- 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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- Rearrangements of carbocation sulfinate ion pairs
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The chirality of alkyl p-toluenesulfinates and of 18O-labeled p-toluenesulfinate ions was utilized to study the stereoselectivity of ion-pair recombinations. The diastereomers of 2-norpinyl (13), 2-norbornyl (16), 2-methyl-2-norbornyl (25), and exo-4-protoadamantyl (34) p-toluenesulfinates were rearranged in formamide or trifluoroacetic acid (TFA). Solvolysis competed to a minor extent. Predominant return of the carbocations to the oxygen atoms of ArSO2- was observed if the isomeric p-toluenesulfinates persisted (kinetic control). On repeated ionization (thermodynamic control), sulfones were eventually formed. With the exception of 25, 1,2 shifts of the p-toluenesulfinate anion proceed faster than oxygen exchange. The migration origin of the carbocation returns preferentially to the oxygen atom of ArSO2- from which the migration terminus departed. Conversely, the sulfinate anion discriminates between positions 1 and 2 of the symmetrical, bridged 2-norbornyl cation in favor of the carbon atom from which it departed. The selectivity of ion-pair recombination decreases in the order 2-norpinyl = 4-protoadamantyl > 2-norbornyl > 2-methyl-2-norbornyl, i.e., with increasing stability of the carbocation. The rearrangements of 13 and 34 proved to be more selective in TFA at 0°C than in formamide at 120-130°C. The p-toluenesulfinates 13 and 34 were compared with the analogous tosylates and 3,5-dinitrobenzoates. More oxygen scrambling was observed with less nucleophilic anions (tosylate ? p-toluenesulfinate > 3,5-dinitrobenzoate). Oxygen scrambling is also enhanced if the anion migrates over a longer distance (2-norpinyl → exo-2-norbornyl vs. 2-norpinyl → endo-2-norbornyl). Wiley-VCH Verlag GmbH, 1997.
- Herpers, Ekkehard,Kirmse, Wolfgang
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p. 2031 - 2041
(2007/10/03)
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- Solvolytic Elimination Reactions of Tertiary α-CSNMe2-Substitutedd Systems
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The tertiary benzylic α-CSNMe2-substituted p-nitrobenzoates and trifluoroacetates of general structure Ar(CH3)C(CSNMe2)(OCOR), 7 and 8, solvolyze to give exclusively elimination products H2C=C(CSNMe2)Ar.A Hammett study gave a nonlinear correlation.Variation in rate with solvent ionizing power was small for the unsubstituted trifluoroacetate derivative of 8, and the β-CD3 isotope effect on rate was negligible.There is, however, a large isotope effect (2.5-2.8) in formation of the elimination product when Ph(CH2D)C(CSNMe2)(OCOCF3) solvolyzes.It is concluded that an intermediate must be involved sine the product-determining step and the rate-determining step have differing isotope effects.The likely intermediate is an α-CSNMe2-substituted cation as an ion pair), despite the fact that the reaction has few characteristics of a typical E1 reaction.Tertiary noorbornyl, cyclohexyl, and 2-propyl α-CSNMe2-substituted systems also react to give exclusively elimination products at rates far in excess of α-CONMe2 analogues.It is suggested that α-CSNMe2 cations are also intermediates and that these cations undergo proton loss at an early ion pair stage.These cations are proposed to derive substitantial stabilization by charge delocalization onto sulfur of the thiocarbonyl group. By way of contrast, the secondary system CH3CH(CSNMe2)(OCOCF3), 25, solvolyzes to give mainly a rearranged product CH3CH(CONMe2)(SCOCH3) via a KΔ mechanism involving neighboring thiocarbonyl participation leading to a cyclized ion.
- Creary, Xavier,Hatoum, Holia N.,Barton, Angela,Aldridge, Timothy E.
