Bischler–Möhlau indole synthesis

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The Bischler–Möhlau indole synthesis is a chemical reaction that forms a 2-aryl-indole from an α-bromo-acetophenone and excess aniline.[1][2][3][4][5]

The Bischler-Möhlau indole synthesis

In spite of its long history, this classical reaction has received relatively little attention in comparison with other methods for indole synthesis, perhaps owing to the harsh reaction conditions that it requires. Recently, milder methods have been developed, including the use of lithium bromide as a catalyst and an improved procedure involving the use of microwave irradiation.[6][7][8]

Reaction mechanism[edit]

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.

The mechanism of the Bischler-Möhlau indole synthesis


  1. ^ Bischler, A. et al. (1892). "Ueber die Entstehung einiger substituirter Indole". Chemische Berichte 25 (2): 2860. doi:10.1002/cber.189202502123. 
  2. ^ Bischler, A. et al. (1893). "Zur Kenntniss einiger α-β- Diphenylindole". Chemische Berichte 26 (2): 1336. doi:10.1002/cber.18930260232. 
  3. ^ Möhlau, R. (1881). "Ueber die Einwirkung primärer aromatischer Aminbasen auf Acetophenonbromid". Chemische Berichte 14: 171. doi:10.1002/cber.18810140146. 
  4. ^ Möhlau, R. (1882). "Ueber Diphenyldiisoindol". Chemische Berichte 15 (2): 2480. doi:10.1002/cber.188201502204. 
  5. ^ Fischer, Emil Hermann; Schmitt, T. (1888). "Ueber Pr-2-Phenylindol". Chemische Berichte 21: 1071. doi:10.1002/cber.188802101200. 
  6. ^ Pchalek, K.; Jones, A. W.; Wekking, M. M. T.; Black, D. S. C. (2005). "Synthesis of activated 3-substituted indoles: An optimised one-pot procedure". Tetrahedron 61: 77. doi:10.1016/j.tet.2004.10.060. 
  7. ^ Sridharan, V.; Perumal, S.; Avendaño, C.; Menéndez, J. C. (2006). "Microwave-Assisted, Solvent-Free Bischler Indole Synthesis". Synlett: 91. doi:10.1055/s-2005-922760. 
  8. ^ Vara, Yosu; Aldaba, Eneko; Arrieta, Ana; Pizarro, José L.; Arriortua, María I.; Cossío, Fernando P. (2008). "Regiochemistry of the microwave-assisted reaction between aromatic amines and α-bromoketones to yield substituted 1H-indoles". Organic & Biomolecular Chemistry 6 (10): 1763. doi:10.1039/B719641E. 

See also[edit]