Reduction of Esters via Aldehydes to Alcohols
Reduction of Esters to Alcohols via Aldehydes: Solvent Selection
Influence of solvent on DIBAL reduction selectivity
Application in the laboratory.
The choice of solvent is critical for DIBAL reductions. In polar solvents, such as THF, the tetrahedral intermediate ( 1 ) forms a Lewis acid/Lewis base complex ( 2 ) in which the solvent causes a weakening of the bond to the previous ester carbonyl oxygen.
The weakening of this bond in polar solvents causes the tetrahedral intermediate to break up faster than it is being formed. The resulting aldehyde reacts immediately with another DIBAL molecule to form the corresponding alcohol.
On the other hand, in non-polar solvents elimination of the aldehyde is slower than hydride transfer to the ester . This fact allows for the hydrolysis of the tetrahedral intermediate ( 1 ) to a semiacetal, which in turn is then being transformed to aldehyde by acid catalysis. .