Bischler-Möhlau indole synthesis

The Bischler-Möhlau indole synthesis is a chemical reaction that forms a 2-aryl-indole from a α-bromo-acetophenone and excess aniline.



Reaction mechanism
For a reaction with such simple starting materials, the reaction mechanism is surprisingly complex. The first two step involve the reaction of the α-bromo-acetophenone with molecules of aniline to form intermediate 4. The charged aniline forms a decent enough leaving group for an electrophilic cyclization to form intermediate 5, which quickly aromatizes and tautomerizes to give the desired indole 7.