- Scope, limitations and mechanistic aspects in the selective homogeneous palladium-catalyzed reduction of alkenes under transfer hydrogen conditions
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A new and efficient mild Pd/P(t-Bu)3 catalyst for selective reduction of various alkenes under transfer hydrogen conditions has been developed leading to the corresponding saturated derivatives in chemical yields varying from 65 to 98%. Mechanistic rationale of this reaction has been also demonstrated.
- Brunel, Jean Michel
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p. 3899 - 3906
(2008/02/03)
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- Synthesis and transformation of 5- and 2-methyl-bicyclo[2.2.1]hept-2-enes and 2-methylenebicyclo[2.2.1]heptane with retrospective δ-migration of hydrogen over oxide catalyst
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5- and 2-Methylbicyclo[2.2.1]hept-2-enes and 2-methylenebicyclo[2.2.1] heptane were synthesized by a new procedure, and their transformations in a flow system over stationary layer of aluminosilicate catalyst were studied at various temperatures. At 15-400°C these compounds undergo isomerization which is accompanied by δ-migration of hydrogen. The isomerization mechanism is discussed in terms of formation of classical carbocations, not invoking nonclassical carbenium ion.
- Gasanov
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p. 947 - 951
(2007/10/03)
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- Thermal rearrangement of 7-methylbicyclo[3.2.0]hept-2-ene: An experimental probe of the extent of orbital symmetry control in the [1,3] sigmatropic rearrangement
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The gas-phase thermal rearrangement of exo-7-methylbicyclo[3.2.0]hept-2-ene yields almost exclusively 5-methylnorbornene products. Inversion (i) of configuration dominates this [1,3] sigmatropic shift although some retention (r) is also observed. Because the [1,3] migration can only occur suprafacially (s) in this geometrically constrained system, the si/sr ratio of 7 observed for the migration of C7 in exo-7-methylbicyclo[3.2.0]hept-2-ene indicates that the orbital symmetry rules are somewhat permissive for the [1,3] sigmatropic migration of carbon.
- Bender, Jared D.,Leber, Phyllis A.,Lirio, Ruel R.,Smith, Randall S.
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p. 5396 - 5402
(2007/10/03)
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- Bicyclo[2.2.1]heptane-2-methanol Transformations on oxide catalysts
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Bicyclo[2.2.1]heptane-2-methanol was synthesized by hydrogenation of bicyclo[2.2.1]hept-5-ene-2-methanol in a flow system on fixed-bed oxide catalysts, and its transformations were studied. Dehydration and isomerization of bicycloheptene structure with the double-bond migration were found to be the main transformation routes. Thus, 2-methylenebicyclo[2.2.1]heptane (norcamphene), the product of dehydration, was obtained with 47.2 or 61.0% yield in the presence of γ-Al2O3 or aluminosilicate, respectively. The majority of norcamphene was isomerized to give bi- and monocyclic unsaturated hydrocarbons differing in position of the double bond.
- Gasanov,Alieva,Musaev
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p. 272 - 274
(2007/10/03)
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- Substituent Effects on 1H Chemical Shifts I-Complete 1H Chemical Shift Assignments of Methyl-Substituted Cyclic Systems
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1H chemical shift assignments are presented for 2-methyladamantane, 2-methylnorbornane (endo and exo) and 2-methylnorbornene (endo and exo).Resonance assignment was achieved using a variety of 1D and 2D homo- and heteronuclear (1H-13C)experiments.The methyl group-induced substituent chemical shift (SCS) is derived and the SCS of protons vicinal to this group is discussed.KEY WORDS Norbornanes Norbornenes Adamantanes 1H NMR Substituent chemical shifts
- Fisher, Julie,Gradwell, Michael J.
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p. 338 - 346
(2007/10/02)
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- Rearrangement and Cleavage of the Grignard Reagent from 5-(Chloromethyl)norbornene
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The Grignard reagents 1-Mg and 2-Mg from endo- and exo-5-(chloromethyl)norbornene rearrange with ring cleavage on heating to yield an allylcyclopentenyl organomagnesium compound (3-Mg).This, in turn, undergoes competitively a variety of reactions, including an alternative cyclization to a bicyclooctene organomagnesium (4-Mg) and formal loss of hydrogen or propene to produce allylcyclopentadienyl- (5-Mg) and cyclopentadienylmagnesium compounds.Endo and exo isomers 1-Mg and 2-Mg rearrange at comparable rates and are partially interconverted, probably via their cleavage and recyclization.Mechanistic possibilities are discussed.
- Hill, E. Alexander,Hsieh, King,Condroski, Kevin,Sonnentag, Heidi,Skalitzky, Donald,Gagas, Donald
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p. 5286 - 5292
(2007/10/02)
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- Chiroptical Studies of Bicyclic α-Diketones
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On the basis of crystallographic analysis it was established that the α-diketone chromophore in bicycloheptane-2,3-diones is planar.C. d. studies of some bicyclic compounds show that the c. d. sign for long-wavelength transition is governed by the octant rule with signs opposite to that known for ketones.The vicinal effect of substituents with the same location in space strongly influences the magnitude of the Cotton effect, but not its sign.
- Polonski, Tadeusz,Dauter, Zbigniew
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p. 1781 - 1788
(2007/10/02)
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- Die Hydrolyse von 6exo-substituierten 2exo- und 2endo-Norbornylestern der p-Toluolsulfonsaeure
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Hydrolysis of the 6exo-substituted 2exo- and 2endo-norbornyl p-toluenesulfonates 1b-l and 2b-l, respectively, in 70percent dioxane led to different amounts of the following products: Unrearranged 2exo-norbornanols 3 and norbornenes 5, accompained in somes cases by small amounts of the rearranged Rendo-epimers 4 and 6 and by nortricyclenes 7.When the 6exo-substituent was a nucleophile group as in 1e-l and 2e-l, various amounts of tricyclic products were also formed by endo-cyclozation.These results show that the 2exo- and 2endo-esters 1 and 2, respectively, react by way of different intermediates.In cases where the 6exo-substituent was an n-electron donor, as in 1m-r and 2m-r, quantitative fragmentation to (3-cyclopentenyl)acetaldehyde (13) occurred.
- Fischer, Walter,Grob, Cyril A.,Sprecher, Georg von,Waldner, Adrian
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p. 928 - 937
(2007/10/02)
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- Ring-opening of Some Radicals containing the Cyclopropylmethyl System
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Mono- and bi-cyclic radicals containing the cyclopropylmethyl system are readily generated by interaction of the appropriate halides with triphenyl- or tributyl-stannane.Each radical studied underwent ring-opening by fission of the more substituted βγ-bond.In the case of the secondary radical (12b) the new double bond was formed preferentially in the trans-configuration.Rate constants, which cannot be determined with high accuracy by this method, lie in the range 1E7-3E8 s-1 at 25 deg C.When generated by the flow method in the e.s.r. cavity α-hydroxycyclopropylmethyl radicals undergo β-fission followed by 1,5-hydrogen atom t ransfer to afford enoxyl radicals.The latter reaction occurs more slowly in water than in non-polar solvents.The rigid hydroxynortricyclyl (43) undergoes preferential fission of the less substituted βγ-bond, possibly because of the dipolar nature of the transition state.
- Beckwith, Athelstan L. J.,Moad, Graeme
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p. 1473 - 1482
(2007/10/02)
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