Diels-alder cycloaddition reactions of cyclopropenone ketals : Dual participation in inverse electron demand (lumo diene controlled) and normal (homo diene controlled) diels-alder reactions. Approaches to the preparation of tropones

Abstract

Diels-Alder cycloadditions of the cyclopropenone ketal 1 with representative electron-deficient, electron-rich and neutral dienes are presented. The results observed are consistent with the potential for the strained olefin of the cyclopropenone ketal to exhibit accelerated participation in both inverse electron demand (LUMO dienecontrolled) and normal(HOMO dienecontrolled) Diels-Alder reactions. Approaches to the introduction of cycloheptatrienones, tropones, based on the room temperature and pressure-promoted Diels-Alder reactions of the cyclopropenone ketal 1 are presented.