694-92-8Relevant articles and documents
Weissberger,Page
, p. 147,151 (1977)
Gassman et al.
, p. 437 (1969)
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.
Stereoselective thermal rearrangement of syn-7-(1,2-Butadienyl)-1-methylbicyclo[2.2.1]hept-2-ene [syn-7-(3-Methylallenyl)-1-methylnorbornene]
Duncan, James A.,Hendricks, Robert T.,Kwong, Katy S.
, p. 8433 - 8442 (2007/10/02)
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.
