The Dimroth rearrangement is a rearrangement reaction taking place with certain 1,2,3-triazoles where endocyclic and exocyclic nitrogen atoms switch place. This organic reaction was discovered in 1909 by Otto Dimroth.
With R a phenyl group the reaction takes place in boiling pyridine for 24 hours
This type of triazole has an amino group in the 5 position. After ring-opening to a diazo intermediate, C-C bond rotation is possible with 1,3-migration of a proton.
Certain 1-alkyl-2-iminopyrimidines also display this type of rearrangement.
In the first step is an addition reaction of water followed by ring-opening of the hemiaminal to the aminoaldehyde followed by ring closure.
References
Dimroth rearrangement Wikipedia(Text) CC BY-SA