Ch. 22 - Conjugated Systems II: Pericyclic Reactions

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Mullins 1st Edition

Ch. 22 - Conjugated Systems II: Pericyclic Reactions

Problem 22

Chapter 21, Problem 22

In each Diels–Alder reaction shown, predict the product that will result.(a)

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Identify the diene and the dienophile in the reaction. The diene should have conjugated double bonds, and the dienophile typically has an electron-withdrawing group.

Consider the stereochemistry of the diene and dienophile. If the diene is in the s-cis conformation, it can participate in the reaction. The dienophile's substituents will affect the stereochemistry of the product.

Draw the cyclic transition state of the Diels–Alder reaction. This involves a concerted movement of electrons, forming a six-membered ring.

Predict the regiochemistry of the product. Consider the electron-withdrawing and electron-donating groups on the diene and dienophile to determine the major product.

Draw the final product, ensuring to show the correct stereochemistry and regiochemistry as determined in the previous steps.

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Key Concepts

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

Diels–Alder Reaction

The Diels–Alder reaction is a [4+2] cycloaddition reaction between a conjugated diene and a dienophile, resulting in the formation of a six-membered ring. This reaction is a key method in organic synthesis for constructing cyclic compounds and is characterized by its stereospecificity and regioselectivity, meaning the orientation of substituents in the product can be predicted based on the structure of the reactants.

Conjugated Dienes

Conjugated dienes are compounds that contain two double bonds separated by a single bond, allowing for delocalization of π electrons. This delocalization enhances the stability of the diene and makes it more reactive in Diels–Alder reactions. Understanding the structure and reactivity of conjugated dienes is crucial for predicting the outcomes of these reactions.

Dienophile

A dienophile is an electron-deficient alkene or alkyne that reacts with a diene in a Diels–Alder reaction. The reactivity of the dienophile is influenced by its substituents; electron-withdrawing groups increase its reactivity, while electron-donating groups decrease it. Recognizing the nature of the dienophile is essential for predicting the product of the Diels–Alder reaction.

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General Features

Related Practice

Textbook Question

Predict the product of the following Diels–Alder reactions. Where a racemic mixture is produced, show both enantiomers and explain how each is formed.

(d)

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Textbook Question

Assuming the diene approaches the dienophile from the top, predict the product of the following Diels–Alder reactions.

(c)

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Textbook Question

What stereochemical result would you expect if the Diels–Alder reaction with the free α,β- unsaturated ketone was faster than reaction with the iminium-bound alkene?

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Textbook Question

Give the diene and dienophile that could be used to make the following Diels–Alder products.

(d)

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Textbook Question

Figure 22.16(a) <IMAGE> shows a unique example where the Diels–Alder reaction gives a single product (no enantiomers) regardless of whether the diene attacks the dienophile from the top or bottom.

(a) Show the product of the diene attacking from the bottom and confirm that the same product is obtained.

(b) What is special about this product that makes this true?

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Textbook Question

Give the diene and dienophile that could be used to make the following Diels–Alder products.

(c)

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