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

Verified step by step guidance

1. Step 1: Identify the components of the Diels–Alder reaction. The reaction involves a conjugated diene (two double bonds in conjugation) and a dienophile (an electron-deficient alkene). In this case, the diene is the structure on the left, and the dienophile is the structure on the right containing the aldehyde group (CHO).
2. Step 2: Analyze the electron flow. The Diels–Alder reaction is a [4+2] cycloaddition, where the four π-electrons from the diene interact with the two π-electrons from the dienophile to form a new six-membered ring.
3. Step 3: Consider regioselectivity. The aldehyde group on the dienophile is electron-withdrawing, which influences the orientation of the reaction. The electron-rich ends of the diene will preferentially interact with the electron-deficient ends of the dienophile.
4. Step 4: Draw the product structure. Combine the diene and dienophile to form a six-membered ring. The new bonds will form between the ends of the diene and the double bond of the dienophile. The aldehyde group will remain attached to the ring at the position where the dienophile was originally located.
5. Step 5: Confirm stereochemistry. The Diels–Alder reaction typically proceeds with syn addition, meaning substituents on the dienophile and diene will end up on the same face of the newly formed ring. Ensure the stereochemistry is consistent with this rule.

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.

Conjugated Dienes

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

Dienophile

A dienophile is a compound that contains a double or triple bond and reacts with a diene in a Diels–Alder reaction. Typically, dienophiles are electron-deficient, which makes them more reactive towards the electron-rich diene. Common examples include alkenes and alkynes with electron-withdrawing groups, such as carbonyls or nitriles, which enhance their reactivity.