- Tandem palladium(0) and palladium(II)-catalyzed allylic alkylation through complementary redox cycles
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Here it goes again: A tandem catalytic process effects sequential Pd 0-catalyzed allylic alkylations through leaving group ionization and PdII-catalyzed allylic alkylations by C-H activation. By employing an oxidative trigger to convert the catalytic species from Pd0 into PdII, both transformations can be conducted in a single reaction vessel using the same precatalyst. This allows for the selective introduction of otherwise indistinguishable allyl groups. Copyright
- Trost, Barry M.,Thaisrivongs, David A.,Hansmann, Max M.
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p. 11522 - 11526
(2013/01/15)
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- Unusual regioselectivity in Pd(0)-catalyzed coupling of allylic monoacetates and nitroalkanes: one-pot isomerization-alkylation
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A hitherto unknown palladium-catalyzed reaction of nitroalkanes with hydroxy allylic acetates is reported. The reaction led to the formation of γ-nitrocarbonyl compounds instead of the usual unsaturated nitroalcohol expected upon displacement of the allylic acetate group.
- Khan, Pasha M.,Bisht, Kirpal S.
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supporting information; experimental part
p. 1407 - 1410
(2010/04/25)
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- Cage escape competes with geminate recombination during alkane hydroxylation by the diiron oxygenase AlkB
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(Chemical Presented) AlkBstops the radical clock: Three structurally analogous radical-clock substrates with a large span in their rearrangement rates are hydroxylated by AlkB to afford similar amounts of rearranged (2) and unrearranged products (1). Such a result is in accord with radical rebound competing with cage escape of the geminate substrate radical. The results show that radical clocks can measure both the radical lifetime and the kinetics of cage escape.
- Austin, Rachel N.,Luddy, Kate,Erickson, Karla,Pender-Cudlip, Marilla,Bertrand, Erin,Deng, Dayi,Buzdygon, Ryan S.,Van Beilen, Jan B.,Groves, John T.
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supporting information; experimental part
p. 5232 - 5234
(2009/04/04)
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- Organic reactions in the solid state: Reactions of enclathrated 3,4- epoxycyclopentanone (= 6-oxobicyclo[3.1.0]hexan-3-one) in Tri-othymotide and absolute configuration of 4-hydroxy- and 4-chlorocyclopent-2-en-1-one
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Several aspects of the heterogeneous actions of aqueous and gaseous HCl on the chemical behavior of 3,4-epoxycyclopentanone (=6- oxablcyclo[3.1.0]hexan-3-one; 1) included in the asymmetric cages of tri-o- thymotide (TOT) clathrates belonging to space groups P3121 are described, showing specific features strikingly at variance with those observed in liquid solutions. In a first step, the substrate underwent an acid-promoted allylic isomerization, as already observed in our previous investigations, to give optically active 4-hydroxycydopent-2-en-1-one (2). In a Consecutive step, a displacement of the OH group was accomplished by the Cl- anion to afford the corresponding chloro compound 3. Polymorphism was encountered in the preparation of TOT/1 clathrates. Recrystallization of TOT in the pure guest 1 yielded micro-twinned crystals belonging to the P31 space group (host/guest ratio 1: 1), whereas the expected P3121 lattice grew from a mixture of TOT, 1 and MeOH. The structural determination of TOT/1 was carried out by X-ray diffraction (Fig. 1). Kinetic measurements were achieved that shed light on some striking features of this type of heterogeneous reactions for solid-liquid and solid-gas systems. Several reactions of pure clathrate antipodes (+)-TOT/1 with gaseous HCl were carried out under various conditions; concentration and enantiomer-excess(ee) determinations of the products 2 and 3 allowed to establish a larger ee for 3, thus demonstrating the influence of the host-guest diastereomeric association on the progression of the reaction. The correlation of optical activities of the host and products for the global reaction disclosed the sequence (+)-(M)-TOT/1 → (- )-2 → (-)-3. A new way for the preparation of 2 was devised. It was further demonstrated that the X-ray structure analysis of the chiral clathrate (M)- TOT/(+)-2 (Fig. 4) associated with chitoptical measurements was an efficient and straightforward method to determine the absolute (+)-(R)-configuration of the guest. The enantioselectivity of the TOT clathrate for 2 was established by two different methods which allowed the appraisal of an accurate revised value of the specific rotation of 2. The enclathration of 3 occurred exclusively in the orthorhombic centrosymmetric host lattice Pbca, thus prohibiting the X-ray structural determination of the guest absolute configuration. The problem of finding a pathway to the intended enantiomer enrichment of 3 was worked out through the action of aqueous HCI on microcrystalline (+)-TOT/(-)-(S)-2 that gave an optically active mixture of unreacted 2 with 3 as sole product. The pure optically active 3 was isolated by Subsequent TLC. The resolution of 3 was achieved by GC over a chiral column and its (unknown) specific rotation measured. The absolute configuration of 3 was established by the measurement of the enantiomer purity of the optically active mixture 3 obtained after the total conversion of (-)-(S)-2 in the presence of thionyl chloride in Et2O, dioxane, and benzene. It was deduced that the (-)-3 enantiomer had the (S)-configuration.
- Gerdil, Raymond,Liu, Huiyou,Bernardinelli, Gerald
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p. 418 - 434
(2007/10/03)
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- Photochemical Cycloadditions. III. Addition of 4-Substituted 2-Cyclopentenones to Allene; Configuration Determination by Lanthanide-Induced Shift Studies
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Photoaddition of 4-substituted 2-cyclopentenones to 1,2-propadiene gave mixtures of the head-to-head and head-to-tail cycloadducts in a ratio of ca. 90:10.The stereoisomeric composition was sensitive to solvent changes, as was the chemical yield of the cycloadducts.Under otherwise identical conditions the highest yields were obtained in non-polar solvents.The configurations of the cycloadducts were determined by LIS and 13C NMR studies.
