Chapter 17, Problem 17.66P

Interpretation Introduction

(a)

Interpretation:

The synthesis of given compound from $\text{phenylethanone }\left(\text{acetophenone}\right)$, using any reagents necessary is to be suggested.

Concept introduction:

In an $\text{α,β-}$ unsaturated carbonyl, nucleophiles in general can attack at two positions: either at the carbonyl carbon or at the $\text{β}$ carbon. Attack of the nucleophile at the carbonyl carbon is called 1, 2-addition, or direct addition. The 1, 2-addition or direct addition product is an allylic alcohol. Phosphorus tribromide (${\text{PBr}}_{\text{3}}$) can convert primary and secondary alcohols into alkyl halides via back-to-back ${\text{S}}_{\text{N}}\text{2}$ reactions.

Answer to Problem 17.66P

The synthesis of given compound from $\text{phenylethanone }\left(\text{acetophenone}\right)$, using any reagents necessary is as shown below,

Explanation of Solution

The given reaction is,

The first step of the reaction is reduction of $\text{α,β-}$ unsaturated carbonyl to give an allylic alcohol. The reagents used for this step is ${\text{NaBH}}_{\text{4}}$ which is a source of ${\text{H}}^{\text{-}}$ nucleophile and water is a source of proton transfer. In second step, the OH group is substituted by Br atom. The reagent used for this reaction is Phosphorus tribromide (${\text{PBr}}_{\text{3}}$) which converts primary and secondary alcohols into alkyl halides via back-to-back ${\text{S}}_{\text{N}}\text{2}$ reactions.

The synthesis of given compound from $\text{phenylethanone }\left(\text{acetophenone}\right)$, using any reagents necessary is as shown below,

Conclusion

The synthesis of given compound from $\text{phenylethanone }\left(\text{acetophenone}\right)$, using any reagents necessary is suggested by a reduction followed by substitution of OH group with Br.

Interpretation Introduction

(b)

Interpretation:

The synthesis of given compound from $\text{phenylethanone }\left(\text{acetophenone}\right)$, using any reagents necessary is to be suggested.

Concept introduction:

The organometallic compounds such as Grignard reagents (RMgX) and alkyllithium reagents behave both as strong bases and as strong nucleophiles. Both alkyllithium reagents and Grignard reagents can react rapidly with water in a substantially exothermic proton transfer reaction to produce an alkane and ${\text{HO}}^{\text{-}}$. Strong bases tend to favor E1 reactions. The E1 reaction products are obtained by eliminating the leaving group and a proton on a carbon adjacent to the one bonded to the leaving group.

Answer to Problem 17.66P

The synthesis of given compound from $\text{phenylethanone }\left(\text{acetophenone}\right)$, using any reagents necessary is as shown below,

Explanation of Solution

The given reaction is,

In the first a new C-C bond is formed and a methyl group is added to the carbonyl carbon. Both alkyllithium reagents and Grignard reagents can react rapidly with water in a substantially exothermic proton transfer reaction to produce an alkane and ${\text{HO}}^{\text{-}}$. So the reagent can be methylmagnesium bromide (${\text{CH}}_{\text{3}}\text{MgBr}$) or methyllithium(${\text{CH}}_{\text{3}}\text{Li}$). An acid workup is needed to protonate the strongly basic ${\text{O}}^{\text{-}}$ generated in the first step and to get uncharged alcohol. The alcohol is further dehydrated i.e. the OH group is eliminated and the $\text{C=C}$ bond is formed. The reagents used are strong acid and heat.

The synthesis of given compound from $\text{phenylethanone }\left(\text{acetophenone}\right)$, using any reagents necessary is as shown below,

Conclusion

The synthesis of given compound from $\text{phenylethanone }\left(\text{acetophenone}\right)$, using any reagents necessary is suggested by the dehydration of an alcohol which is made by Grignard reagent.

Interpretation Introduction

(c)

Interpretation:

The synthesis of given compound from $\text{phenylethanone }\left(\text{acetophenone}\right)$, using any reagents necessary is to be suggested.

Concept introduction:

In an $\text{α,β-}$ unsaturated carbonyl, nucleophiles in general can attack at two positions: either at the carbonyl carbon or at the $\text{β}$ carbon. Attack of the nucleophile at the carbonyl carbon is called 1, 2-addition, or direct addition. The 1, 2-addition or direct addition product is an allylic alcohol. The Williamson ether synthesis can be used to synthesize either symmetric or unsymmetric ethers via an ${\text{S}}_{\text{N}}\text{2}$ reaction between an alkoxide anion and an alkyl halide (RX). The Williamson synthesis takes place under basic conditions.

Answer to Problem 17.66P

The synthesis of given compound from $\text{phenylethanone }\left(\text{acetophenone}\right)$, using any reagents necessary is as shown below,

Explanation of Solution

The given reaction is,

The first step of the reaction is reduction of $\text{α,β-}$ unsaturated carbonyl to give an allylic alcohol. The reagents used for this step is ${\text{NaBH}}_{\text{4}}$ which is a source of ${\text{H}}^{\text{-}}$ nucleophile and water is a source of proton transfer. The product is ether, so the Williamson ether synthesis can be used to synthesize either symmetric or unsymmetric ethers via an ${\text{S}}_{\text{N}}\text{2}$ reaction between an alkoxide anion and an alkyl halide. The base used $\text{NaH}$ makes and alkoxide anion which further reacts with methyl bromide to give given product.

The synthesis of given compound from $\text{phenylethanone }\left(\text{acetophenone}\right)$, using any reagents necessary is as shown below,

Conclusion

The synthesis of given compound from $\text{phenylethanone }\left(\text{acetophenone}\right)$, using any reagents necessary is suggested by the reduction followed by the Williamson synthesis of an ether.