Animated Solution for Chemistry - Organic Chemistry: The major product obtained in the following reaction is

The Power of DIBAL-H

When tackling complex organic transformations, identifying the specific reducing power of your reagent is half the battle. In this problem, we are presented with a fascinating bicyclic molecule containing two distinct reducible functional groups: a nitrile ($-CN$) and a cyclic ester, commonly known as a lactone.

Our reagent of choice is DIBAL-H (Diisobutylaluminium hydride). Unlike its aggressive cousin Lithium Aluminum Hydride ($LiAl{H}_4$), DIBAL-H is a bulky, electrophilic reducing agent that exhibits remarkable selectivity, especially at low temperatures.

Let's carefully analyze the starting molecule. We have a cyclohexane ring fused with a five-membered lactone ring. Notice the cyano group attached to the same carbon as the lactone oxygen.

When DIBAL-H is introduced into the system, it seeks out electrophilic centers. In our molecule, it will attack two specific sites: the carbon of the cyano group and the carbonyl carbon of the lactone ring.

First, let's look at the cyano group. DIBAL-H donates a single hydride to the nitrile carbon, breaking one of the pi bonds and forming an intermediate imine ($-CH=NH$). Because DIBAL-H is bulky and the reaction is typically run at low temperatures, the reduction stops here.

Upon the subsequent aqueous workup (which is standard even if not explicitly written in the reaction arrow), this imine intermediate undergoes hydrolysis, converting smoothly into an aldehyde group ($-CHO$).

Simultaneously, the lactone ring experiences its own transformation. DIBAL-H donates a hydride to the carbonyl carbon of the cyclic ester. This forms a stable tetrahedral aluminum intermediate.

When water is added during the workup, this intermediate collapses, breaking the carbon-oxygen single bond of the ester linkage. The carbonyl carbon is liberated as an aldehyde, while the oxygen atom remains attached to the cyclohexane ring, becoming a hydroxyl group ($-OH$).

Putting it all together, let's map the final structure. The top-right carbon of the cyclohexane ring, which originally held the nitrile and the lactone oxygen, now holds a newly formed aldehyde group and a hydroxyl group.

The bottom-right carbon was attached to a $-C{H}_2-$ group that formed the rest of the lactone ring. This $-C{H}_2-$ group is now terminated by the second aldehyde group, forming a $-C{H}_2-CHO$ chain.

This precise structural arrangement perfectly matches option (d). Always remember: DIBAL-H is your go-to reagent for stopping at the aldehyde station!