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Note: On this page you can also find  quasi-Favorskii rearrangement and Wallach degradation.


* The Favorskii rearrangement is the base catalyzed rearrangement of enolizable α-haloketones or cyclopropanones to carboxylic acids or their derivatives.

The α-haloketones must contain acidic α'-hydrogens.

 favorskii rearrangement 1-1


* In Favorskii rearrangement, the esters are formed if alkoxides are used as bases. Whereas the amides are formed when amines are used as bases.

* The Favorskii rearrangement of α-halo cyclic ketones results in ring contraction.



* Initially, the α'-carbon is deprotonated to generate an enolate ion which is followed by intra molecular nucleophilic substitution to give a cyclopropanone by ring closure.

* Thus formed cylcopropanone undergoes nucleophilic addition by a base at the carbonyl carbon which is followed by the cleavage of the CO-Cα bond. Usually the cleavage occurs so as to give less substituted and more stable carbanion.

 favorskii rearrangement 1-2


1) In the following Favorskii rearrangement, 2-Chlorocyclohexanone can be converted into ethyl cyclopentanecarboxylate by treating with sodium ethoxide. The six membered ring is contracted to the five membered one.

favorskii rearrangement 1-3


2) 3-Bromobutan-2-one yields 2-methypropanoic acid as major product when treated with alkali. The ring opening of cyclopropanone derivative occurs to give less substituted carbanion. 

favorskii rearrangement 1-4


3) The α-haloketones will rearrange to amides when the Favorskii reaction is catalyzed by amines. 

favorskii rearrangement 1-5


4) Synthesis of cubane involves favoroskii rearrangement step as shown below.



5) α,α-dihaloketones or α,α'-dihaloketones rearrange to give α, β-unsaturated carboxylic acid derivatives under Favorskii conditions. For example, 1,3-Dibromobutan-2-one will give ethyl but-2-enoate when treated with sodium ethoxide.

 favorskii rearrangement 1-7


6) The rearrangement of α,α'-dihaloketones to α-hydroxycarboxylic acids, followed by oxidative decarboxylation to the ketones is known as Wallach degradation.

favorskii rearrangement 1-8 wallach degradation


7) The rearrangement of non enolizable α-haloketones in presence of bases is called quasi-Favorskii rearrangement. The synthesis of powerful pain killer Pethidine (also known as Demerol or Meperidine) makes use of this rearrangement. 

favorskii rearrangement 1-9

The quasi-Favorskii rearrangement involves no cyclopropanone intermediate and  follows a semibenzilic mechanism as shown below.

semibenzilic rearrangement favorskii rearrangement 1-10



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Author: Aditya vardhan Vutturi