See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: The conversion shown is from cyclohexene to bicyclo[4.1.0]heptane (norcarane), which involves adding a CH2 group across the double bond to form a cyclopropane ring fused to the cyclohexane ring. This is a carbene addition reaction. Step 1 - Identify the transformation: The starting material is cyclohexene (a six-membered ring with one double bond). The product is bicyclo[4.1.0]heptane, which is a cyclohexane ring with a cyclopropane ring fused across what was the double bond. This requires adding a :CH2 (methylene carbene) across the C=C double bond in a syn addition. Step 2 - Identify the reagent: Diazomethane (CH2N2) upon heating (Delta) loses N2 gas and generates methylene carbene (:CH2). This reactive carbene intermediate undergoes stereospecific syn addition across the double bond of cyclohexene to give the bicyclic cyclopropane product (norcarane). Step 3 - Evaluate other options: - (b) CBr4 / RLi generates dibromomethylene carbene (:CBr2), which would give a gem-dibromocyclopropane, not the unsubstituted cyclopropane product shown. - (c) H2C=CH2 is ethylene itself; it does not add across a double bond to form a cyclopropane under normal conditions. - (d) t-BuOK is a strong base used for E2 elimination reactions, not for cyclopropanation. Step 4 - Conclusion: CH2N2 / Delta is the correct reagent because it generates :CH2 carbene in situ, which adds across the cyclohexene double bond to yield bicyclo[4.1.0]heptane. Therefore, the correct answer is A.