Login processing...

Chapter 15: α-Carbon Chemistry: Enols, Enolates, and Enamines Back To Chapter

15.33: Alkylation of β-Ketoester Enolates: Acetoacetic Ester Synthesis

TABLE OF
CONTENTS

JoVE Core
Organic Chemistry

A subscription to JoVE is required to view this content.

Education

Alkylation of β-Ketoester Enolates: Acetoacetic Ester Synthesis

Previous Video Next Video

Previous Video
15.32: Factors Affecting α-Alkylation of Ketones: Choice of Base

Next Video
15.34: Alkylation of β-Diester Enolates: Malonic Ester Synthesis

Embed Languages Add to Favorites ADD TO PLAYLIST

TRANSCRIPT

In acetoacetic ester synthesis, β-keto esters containing acidic α protons are converted to substituted acetones in the presence of a base via an alkylated ester intermediate.

The reaction begins with an alkoxide base abstracting the α proton of the substrate to generate a nucleophilic enolate ion.

The carbanion then attacks the electrophilic carbon of the alkyl halide in an S_N2 reaction to give an alkylated ester with a new C–C bond.

Subsequent hydrolysis, followed by acidification produces a β-keto acid, which, upon heating, undergoes a concerted process and expels CO₂ to produce an enol that tautomerizes to the stable keto form of the substituted acetone.

Since in the reaction, only one proton is removed, the resulting acetone is monosubstituted.

If, however, the monoalkylated intermediate undergoes a second alkylation process, the resulting acetone will be disubstituted.

15.33: Alkylation of β-Ketoester Enolates: Acetoacetic Ester Synthesis

Acetoacetic ester synthesis is a method to obtain ketones from alkyl halides and β-keto esters. The reaction occurs in the presence of an alkoxide base that abstracts the acidic proton of the β-keto esters. The step results in an enolate ion which is doubly stabilized. The enolate then reacts with an alkyl halide via the S_N2 process to produce an alkylated ester intermediate with a new C–C bond. The hydrolysis of the intermediate, followed by acidification, results in an alkylated β-keto acid. Under high-temperature conditions, the β-keto acid undergoes decarboxylation to form a ketone. However, if the alkylation is repeated before hydrolysis and decarboxylation steps, a disubstituted ketone is obtained.

Tags

Alkylation Î²-ketoester Enolates Acetoacetic Ester Synthesis Ketones Alkyl Halides Î²-keto Esters Alkoxide Base Enolate Ion SN2 Process Alkylated Ester Intermediate C-C Bond Hydrolysis Acidification Alkylated Î²-keto Acid Decarboxylation High-temperature Conditions Disubstituted Ketone

X

Simple Hit Counter