14.21 : אסטרים לכוהל: תגובת Grignard

Organomagnesium halides, known as Grignard reagents, reduce esters to tertiary alcohols, while formate esters are reduced to secondary alcohols.

Notably, the reaction introduces two identical alkyl groups derived from the Grignard reagent.

The reaction requires two equivalents of a Grignard reagent and proceeds via a ketone intermediate.

The mechanism begins with a nucleophilic attack by a Grignard reagent, a carbanion, at the carbonyl carbon, forming a tetrahedral intermediate.

Next, the carbonyl group is reconstructed with the departure of an alkoxide ion as a leaving group to yield a ketone.

Since ketone is more reactive towards the Grignard reagent, the ketone intermediate is not isolated and enters the next step.

Subsequently, the second equivalent of the Grignard reagent attacks the ketone, forming an alkoxide intermediate.

Finally, protonation of the alkoxide yields tertiary alcohol as the final product.