Chapter 19, Problem 19.52P

Interpretation Introduction

(a)

Interpretation:

How to carry out the given synthesis is to be proposed.

Concept introduction:

A protecting group temporarily converts a functional group into one that is unreactive under the conditions necessary for a step in the synthesis. Ketones, aldehydes, and alcohols can often be protected in the form of an acetal or ether. Generally, acetone in acidic condition can protect diol. Phosphorous tribromide ${\text{(PBr}}_{\text{3}}\text{)}$ can convert primary and secondary alcohol to alkyl halide via back-to-back ${\text{S}}_{\text{N}}\text{2}$ reactions (invert stereochemistry). Potassium cyanide $\text{(KCN)}$ can substitute the Br group via ${\text{S}}_{\text{N}}\text{2}$ reaction (invert stereochemistry). Lithium aluminum hydride $\left({\text{LiAlH}}_{\text{4}}\right)$ is a source of hydride ${\text{(H}}^{\text{-}})$ used to reduce the nitrile to an amine in the protic solvent.

Interpretation Introduction

(b)

Interpretation:

How to carry out the given synthesis is to be proposed.

Concept introduction:

A protecting group temporarily converts a functional group into one that is unreactive under the conditions necessary for a step in the synthesis. Ketones, aldehydes, and alcohols can often be protected in the form of an acetal or ether. Generally, acetone in acidic condition can protect diol. Chromic acid $\left({\text{H}}_{\text{2}}{\text{CrO}}_{\text{4}}\right)$ will oxidize a primary alcohol

to a carboxylic acid or a secondary alcohol to a ketone.