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.
2,4-Diphenylisoxazol-5(2H)-one (2) has been photolysed in the presence of alcohols, amines and in inert solvents, and the products are shown to arise by two competitive singlet state photolytic processes. The minor pathway involves loss of carbon dioxide to give an imino carbene which is captured by nucleophiles: the major pathway involves isomerization to a ketene which is rapidly decarbonylated, and the resultant carbene captured by solvent. The presence of acetone or other triplet sensitizers induces a third competitive pathway involving triplet states.