The Fischer indole synthesis uses a protic or Lewis acid catalyst to convert a phenylhydrazine and an aldehyde or ketone to an indole. The phenylhydrazine makes an iminium ion with the carbonyl compound, which tautomerizes to the ene-hydrazine. A [3,3]-sigmatropic rearrangement disrupts the aromatic ring, but a subsequent proton transfer restores it. Cyclization (5-exo-trig), followed by loss of ammonia produces the indole system.
- Reagents: Protic or Lewis Acid Catalyst
- Reactant: Phenylhydrazine or Derivative, Aldehyde or Ketone
- Product: Substituted Indole
Mechanism
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Related Reactions
- Gewald Reaction
- Synthesis of Indoles
