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 give substituted quinoline-4-carboxylic acids.^[1][2]

Several reviews have been published.^[3][4][5]

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Reaction mechanism

The reaction of isatin with a base such as potassium hydroxide hydrolyses the amide bond to give the keto-acid 2. This intermediate can be isolated, but is typically not. 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 quiniline (5).

Variations

Halberkann variant

Reaction of N-acyl isatins with base gives 2-hydroxy-quinoline-4-carboxylic acids.^[6]

References

See also

• Camps quinoline synthesis
• Friedländer synthesis
• Niementowski quinazoline synthesis