Theory and Defination :
The Curtius rearrangement is an organic reaction used to convert an acyl azide to an isocyanate under thermal conditions. The mechanism involves were an alkyl shift of the R group from the carbonyl carbon to the closest nitrogen with the release of nitrogen gas. The release of gas drives the reaction forward and results in the formation of the isocyanate product which can potentially react further in the presence of nucleophiles in solution.The Curtius rearrangement occurs with complete retention of configuration at the migrating carbon, and the migration from the carbon to the nitrogen atom is an irreversible intra molecular reaction in first order kinetics.
The Curtius rearrangement has been used for the preparation of non-commercially available iso cyantes from a diverse assortment of carboxylic acids.In addition, this rearrangement is good for the preparation of tetrazoles, cyanamides, oxazolidones, etc. It has also been found that benzene sulfonyl azide also undergoes a similar rearrangement and gives a sulfury laniline intermediate.
General Reaction :
Mechanism :
It invilves two steps formation of azides and then decomposition.
Reaction with water to the unstable carbamic acid derivative which will undergo spontaneous decarboxylation.
Isocyanates
are versatile starting materials
Isocyanates are also of high interest as monomers for polymerization work and in the derivatisation of biomacromolecules.
Examples and Application :
The curtius rearrangement provides a way to replace a carboxyl group with amine functionality, a transformation of pronounced synthetic value. Streamlined preparation of the starting acyl azides, alternative methods that avoid isolation of these potentially unstable acyl azides altogether and improved ways to intercept the isocyanate products, including metal-catalyzed reactions, have added to the preparative utility of the curtius rearrangement.Curtius rearrangement including many excellent examples while describing some classic examples, will emphazise recent application of the reaction, including its application in synthetically challenging, highly functionalized molecular framework.
1) One-Pot Rearrangement of
Carboxylic Acids to Carbamates
2) Mild and Efficient One-Pot
Curtius Rearrangement
3) Radical Azidonation of Aldehydes
