Baeyer indole synthesis
The Baeyer-Indole-Synthesis or Baeyer-Emmerling-Indole-Synthesis is a name reaction of organic chemistry . It is the synthesis of indoles from ortho - nitro cinnamic acid . This leads to an alkaline reduction of the nitro group by iron .
The reaction was first reported in 1869 by the German chemists Adolf von Baeyer (1835–1917) and Adolph Emmerling (1842–1906).
Overview reaction
During the synthesis, the ( E ) - o -nitrocinnamic acid ( trans - o -nitrocinnamic acid) is reduced. As a product, indole is obtained:
The reaction works analogously with ( Z ) - o -nitrocinnamic acid ( cis - o -nitrocinnamic acid).
The blue marked bond in the product is the newly formed carbon - nitrogen bond, which leads to ring closure.
Reaction mechanism
The following reaction mechanism is described in the literature:
First, the o -nitrocinnamic acid is reduced by the iron. In addition, a potassium salt is formed, and anion 1 is obtained as an intermediate . In the second step, protonation occurs , whereby the protons come from the water molecules. The nitroso compound 2 is formed by the subsequent elimination of water . Then there is a further reduction by iron. In the anion 3 , electron rearrangements lead to ring closure. Intermediate stage 4 is obtained by the protonation that follows . In this, a water molecule leads to the regression of the carboxy group and the carboxylic acid 5 is formed . In the next two steps, electron rearrangements result in the splitting off of a carbon dioxide and water molecule, whereby the molecule 6 is formed. In the last step, isomerization takes place and indole 7 is obtained as the product .
Individual evidence
- ^ A b Zerong Wang: Comprehensive Organic Name Reactions and Reagents , Wiley, 2010, ISBN 9780470638859 , pp. 140-143, doi: 10.1002 / 9780470638859 .
- ↑ A. Baeyer and A. Emmerling: Synthesis of the Indole In: Reports of the German Chemical Society. 2, 1869, pp. 679-682, doi: 10.1002 / cber.186900201268 .