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The Bischler–Möhlau indole synthesis, also often referred to as "The Bischler Indole Synthesis[1]," is a chemical reaction that forms a 2-aryl-indole from an α-bromo-acetophenone and excess aniline; it is named after August Bischler and Richard Möhlau [2][3][4][5][6].

The general Bischler-Möhlau Indole Synthesis (Note: This image depicts, specifically, the Bischler Indole Synthesis)

In spite of its long history, this classical reaction had received relatively little attention in comparison with other methods for indole synthesis, owing to the reactions harsh conditions, poor yields and unpredictable regioselectivity. 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.[7][8][9]

History

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The Bischler-Möhlau Indole Synthesis was discovered and formulated through the separate, but complimentary, findings of German Scientist Richard Möhlau in 1882[10] and Russia-born chemist August Bischler (with partner H. Brion) in 1892[11]. While neither scientist collaborated on their indole synthesis, they both had produced very similar procedures: a starting aromatic ketone structure, an excess of some aromatic amine, and a final indole product.[10][11] The images below depict the original indole synthesis equations written by Möhlau and Bischler, respectively:

This image depicts August Bischler's original chemical description of this Indole Synthesis as it appeared in "Ueber die Entstehung einiger substituirter Indole" (including the original "=" notation, which at the time functioned as our modern "arrow" would in chemical equations).[11]
This equation depicts Richard Möhlau's original chemical description of this indole synthesis, as it appeared in "Ueber die Einwirkung primärer aromatischer Aminbasen auf Acetophenonbromid"[10]





Indole Synthesis
Bischler C6H5COCH2Br + NH3 = C8H7N +HBr + H2O
Möhlau C6H5COCH2Cl + NH3 = C6H5CNCH2 + HCl + H2O
(equation notation written as seen in the original articles)[10][11]

Being that both scientists had published their works for Indole Synthesis within the same decade, the general indole synthesis process was given the name "Bischler-Möhlau Indole Synthesis."


This original procedure for the indole synthesis is known to have inconsistent results and yields, but has been modified into new Indole Synthesis:

References

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  1. ^ "Bischler Indole Synthesis", Indole Ring Synthesis, John Wiley & Sons, Ltd, pp. 249–259, 2016-06-17, doi:10.1002/9781118695692.ch23., ISBN 978-1-118-69569-2, retrieved 2020-04-13 {{citation}}: Check |doi= value (help)
  2. ^ Bischler, Aug. (1892). "Ueber die Entstehung einiger substituirter Indole". Berichte der Deutschen Chemischen Gesellschaft. 25 (2): 2860–2879. doi:10.1002/cber.189202502123. ISSN 0365-9496.
  3. ^ Bischler, Aug.; Fireman, P. (1893). "Zur Kenntniss einiger α-β- Diphenylindole". Berichte der Deutschen Chemischen Gesellschaft. 26 (2): 1336–1349. doi:10.1002/cber.18930260232. ISSN 0365-9496.
  4. ^ Möhlau, R. (1881). "Ueber die Einwirkung primärer aromatischer Aminbasen auf Acetophenonbromid". Chemische Berichte. 14: 171. doi:10.1002/cber.18810140146.
  5. ^ Möhlau, R. (1882). "Ueber Diphenyldiisoindol". Chemische Berichte. 15 (2): 2480. doi:10.1002/cber.188201502204.
  6. ^ Fischer, Emil Hermann; Schmitt, T. (1888). "Ueber Pr-2-Phenylindol" (PDF). Chemische Berichte. 21: 1071. doi:10.1002/cber.188802101200.
  7. ^ 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.
  8. ^ 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.
  9. ^ 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.
  10. ^ a b c d Möhlau, Richard (1881-01-01). "Ueber die Einwirkung primärer aromatischer Aminbasen auf Acetophenonbromid". Berichte der deutschen chemischen Gesellschaft. 14 (1): 171–175. doi:10.1002/cber.18810140146. ISSN 0365-9496.
  11. ^ a b c d Bischler, Aug. (1892-07-01). "Ueber die Entstehung einiger substituirter Indole". Berichte der deutschen chemischen Gesellschaft. 25 (2): 2860–2879. doi:10.1002/cber.189202502123. ISSN 0365-9496.
  12. ^ Buu-Hoï, Ng. Ph.; Jacquignon, P.; Loc, T. B. (1958). "143. Carcinogenic nitrogen compounds. Part XXIV. The synthesis of indole and quinoline compounds from cyclic ketones". J. Chem. Soc. 0 (0): 738–740. doi:10.1039/jr9580000738. ISSN 0368-1769.
  13. ^ a b c "Bischler Indole Synthesis", Indole Ring Synthesis, John Wiley & Sons, Ltd, pp. 249–259, 2016-06-17, doi:10.1002/9781118695692.ch23., ISBN 978-1-118-69569-2, retrieved 2020-04-13 {{citation}}: Check |doi= value (help)
  14. ^ Blackhall, A.; Thomson, R. H. (1954). "Aromatic keto-enols. Part III. Some heterocyclic quinols". Journal of the Chemical Society (Resumed): 3916. doi:10.1039/jr9540003916. ISSN 0368-1769.
  15. ^ Japp, Francis R.; Murray, T. S. (1894). "LXXII.—Preparation of 2′ : 3′-diphenylindoles from benzoïn and primary benzenoid amines". J. Chem. Soc., Trans. 65 (0): 889–899. doi:10.1039/ct8946500889. ISSN 0368-1645.
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