- Stensen, Wenche,Svendsen, John S.,Hofer, Otmar,Sydnes, Leiv K.
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p. 259 - 268
(2007/10/02)
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- A PALLADIUM-CATALYZED ROUTE TO MONO- AND DIPROTECTED CIS-2-CYCLOPENTENE-1,4-DIOLS
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The ?-allylpalladium complex arising from cyclopentadiene monoepoxide has been shown to react with carboxylic acids and derivatives both as a nucleophile and an electrophile.This reaction represents an attractive synthetic route to protected versions of cis-2-cyclopentene-1,4-diol.
- Deardorff, Donald R.,Myles, David C.,MacFerrin, Kurtis D.
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p. 5615 - 5618
(2007/10/02)
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- A REGIO- AND STEREO-CONTROLLED SYNTHESIS OF α,β-UNSATURATED CARBONYL COMPOUNDS
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α,β-Unsaturated carbonyl compounds and butenolides are readily prepared by the rhodium(I) catalyzed isomerization of 1,3-diene monoepoxides and α-alkylidene-γ-butyrolactones, respectively.The former transformation is formally regarded as the equivalent of a regiospecific aldol condensation of an unsymmetrical ketone.
- Sato, Susumu,Matsuda, Isamu,Izumi, Yusuke
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p. 1527 - 1530
(2007/10/02)
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- A Versatile Synthesis of Four-, Five-, and Six-membered Cyclic Ketones Using Methyl Methylthiomethyl Sulfoxide
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Cyclization of 1,n-dihaloalkanes with methyl methylthiomethyl sulfoxide in the presence of a base (n-BuLi or KH) gave three-, four-, five-, and six-membered 1-methylsulfinyl-1-methylthiocycloalkanes.These cyclization products were easily converted to the corresponding ketones by acid hydrolysis except 1-methylsulfinyl-1-methylthiocyclopropane which afforded a complicated mixture.The combination of the cyclization with the acidhydrolysis thus provides a new method for synthesizing four-, five-, and six-membered cycloalkanones.Several representative preparations, such as those of substituted cyclobutanones, 3-cyclopentanone, and tetrahydro-4-pyrone are described.
- Ogura, K.,Yamashita, M.,Suzuki, M.,Furukawa, S.,Tsuchinashi, G.
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p. 1637 - 1642
(2007/10/02)
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- Reactivity and Structure of (s-cis-1,3-Diene)zirconocene Complexes
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For (s-cis-η4-diene)zirconocene complexes 1 the rates of thermal automerization as well as the reaction with carbon monoxide exhibit a comparable and pronounced dependence on substituents of the diene ligand.Based on X-ray structures of the complexes with 2,3-dimethyl- (1d) and 2,3-diphenylbutadiene (1f), this substituent effect is interpreted as arising from a different ?-bonding character of these ligands.Hydrolysis of the carbonylation products obtained from 1 yields cyclopentenones.
- Erker, Gerhard,Engel, Klaus,Krueger, Carl,Chiang, An-Pei
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p. 3311 - 3323
(2007/10/02)
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- Vinyl Epoxide Hydrolysis Reactions
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The rates of hydrolysis of cyclopentadiene oxide (3), cyclohexadiene oxide (4), cycloheptadiene oxide (5), cyclooctadiene oxide (6), butadiene oxide (7), and styrene oxide (8) have been determined as a function of pH.Each epoxide exhibited acid-catalyzed hydrolysis at low pH, and 3-5 showed significant rates for "spontaneous" reaction with solvent at intermediate pH values.The hydrolyses of several of the vinyl epoxides (4 and 5) showed kinetic terms in HO- at pH > ca. 13.Specific chloride effects attributed to nucleophilic addition of Cl- to neutral epoxide were observed for those compounds (3, 4, and 8) hydrolyzed in KCl solutions.From kinetic and product studies, mechanisms for hydrolyses of the vinyl epoxides are postulated.Acid-catalyzed hydrolyses of 3, 4, 5, and 6 were found to be A-1 in nature, proceeding via intermediate allyl cations.Product distributions depended on the structure of the cation.Mechanisms and product distributions for the spontaneous hydrolyses of vinyl epoxides were found to be variable, and dependent on the structure of the epoxide.
- Ross, Angela M.,Pohl, Terese M.,Piazza, Kathryn,Thomas, Michael,Fox, Bonnie,Whalen, Dale L.
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p. 1658 - 1665
(2007/10/02)
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- CONVERSION OF 3-CYCLOPENTENYL HYDROPEROXIDE INTO 5-SUBSTITUTED-2,3-DIOXABICYCLOHEPTANES
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3-Cyclopentenyl hydroperoxide 8 has been prepared from cyclopentadiene via hydroboration and autoxidation.Bromination of 8 followed by treatment with an appropriate silver salt has afforded the 5-substituted-2,3-dioxabicycloheptanes 11 (endo-bromo), 13 (exo-bromo), and 12 (exo-trifluoroacetoxy).
- Bloodworth, A. J.,Eggelte, H. J.
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p. 2001 - 2004
(2007/10/02)
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- Cyclic ketone mercaptal S-oxides
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Novel cyclic ketone mercaptal S-oxides and a process for preparing these compounds which comprises reacting formaldehyde mercaptal S-oxides with specific difunctional compounds.
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