Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
The addition of difluorocarbene to bicyclo[2.2.2]octa-2,5-diene gave the exo and endo 1:1 cyclopropane adducts. In contrast to norbornadiene, no homo-1,4 adduct was formed. The adducts were thermally stable under the conditions of their formation and separation (〈170°). However, smooth equilibration was achieved on heating at 250° for 36 h. The same mixture resulted from either isomer. At 250° ΔΔG = 1.83 kcal/mol; the endo isomer being the more stable. Heating to higher temperatures caused decomposition, rather than further reaction to the intramolecular [2+2]cyclization products. The kinetic and thermodynamic product compositions were essentially the same on extrapolating to the same temperature, viz. endo/exo = 19-22 at 25°. The mechanisms by which the cyclo-addition and the stereomutation of the cis-fused cyclopropane moiety occur are discussed.
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