Thermal decomposition of cis-2,4-dimethyl-trans-3-vinyloxetan

Abstract

The thermal decomposition of the title compound yields penta-1,3-diene and ethanal as major products when pyrolysed in the gas phase between 326 and 384°C. This fragmentation reaction is kinetically first order and probably occurs by a biradical mechanism. Arrhenius parameters have been determined for this decomposition: log k/s^–1= 13.42±0.60–(200.3±7.5 kJ mol^–1)/RTln 10. As well as the major decomposition pathway there are several minor ones. A ring expansion reaction to yield 2,6-dimethyl-3,6-dihydro-2H-pyran and a trans–cis isomerization to trans-2,4-dimethyl-3-vinyloxetan both occur to the extent of from 2 to 3 % of the fragmentation reaction. Both these compounds are themselves thermally unstable at the reaction temperatures.

The results are compared with those reported for other oxetans and also for appropriately substituted cyclobutanes.