Spiropentane thermal rearrangement

Dolbier WR, Sellers SF (1982) J. Am. Chem. Soc. 104 2494. A review of the authors works on thermal rearrangements of gem-difluorocyclopropanes covering, inter alia, cyclopropane thermolysis, methylene cyclopropane and spiropentane rearrangements, vinyl-cyclopropane and cyclopropylcarbinyl isomerizations has been published Dolbier WR (1981) Acc. Chem. Res. 14 195... 

The thermal rearrangement of spiropentanes to methylenecyclobutanes proceeds via two successive bond cleavages. First, a peripheral bond breaks to give a 1,3-diradical 28, and then a radical bond breaks to give a 1,4-diradical 29, until ring closure yields the product(s). 

Spiropentanes undergo a thermal rearrangement to methylenecyclobutanes for the parent system is 54.5 kcal / mol. 

In analogy with the spiropentane to methylenecyclobutane rearrangement, one may expect that kinetic studies on 1-methylenespiropentane will be on interest. Thermal reactions of substituted methylenespiropen-tane have just been reported 33>. 

The thermal decompositions of several types of strained hydrocarbons produce diradicals containing the cyclopropylmethyl unit. 1,3-Diradicals of type 2 are formed on thermolysis of spiropentane (1) in the gas phase, in a sealed tube, or in a flow system. Diradical 2 not only ring closes back to spiropentane, but also rearranges by -scission to produce the new delocalized diradical 3, ring closure of which generates methylenecyclobutane 4) A competing reaction which yields allene and ethene is minor, provided the pyrolysis temperature is not allowed to rise higher than ca. 400 °C. 

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