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Fischer indole synthesis
The Fischer indole synthesis is a chemical reaction that produces the aromatic heterocycle indole from a (substituted) phenylhydrazine and an aldehyde or ketone under acidic conditions. The reaction was discovered in 1883 by Hermann Emil Fischer. Today antimigraine drugs of the triptan class are often synthesized by this method.
The choice of acid catalyst is very important. Bronsted acids such as HCl, H2SO4, and polyphosphoric acid have been used successfully. Lewis acids such as boron trifluoride, zinc chloride, iron chloride, and aluminium chloride are also useful catalysts.
Additional recommended knowledge
The reaction of a (substituted) phenylhydrazine with an aldehyde or ketone initially forms a phenylhydrazone which isomerizes to the respective enamine (or 'ene-hydrazine'). After protonation, a cyclic [3,3]-sigmatropic rearrangement occurs producing an imine. The resulting imine forms a cyclic aminoacetal (or aminal), which under acid catalysis that eliminates NH3, resulting in the energetically favorable aromatic indole.
Methanesulfonic acid can be used as the acid catalyst in this reaction.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Fischer_indole_synthesis". A list of authors is available in Wikipedia.|