Thermal bridgehead double inversion of the 6-methylene-and 6-ethylidene-2-methylbicyclo(3. 1. 0) hexanes and related materials. Rotational kinetic deuterium isotope effects and the mechanism of the thermal interconversion of cis- and trans-2,3-dimethylmethylenecyclopropanes via orthogonal and planar trimethylenemethane singlet biradicals
Endo- and exo-2-methyl-6-methylenebicyclo(3.1.0)hexane (N and X) interconverted at 164/sup 0/C at a rate comparable to that for cis to trans isomerization of the 2,3-dimethylmethylenecyclopropanes (C and T) allowing the possibility that the planar trimethylenemethane singlet is responsible for the racemization observed with optically active T. Pyrolysis of the four 2-methyl-6-ethylidenebicyclo(3.1.0)hexanes revealed an average of 8 percent preservation of the exo ethylidene stereochemistry in the bridgehead double inversion reaction. The kinetic deuterium isotope effect on the interconversion of endo- and exo-6,2-methyl-6-dideuteriomethylenebicyclo(3.1.0)hexanes, k/sub H/sub 2///k/sub D/sub 2// = 1.08 +- 0.02, suggests that exo methylene rotation occurs after rate-determining formation of a planar trimethylenemethane biradical since exo methylene rotation in the formation of anti- and syn-2-methylethylidenecyclopropane from trans-2,3-dimethyldideuteriomethylenecyclopropane has an isotope effect of 1.31 +- 0.04. Detailed mechanisms for the stereochemical and kinetic data from pyrolysis of T and C which involve mainly orthogonal and, to a lesser extent, planar or bisorthogonal trimethylenemethane biradicals are presented. The origin and magnitude of rotational kinetic isotope effects in these interconversions is discussed.
- Research Organization:
- Indiana Univ., Bloomington
- OSTI ID:
- 7087556
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 99:17
- Country of Publication:
- United States
- Language:
- English
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