- Stereospecific SN2' Reactions of exo-4-Substituted 3-Halogenbicyclooct-2-enes
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Stereochemically pure samples of exo-bicyclooctan-2-ol are obtained from hydrolysis followed by hydrogenation-hydrogenolysis of exo-3,4-dihalogenobicyclooct-2-enes.Attempted tosylation of the intermediate hydroxy-halides in these reactions by the Tipson procedure gave only exo-4-chloro-3-halogenobicyclooct-2-enes.No inversion of configuration was detected in the reactions of exo-3,4-dihalogenobicyclooct-2-enes with sodium halides in aprotic dipolar solvents.These results lead to the conclusion that the SN2' reaction in this system occurs upon covalent substrates with retention of relative configuration but inversion of absolute configuration.
- Maskill, H.,Wilson, Alan A.
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- BRIDGING STRAIN IN THE SOLVOLYSIS OF EPIMERIC BICYCLIC TOLUENESULFONATES
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The large variations in the rate ratios for the epimeric bicyclic p-toluenesulfonates 1 to 5 are ascribed to differential bridging strain accompanying the formation of intermediate cations.
- Grob, Cyril A.,Waldner, Adrian
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- Corner Attack on exo- and endo-Tricyclo2,4>octane by Deuteron and Mercuric Ions
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Reaction of endo-tricyclo2,4>octane (1) with deuteron in methanol-d1 gave a mixture (62:38) of methoxy ethers 3b and 4b from cleavage of the most substituted cyclopropane bond.The reaction proceeds by attack of deuterium at the corner of the cyclopropane.Trapping of the intermediate cation 5b is competitive with rearrangement to the nonclassical cation 6b.Reaction of exo-tricyclo2,4>octane (2) under similar conditions gave methoxy ether 11b, which results from rupture of an external cyclopropyl bond, and methoxy ether 12b formed from rapture of the internal cyclopropyl bond with inversion at the site of both electrophilic and nucleophilic attack.Reaction of hydrocarbon 1 with mercuric acetate in methanol gave 4-endo-(acetoxymercurio)-2-endo-methoxybicyclooctane (3c) from attack of the mercuric ion at the corner of the cyclopropane and nucleophilic attack by methanol with inversion without molecular rearrangement.Similar reaction of the exo hydrocarbon 2 gave product 12c from internal bond rupture without molecular rearrangement and with inversion of configuration at the site of electrophilic and nucleophilic attack.In addition an almost equal quantity of 11c, a product of rupture of the external cyclopropyl bond, was formed.The stereochemistry of mercuric ion and deuteron attack at C2 at the corner of the cyclopropane ring of 1 and 2 is rationalized by consideration of the symmetry and energy of the molecular orbitals involved.
- Coxon, James M.,Steel, Peter J.,Whittington, Barry I.,Battiste, Merle A.
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- Hydroalumination of alkenes by the LiAlH4*3AlBr3 system
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The hydroalumination of a series of alkenes and some fused aromatic hydrocarbons by the LiAlH4*3AlBr3 system in low-polar solvents was studied.Alkenes with mono-, di-, tri-, and tetraalkyl substituted, mono- and diaryl substituted double bonds and anthracene react at room temperature to give the corresponding dibromoaluminoalkanes in high yields.Benzylidenefluorene, tetraphenylethylene, naphthalene, and phenanthrene do not undergo hydroalumination under these conditions.Camphene, bicyclooct-2-ene, and norbornene afford the corresponding organoaluminum compounds with high stereoselectivity.Oxidation and halo- and acyldemetallation of the resulting alkyl- and arylalanes were carried out.
- Gorobets, E. V.,Shitikova, O. V.,Lomakina, S. I.,Tolstikov, G. A.,Kuchin, A. V.
