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Chapter 19: Problem 9

Show how to use alkylation or acylation of an enamine to convert acetophenone to the following compounds.

Short Answer

Expert verified
Question: Describe the process of converting acetophenone to an alkylated and acylated product using alkylation or acylation of an enamine. Answer: The conversion process involves three main steps: 1) Formation of the enamine intermediate, where acetophenone is reacted with a secondary amine like pyrrolidine. 2) Alkylation or acylation of the enamine intermediate, where it reacts with an alkyl halide (e.g., ethyl bromide) for alkylation or an acyl halide/anhydride (e.g., acetyl chloride) for acylation. 3) Hydrolysis and tautomerization, where the iminium ion formed in step 2 is hydrolyzed and tautomerizes to yield the final alkylated or acylated product.

Step by step solution

01

Identification of target compounds and their corresponding enamine

First, let's identify the desired compounds and their corresponding enamine: Compound 1: Acetophenone Enamine 1: Since we're converting acetophenone, there's no need to identify an enamine here. Compound 2: An alkylated product of acetophenone Enamine 2: To achieve this, we'll need to convert acetophenone to its corresponding enamine by reacting it with a secondary amine. Compound 3: An acylated product of acetophenone Enamine 3: To achieve this, we'll need to convert acetophenone to its corresponding enamine by reacting it with a secondary amine, as well. Now, let's provide the step-by-step solutions for these transformations:
02

Formation of the enamine intermediate

To form the enamine intermediate, we need to react acetophenone with a secondary amine such as pyrrolidine in the presence of a suitable acid catalyst (e.g., p-toluenesulfonic acid) under mild heating conditions. This will form the corresponding enamine, by removing a water molecule as a result of an amine reacting with the carbonyl group in acetophenone.
03

Alkylation of the enamine intermediate

For the conversion to Compound 2, we will alkylate the enamine intermediate. To do this, we will need an alkyl halide (e.g., ethyl bromide). React the enamine with the alkyl halide in a polar, aprotic solvent (e.g., DMF). The enamine will act as a nucleophile and perform a nucleophilic substitution (S_N2) reaction with the alkyl halide. This process results in an alkylated iminium ion.
04

Hydrolysis and tautomerization to the alkylated product

Following alkylation, the iminium ion will be hydrolyzed in the presence of water and an acid (e.g., HCl) to yield the hydrolyzed ketone. The imine tautomerizes to the ketone, and thus, we obtain the final alkylated product (Compound 2).
05

Acylation of the enamine intermediate

For the conversion to Compound 3, we will instead acylate the enamine intermediate. Acylation involves reacting the enamine with an acyl halide or anhydride (e.g., acetyl chloride or acetic anhydride) in a suitable solvent (e.g., DCM). The enamine will attack the acyl group, forming an iminium ion with an acyl group attached.
06

Hydrolysis and tautomerization to the acylated product

Following acylation, the iminium ion is hydrolyzed in the presence of water and an acid (e.g., HCl) to yield the hydrolyzed ketone. The imine tautomerizes to the ketone, and thus, we obtain the final acylated product (Compound 3). These step-by-step solutions demonstrate how alkylation or acylation of an enamine can be used to convert acetophenone to the desired compounds.

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