Chapter 21, Problem 21.57P

What Wittig reagent and carbonyl compound are needed to prepare each alkene? When two routes are possible, indicate which route, if any, is preferred.

a. ${\left({\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\right)}_{\text{2}}\text{C}={\text{CHCH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{3}}$ b. c. d.

Interpretation Introduction

(a)

Interpretation: The Wittig reagent and carbonyl compound that are needed to prepare the given alkene are to be predicted, and the preferred route is to be identified, if any.

Concept introduction: One should follow the two steps retro synthesis to find out the starting materials that are needed to prepare the given alkene. The first step is cleaving of $\text{C}=\text{C}$ into two components, carbonyl and Wittig reagent. The second step is selection of preferred pathway. While selection one should consider that pathway in which Wittig reagent is derived from an unhindered alkyl halide, like ${\text{CH}}_{\text{3}}\text{X}$ or ${\text{RCH}}_{\text{2}}\text{X}$.

Answer to Problem 21.57P

The Wittig reagent and carbonyl compound that are needed to prepare the given alkene are ${\left({\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\right)}_{\text{2}}\text{C}=\text{O}$ and ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{CH}={\text{PPH}}_{\text{3}}$. The preferred pathway is Route 1.

Explanation of Solution

One should follow the two steps retrosynthesis to find out the Wittig reagent and carbonyl compound that are needed to prepare the given alkene. The first step is cleaving of $\text{C}=\text{C}$ into two components, carbonyl and Wittig reagent.

Figure 1

The second step is selection of preferred pathway. The Wittig reaction involves two pathways to synthesize unsymmetrical alkene and only one pathway to synthesize symmetrical alkene.

While selection one should consider that pathway in which Wittig reagent is derived from an unhindered alkyl halide, like ${\text{CH}}_{\text{3}}\text{X}$ or ${\text{RCH}}_{\text{2}}\text{X}$.

Figure 2

The first step for the preparation of Wittig reagent, formation of phosphonium salts, takes place through the ${\text{S}}_{\text{N}}\text{2}$ reaction of ${\text{Ph}}_{\text{3}}\text{P}$ with an alkyl halide. Since ${\text{S}}_{\text{N}}\text{2}$ reaction prefers $1^{\text{ο}}$ alkyl halide (unhindered), the preferred path would be Route 1.

Thus, the Wittig reagent and carbonyl compound that are needed to prepare the given alkene are ${\left({\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\right)}_{\text{2}}\text{C}=\text{O}$ and ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{CH}={\text{PPH}}_{\text{3}}$.

Conclusion

The Wittig reagent and carbonyl compound that are needed to prepare the given alkene are ${\left({\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\right)}_{\text{2}}\text{C}=\text{O}$ and ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{CH}={\text{PPH}}_{\text{3}}$. The preferred pathway is Route 1.

Interpretation Introduction

(b)

Interpretation: The Wittig reagent and carbonyl compound that are needed to prepare the given alkene are to be predicted, and the preferred route is to be identified, if any.

Concept introduction: One should follow the two steps retro synthesis to find out the starting materials that are needed to prepare the given alkene. The first step is cleaving of $\text{C}=\text{C}$ into two components, carbonyl and Wittig reagent. The second step is selection of preferred pathway. While selection one should consider that pathway in which Wittig reagent is derived from an unhindered alkyl halide, like ${\text{CH}}_{\text{3}}\text{X}$ or ${\text{RCH}}_{\text{2}}\text{X}$.

Answer to Problem 21.57P

The Wittig reagent and carbonyl compound that are needed to prepare the given alkene are ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{CHO}$ and ${\text{CH}}_{\text{3}}\text{CH}={\text{PPH}}_{\text{3}}$. The preferred pathway is Route 1.

Explanation of Solution

One should follow the two steps retrosynthesis to find out the Wittig reagent and carbonyl compound that are needed to prepare the given alkene. The first step is cleaving of $\text{C}=\text{C}$ into two components, carbonyl and Wittig reagent.

Figure 3

The second step is selection of preferred pathway. The Wittig reaction involves two pathways to synthesize unsymmetrical alkene and only one pathway to synthesize symmetrical alkene.

While selection one should consider that pathway in which Wittig reagent is derived from an unhindered alkyl halide, like ${\text{CH}}_{\text{3}}\text{X}$ or ${\text{RCH}}_{\text{2}}\text{X}$.

Figure 4

The first step for the preparation of Wittig reagent, formation of phosphonium salts, takes place through the ${\text{S}}_{\text{N}}\text{2}$ reaction of ${\text{Ph}}_{\text{3}}\text{P}$ with an alkyl halide. Since ${\text{S}}_{\text{N}}\text{2}$ reaction prefers $1^{\text{ο}}$ alkyl halide (unhindered), the preferred path would be Route 1.

