Calculations up to the MP2/6-31G*//HF/3-21G level have been carried out to study the thermal cycloreversion of 2,2,6-trimethyl-4H-1,3-dioxin-4-one (1) and 2,2,4-trimethyl-6H-1,3-oxazin-6-one (3). At this level of calculation, the enthalpy of activation for the thermal cycloreversion of dioxinone 1 was found to be 31.3 kcal/mol with zero-point vibrational energy correction. The experimental value for the reaction in solution is 30.4 kcal/mol. The enthalpy of activation for the as of yet unsynthesized oxazinone 3 was found to be 44.2 kcal/mol with zero-point correction. Contrasting with the standard view that the thermal cycloreversion of dioxinone 1 is a retro-Diels-Alder reaction is the structural information from the HF/3-21G-optimized transition state 5 which shows the plane of the acetone dienophile tilted roughly 90° to the plane of the acylketene diene.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Organic Chemistry|
|State||Published - 1995|
ASJC Scopus subject areas
- Organic Chemistry