Question

Question: Epoxides are converted to allylic alcohols with non-nucleophilic bases such as lithiumdiethylamide $\left[\mathrm{LiN}{\left({\mathrm{CH}}_2{\mathrm{CH}}_3\right)}_2\right]$ . Draw a stepwise mechanism for the conversion of1,2-epoxycyclohexane to cyclohex-2-en-1-ol with this base. Explain why a strong bulky basemust be used in this reaction.

Short answer

Answer

First step:

Second step:

Step-by-step solution

Step-by-Step Solution Step 1: Conversion of epoxide to allylic alcohols

The non-nucleophilic base$\left[\mathrm{LiN}{\left({\mathrm{CH}}_2{\mathrm{CH}}_3\right)}_2\right]$functions by abstracting a proton from the -carbon position of the epoxide ring.The mechanism is shown below:

Proton abstraction and alkoxide ion formation

Hydrolysis of alkoxide ion

The alkoxide ion that is formed is hydrolyzed to form allylic alcohol.The reaction is shown below:

Hydrolysis of the alkoxide to form allylic alcohol

Determination of the type of bond present

$\mathbf{\left[}\mathbf{LiN}{\mathbf{\left(}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{2}}\mathbf{\right]}$is a bulky non-nucleophilic base.A bulky base is required since a lighter base may dissociate and act as a nucleophile. This nucleophile attacks one of the epoxide carbon centers and opens the ring.