Capitalizing on in situ activation with the cyclic phosphonic anhydride PPAA (1), the conversion of carboxylic acids into hydroxamic acids has been reduced to an experimentally simple one-pot operation that addresses the issue of polyacylation without resorting to a large excess of hydroxylamine or to protection. Scope and selectivity were satisfactory with a wide range of substrates, including α, β-unsaturated acids and hydroxyacids.
