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.
A number of N-arylisoxazol-5(2H)-ones (aryl = phenyl, isoquinolin-1-yl, quinolin-2-yl, 2-phenylquinazolin-4-yl and benzothiazol-2-yl) have been reacted with lithium azide to give 2-(1-aryltetrazol-5-yl)acetic esters, which have been C- methylated and hydrolysed. The resulting 2-(1-aryltetrazol-5-yl) propanoic acids had low antiinflammatory activity, as judged by inhibition of synthesis of prostaglandin PGE2 or tumour necrosis factor α.