Identify the correct reactant that undergoes the following sequence of reactions to yield the given product: Reactant 1. LDA, then CH₃I 2. LiAlH₄ , then H₃O^+ 3. TsOH, propanone,

Step-by-step solution

The given sequence of reactions involves alpha-alkylation of a lactone, reduction to a diol, and subsequent protection as an acetonide. Analyzing option (4), the reactant is a bicyclic -lactone. The ring oxygen is directly attached to one of the fusion carbons, and the carbonyl group is separated from the other fusion carbon by a single methylene ( CH₂ ) group. In the first step, treatment with the strong base LDA forms an enolate at the -position of the lactone (the CH₂ group adjacent to the carbonyl). Reaction wi