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

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 degrees 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. (C) 1998 Elsevier Science Ltd. All rights reserved.