Abstract: Whereas the thermal reaction of the aryl methyl ketenes la and lb with 2 resulted, as anticipated, in the periselective formation of the vinylcyclobutanones 3-6, the aminium ion salt initiated cycloaddition afforded selectively the Diels-Alder products 10 and 12. The potential role of Bronsted and Lewis acids, the suitability of different one-electron oxidants, and the effect of reactant concentration, reaction time, and added neutral amines was ...
