LiAlH₄ is used as strong reducing agent. The hydride produced acts as a nucleophile and attacks the electrophillic carbon of carbonyl group. In given example two reactions are observed.
Reaction 1:
In first step LiAlH₄ when treated with Ester produces corresponding Aldehyde and alcohol.
Reaction 2:
This aldehyde produced further reacts with LiAlH₄ to give a reduced product (Alcohols). In this case Butanol is produced.
The reaction schemes are shown as felow,