Thermolysis of Other Cyclobutane Derivatives

Lucchini, P. J. Kocienski, G. T. Evans, and J. Ciabattoni, Tetrahedron Letters, 1972, 

Other than a biradical mechanism. The presence of a cyano-group in a cyclobutane causes no change in mechanism in gas-phase thermolyses but it does lower the activation energy.  

Reaction of (380) with phenylethynylmagnesium bromide gives two products which were shown to be (381) and (382) spectroscopically. The assignment of configuration to (381) and (382) was based upon the quantitative thermolysis of one of the two, (382), to (383). Upon thermolysis of (381), an intermediate was obtained which was very susceptible to oxidation. In the presence of oxygen, (385) and (386) were isolated, but the details of their formation have 

The labelling experiment with (387a) showed that the mechanism is an intramolecular Diels-Alder reaction followed by a retro-Diels-Alder reaction then valence isomerization. 

Ethylene, keten, cyclopropane, and carbon monoxide were the products observed in a kinetic investigation of the pyrolysis of cyclobutanone in the temperature range 360.0—406.3 °C. The activation parameters and product analyses were better accommodated by concerted mechanisms than by reactidns through biradical intermediates. Pyrolysis of 2-propylcyclobutanone (388) gives ethylene and pent-l-ene in the ratio 3.8 1 at 350 C, and a biradical mechanism cannot easily account for this result. It is quite compatible with 

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Thermolysis of Other Cyclobutane Derivatives The kinetics of the pyrolysis of cyclobutane between 969 and 1280 K at very low pressure to give mainly ethylene have been reported, and shown to be consistent with a reaction through a 1,4-biradical. The products of the vapour-phase pyrolysis of the specifically deuteriated cis-1,2-dimethylcyclobutane (373) are shown iri Scheme Although the results are compatible with a major concerted... 

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