Chapter 12, Problem 12.63P

Devise a synthesis of each compound from acetylene and any other required reagents.

a. b. c. d.

Interpretation Introduction

(a)

Interpretation: Synthesis of the given compound from acetylene and other required reagents is to be devised.

Concept introduction: Terminal alkynes can be converted into internal alkynes by forming new $\text{C}-\text{C}$ bond. This bond is formed by treatment of alkyne by strong base and alkyl halide.

In presence of sodium metal in ammonia, the is alkyne is reduced to $trans\text{-alkene}$. The addition of ${\text{H}}_{\text{2}}$ takes place in anti fashion to the triple bond. The mechanism involves the addition of electron followed by protonation.

Answer to Problem 12.63P

Synthesis of the given compound from acetylene and other required reagents is shown in Figure 1.

Explanation of Solution

Synthesis of the given compound is shown below.

Figure 1

In the first step acetylene is converted to $\text{but-2-yne}$ by forming two new $\text{C}-\text{C}$ bonds. These bonds are formed by treatment of acetylene by strong base ${\text{NaNH}}_{\text{2}}$ and methyl bromide.

In the final step, $\text{but-2-yne}$ is treated with $\text{Na},{\text{NH}}_{\text{3}}$. The addition of ${\text{H}}_{\text{2}}$ takes place in anti fashion to the triple bond. Hence, the final product is $trans\text{-but-2-ene}$.

Conclusion

Synthesis of the given compound from acetylene and other required reagents is shown in Figure 1.

Interpretation Introduction

(b)

Interpretation: Synthesis of the given compound from acetylene and other required reagents is to be devised.

Concept introduction: Terminal alkynes can be converted into internal alkynes by forming new $\text{C}-\text{C}$ bond. This bond is formed by treatment of alkyne by strong base and alkyl halide.

The addition of ${\text{H}}_{\text{2}}$ in presence of catalyst is known as catalytic hydrogenation reaction. This is a syn addition. Alkyne is reduced to alkane. In this reaction two weak pi bond of alkene and sigma bond between ${\text{H}}_{\text{2}}$ is broken and four $\text{C}-\text{H}$ bonds are formed.

Answer to Problem 12.63P

Synthesis of the given compound from acetylene and other required reagents is shown in Figure 2.

Explanation of Solution

Synthesis of the given compound is shown below.

Figure 2

In the first step acetylene is converted to $\text{2, 7-dimethyloct-4-yne}$ by forming two new $\text{C}-\text{C}$ bonds. These bonds are formed by treatment of acetylene by strong base ${\text{NaNH}}_{\text{2}}$ and $\text{2-methylbromide}$.

In the final step, $\text{2, 7-dimethyloct-4-yne}$ is treated with ${\text{H}}_{\text{2}}$ in presence of $\text{Pd}$ catalyst. Alkyne is reduced to alkane. Hence, the final product is $\text{2, 7-dimethyloctane}$.

Conclusion

Synthesis of the given compound from acetylene and other required reagents is shown in Figure 2.

Interpretation Introduction

(c)

Interpretation: Synthesis of the given compound from acetylene and other required reagents is to be devised.

Concept introduction: Terminal alkynes can be converted into internal alkynes by forming new $\text{C}-\text{C}$ bond. This bond is formed by treatment of alkyne by strong base and alkyl halide.

The addition of ${\text{H}}_{\text{2}}$ in presence of catalyst is known as catalytic hydrogenation reaction. Lindlar catalyst consists of palladium deposited on calcium carbonate which is poisoned or deactivated by lead or sulfur. In presence of Lindlar catalyst, alkyne is reduced to $cis\text{-alkene}$.

In presence of peroxide alkene is oxidized to epoxide this is known as epoxidation. The weak pi bond of alkene and weak $\text{O}-\text{O}$ bond of peroxide are broken and two new $\text{C}-\text{O}$ bonds are formed. Breaking of bonds and formation of bonds takes place in single step. $\text{mCPBA}$ is $\text{meta-chloroperoxybenzoic}\text{acid}$.

Answer to Problem 12.63P

Synthesis of the given compound from acetylene and other required reagents is shown in Figure 3.

Explanation of Solution

Synthesis of the given compound is shown below.

Figure 3

In the first step, acetylene is converted to $\text{but-2-yne}$ by forming two new $\text{C}-\text{C}$ bonds. These bonds are formed by treatment of acetylene by strong base ${\text{NaNH}}_{\text{2}}$ and methyl bromide. Then $\text{but-2-yne}$ is treated with with ${\text{H}}_{\text{2}}$ and Lindlar catalyst. The addition of ${\text{H}}_{\text{2}}$ takes place in syn fashion to the triple bond. The product formed is $\left(Z\right)\text{-but-2-ene}$. In the final step, $\left(Z\right)\text{-but-2-ene}$ is treated with $\text{mCPBA}$ ($\text{meta-chloroperoxybenzoic}\text{acid}$), alkene is oxidized to epoxide. Hence, the final product is $\left(2R,3S\right)\text{-2, 3-dimethyloxirane}$.

Conclusion

Synthesis of the given compound from acetylene and other required reagents is shown in Figure 3.

Interpretation Introduction

(d)

Interpretation: Synthesis of the given compound from acetylene and other required reagents is to be devised.

Concept introduction: Terminal alkynes can be converted into internal alkynes by forming new $\text{C}-\text{C}$ bond. This bond is formed by treatment of alkyne by strong base and alkyl halide.

The addition of ${\text{H}}_{\text{2}}$ in presence of catalyst is known as catalytic hydrogenation reaction. Lindlar catalyst consists of palladium deposited on calcium carbonate which is poisoned or deactivated by lead or sulfur. In presence of Lindlar catalyst, alkyne is reduced to $cis\text{-alkene}$.

In presence of peroxide alkene is oxidized to epoxide this is known as epoxidation. The weak pi bond of alkene and weak $\text{O}-\text{O}$ bond of peroxide are broken and two new $\text{C}-\text{O}$ bonds are formed. Breaking of bonds and formation of bonds takes place in single step. $\text{mCPBA}$ is $\text{meta-chloroperoxybenzoic}\text{acid}$.

Answer to Problem 12.63P

Synthesis of the given compound from acetylene and other required reagents is shown in Figure 4.

Explanation of Solution

Synthesis of the given compound is shown below.

Figure 4

In the first step acetylene is converted to $\text{but-2-yne}$ by forming two new $\text{C}-\text{C}$ bonds. These bonds are formed by treatment of acetylene by strong base ${\text{NaNH}}_{\text{2}}$ and methyl bromide. Then $\text{but-2-yne}$ is treated with with ${\text{H}}_{\text{2}}$ and Lindlar catalyst. The addition of ${\text{H}}_{\text{2}}$ takes place in syn fashion to the triple bond. The product formed is $\left(Z\right)\text{-but-2-ene}$. In the final step, $\left(Z\right)\text{-but-2-ene}$ is treated with $\text{mCPBA}$ ($\text{meta-chloroperoxybenzoic}\text{acid}$), alkene is oxidized to epoxide. Epoxidation is followed by ring opening with ${\text{H}}_3{\text{O}}^{+}$. Hence, the final product is $\left(2R,3R\right)\text{-butane-2, 3-diol}$.

Conclusion

Synthesis of the given compound from acetylene and other required reagents is shown in Figure 4.