5-hydroxyisoxalidin-3-ones and acetoacetyl hydroxamates derived from diketene and N-substituted hydroxylamines and their reactions with amines and hydrazines

The direction of diketene reaction with N-substituted hydroxylamines depend s on the nature of substituent on the nitrogen atom: With benzyl- and arylh ydroxylamines, the reaction products are 5-hydroxy-5-methylisoxazolidin-3-o nes, and with arylhydroxamic acids, acetoacetyl N-arylhydroxamates (N-aceto acetyloxybenzamides). In solutions, 5-hydroxy-5-methylisoxazolidin-3-ones a re in tautomeric equilibrium with the N-hydroxyacetoacetamide form. Acetoac etyl hydroxamates are present exclusively in their linear form both in pola r and in nonpolar media. The condensation products of the latter compounds with amines and hydrazines tend to ring-chain and/or prototropic tautomeris m and configurational isomerism. The population of the tautomeric forms dep ends on the nature of the hydroxylamine component, the electronic propertie s of substituents in the amine and hydrazine components, and the nature of the solvent. Amino derivatives of N-hydroxyacetoacetamides are represented by the cyclic (5-aminoisoxazolidin-3-ones) and enamine forms; with hydrazin o derivatives, the tautomeric mixture also includes the hydrazone forms as two configurational tautomers. Electron-acceptor substituents and nonpolar solvents shift the tautomeric equilibrium to the cyclic form. Amino and hyd razino derivatives of acetoacetyl hydroxamates are present exclusively in t he enamine (enhydrazine) form as two geometric isomers.