Predict the products of the following proposed Diels–Alder reactions. Include stereochemistry where appropriate.
(a)

Verified step by step guidance

1. Step 1: Identify the reactants in the Diels–Alder reaction. The diene is the conjugated system with two double bonds, and the dienophile is the molecule with one double bond and an electron-withdrawing group (in this case, the aldehyde group).
2. Step 2: Recall the mechanism of the Diels–Alder reaction. It is a [4+2] cycloaddition reaction where the diene contributes four π-electrons and the dienophile contributes two π-electrons to form a cyclic product.
3. Step 3: Analyze the stereochemistry. The Diels–Alder reaction is stereospecific, meaning the stereochemistry of the dienophile and diene will influence the stereochemistry of the product. The aldehyde group on the dienophile will determine the orientation of substituents in the product.
4. Step 4: Draw the cyclic product. Combine the diene and dienophile to form a six-membered ring. The new σ-bonds will form between the ends of the diene and the carbons of the dienophile's double bond. Ensure the aldehyde group is positioned correctly based on the stereochemistry.
5. Step 5: Confirm the regiochemistry and stereochemistry of the product. The electron-withdrawing group (aldehyde) on the dienophile will direct the reaction to form the most stable product, typically favoring endo addition (where substituents are oriented towards the newly formed π-system).

Key Concepts

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, meaning the stereochemistry of the reactants is preserved in the products.

Stereochemistry

Stereochemistry refers to the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In the context of the Diels–Alder reaction, understanding stereochemistry is crucial for predicting the configuration of the product, as the reaction can lead to the formation of chiral centers and specific stereoisomers depending on the orientation of the reactants.

Electron Density and Reactivity

In organic chemistry, the reactivity of molecules is often influenced by the distribution of electron density. In the Diels–Alder reaction, the diene must be electron-rich, while the dienophile is typically electron-poor, often containing electron-withdrawing groups. This difference in electron density facilitates the formation of the new sigma bonds during the cycloaddition process.