Identify the major product of the following reaction sequence: [ (ii) Catalytic H ⁺ , heat ] (i) Excess CH ₃ MgBr , then H ₃ O ⁺ ?

Step-by-step solution

The given reactant is a lactone, specifically 3,3-dimethylisobenzofuran-1(3H)-one. In the first step, it reacts with an excess of the Grignard reagent, methylmagnesium bromide ( CH ₃ MgBr ). The Grignard reagent attacks the electrophilic carbonyl carbon of the ester group. Two equivalents of CH ₃ MgBr are consumed per lactone molecule. The first equivalent opens the lactone ring to form a ketone intermediate bearing a tertiary alkoxide group. The second equivalent then attacks the newly formed ketone carbonyl. Subs