Predict the products of the following Diels–Alder reactions.
(a)
(b)

Verified step by step guidance

1. Step 1: Identify the components of the Diels–Alder reaction. The reaction involves a conjugated diene and a dienophile. In image (a), the diene is the methoxy-substituted cyclopentadiene, and the dienophile is the alkyne with an ester group (COOCH₃). In image (b), the diene is the methoxy-substituted cyclohexadiene, and the dienophile is the cyclohexenone.
2. Step 2: Analyze the electronic effects. The methoxy group (-OCH₃) on the diene is an electron-donating group, which increases the nucleophilicity of the diene. The ester group (COOCH₃) in image (a) and the ketone group (C=O) in image (b) are electron-withdrawing groups, which enhance the electrophilicity of the dienophile.
3. Step 3: Predict the regioselectivity. In both cases, the electron-donating group on the diene will direct the reaction to form the most stable product. The electron-withdrawing group on the dienophile will align with the electron-rich part of the diene to maximize stabilization.
4. Step 4: Draw the cyclic adduct. The Diels–Alder reaction forms a six-membered ring by combining the diene and dienophile. For image (a), the product will be a bicyclic compound with the ester group attached to the newly formed ring. For image (b), the product will be a bicyclic compound with the ketone group attached to the newly formed ring.
5. Step 5: Consider stereochemistry. The Diels–Alder reaction is stereospecific, meaning the stereochemistry of the substituents on the diene and dienophile will be preserved in the product. Ensure that the substituents are correctly positioned in the final structure based on their original orientation.

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 and regioselectivity, making it a powerful tool for chemists.

Diene and Dienophile

In the context of the Diels–Alder reaction, a diene is a molecule containing two double bonds, while a dienophile is a compound that contains a double or triple bond and reacts with the diene. The reactivity of these components is influenced by their electronic properties, such as electron-donating or withdrawing groups, which can enhance or diminish the reaction's efficiency.

Regioselectivity and Stereochemistry

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others, while stereochemistry involves the spatial arrangement of atoms in the resulting product. In Diels–Alder reactions, the orientation of substituents on the diene and dienophile can significantly affect the final product's structure, leading to different regioisomers and stereoisomers.