Bischler–Möhlau indole synthesis

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 [de] .

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.

[11] These two researchers did not collaborate with each other, but instead independently developed very similar procedures starting from an aromatic ketone structure with an excess of some aniline and ultimately producing a product.

[10][11] The images below depict the original indole synthesis equations written by Möhlau and Bischler, respectively:

This original procedure for the indole synthesis is known to have inconsistent results and yields, but has been modified into new indole synthesis procedures: The first two step involve the reaction of the α-bromo-acetophenone with molecules of aniline to form intermediate 4.

The Bischler-Möhlau indole synthesis
The Bischler-Möhlau indole synthesis
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 ]
The mechanism of the Bischler-Möhlau indole synthesis
The mechanism of the Bischler-Möhlau indole synthesis