- Transition Metal-Diene Complexes. Part 4. The Crystal and Molecular Structure and Isomerization of η-Cyclopentadienyl(η-3-methoxycarbonyl-cyclohexa-1,4-diene)rhodium(I)
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Crystals of the title compound, , are monoclinic, space group I2/a with cell dimensions a=28.124(14), b=6.141(8), c=14.569(11) Angstroem, β=112.43(9) deg, and Z=8.The intensities of 1 325 reflections above background were collected by counter methods and refined to R 0.052.The rhodium atom is bonded to the five carbon atoms of the planar cyclopentadienyl ring and to the four olefinic carbon atoms of the cyclohexa-1,4-diene.The cyclohexa-1,4-diene ring is in the boat conformation with the two saturated carbon atoms lying 0.66, 0.70 Angstroem above the plane of the four olefinic carbons in a direction away from the metal.The carbomethoxy-subtituent is planar and occupies an axial position with respect to the cyclohexadiene boat.The title complex undergoes a kinetically controlled isomerization when heated in toluene or acid-free o-dichlorobenzene to a mixture of complexes containing co-ordinated 5-methoxy-carbonyl- (major product) and 2-methoxycarbonyl-cyclohexa-1,3-diene (minor product).In the presence of acid in o-dichlorobenzene the major product undergoes a secondary isomerization to the complex containing co-ordinated 1-methoxycarbonylcyclohexa-1,3-diene.For the primary isomerization a mechanism involving the formation of a hydro-η3-allylic intermediate is proposed in which the rate-determining step is a carbon-to-metal hydride-ion transfer.For the secondary isomerization, in the presence of acid, a reverse metal-to-carbon hydrogen transfer is believed to operate.
- Drew, Michael G. B.,Regan, Catrionia M.,Nelson, S. Martin
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- Substituent effects on the dehydration of arene hydrates in aqueous solution
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Rate constants have been determined by UV spectrophotometry at 25 °C for the acid-catalyzed dehydration of different types of monocyclic arene hydrates including those substituted at the 1-, 2- or 3-positions. General acid catalysis was not observed, and linear plots of pseudo-first-order rate constants for dehydration against hydronium concentration were obtained. A Hammett plot of the second-order rate constants for acid-catalyzed dehydration, kH (M-1s-1), of unsubstituted- (8a), 3-substituted (8b, 8c, 8d, 8e) and 1-substituted-benzene hydrates (14f and 14h) shows an excellent correlation with σ+ values and yields a large negative ρ-value of -6.5. The results are consistent with rate-determining formation of a benzenium ion in which direct mesomeric interaction with the substituent occurs, presumably permitted by the coplanar arrangement of the diene and carbocation centre in the intermediate. Data points for 2-substituted arene hydrates (13f, 13g, 13h, 13i) deviate negatively from the Hammett plot as direct mesomeric interaction with the substituent is not possible in the corresponding benzenium intermediates. Copyright 2013 John Wiley & Sons, Ltd. A large negative ρ-value of -6.5 is obtained in a correlation of rate constants for the acid-catalyzed dehydration of arene hydrates with σ+ values. Copyright
- O'Mahony, Michelle J.,More O'Ferrall, Rory A.,Boyd, Derek R.,Lam, Casey M.,O'Donoghue, Annmarie C.
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supporting information
p. 989 - 996
(2014/01/06)
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- Enantioselective divergent approaches to both (-)-platensimycin and (-)-platencin
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Enantioselective divergent approaches to (-)-platencin and (-)-platensimycin have been developed. A rationally designed chiral synthetic intermediate, possessing a useful α,β-unsaturated sulfone functionality, which served as a masked ketone as well as a good Michael acceptor, was successfully prepared via the highly enantioselective catalytic asymmetric intramolecular cyclopropanation (CAIMCP) developed in our laboratory. Copyright
- Hirai, Sho,Nakada, Masahisa
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experimental part
p. 518 - 530
(2011/03/19)
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- An enantioselective approach to (-)-platencin via catalytic asymmetric intramolecular cyclopropanation
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This Letter describes an enantioselective approach to (-)-platencin. A uniquely functionalized chiral intermediate, which was prepared via the highly enantioselective catalytic asymmetric intramolecular cyclopropanation (CAIMCP) that we have developed, was successfully transformed to Nicolaou's intermediate in his total synthesis of (-)-platencin.
