Cis-1,2-Divinylcyclopropane

In this compound the Cope rearrangement, which occurs with cis-1,2-divinylcyclopropane, will not produce a new compound, viz.. 

Cis-1,2-divinylcyclopropane also rearranges rapidly (Equation 12.106). The free energy of activation is 20 kcal mole-1, and A Hi is 19.4 kcal mole-1.172 The trans isomer, in contrast, rearranges only at 190°C, presumably the temperature required for its isomerization to the cis form.173... 

Ozkan, I., Zora, M. Transition Structures, Energetics, and Secondary Kinetic Isotope Effects for Cope Rearrangements of cis-1,2-Divinylcyclobutane and cis-1,2-Divinylcyclopropane A DFT Study. J. Org. Chem. 2003, 68, 9635-9642. 

The present [3 + 4] annulation methodology for the synthesis of seven-membered carbocycles involves a straightforward procedure that also provides the product functionalities (e.g., masked and unmasked ketone carbonyl and trimethylsilyl groups) that can be transformed to hitherto inaccessible or difficult-to-prepare cycloheptane structures. The prior approach,7-9 based on Cope rearrangement of cis-1,2-divinylcyclopropane, bears an intrinsic drawback in that there exist a limited number of methods for stereoselective preparation of the substrate. 

Other derivatives behave similarly making this one of the few cis-1,2-divinylcyclopropanes which does not undergo a 3,3-shift even though favorably arranged geometrically. Thermodynamic factors may be involved since the 3,3-shift product in one case has been demonstrated to revert to the tricyclo 5.4.0.0 system which then gives the 1,3-shift product (Scheme 12.21). ... 

FIGURE 20.59 The energy diagram for the Cope rearrangement of cis-1,2 -divinylcyclopropane. 

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