Beckmann rearrangement

Schematic of the Beckmann rearrangement. Reagents: oxime, acid catalyst. Product: amide. Comments: The R group trans to the leaving group migrates to the nitrogen.

The Beckmann rearrangement is an organic reaction used to convert an oxime to an amide under acidic conditions. The reaction begins by protonation of the alcohol group forming a better leaving group. The R group trans to the leaving group then migrates to the nitrogen, resulting in a carbocation and the release of a water molecule. This trans [1-2]-shift allows for the prediction of the regiochemistry of this reaction. The water molecule then attacks the carbocation and after deprotonation and tautomerization results in the final amide product.[1]

Mechanism

Mechanism of the Beckmann rearrangement. [1,2]-shift, the R group trans to the leaving group migrates to the nitrogen.

References:

1.
Beckmann, E. Ber. Dtsch. Chem. Ges. 1886, 19, 988–993.