The ester shown is treated with an excess of methylmagnesium bromide, followed by aqueous work-up. Which structure is the product?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: A

Methyl propanoate undergoes nucleophilic acyl substitution to give butan-2-one, which is more reactive than the ester and adds a second methyl group at once. After work-up the product is the tertiary alcohol 2-methylbutan-2-ol, with two identical methyl groups from the Grignard reagent.

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