91Ó°ÊÓ

Aldehyde reactions include Wittig, Grignard, and reduction reactions.The Wittig reagent does the aldehyde conversion to an alkene, and the Grignard reagent does the aldehyde conversion to a secondary alcohol.

The benzyl alcohol on reaction with ${\text{PBr}}_{\text{3}}$gives benzyl bromide. On further reaction of benzyl bromide with Mg, ether gives Grignard reagent. The Grignard reagent on reaction with formaldehyde gives primary alcohol, followed by oxidation which gives phenylacetaldehyde product.

Synthesis of compound (a) from phenylacetaldehyde.

An alternate route for the formation of phenylacetaldehyde is as shown below.

Synthesis of phenylacetaldehyde by using Wittig reagent

The intermediate alcohol is formed by hydroboration of a double bond formed by the Wittig reaction of benzaldehyde and methylenetriphenylphosphorane.

b.

The given product contains a secondary amine and a double bond, recognized as enamine. The formation of enamine is done by amine and acetophenone. This acetophenone is formed when benzaldehyde reacts with Grignard reagent (methylmagnesium bromide) and is followed by oxidation ${\text{CrO}}_{\text{3}}{\text{,H}}_{\text{3}}{\text{O}}^{\text{+}}$. The reaction is shown below.

Synthesis of compound (b) from benzaldehyde

Synthesis of compound (c) from benzaldehyde