Vinylcyclopropane rearrangement

What is vinylcyclopropane rearrangement?

Neureiter first reported the thermal [1,3]-sigmatropic carbon shift of vinylcyclopropanes to cyclopentenes in 1959. This reaction, also known as the vinylcyclopropane rearrangement or vinylcyclopropane-cyclopentene rearrangement, is predominantly observed because the heat of formation of cyclopentene is lower than that of vinylcyclopropane, and the activation energy for the rearrangement is lower than that of epimerization.

Vinylcyclopropane rearrangement - general reaction scheme - vinylcyclopropane-cyclopentene rearrangement
Vinylcyclopropane rearrangement (three possible reactions)

The vinylcyclopropane can undergo three types of reactions, including [1,5]-H shift, thermal isomerization, and [1,3]-sigmatropic alkyl shift. The activation energy for the rearrangement can be further lowered by an extra group on the cyclopropane ring or vinyl moiety, as well as by an additional substituent at C2.

Various activation energies for different substituents have been measured. The reaction is favored for spiral cyclic vinylcyclopropane and vinylcyclopropane with additional elements of unsaturation. However, an additional group on the vinyl moiety and at the cis-position decreases the reaction rate.

In certain bicyclic vinylcyclopropane systems, temperature-independent reactions occur, with a constant ratio of 6:4 between trans-5,6-diphenylbicyclo[3.1.0]hex-2-ene and trans-4,5-diphenylbicycl[3.1.0]hex-2-ene within a temperature range of 130–170 ΒΊC. These systems can theoretically replace each carbon atom with other atoms such as N, O, S, P, or Si, and still undergo rearrangement to form five-membered rings.

Lower activation barriers are observed in the cases of 2-vinylphosphiranes, and when a phosphorus atom coordinates with Cr(CO)5, activation energies are further reduced. Vinylcyclopropane systems can also undergo epimerization or [1,5]-H shifts to give 1,4-pentadienes or isomers. The presence of incompatible functionalities limits the use of these reactions.

References

Notes- Pyrolysis of 1,1-Dichloro-2-vinylcyclopropane Synthesis of2-Chlorocyclopentadiene
Norman Neureiter
The Journal of Organic Chemistry 1959 24 (12), 2044-2046
DOI: 10.1021/jo01094a621

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