Abstract
The thermolysis of the 1:1-cycloadduct 3, synthesized by the addition of cyclopentadienequinone (1) and 3-methyl-2,4-diphenyl-5-oxazolone (2), yields 5,6-dihydro-2-methyl-1,3-diphenyl-2H-isoindol-4,7-dione (5) and not the tetracyclic ketone 4 (cf. [2]). The structure of 5 is elucidated by spectral data and by dehydrogenation to the 2H-isoindole-4,7-dione 6.