Synthetic methods. Part 23. Rearrangement of some hydroxamic acids into amides. A self-condensation leading to disproportionation

Pyruvic acids have been shown to react with p-nitroso-N,N-dimethylaniline (1) to produce p-dimethyl-aminoacetanilides (3) via the corresponding hydroxamic acids (4). Three such intermediates (4a, c, d) have been isolated and their structure proved by n.m.r. and mass spectroscopy and elemental analysis. Solutions of the hydroxamic acids (4) have been shown to undergo concentration-dependent self-condensation and disproportionation leading to the amides (3) and acids (5). Rational pathways for these transformations are discussed. Spectral correlations permit differentiation between the amides (3) and the corresponding hydroxamic acids (4).