Ketene-diene [4 + 2] cycloaddition products via cation radical initiated diels-alder reaction or vinylcyclobutanone rearrangement

Article abstract of DOI:10.1021/ja00059a010

Whereas the thermal reaction of the aryl methyl ketenes 1a and 1b 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