497-35-8Relevant articles and documents
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
Gasanov
, p. 947 - 951 (2007/10/03)
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.
Rearrangements of carbocation sulfinate ion pairs
Herpers, Ekkehard,Kirmse, Wolfgang
, p. 2031 - 2041 (2007/10/03)
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.
Pyrolysis of Three Acetates of Methylbicycloheptan-2-ols and the Parent Alcohols
Vainiotalo, Pirjo,Pohjala, Esko,Maelkoenen, Pentti
, p. 1537 - 1540 (2007/10/02)
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.
