Identify the major product formed in the following reaction sequence.

Step-by-step solution

The given reactant is a -lactone (a cyclic ester). When a lactone reacts with an excess of an organolithium reagent such as ethyl lithium ( CH ₃ CH ₂ Li ), two equivalents of the nucleophile add to the carbonyl carbon. The first equivalent of CH ₃ CH ₂ Li attacks the ester carbonyl group. The ring opens to form a ketone intermediate with an alkoxide group: CH ₃ CH ₂- C (= O )- CH ₂ CH ₂ CH ₂ CH ( CH ₃) O ^- Li ^+ . Because excess CH ₃ CH ₂ Li is present, a second equivalent attacks the newly formed ketone carbonyl