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

Verified step by step guidance

1. Step 1: Identify the diene and dienophile in the reaction. The structure on the left with two conjugated double bonds is the diene, and the structure on the right with a single double bond and an aldehyde group (CHO) is the dienophile.
2. Step 2: Recall the Diels–Alder reaction mechanism. It is a [4+2] cycloaddition reaction where the diene contributes four π-electrons and the dienophile contributes two π-electrons to form a six-membered ring.
3. Step 3: Analyze the substituents on the diene and dienophile. The diene has a methoxy group (-OCH₃) attached to one of its double bonds, which is an electron-donating group. The dienophile has an aldehyde group (-CHO), which is an electron-withdrawing group. These groups influence the regioselectivity and stereochemistry of the reaction.
4. Step 4: Predict the regioselectivity of the reaction. The electron-donating methoxy group on the diene will direct the reaction such that the electron-withdrawing aldehyde group on the dienophile aligns to form the most stable product. This typically results in the formation of a product with substituents in a 1,2- or 1,4-relationship on the newly formed six-membered ring.
5. Step 5: Consider stereochemistry. The Diels–Alder reaction is stereospecific, meaning that the stereochemistry of the dienophile is preserved in the product. If the dienophile is planar, the substituents will be added in a cis configuration relative to each other on the ring. Additionally, the endo rule suggests that the electron-withdrawing group (aldehyde) will preferentially adopt the endo position (pointing towards the π-system of the diene) in the transition state.

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 influences the stereochemistry of 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-Withdrawing and Electron-Donating Groups

In organic chemistry, electron-withdrawing groups (EWGs) and electron-donating groups (EDGs) influence the reactivity of molecules. In the Diels–Alder reaction, EDGs, like the methoxy group (OCH3), enhance the reactivity of the diene, while EWGs, like the aldehyde group (CHO), increase the reactivity of the dienophile. Recognizing these effects is essential for predicting the outcome of the reaction.