16. Conjugated Systems

Which of the following is the least reactive diene in a Diels-Alder reaction?

Which of the following compounds would be the most reactive as the diene in a Diels-Alder $[4+2]$ cycloaddition?

Predict the products of the following Diels–Alder reactions.

(c)

(d)

We predicted that the products would have a 1,2- or 1,4-relationship of the proper substituents. Draw the charge-separated resonance forms of the reactants to support these predictions.

(a) (b)

Which combination of diene and dienophile would react to give the following Diels-Alder product: a cyclohexene ring with a single ketone group at the $1$-position and no other substituents?

How would the following substituents affect the rate of a Diels–Alder reaction?

b. an electron-donating substituent in the dienophile

An important variation of the Diels–Alder reaction is intramolecular, in which the diene and the dienophile are connected. This type of Diels–Alder reaction makes two new rings. Draw the compound produced in each of these examples; try to predict stereochemistry (using models will help). In some cases, Lewis acid catalysts are used; that can be ignored for this problem.

(c)

The C ring of estrone (a steroid) is formed by a Diels–Alder reaction using the two reactants shown here. What is the product of this reaction?

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)

Predict the product of the following reactions. [When all of the reactions from this chapter are shown together, you must first decide which type of reaction each is. Is it a Diels–Alder, an electrocyclic, or a sigmatropic rearrangement? Drawing the product will be easier once this determination is made.]

(a)

An important variation of the Diels–Alder reaction is intramolecular, in which the diene and the dienophile are connected. This type of Diels–Alder reaction makes two new rings. Draw the compound produced in each of these examples; try to predict stereochemistry (using models will help). In some cases, Lewis acid catalysts are used; that can be ignored for this problem.

(a)

(b)

Which of the following dienes is the most reactive in a $\mathrm{Diels}-\mathrm{Alder}$ reaction?

Which of the following dienes can undergo a Diels-Alder reaction?