Identify the major product (B) in the following reaction sequence:

Step-by-step solution

The given starting material is 1,2-dibromocyclopentane. When it reacts with 1 equivalent of magnesium (Mg) in the presence of dry ether, it forms a mono-Grignard reagent. Magnesium inserts into one of the carbon-bromine bonds to form 2-bromocyclopentylmagnesium bromide. This is intermediate A. Upon heating ( ), this intermediate undergoes an intramolecular elimination reaction. The carbon atom bonded to magnesium has a partial negative charge (carbanion character) and acts as an internal nucleophile. It donates its