Show how Diels–Alder reactions might be used to synthesize the following compounds.
(i)

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Step 1: Identify the target molecule as a bicyclic compound with a sulfone group and two cyano groups attached to the bridgehead carbons. This structure suggests that it could be synthesized using a Diels–Alder reaction followed by functional group modifications.

Step 2: Recognize that the Diels–Alder reaction involves a conjugated diene and a dienophile. The bicyclic structure indicates that the reaction likely involves a cyclic diene and a dienophile with electron-withdrawing groups to facilitate the reaction.

Step 3: Propose the diene as cyclopentadiene, which is commonly used in Diels–Alder reactions to form bicyclic systems. Cyclopentadiene has the necessary conjugated double bonds to act as the diene.

Step 4: Suggest the dienophile as a molecule containing electron-withdrawing groups such as cyano groups (–CN). A possible dienophile could be fumaronitrile (trans-1,2-dicyanoethene), which has two cyano groups that can stabilize the transition state during the reaction.

Step 5: After the Diels–Alder reaction forms the bicyclic intermediate, introduce the sulfone group (–SO2) through an oxidation reaction. This can be achieved by treating the intermediate with a sulfonylating agent such as sulfur dioxide (SO2) or a sulfonyl chloride under appropriate conditions.

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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 powerful tool in organic synthesis due to its ability to create complex cyclic structures in a single step, often with high stereoselectivity and regioselectivity.

Conjugated Dienes

Conjugated dienes are compounds that contain two double bonds separated by a single bond, allowing for resonance stabilization. This property enhances their reactivity in Diels–Alder reactions, as the electron-rich diene can effectively interact with an electron-deficient dienophile, facilitating the cycloaddition process.

Stereochemistry in Diels–Alder Reactions

Stereochemistry plays a crucial role in Diels–Alder reactions, as the orientation of substituents on the diene and dienophile can influence the final product's configuration. The reaction typically proceeds with a concerted mechanism, preserving the stereochemistry of the reactants, which is essential for predicting the structure of the synthesized compound.

Show how Diels–Alder reactions might be used to synthesize the following compounds.(i)