-dimethyl-1,6-heptadiene, and 1,4-dicyanobenzene yields three distinct types of 1:1:1: adducts: an acyclic product, 4-(1-methoxymethyl-1,5-dimethyl-5-hexenyl)benzonitrile (8,5percent); a cis-trans pair of cyclohexanes, 4-(3-methoxymethyl-1,3-dimethylcyclohexyl)benzonitrile (9 cis (12percent) and 9 trans (11percent)); and a cis-trans pair of cycloheptanes, 4-(4-methoxy-1,4-dimethylcycloheptyl)benzonitrile (10 cis (12percent) and 10 trans (10percent)).Variation in the concentration of the nucleophile, methanol, and codonor, biphenyl, affects the product ratio and it has been possible to establish the mechanisms for the formation of these products.The acyclic product is formed by a typical photo-NOCAS reaction, that is, addition (anti-Markovnikow) across one of the heptadiene double bonds.The cyclohexane products are formed following 1,6-endo cyclization of the intermediate β-alkoxy radical.And the cycloheptane products result from 1,7-endo, endo cyclization of the initially formed 2,6-dimethyl-1,6-heptadiene radical cation.Comparison of the relative rates of these cyclization processes can be made with those of the next smaller homolog, 2,5-dimethyl-1,5-hexadiene.Key words: photochemistry, photoinduced electron transfer, radical ions, radicals, cyclization.
- Connor, Dennis A.,Arnold, Donald R.,Bakshi, Pradip K.,Cameron, T. Stanley
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p. 762 - 771
(2007/10/03)
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- Direct oxidative cleavage of epoxides to dicarbonyl compounds by ceric ammonium nitrate
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Direct oxidative cleavage of the epoxides (1a-g) with ceric ammonium nitrate in aqueous acetonitrile yields the dicarbonyl compounds (2a-g) in excellent yield.
- Roy, Subhas Chandra,Adhikari, Sankar
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- REMOTE OXIDATION OF KETONES TO γ- AND δ-DIKETONES
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A single stage remote oxidation of ketones to γ- and δ-diketones has been carried out in a sodium peroxysulfate-iron(II) sulfate system.
- Troyanskii, E.I.,Mizintsev, V. V.,Lazareva, M. I.,Demchuk, D. V.,Nikishin, G. I.
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p. 1879 - 1884
(2007/10/02)
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- REGIOSELECTIVE HYDRATION OF ALKYNONES BY PALLADIUM CATALYSIS
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Diketones are regioselectively prepared from alkynyl ketones under mild conditions by palladium catalysis; 5-heptyn-2-one and 2-(2-nonynyl)cyclohexanone give 1,4-diketones whereas 2-(2-heptynyl)cyclopentanone and 5,6-didehydroprostaglandin E2 methyl ester afford 1,5-diketones.
- Imi, Katsuharu,Imai, Kumiko,Utimoto, Kiitiro
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p. 3127 - 3130
(2007/10/02)
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- A Convenient Synthesis of Acyclic 1,n-Diketones (n=5-8) from 2-t-Butylperoxycycloalkanones
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The reaction of organolithium with 2-alkyl-2-t-butylperoxycycloalkanones, readily available from t-butylperoxylation of 2-alkylcycloalkanones, gave 2-t-butylperoxy-1-cycloalkanol derivatives quantitatively, thermal decomposition of which with or without an acid afforded 1,n-diketones (n=5-8) in excellent yields.
- Nishinaga, Akira,Rindo, Katsuhiko,Matsuura, Teruo
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p. 1038 - 1041
(2007/10/02)
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- Pyran Annelation: An Effective Route to a Tricyclic Dienone
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A new pyran annelation reaction was investigated. 2,6-Dimethyl-4H-pyran-4-one (2) was converted to 2((p-tolylsulfonyl)methyl)-6-methyl-4H-pyran-4-one (7) which was alkylated at the C-2 methylene position regioselectively, and the p-tolylsulfonyl group can be easily eliminated with an aluminium amalgam reduction.On the other hand the pyran-4-one ring was easily transformed into an 1,5-diketone derivative.By joining and applying these selective alkylations and transformations, tricyclic dienone 22 was effectively synthesized from 2.
