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Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
Chapter 20, Problem 42c

What starting materials are required to synthesize the following compounds, using the Fischer indole synthesis?
c. Chemical structure of an imine compound with a nitrogen atom and adjacent aromatic rings.

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1
Identify the target compound's structure and recognize that the Fischer indole synthesis involves the reaction of a phenylhydrazine derivative with a carbonyl compound (usually a ketone or aldehyde) under acidic conditions to form an indole.
Analyze the structure of the target indole compound to determine the substituents on the indole ring. This will help deduce the required phenylhydrazine derivative and the carbonyl compound.
Determine the phenylhydrazine derivative by identifying the substituents on the benzene ring of the indole. For example, if the indole has a methyl group on the benzene ring, the phenylhydrazine should have a corresponding methyl group in the same position.
Determine the carbonyl compound (ketone or aldehyde) by analyzing the substituents on the pyrrole ring of the indole. The carbonyl compound contributes the two-carbon fragment that forms the pyrrole ring.
Combine the phenylhydrazine derivative and the carbonyl compound under acidic conditions to complete the Fischer indole synthesis. Ensure the reaction conditions are appropriate for the specific substituents on the starting materials.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Fischer Indole Synthesis

The Fischer indole synthesis is a well-known organic reaction that converts phenylhydrazines and ketones or aldehydes into indoles. This reaction involves the formation of a hydrazone intermediate, which undergoes rearrangement and cyclization to yield the indole product. Understanding this synthesis is crucial for identifying the starting materials needed for specific indole derivatives.
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Phenylhydrazine

Phenylhydrazine is an organic compound that serves as a key reactant in the Fischer indole synthesis. It contains a hydrazine functional group attached to a phenyl ring, which is essential for forming the indole structure. Recognizing the role of phenylhydrazine helps in determining the appropriate starting materials for synthesizing various indole compounds.
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Rearrangement and Cyclization

Rearrangement and cyclization are critical steps in the Fischer indole synthesis, where the initial hydrazone undergoes structural changes to form the indole ring. This process involves the migration of groups and the formation of new bonds, leading to the cyclic structure characteristic of indoles. A solid grasp of these mechanisms is necessary to predict the products and starting materials in the synthesis.
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