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p. 1573 - 1578
(2007/10/02)
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- Rearrangements of 6-Bicyclooctyl Cations
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6-Bicyclooctyl cations were generated by nitrous acid deaminations of the amines 12, 14 and by acetolyses of the tosylates 9, 20.The major products are bicyclooctan-exo-6-ol (17), bicyclooctan-exo-2-ol (18), and bicyclooctan-2-
- Brandt, Sigrid,Kirmse, Wolfgang,Moench, Dietmar,Wroblowsky, Heinz-Juergen
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p. 887 - 893
(2007/10/02)
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- DEAMINATION OF BICYCLOOCTAN-2-YL- AND BICYCLOOCTAN-2-YL-AMINES. EVIDENCE FOR CLASSICAL PRECURSORS OF NON-CLASSICAL CARBONIUM IONS
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Bicyclo octan-2-yl- and exo-bicyclooctan-2-yl-amines have been deaminated in acetic acid by nitrous acid and via their N-phenyltriazenes; their ethyl N-nitrosocarbamates have also been solvolysed in ethanol.Product distributions by a given method from the structurally isomeric starting materials are similar to each other and to common product distribution obtained from bicyclooctan-2-yl and exo-bicyclooctan-2-yl toluene-p-sulphonates.Each amine gives, however, a small but unmistakable excess of the structurally unrearranged product compared (in the case of subtitution) with the distribution obtained from the solvolysis of the corresponding bicyclo-octyl toluene-p-sulphonates. endo-Bicyclooctan-2-ylamine has also been deaminated in acetic acid by nitrous acid and via its ethyl N-nitrosocarbamate in ethanol.The prouct ratios of these reactions are characteristically different from those of the isomric amines but, as far as substitution is concerned, are similar to what is obtained from endo-bicyclooctan-2-yl toluene -p-sulphonate.A common mechanism describes all the deaminative reactions.We propose that classical carbonium ions are the initial products of fragmentation of diazo-intermediates.These are intercepted to only a small extent to give products structurally and stereochemically characteristic of the original amines; to an even smaller extent they rearrange to isomeric classical carbonium ions, which in turn may be intercepted.The predominant reaction of the initially formed classical carbonium ions is rearrangement to non-classical isomers.From both becyclooctan-2-yl- and exo-bicyclooctan-2-yl-amines, the same unsymmetrical nonclassical carbonium ion is produced as has been implicated in the solvolysis of the corresponding toluene-p-sulphonates. endo-Bicyclooctan-2-ylamine deamination gives rise to an isomeric symmetrical non-classical carbonium ion, the same one that intervenes in the solvolysis of endo-bicyclo-octan-2-yl toluene-p-sulphonate.Symmetrical and unsymmetrical non-classical carbonium ions once formed give product ratios largely independent of their origins or modes of formation although the symmetrical one appears to undergo a small extent of isomerization to the (more stable) unsymmetrical species.These results are contrasted with those obtained from simple carbocyclic systems (without branching at the β-carbon) in which deamination and toluene-p-sulphonate solvolysis give characteristically different and unrelated product distributions.
- Maskill, Howard,Wilson, Alan A.
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p. 119 - 128
(2007/10/02)
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- Differential Bridging in the Solvolysis of Epimeric Bicyclic Sulfonates. Norbornanes, Part 17
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The solvolysis rates and products of the 2-exo- and 2-endo-norbornyl, bicyclooct-8-yl, bicyclonon-2-yl, bicyclooct-6-yl, bicyclooct-2-yl and bicyclonon-6-yl p-toluenesulfonates 10-15, respectively, are reported.The exo/endo rate ratios for these epimeric secondary tosylates in 80percent EtOH varied from 1125 for 11 to 1.6 for 15.The relative rates varied between 2278 for exo-10 and 4E-3 for endo-11.The hydrolysis products were mainly rearrenged alcohols and olefins.The unrearrenged alcohols from the exo-tosylates were formed with complete or predominant retention of configuration, whereas those derived from the endo-tosylates were mostly inverted.These results confirm the hypothesis that relative rates, as well as products, are largely determined by the degree of bridging between the cationic center and a dorsal C-atom in the transition state and in the resulting ion pairs.Since bridging is a directed bonding interaction, it is subject to the same angle and conformational strains as ordinary covalent bonds.But bridging requires less geometrical change than the formation of normal bonds and of nonclassical ions.
- Grob, Cyril A.,Waldner, Adrian,Zutter, Ulrich
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p. 717 - 729
(2007/10/02)
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- 222. Inductivity and Bridging in 2-Bicyclooctyl Cations. Polar Effects, Part II.
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The solvolysis rates and products of several 6-substituted 2-exo- and 2-endo-bicyclooctyl p-toluenesulfonates, 12 and 13, respectively, are reported.Inductivity, as measured by the reaction constants pI, is considerably less in the exo-series 12 (pI = -1.50) than in the corresponding 2-exo-norbornyl p-toluenesulfonates 1 (pI = -2.0).It is proposed that, for geometrical reasons, bridging of the cationic center C(2) by C(6) is not as strong in the bicyclooctane series 12 as it is in the norbornane series 1.On the other hand, inductivity is higher in the 2-endo-bicyclooctane series 13 (pI = -1.0) than in the corresponding 2-endo-norbornane series 3 (pI = 0.78), probably, because in the former case bridging of C(6) is less hindered by the departing anion.The relative yields of exo- and endo-substitution products from the series 12 and 13, are in accord with graded bridging of C(6) in the incipient bicyclooctyl cations.But almost constant bridging of C(2) by C(7) is indicated in the ionization of the 2-endo-bicyclooctane series 13.Consequently, in the free unsubstituted bicyclooctane cation C(2) is bridged symmetrically by C(6) and C(7), in contrast to the current concept of 'non-classical' two-electron-three-center bonding.
- Grob, Cyril A.,Sawlewicz, Pawel
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p. 1906 - 1917
(2007/10/02)
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- BRIDGING STRAIN IN BICYCLIC CARBOCATIONS
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The solvolysis rates and products of 6-exo- and 6-endo-bicyclooctyl toluenesulfonate confirm that differential bridging strain is a major factor in determining the reactivity of epimeric bicyclic sulfonates.
- Grob, Cyril A,Zutter, Ulrich
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p. 2849 - 2852
(2007/10/02)
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