Chapter 12, Problem 12.65P

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.

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 the 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 metachloroperoxybenzoic acid.

Answer to Problem 12.65P

Synthesis of the given compound from acetylene and other required reagents is shown below.

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. Then $\text{but-2-yne}$ is treated with ${\text{H}}_{\text{2}}$ and Lindlar’s 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 $\text{mCPBA}$, 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 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.

In presence of sodium metal in ammonia, the 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 12.65P

Synthesis of the given compound from acetylene and other required reagents is shown below.

Explanation of Solution

Synthesis of the given compound is shown below.

Figure 2

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 the 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 $trans\text{-but-2-ene}$.

In the final step, $\left(E\right)\text{-but-2-ene}$ is treated with $\text{mCPBA}$, that is, alkene is oxidized to two enantiomers of epoxide.

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 $cis\text{-alkene}$.

Addition of two hydroxyl groups on double bond to form $1,2\text{-diol}$ is known as dihydroxylation. In presence of ${\text{OsO}}_4$, syndihydroxylation takes place. In this reaction two hydroxyl groups are added on the same side of the double bond.

Answer to Problem 12.65P

Synthesis of the given compound from acetylene and other required reagents is shown below.

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 ${\text{H}}_{\text{2}}$ and Lindlar’s 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, $\left(Z\right)\text{-but-2-ene}$ undergoes syn dihydroxylation to form the desired alcohol.

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 metachloroperoxybenzoic acid.

Answer to Problem 12.65P

Synthesis of the given compound from acetylene and other required reagents is shown below.

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 ${\text{H}}_{\text{2}}$ and Lindlar’s 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 $\text{mCPBA}$, alkene is oxidized to epoxide. Epoxidation is followed by ring opening with ${\text{H}}_3{\text{O}}^{+}$ to form two enantiomers of diols.

Conclusion

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