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Chapter 19: Problem 77

Using your roadmaps as a guide, show how to convert cyclohexane and ethanol into racemic ethyl 2-oxocyclopentanecarboxylate. You must use ethanol and cyclohexane as the source of all carbon atoms in the target molecule. Show all reagents and all molecules synthesized along the way.

Short Answer

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Question: Describe a synthesis of racemic ethyl 2-oxocyclopentanecarboxylate using cyclohexane and ethanol as starting materials. Answer: The synthesis involves 4 steps: 1) Ring contraction of cyclohexane to cyclopentene using H2O2, a metal catalyst, CrO3, H2SO4, and selenium; 2) Formation of cyclopentanone via ozonolysis with reductive workup (H2O2); 3) Introduction of carboxylate group through Baeyer-Villiger oxidation using m-chloroperbenzoic acid (mCPBA); 4) Formation of racemic ethyl 2-oxocyclopentanecarboxylate by esterification of the resulting lactone using ethanol and concentrated H2SO4.

Step by step solution

01

Ring contraction of cyclohexane to cyclopentene

To transform cyclohexane into a five-membered ring, we can perform a ring contraction by oxidizing the cyclohexane to cyclohexanol, then converting it to cyclohexanone, and finally to cyclopentene via a rearrangement. The reagents and reaction conditions needed for these reactions are H2O2 and a metal catalyst for the selective oxidation to cyclohexanol, chromic anhydride (CrO3) in sulfuric acid (H2SO4) for oxidation from cyclohexanol to cyclohexanone, and a molecular rearrangement using selenium (Se) for the conversion from cyclohexanone to cyclopentene.
02

Formation of cyclopentanone

With cyclopentene as an intermediate, we can now introduce a carbonyl group at position 2 by performing the ozonolysis reaction. Ozonolysis involves the reaction of the C=C bond with ozone, followed by reductive or oxidative workup to yield the desired product. In this case, we will use reductive workup (H2O2) in order to prevent over-oxidation of the product. This will give us cyclopentanone.
03

Introduction of the carboxylate group

To introduce the carboxylate group, we will perform a Baeyer-Villiger oxidation on cyclopentanone. This reaction involves the use of a peroxyacid, such as m-chloroperbenzoic acid (mCPBA), to oxidize the carbonyl carbon of the ketone, leading to an ester product. In this case, mCPBA will form a lactone (2-oxocyclopentanecarboxylic acid) as the product.
04

Formation of ethyl 2-oxocyclopentanecarboxylate

The final step of the synthesis involves converting the lactone (2-oxocyclopentanecarboxylic acid) into the racemic ethyl ester, ethyl 2-oxocyclopentanecarboxylate, using ethanol as the source for the ethyl group. This can be achieved by performing an esterification reaction of the lactone with ethanol in the presence of an acid catalyst, such as concentrated sulfuric acid (H2SO4). The reaction will yield a racemic mixture of the ethyl 2-oxocyclopentanecarboxylate product. By following these four steps, we have successfully converted cyclohexane and ethanol into racemic ethyl 2-oxocyclopentanecarboxylate, fulfilling the requirements of the given exercise.

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Most popular questions from this chapter

Write a mechanism for the hydrolysis of the following iminium chloride in aqueous HCl.

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