Pfitzinger reaction

The Pfitzinger reaction (also known as the Pfitzinger-Borsche reaction) is the chemical reaction of isatin with base and a carbonyl compound to yield substituted quinoline-4-carboxylic acids.

[3][4][5] The reaction of isatin with a base such as potassium hydroxide hydrolyses the amide bond to give the keto-acid 2.

A ketone (or aldehyde) will react with the aniline to give the imine (3) and the enamine (4).

The enamine will cyclize and dehydrate to give the desired quinoline (5).

Reaction of N-acyl isatins with base gives 2-hydroxy-quinoline-4-carboxylic acids.