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p. 1887 - 1897
(2007/10/02)
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- Stereoselective thermal rearrangement of syn-7-(1,2-Butadienyl)-1-methylbicyclo[2.2.1]hept-2-ene [syn-7-(3-Methylallenyl)-1-methylnorbornene]
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The synthesis and separate thermal rearrangements of (±)-(1R*,4S*,7S*)-7-[(R*)-1,2-butadienyl]-1- methylbicyclo[2.2.1]hept-2-ene (8a) and (±)-(1R*,4S*,7S*)-7-[(S*)-1,2-butadienyl]-1- methylbicyclo[2.2.1]hept-2-ene (8b) are described. Both 8a and 8b are shown to rearrange to (±)-cis-1-ethylidene-3a,4,5,7a-tetrahydro-6-methylindene (9) and (±)-cis-1-ethylindene-3a,4,5,7a-tetrahydro-3a-methylindene (10) with greater than 90% stereoselectivity. Epimer 8a gives predominantly (E)-9 and (Z)-10, whereas 8b gives predominantly (Z)-9 and (E)-10, results consistent with either a six-electron [σ2s + π2s + π2s] Cope or eight-electron [σ2s + π2s + (π2s + π2a)] augmented Cope process. Stereochemical assignments (8a vs 8b, (E)-9 vs (Z)-9, and (E)-10 vs (Z)-10) are based upon experiments in nuclear Overhauser effect (NOE) difference spectroscopy.
- Duncan, James A.,Hendricks, Robert T.,Kwong, Katy S.
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p. 8433 - 8442
(2007/10/02)
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- THE PHOTOCHEMICAL NUCLEOPHILE-OLEFIN COMBINATION, AROMATIC SUBSTITUTION REACTION (PART 2): METHANOL-CYCLIC OLEFINS, 1,4-DICYANOBENZENE
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Direct irradiation of acetonitrile-methanol (3:1) solutions of 1,4-dicyanobenzene and the cyclic olefins, cyclohexene, 1-methylcyclohexene, norbornene, and 2-methylnorbornene, leads to formation of regio- and stereoisomers of the 1:1:1 (alcohol : olefin : aromatic) adducts.This reaction can be photosensitized by electron transfer; addition of electron donors, biphenyl or phenanthrene, to the irradiation mixture generally increases the efficiency and yield of adduct formation.The efficiency of the reaction and the ratio of isomeric adducts are also affected by the addition of salts, particularly magnesium perchlorate.All of the possible regio- and stereoisomers from cyclohexene and 1-methylcyclohexene have been identified, two from cyclohexene and four from 1-methylcyclohexene.Three of the four possible isomers from norbornene were characterized; the endo, endo isomer was not detected.There are eight possible isomers from 2-methylnorbornene; six were detected and five have been isolated and identified.The two sterically hindered isomers, those having both the 4-cyanophenyl and the methoxy groups in the endo position, and exo-3-(4-cyanophenyl)-endo-2-methoxy-exo-2-methylnorbornane, were not characterized.The structures of the products were established largely on the basis of the 1H and 13C nuclear magnetic resonance spectra.The mechanism of the reaction is discussed, with emphasis on those factors that may affect the product ratio.The most striking observation is that the reaction is regioselective when magnesium perchlorate is added to the irradiation mixture.
- Arnold, Donald R.,Snow, Miles S.
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p. 3012 - 3026
(2007/10/02)
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- Pyrolysis of Three Acetates of Methylbicycloheptan-2-ols and the Parent Alcohols
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The acetates of exo-2-methyl-endo-bicycloheptan-2-ol, endo-2-methyl-exo-bicycloheptan-2-ol, and 1-methyl-exo-bicycloheptan-2-ol together the parent alcohols have been pyrolysed at several temperatures and the product distribution determined.The mechanism and direction of elimination in relation to structure are discussed qualitatively.The formation of the principal products is consistent with a concerted elimination involving a six-membered cyclic transition state.Wagner-Meerwein rearrangement occurs as a competing reaction in cases where the formation of a tertiary structure is possible at the expense of a secondary one.In the case studied a two-step reaction is considerably faster than direct pyrolysis of the secondary structure.