Thus, the Wittig reagent and carbonyl compound that are needed to prepare the given alkene are ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{CHO}$ and ${\text{CH}}_{\text{3}}\text{CH}={\text{PPH}}_{\text{3}}$.

Conclusion

The Wittig reagent and carbonyl compound that are needed to prepare the given alkene are ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{CHO}$ and ${\text{CH}}_{\text{3}}\text{CH}={\text{PPH}}_{\text{3}}$. The preferred pathway is Route 1.

Interpretation Introduction

(c)

Interpretation: The Wittig reagent and carbonyl compound that are needed to prepare the given alkene are to be predicted, and the preferred route is to be identified, if any.

Concept introduction: One should follow the two steps retrosynthesis to find out the starting materials that are needed to prepare the given alkene. The first step is cleaving of $\text{C}=\text{C}$ into two components, carbonyl and Wittig reagent. The second step is selection of preferred pathway. While selection one should consider that pathway in which Wittig reagent is derived from an unhindered alkyl halide, like ${\text{CH}}_{\text{3}}\text{X}$ or ${\text{RCH}}_{\text{2}}\text{X}$.

Answer to Problem 21.57P

The Wittig reagent and carbonyl compound that are needed to prepare the given alkene are shown in Figure 6. The preferred pathway is Route 1.

Explanation of Solution

One should follow the two steps retrosynthesis to find out the Wittig reagent and carbonyl compound that are needed to prepare the given alkene. The first step is cleaving of $\text{C}=\text{C}$ into two components, carbonyl and Wittig reagent.

Figure 5

The second step is selection of preferred pathway. The Wittig reaction involves two pathways to synthesize unsymmetrical alkene and only one pathway to synthesize symmetrical alkene.

While selection one should consider that pathway in which Wittig reagent is derived from an unhindered alkyl halide, like ${\text{CH}}_{\text{3}}\text{X}$ or ${\text{RCH}}_{\text{2}}\text{X}$.

Figure 6

The first step for the preparation of Wittig reagent, formation of phosphonium salts, takes place through the ${\text{S}}_{\text{N}}\text{2}$ reaction of ${\text{Ph}}_{\text{3}}\text{P}$ with an alkyl halide. Since ${\text{S}}_{\text{N}}\text{2}$ reaction prefers $1^{\text{ο}}$ alkyl halide (unhindered), the preferred path would be Route 1.

Thus, the Wittig reagent and carbonyl compound that are needed to prepare the given alkene are,

Figure 7

Conclusion

The Wittig reagent and carbonyl compound that are needed to prepare the given alkene are shown in Figure 6. The preferred pathway is Route 1.

Interpretation Introduction

(d)

Interpretation: The Wittig reagent and carbonyl compound that are needed to prepare the given alkene are to be predicted, and the preferred route is to be identified, if any.

Concept introduction: One should follow the two steps retrosynthesis to find out the starting materials that are needed to prepare the given alkene. The first step is cleaving of $\text{C}=\text{C}$ into two components, carbonyl and Wittig reagent. The second step is selection of preferred pathway. While selection one should consider that pathway in which Wittig reagent is derived from an unhindered alkyl halide, like ${\text{CH}}_{\text{3}}\text{X}$ or ${\text{RCH}}_{\text{2}}\text{X}$.

Answer to Problem 21.57P

The Wittig reagent and carbonyl compound that are needed to prepare the given alkene are shown in Figure 7. The preferred pathway is Route 1.

Explanation of Solution

One should follow the two steps retrosynthesis to find out the Wittig reagent and carbonyl compound that are needed to prepare the given alkene. The first step is cleaving of $\text{C}=\text{C}$ into two components, carbonyl and Wittig reagent.

Figure 8

The second step is selection of preferred pathway. The Wittig reaction involves two pathways to synthesize unsymmetrical alkene and only one pathway to synthesize symmetrical alkene.

While selection one should consider that pathway in which Wittig reagent is derived from an unhindered alkyl halide, like ${\text{CH}}_{\text{3}}\text{X}$ or ${\text{RCH}}_{\text{2}}\text{X}$.

Figure 9

The first step for the preparation of Wittig reagent, formation of phosphonium salts, takes place through the ${\text{S}}_{\text{N}}\text{2}$ reaction of ${\text{Ph}}_{\text{3}}\text{P}$ with an alkyl halide. Since ${\text{S}}_{\text{N}}\text{2}$ reaction prefers $1^{\text{ο}}$ alkyl halide (unhindered), the preferred path would be Route 1.

Thus, the Wittig reagent and carbonyl compound that are needed to prepare the given alkene are,

Figure 10

Conclusion

The Wittig reagent and carbonyl compound that are needed to prepare the given alkene are shown in Figure 10. The preferred pathway is Route 1.