Ethyl 4-oxopentanoate is treated with (i) ethylene glycol, H+ (cat.), remove water; (ii) excess CH3MgBr, ether; (iii) dilute H3O+ work-up. The final product is

JEE Advanced levelSingle correct optionDifficulty 3 of 3o1100

Ethyl 4-oxopentanoate is treated with (i) ethylene glycol, $H X^{+}$ (cat.), remove water; (ii) excess $CH X_{3} MgBr$ , ether; (iii) dilute $H X_{3} O X^{+}$ work-up. The final product is

The ketone is first protected as a ketal, which is inert to the Grignard reagent. Excess

CH X_{3} MgBr

converts the ester into the tertiary alcohol

- C (CH X_{3}) X_{2} OH

(two methyls added). Aqueous acid then restores the ketone, giving

CH X_{3} - CO - CH X_{2} CH X_{2} - C (OH) (CH X_{3}) X_{2}