- Vainiotalo, Pirjo,Pohjala, Esko,Maelkoenen, Pentti
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p. 1537 - 1540
(2007/10/02)
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- Carbon Participation in the Solvolysis of Tertiary Norbornyl Derivatives. Norbornanes, Part 15. 6-Substituted 2-Methylnorbornyl 2-exo- and 2-endo-2,4-Dinitrophenyl Ethers
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The solvolysis rates and products of the tertiary 2-methyl-2-exo- and -2-endo-norbornyl 2,4-dinitrophenyl ethers; 1 and 2, (X=2,4-(NO2)2C6H3O) have been determined.The different sensitivities of the rates of these ethers to the inductive effect of substituents at C(6) indicate that graded bridging of C(2) by C(6) occurs in the ionization of the exo-ethers 1, not, however, in the ionization of the endo ethers 2.In both cases hydrolysis leads to 2-methyl-2-exo-norbornanols only.Consequently, substitution takes place with retention at C(2) in the exo-series 1 and with inversion at C(2) in the endo-series 2.It is concluded that stereoelectronic and polar effects, rather than steric bulk effets, determine the high exo/endo rate ratios of the parent norbornyl derivatives 1a and 2a.
- Grob, Cyril A.,Waldner, Adrian
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p. 2481 - 2488
(2007/10/02)
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- EPIMERIC 2-NORBORNYL CATIONS IN THE SOLVOLYSIS OF 6-exo- AND 6-endo-SUBSTITUTED 2-exo-NORBORNYL p-TOLUENESULFONATES
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Solvolysis of 6-exo- and 6-endo-substituted 2-exo-norbornyl tosylates 1 and 3, respectively, yields identical or different product mixtures depending on the inductive effect of the substituent, indicating that induction involves graded ?-participation.
- Grob, Cyril A.,Guenther, Bettina,Hanreich, Reinhard,Walder, Adrian
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p. 835 - 838
(2007/10/02)
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- Stereochemistry of acid-catalyzed cleavage of 7-chloro-1-methylnortricyclene in deuterated medium; evidence for edge protonation of nortricyclenes
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Cleavage of 7-chloro-1-methylnortricyclene (1e) in D2SO4-DOAc yields deuterated syn-7-chloro-1-methyl-exo-2-norbornyl acetate (3a-d) (1.04 excess d per molecule) and deuterated anti-7-chloro-1-methyl-exo-2-norbornyl acetate (3b-d) (1.28 excess d per molecule) as the kinetic products. 1H and 2H nuclear magnetic resonance spectroscopic analysis of the corresponding alcohols complexed with Eu(fod)3 shows the deuterium is located endo at C-6 and in the methyl group of the syn-7-chloroacetate, endo at C-6 and C-2, at C-7, and in the methyl group of the anti-7-chloroacetate.That the deuterium at C-6 of both acetates is 80-90percent stereochemically pure endo, in our view, establishes that the bond farthest removed from the electron-withdrawing chlorine is preferentially cleaved via edge deuteronation.
- Werstiuk, Nick Henry,Cappelli, Frank Peter
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p. 1725 - 1737
(2007/10/02)
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- RATE OF REACTION OF ORGANIC ACIDS WITH UNSATURATED BRIDGED BICYCLIC HYDROCARBONS
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The rate constants were determined for the addition of acetic acid and trifluoroacetic acid to 15 unsaturated hydrocarbons with the bicycloheptane, bicyclo- and bicyclooctane, and cyclohexene structures.The reactivity of the compounds
- Bobyleva, A. A.,Belikova, N. A.,Dzhigirkhanova, A. V.,Plate, A. L.
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p. 797 - 804
(2007/10/02)
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