Two equivalents of magnesium organometallic add to the ester, to form tertiary alcohols in which two substituents are the same. The mechanism consists of the nucleophilic addition of the organometallic to the carbonyl of the ester. After the first addition, a ketone is formed which is attacked again by a second equivalent of magnesium to form the final alcohol.

esteres-organometalicos

The reaction mechanism occurs in the following steps:

esteres-organometalicos

The ketone is more reactive than the ester and a second equivalent of magnesium attacks it to form the alcohol.

esteres-organometalicos