Question

1,4-Benzoquinone is a good Diels–Alder dienophile. Predict the products of its reaction witha. buta-1,3-dieneb. cyclopenta-1,3-diene

Accepted Answer

Identify the components of the Diels–Alder reaction: 1,4-Benzoquinone is the dienophile (electron-deficient alkene), and the diene is either buta-1,3-diene or cyclopenta-1,3-diene. The reaction involves a [4+2] cycloaddition, where the diene contributes 4 π-electrons and the dienophile contributes 2 π-electrons. Analyze the structure of 1,4-Benzoquinone: It has two conjugated carbonyl groups (C=O) that withdraw electron density from the double bonds, making it highly reactive as a dienophile. The double bonds in 1,4-Benzoquinone will participate in the cycloaddition reaction. For part (a), align buta-1,3-diene with 1,4-Benzoquinone: Ensure the diene adopts an s-cis conformation (required for the Diels–Alder reaction). The reaction will form a six-membered ring, with the new bonds forming between the terminal carbons of the diene and the carbons of the dienophile's double bond. For part (b), align cyclopenta-1,3-diene with 1,4-Benzoquinone: Cyclopenta-1,3-diene is already locked in an s-cis conformation, making it highly reactive. The reaction will form a bicyclic product, where the six-membered ring from the Diels–Alder reaction is fused to the five-membered ring of the diene. Draw the products: For both reactions, the newly formed six-membered ring will contain two carbonyl groups (C=O) from the original 1,4-Benzoquinone. In part (a), the product will be a single six-membered ring, while in part (b), the product will be a bicyclic compound with a fused ring system.

1,4-Benzoquinone is a good Diels–Alder dienophile. Predict the products of its reaction with
a. buta-1,3-diene
b. cyclopenta-1,3-diene

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Key Concepts

Diels–Alder Reaction

Dienophile

Regioselectivity