- Yamamoto, Makoto,Iwasa, Seiji,Takatsuka, Kenichi,Yamada, Kazutoshi
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p. 346 - 349
(2007/10/02)
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- ON THE SYNTHESIS OF 1,n-DIKETONES USING MONO-SUBSTITUTED DERIVATIVES OF TOSYLMETHYL ISOCYANIDE
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A new method is described for the synthesis of symmetrical and unsymmetrical diketones.Particularly good results are obtained in the synthesis of 1,6- and 1,5-diketones.Procedures are reported for 1,2-diketones.The moderate results obtained for 1,4-diketones and the lack of success for 1,3-diketones are discussed.
- Leusen, Albert M. van,Oosterwijk, Roelof,Echten, Erik van,Leusen, Daan van
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- Functionalisation of Saturated Hydrocarbons. Part 3. The Oxidation of 3β,5α,6β-Triacetoxycholestane using the Gif System
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The minor products from the oxidation of 3β,5α,6β-triacetoxycholestane using the Gif System have been identified.The nature of the side-chain fragmentation to give 20-ketones has been clarified.Some mechanistic explanation has been offered for this unusual process.
- Barton, Derek H. R.,Goektuerk, A. Kayhan,Jankowski, Krzysztof
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p. 2109 - 2118
(2007/10/02)
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- Oxidation by cobalt(III)acetate. Part 9. Effect of substituents on the oxidative Cleavage of glycols in acetic acid
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The kinetics of oxidative cleavage of glycols by obalt(III) acetate in acetic acid have been studied.The substrates examined include cis- and trans-cyclopentane- and cyclohexane-1,2-diols and their mono- and dimethyl derivatives.The rates were first-order in both cobalt(III)acetate and substrate in all cases.In the oxidation of five-membered ring diols, cis-diols were generally oxidized faster than the trans-isomers.Complex results were obtained in the case of six-membered ring diols.Thermodynamic parameters were calculated for all the substrates.A mechanism involving a bidente complex of cobalt(III) acetate dimer and glycol is sugge sted, except for the case of trans-cyclopentane-1,2-diols, for which a monodentate intermediate is proposed.
- Gunji, Tomokazu,Hirano, Masao,Morimoto, Takashi
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p. 1827 - 1832
(2007/10/02)
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- Organosulfur Chemistry. II. Use of Dimethyl Sulfoxide; a Facile Synthesis of Cyclic Sulfides
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A versatile and short-reaction-time synthesis of twelve four-, five- and six-membered thiacycloalkanes (IIa-l)from the appropriate α,ω-dibromoalkanes (Ia-l)has been developed.Technical-grade dimethyl sulfoxide was proved to be by far the best for this cyclization.The pronounced effect for ring formation was recognized to be in order of five-membered ring (thiolanes) > six-membered ring (thianes) > four-membered ring (thietanes).Startling were 2-methylthiolane (IIf) and 2,5-dimethylthiolane (IIg; cis/trans mixture), both obtained in high yields although α-methyl - and α,α'-dimethyl substitution in general showing a remarkable retardation for cyclization.On the other hand, in both 3,3-dimethylthietane (IId) and 4,4-dimethylthiane (IIl) cyclization was much more efficient than other counterparts in each series, which is referred to as the gem-dimethyl effect.Keywords: thiacycloalkane; thietane; thiolane; thiane; dimethyl sulfoxide; cyclization: α,ω-dibromoalkane; sodium sulfide nonahydrate; refractive index
- Nagasawa, Kazuo,Yoneta, Akemi
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p. 5048 - 5052
(2007/10/02)
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- DIRECT REMOTE OXIDATION OF ALIPHATIC KETONES TO γ- AND δ-DIKETONES
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Aliphatic ketones are converted into γ- and δ-diketones in onepot oxidation reaction on treatment with Na2S2O8 in presence of Fe(II)ions.
- Nikishin, Gennady I.,Troyansky Emmanuil I.,Lazareva, Margarita I.
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p. 4987 - 4988
(2007/10/02)
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