Ozonolysis of the pyrrolidinediones 4 afforded the pyrrolidinetriones 5, which in the presence of Lewis acids were converted into maleimide 6. Analogously, ozonolysis of the pyrrolidinones 7 gave the pyrrolidinediones 8, which were converted into the pyridinetriones 11a, b via Lewis acid catalyzed isomerization to yield the trihydroxypyridones 10 and ensuing air oxidation. In solution two tautomeric