Q52E - Organic Chemistry (Mcmurry)

Question

Show the structure and stereochemistry of the alcohol that would result if 1,2-epoxycyclohexane were reduced with lithium aluminium deuteride, ${\mathbf{LiAlD}}_{\mathbf{4}}$?

Step-by-Step Solution

Answer

The structure and stereochemistry of $(1\mathrm{R},2\mathrm{R})-(2-{}^2\mathrm{H}_1)$ cyclohexanol are given below.

Step 1: Structure of 1,2-epoxycyclohexane

1,2-epoxycyclohexane

Cyclohexane represents a cyclic group of six carbon atoms. This cyclohexane group is attached to an oxygen atom at the first and second carbon atoms. This is represented in the above figure. 

Step 2: Reduction of epoxides

Generally, epoxides are reduced using lithium aluminum hydride to produce alcohols. Here, deuterium is used. It also produces alcohol that has regiospecificity.

Step 3: Attack of deuterium on the second carbon atom

Deuterium is a higher version of hydrogen. ${\mathrm{LiAlD}}_4$ dissociates into ${{\mathrm{AlD}}_4}^{-}$ and ${\mathrm{Li}}^{+}$. This ${\mathrm{D}}^{-}$in ${{\mathrm{AlD}}_4}^{-}$ attacks the carbon atom with less steric hindrance, i.e., the second carbon atom. 

Step 4: Reduction in acidic medium

There will be a negative charge on the oxygen atom that is protonated, forming a hydroxyl group at the first carbon atom. Thus, it forms alcohol. 

Step 5: Structure and stereochemistry

The structure formed is given below.

Product’s structure

The compound formed as a product is an alcohol that is regiospecific. Deuterium is away from the carbon atom while hydrogen is near. The hydroxyl group is also near the first carbon atom.