See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: Organolithium reagents are strong nucleophiles/bases. When a vinyllithium (alkenyllithium) reacts with an acyl chloride such as methyl chloroformate (ClC(=O)OMe), the carbon bearing the lithium acts as a carbanion nucleophile. Step 1: Identify the reagents. The starting material is 2-lithio-2-norbornene (a vinyllithium species where the lithium is attached directly to the sp2 carbon C2 of the norbornene double bond). The electrophile is methyl chloroformate, ClC(=O)OMe. Step 2: Reaction pathway. Vinyllithium reagents react with acyl chlorides (including chloroformates) via nucleophilic addition at the carbonyl carbon. The C-Li bond acts as the nucleophile, attacking the electrophilic carbonyl carbon of ClC(=O)OMe. The chloride is displaced as a leaving group (LiCl is formed as a byproduct). Step 3: Product formation. The vinyl carbon (C2 of norbornene) forms a new C-C bond with the carbonyl carbon of ClC(=O)OMe, replacing the C-Li bond with a C-C(=O)OMe bond. This installs a -CO2Me (methoxycarbonyl/ester) group directly on C2 of the norbornene double bond, giving methyl bicyclo[2.2.1]hept-2-ene-2-carboxylate. Step 4: Why other options fail. - Option (a): Replacement of Li with Cl would require a halogenation reaction (e.g., reaction with a halogen source), not with methyl chloroformate. The chlorine in ClC(=O)OMe is not transferred to carbon here. - Option (c): Loss of the lithium substituent to give unsubstituted norbornene would imply protonation or elimination, not reaction with an electrophilic carbonyl reagent. - Option (d): Norbornane implies full reduction/saturation of the double bond, which does not occur under these conditions. Therefore, the correct answer is B.