Question

Consider the following compound.

The compound undergoes reaction with two equivalents of diisobutyl aluminium hydride followed by acid hydrolysis to provide P as the major product. The structure of P is:

• A. Structure with both functional groups reduced to $-\text{CHO}$.
• B. Structure with ester reduced to $-\text{CHO}$ and nitrile remaining intact as $-\text{CN}$.
• C. Structure with ester reduced to $-\text{CH}_2\text{OH}$ and nitrile remaining intact as $-\text{CN}$.
• D. Structure with ester reduced to $-\text{CH}_2\text{OH}$ and nitrile reduced to $-\text{CH}_2\text{NH}_2$.

Hint:

At low temperatures (e.g., $-78\ ^\circ\text{C}$), DIBAL-H is the premier reagent for stopping reductions of both esters and nitriles at the aldehyde stage.

Answer 1

The Correct Option is A

Step 1: Spot the two reactive groups.
The starting compound carries two different groups on a ring: an ester ($-\text{CO}_2\text{Et}$) and a nitrile ($-\text{CN}$). The reagent is DIBAL-H, two equivalents, followed by acid workup. We must decide what each group becomes.

Step 2: Remember the special habit of DIBAL-H.
DIBAL-H is a gentle, bulky hydride that likes to stop halfway. Instead of fully reducing groups down to alcohols or amines, it usually delivers just enough hydride to reach the aldehyde stage and then stops, because the intermediate it forms is stable until the acid workup releases the aldehyde.

Step 3: Apply it to the ester.
An ester treated with DIBAL-H takes one hydride, forms a stable intermediate, and on acid hydrolysis gives an aldehyde ($-\text{CHO}$), not a primary alcohol. So the ester end becomes $-\text{CHO}$.

Step 4: Apply it to the nitrile.
A nitrile with DIBAL-H also stops at the imine stage, which on acid workup gives an aldehyde as well. So in principle the nitrile too can be turned into $-\text{CHO}$ under these conditions.

Step 5: Account for two equivalents.
Two equivalents of DIBAL-H are enough to hit both the ester and the nitrile, each taking its own hydride. Both reduce to the aldehyde stage, and neither over reduces to alcohol or amine because DIBAL-H stops cleanly at the aldehyde level.

Step 6: Write the product P.
So P has both original groups converted to $-\text{CHO}$, giving a dialdehyde on the ring.

\[ \boxed{\text{Both the ester and nitrile are reduced to } -\text{CHO (a dialdehyde)}} \]