Q.18 Identify the CORRECT product in the following reaction:

Introduction (SEO Optimized)

Questions based on the Diels–Alder reaction are extremely common in JEE Advanced, NEET, and other competitive organic chemistry exams. These problems test a student’s understanding of concerted cycloaddition, endo rule, stereochemistry, and orbital interactions.

In this article, we analyze a Diels–Alder reaction involving furan as the diene and a maleimide derivative as the dienophile, and determine the correct product by applying fundamental reaction principles. Each option is explained clearly to avoid common exam traps.

 Key Concepts Used

1️⃣ Diels–Alder Reaction

• A [4 + 2] cycloaddition

• Occurs in a single step (concerted)

• Forms a bicyclic system when cyclic dienes are used

2️⃣ Nature of Reactants

• Furan → electron-rich diene

• Maleimide → strong electron-deficient dienophile

3️⃣ Endo Rule

• The endo product is favored due to:

  • Secondary orbital overlap

  • Maximum stabilization in the transition state

 Reaction Analysis

Step 1: Identify the Diene and Dienophile

• Furan acts as the diene

• N-phenyl maleimide acts as the dienophile

Step 2: Apply the Endo Rule

• The carbonyl (C=O) groups of the dienophile prefer to orient towards the diene π-system

• This gives the endo adduct, not the exo one

Step 3: Predict the Framework

• Reaction forms a bicyclic bridged structure

• The oxygen bridge from furan remains intact

• The phenyl group remains attached to nitrogen

 Correct Product

Option (B)

This structure:

• Shows correct endo orientation

• Preserves correct stereochemistry

• Matches the expected bicyclic Diels–Alder adduct

 Explanation of All Options

 Option (A)

• Shows incorrect orientation of carbonyl groups

• Violates the endo rule

• Represents an energetically unfavorable transition state

Option (B) ✔

• Correct endo product

• Carbonyl groups oriented toward the bridge

• Matches experimental and theoretical prediction
  ✔ Correct Answer

 Option (C)

• Incorrect bridge placement

• Does not follow concerted cycloaddition stereochemistry

• Not a valid Diels–Alder product

 Option (D)

• Represents an exo product

• Less stable due to lack of secondary orbital overlap

• Exo products are minor in Diels–Alder reactions

 Quick Exam Tip

For Diels–Alder reactions:

• Always check endo vs exo

• Carbonyl-containing dienophiles almost always give endo products

• Cyclic dienes → bicyclic adducts

 Conclusion

This problem highlights the importance of the endo rule in predicting Diels–Alder products. When an electron-rich diene like furan reacts with a carbonyl-substituted dienophile such as maleimide, the endo product dominates due to favorable orbital interactions.

By systematically analyzing the reactants, mechanism, and stereochemistry, the correct product can be identified confidently.

Final Answer: Option (B)