- Hirai, Sho,Nakada, Masahisa
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scheme or table
p. 5076 - 5079
(2011/01/04)
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- Asymmetric synthesis by the intramolecular haloetherification reaction of ene acetal: Discrimination of prochiral dienes in cyclohexane systems
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A novel asymmetric synthesis of the cyclohexane derivative functionalized by some substituents has been developed from the diene acetals (1), prepared from the corresponding diene aldehyde and (+)-hydrobenzoin. The treatment of 1 with NBS in the presence
- Fujioka, Hiromichi,Kotoku, Naoyuki,Sawama, Yoshinari,Kitagawa, Hidetoshi,Ohba, Yusuke,Wang, Tsung-Lung,Nagatomi, Yasushi,Kita, Yasuyuki
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p. 952 - 957
(2007/10/03)
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- Protonated benzene: A case for structural memory effects?
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Photoionization tandem-mass spectrometry of selectively deuterium labeled precursor molecules is used to probe the structure of protonated benzene which had been questioned in a provocative publication by Mason and co-workers (J. Chem. Soc., Chem. Commun. 1995, 1027). Specifically, we address the intriguing aspect of a postulated delayed hydrogen ring-walk by modulating the internal energy content of mass-selected C6H7-nDn + ions. To this end, ionization of selectively deuterated precursors by tunable synchrotron photons is combined with chemical monitoring of H +/D+ transfer from C6H7-nD n+ to a strong base B. The resulting BH +/BD+ ratios monotonically decrease with increasing internal energy content and, due to the virtue of the regioselective deuterium label incorporations, thereby disprove a delayed hydrogen ring-walk or any other "structural memory effect" in C6H7-nD n+ ions. As a consequence, the experimental studies of Mason et al. were reconsidered using sector-field mass spectrometry. These extensive studies suggest that the previous observations might have been obscured by a combination of isobaric impurities, metastable-ion contributions, and artifact signals.
- Schroeder, Detlef,Loos, Jessica,Schwarz, Helmut,Thissen, Roland,Dutuit, Odile
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p. 9931 - 9937
(2008/04/18)
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- Half-sandwich ruthenium (II) compounds comprising nitrogen containing ligands for treatment of cancer
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Compounds which may be used in the treatment and/or prevention of cancer have the formula (I) wherein: R1, R2, R3, R4, R5 and R6 independently represents H, alkyl, —CO2R′, aryl or akylaryl, which latter two groups are optionally substituted on the aromatic ring; R′ represent alkyl, aryl or alkaryl; X is halo, H2O, (R′)(R″)SO, R′CO2— or (R′)(R″)C═O, where R″ represents alkyl, aryl or alkaryl; Y is a counterion; m is 0 or 1; q is 1, 2 or 3; C′ is C1 to C12 alkylene, optionally substituted in or on the alkylene chain, bound to two A groups; p is 0 or 1 and r is 1 when p is 0 and r is 2 when p is 1; and A and B are: each independently N-donor nitrite ligands; or B is halo and A is an N-donor pyridine ligand, optionally substituted at one or more of the carbon atoms of the pyridine ring; or p is 0, A is NR7R8 and B is NR9R10, wherein R7, R8, R9 and R10 independently represent H or alkyl, and A and B are linked by an alkylene chain, optionally substituted in or on the alkylene chain, or p is 1, A is NR7 and B is NR9R10, wherein R7, R9 and R10 are as previously defined, and A and B are linked by an alkylene chain, optionally substituted.
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- Catalytic Asymmetric C-C Bond Formation: Asymmetric Synthesis of cis-Decalin Derivatives by Palladium-Catalyzed Cyclization of Prochiral Alkenyl Iodides
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A catalytic asymmetric synthesis by the use of a Heck-type reaction has been realized for the first time, giving the cis-decalin derivative 5 in up to 46percent ee.
- Sato, Yoshihiro,Sodeoka, Mikiko,Shibasaki, Masakatsu
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p. 4738 - 4739
(2007/10/02)
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