Chapter 26, Problem 26.49P

Draw the product formed from the ring-closing metathesis of each compound. Then, devise a synthesis of each metathesis starting material from benzene, alcohols with less than five carbons, and any needed organic and inorganic reagents.

a. b.

Interpretation Introduction

(a)

Interpretation: The product formed from the ring-closing metathesis of given compound is to be drawn, and the synthesis of metathesis starting material using ${\text{CH}}_{\text{2}}{\left({\text{CO}}_{\text{2}}\text{Et}\right)}_{\text{2}}$, alcohols with less than five carbons, and any needed organic and inorganic reagents is to be stated.

Concept introduction: The ring-closing metathesis (RCM) by Grubbs catalyst occurs, when the starting material is diene. This reaction is facilitated under high-dilution condition as it favors intramolecular metathesis instead of intermolecular metathesis.

Answer to Problem 26.49P

The product formed from the ring-closing metathesis of given compound is

The synthesis of metathesis starting material using ${\text{CH}}_{\text{2}}{\left({\text{CO}}_{\text{2}}\text{Et}\right)}_{\text{2}}$, alcohols with less than five carbons, and any needed organic and inorganic reagents is,

Explanation of Solution

The given compound is a diene.

The ring-closing metathesis (RCM) by Grubbs catalyst occurs, when the starting material is diene. This reaction is facilitated under high-dilution condition as it favors intramolecular metathesis instead of intermolecular metathesis.

The product formed from the ring-closing metathesis of given compound is drawn in Figure 1.

Figure 1

The synthesis of metathesis starting material involves ten steps. The first step is Friedel-Crafts alkylation of benzene with $1,1$-dichloropropane in the presence of ${\text{AlCl}}_{\text{3}}$ catalyst to yield the ($1$-chloropropyl) benzene. The second step is treatment of ($1$-chloropropyl) benzene with water to yield $1$-phenylpropan-$1$-ol. The third step is protection of the $\text{OH}$ group by $\text{TMSCl}$. The fourth step is chlorination of protected alcohol in the presence of $hv$. The fifth step is nucleophilic attack of ${}^{-}\text{OH}$ on the carbon atom of $\text{C}-\text{Cl}$ bond to convert it into corresponding alcohol $\left({\text{1}}^{\text{ο}}\right)$. The sixth step is oxidation of primary alcohol by $\text{PCC}$ to convert it into corresponding aldehyde. The seventh step is Wittig reaction with ${\text{CH}}_{\text{2}}={\text{PPh}}_{\text{3}}$ to convert the $\text{C}=\text{O}$ bond of $\text{CHO}$ group to the $\text{C}=\text{C}$ bond. The eighth step is deprotection of the $\text{OH}$ group (protected by $\text{OTMS}$) group by $\text{TBAF}$. The ninth step is conversion of the $\text{OH}$ group to the alkoxide salt by $\text{NaH}$. The tenth step is treatment of alkoxide salt with $3$-chloroprop-$1$-ene to yield the desired product.

Figure 2

Conclusion

The product formed from the ring-closing metathesis of given compound is drawn in Figure 1. The synthesis of metathesis starting material using ${\text{CH}}_{\text{2}}{\left({\text{CO}}_{\text{2}}\text{Et}\right)}_{\text{2}}$, alcohols with less than five carbons, and any needed organic and inorganic reagents is shown in Figure 2.

Interpretation Introduction

(b)

Interpretation: The product formed from the ring-closing metathesis of given compound is to be drawn, and the synthesis of metathesis starting material using ${\text{CH}}_{\text{2}}{\left({\text{CO}}_{\text{2}}\text{Et}\right)}_{\text{2}}$, alcohols with less than five carbons, and any needed organic and inorganic reagents is to be stated.

Concept introduction: The ring-closing metathesis (RCM) by Grubbs catalyst occurs, when the starting material is diene. This reaction is facilitated under high-dilution condition as it favors intramolecular metathesis instead of intermolecular metathesis.

Answer to Problem 26.49P

The product formed from the ring-closing metathesis of given compound is,

The synthesis of metathesis starting material using ${\text{CH}}_{\text{2}}{\left({\text{CO}}_{\text{2}}\text{Et}\right)}_{\text{2}}$, alcohols with less than five carbons, and any needed organic and inorganic reagents is,

Explanation of Solution

The given compound is a diene.

The ring-closing metathesis (RCM) by Grubbs catalyst occurs, when the starting material is diene. This reaction is facilitated under high-dilution condition as it favors intramolecular metathesis instead of intermolecular metathesis.

The product formed from the ring-closing metathesis of given compound is drawn in Figure 3.

Figure 3

The synthesis of metathesis starting material involves nine steps. The first step is Friedel-Crafts alkylation of benzene with chloromethane in the presence of ${\text{AlCl}}_{\text{3}}$ catalyst to yield toluene. The second step is oxidation of toluene by ${\text{CrO}}_{\text{2}}{\text{Cl}}_2$ (chromyl chloride) to yield benzaldehyde. The third step is Wittig reaction of benzaldehyde with ${\text{CH}}_{\text{2}}={\text{PPh}}_{\text{3}}$ to yield styrene. The fourth step is hydroboration oxidation of styrene to yield $2$-phenylethanol $\left({\text{1}}^{\text{ο}}\text{alcohol}\right)$. The fifth step is oxidation of primary alcohol by $\text{PCC}$ to convert it into corresponding aldehyde ($3$-phenylpropanal). The sixth step is Wittig reaction of $3$-phenylpropanal with ${\text{CH}}_{\text{2}}={\text{PPh}}_{\text{3}}$ to yield allylbenzene. The seventh step is hydroboration oxidation of allylbenzene to yield $3$-phenylpropan-$1$-ol $\left({\text{1}}^{\text{ο}}\text{alcohol}\right)$. The eighth step is oxidation of primary alcohol by $\text{PCC}$ to convert it into corresponding aldehyde. The ninth step is acetal formation, using two equivalents of prop-$2$-en-$1$-olin the presence of $\text{TsOH}$ to yield the desired compound.

Figure 4

Conclusion

The product formed from the ring-closing metathesis of given compound is drawn in Figure 3. The synthesis of metathesis starting material using ${\text{CH}}_{\text{2}}{\left({\text{CO}}_{\text{2}}\text{Et}\right)}_{\text{2}}$, alcohols with less than five carbons, and any needed organic and inorganic reagents is shown in Figure 4.