Cycloaddition reactions of quinoneimine N-oxides and of fluorenoneimine N-oxide: exocyclic nitrones conjugated with electron-withdrawing rings

Abstract

N-Phenyl-p-benzoquinoneimine N-oxide is generally unreactive in 1,3-dipolar cycloaddition reactions, but with acetylenedicarboxylate esters it gives indolones, formed from the initial adducts by a rearrangement which entails an alkoxycarbonyl migration. The analogous nitrone derived from anthraquinone gives unrearranged adducts with a variety of 1,3-dipolarophiles; monosubstituted alkynes and alkenes give 4-substituted-isoxazolines and -isoxazolidines. Fluorenoneimine N-oxide behaves similarly. We also describe some reactions of diphenylcyclopropenone which were performed in an attempt to prepare cyclopropenoneimine N-oxides.