To be complete, I wasn’t reducing an ester, it was a thioimide. It was an (OH-protected) aldol adduct utilizing a thiazolidinethione as a chiral auxiliary. We developed the conditions for the aldol addition in our laboratory. Suffice it to say we did the diastereoselective aldol addition a lot . Partial reduction of the thioimide to the aldehyde was a common next transformation, so we always had a fresh bottle of DIBAL in the fridge. I reduced 5 different thioimides this way who knows how many times as I ran through the synthetic scheme who knows how many times.
DIBAL is useful in organic synthesis for a variety of reductions, including converting carboxylic acids , their derivatives, and nitriles to aldehydes . DIBAL efficiently reduces α-β unsaturated esters to the corresponding allylic alcohol.  By contrast, LiAlH 4 reduces esters and acyl chlorides to primary alcohols , and nitriles to primary amines [use Feiser work-up procedure]. DIBAL reacts slowly with electron-poor compounds, and more quickly with electron-rich compounds. Thus, it is an electrophilic reducing agent whereas LiAlH 4 can be thought of as a nucleophilic reducing agent.