Wikipedia
Lossen rearrangement
The Lossen rearrangement is the conversion of a hydroxamic acid (1) to an isocyanate (3) via the formation of an O-acyl, sulfonyl, or phosphoryl intermediate hydroxamic acid O-derivative (2) and then conversion to its conjugate base. Here, 4-toluenesulfonyl chloride is used to form a sulfonyl Ortho-derivative of hydroxamic acid.
The isocyanate can be used further to generate ureas in the presence of amines (4) or generate amines in the presence of HO (5).