Fischer indole synthesis

The Fischer indole synthesis is a name reaction in organic chemistry, which was first described in 1883 by Emil Fischer. The Fischer indole synthesis is used for the production of indoles. This is done by heating of hydrazines and ketones ( or aldehydes ) in the presence of an acid catalyst:

Reaction mechanism

The mechanism was first described by Robinson and GM R. Robinson, consists of several steps. In the first step phenylhydrazine 1 reacts with a ketone (or aldehyde). Here, the phenylhydrazone 6 forms elimination of water. 6 and 7 are in the enamine tautomeric equilibrium. It follows on a [3,3 ] sigmatropic rearrangement. This causes the formation of a CC bond to form the quinoid compound 8 is followed by the re-aromatization, with an aromatic amine 9 is formed. After an internal nucleophilic attack to form an aminal 10 After the acid-catalyzed elimination of ammonia and deprotonation, the desired indole produced 13