Thermal rearrangements of 7,7-dihalo-trans-bicyclo[4.1.0]hept-3-enes.

Article abstract of DOI:10.1016/S0040-4039(98)01110-1

Derivatives of trans-bicyclo[4.1.0]hept-3-ene with chlorine and bromine substituents the 7 position were synthesized and their thermal rearrangements were examined. Thermolysis of the dichloride leads to the formation of the cis-fused isomer, while heating the dibromide results in ring-expanded products. Thermal rearrangement of the bromochloro derivative provided a mixture of ring-isomerized and ring-expanded products. The halogenated compounds are very labile relative to the unsubstituted molecule with rate accelerations on the order of 1000 or more at 120 °C. When solvents of widely varying polarity were employed, the isomerization rate coefficients for the halogenated derivatives vary by a factor of 1.0-3.2. Therefore, it is unlikely that these compounds rearrange via ionic intermediates.