Lossen rearrangement


The Lossen rearrangement is the conversion of an acyl hydroxamate to an isocyanate and carboxylic acid side product. The isocyanate can be used further to generate ureas in the presence of amines or generate amines in the presence of H2O.

Reaction mechanism

The acyl hydroxamate is first converted to its conjugate base. A concerted rearrangement event then occurs in which the amide substituent migrates to the amide nitrogen, the nitrogen donates a pair of electrons to form the isocyanate C=N double bond, and the N–O σ-bond breaks.