Q59. Question: Treatment of 伪, 尾-un... [FREE SOLUTION]

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Chapter 23: Q59. (page 924)

Question: Treatment of 伪, 尾-unsaturated carbonyl compound X with base forms the diastereomer Y. Write a stepwise mechanism for this reaction. Explain why one stereogenic center changes configuration but the other does not.

Short Answer

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Answer

Stepwise mechanism for the reaction:

Step 1

Step 2

$纬$ -hydrogen is required for abstraction which is not present for other stereogenic centers. Therefore, only one stereogenic center changes configuration.

Step by step solution

Step 1: α,β- unsaturated compound

Organic compound containing two functional groups, the carbonyl group and carbon-carbon double bond are known as $伪, 尾$ -unsaturated compound

$伪, 尾 -$ unsaturated compound contains a diene skeleton

Step-wise mechanism

The stepwise mechanism for the provided reaction is shown as follows:

The base abstracts the proton from $纬$ hydrogen of $伪, 尾 -$ unsaturated compound X and gives an enolate.

Abstraction of proton

Here, the reformation of the C=O group then protonation of hydrogen at asymmetric center can result in inversion of configuration

Protonation at asymmetric center

$纬$ $纬$ -hydrogen is required for abstraction which is not present for other stereogenic center. Therefore, only one stereogenic center changes the configuration