Bicyclo hept-2-enes thermal isomerizations

Precedence for this pathway comes from Wiberg s study of the thermal isomerization of tricyclo[4.1.0.0 ]heptane which gives bicyclo[3.2.0]hept-6-ene, which most reasonably is formed from cw,fran5-l,3-cycloheptadiene (Scheme 5.1) ... 

The reaction of 3,3-disubstituted cyclopropenes with mono- and 1,2-disubstituted alkenes proceeds only with difficulty and leads to low yields of cyclopropanes. In the case of but-l-ene, an 8% yield, with hex-1-ene and hept-l-ene between 5 and 10% yield, and with cyclooctene about 10% of the cyclopropane product is formed. In these cases, the major product is the formal dimer of the intermediate ethenylcarbene complex, i.e. the corresponding (fj-hexatriene. When copper(I) chloride is used as catalyst rather than the copper halide/phosphane or phosphite system, about half the yield of the [2-f-1] cycloadduct is obtained along with an increased amount of the hexatriene. Mechanistically, these acyclic trienes could also be formed from an (alk-l-enyl)bicyclo[1.1.0]butane intermediate without any carbene being involved. Bicyclo[1.1.0]butanes are low yield (< 20%) byproducts of the thermal dimerization reaction of methyl 3,3-dimethylcyclopropenecarboxylate (1). On the other hand, bicyclo[l. 1. Ojbutanes, such as 3, are known to undergo isomerization to form 1,3-dienes. ... 

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