Ethyl 5-oxo-2-phenyl-2,5-dihydroisoxazole-4-carboxylate (2) was photolysed at 300 nm in the presence of phenols, enols, anilines, enamines , aryl thiols and thioenols affording enamines. Treatment of these enamines with Lewis or protic acids gives the respective benzo and five- membered ring systems.
Isoxazolones unsubstituted at C3 react with lithium amides or alkyllithiums to give ketenimines . The presence of an ethoxycarbonyl group at C4 allows capture of this species by addition of a second equivalent of the lithiated species to give enolates which can be alkylated in situ. The presence of a phenyl group at C4 gives a ketenimine which reacts intramolecularly in the presence of lithium amides, whereas alkyllithiums undergo addition in synthetically useful processes.