- 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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- 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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- 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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- 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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