Chapter 16, Problem 23P

Show how each of the following compounds can be synthesized from cyclopentanol and any necessary organic or inorganic reagents. In many cases the desired compound can be made from one prepared in an earlier part of the problem.

$1$-Phenylcyclopentanol

$1$-Phenylcyclopentene

trans- $2$-Phenylcyclopentanol

$$

$\text{1-Phenyl-1,5-pentanediol}$

Interpretation Introduction

Interpretation:

Each of the given product is to be synthesized from cyclopentanol and necessary organic or inorganic reagents.

Concept introduction:

Alcohols can be prepared from a variety of reagents.

Reaction of Grignard reagents with carbonyl compounds produces the corresponding alcohols.

Grignard reagents also react with oxiranes to produce alcohols.

The allylic and benzylic carbon atoms are selectively brominated using NBS reagent.

Alcohols undergo dehydration in acidic medium, producing alkenes. These alkenes can be converted to diols using osmium tetra oxide.

Answer to Problem 23P

Solution:

Explanation of Solution

Synthesis of $\text{1-phenylcyclopentanol}$ from cyclopentanol.

The structure for cyclopentanol and $\text{1-phenylcyclopentanol}$ is as follows:

In $\text{1-phenylcyclopentanol}$, one phenyl ring is attached to the carbon atom bearing the hydroxyl group in cyclopentanol. This could be prepared by oxidation of cyclopentanol in presence of a mild oxidizing agent such as pyridinium chlorochromate in dichloromethane. This reaction will oxidize cyclopentanol into cyclopentanone. Cyclopentanone, when treated with phenyl magnesium bromide (Grignard reagent (PhMgBr)) in presence of diethyl ether with acidic workup, will form $\text{1-phenylcyclopentanol}$. The sequence of reactions starting from cyclopentanol to yield the final given product $\text{1-phenylcyclopentanol}$ is shown below.

Synthesis of $1-phenylcyclopentene$ from cyclopentanol.

The structure for cyclopentanol and $1-phenylcyclopentene$ is as follows:

In $\text{1-phenylcyclopentene}$, one phenyl ring is attached to a cyclopentane ring. The phenyl ring attached to the cyclopentane ring could be prepared by oxidation of cyclopentanol in presence of a mild oxidizing agent such as pyridinium chlorochromate in dichloromethane. This reaction will oxidize cyclopentanol into cyclopentanone. Cyclopentanone, when treated with phenyl magnesium bromide (Grignard reagent) in presence of diethyl ether with acidic workup, will form $\text{1-phenylcyclopentanol}$. This $\text{1-phenylcyclopentanol}$, when heated with sulfuric acid at ${200}^{0}C$, undergoes dehydration and results in the formation of $\text{1-phenylcyclopentene}$.

The sequence of reactions starting from cyclopentanol to yield the final given product $\text{1-phenylcyclopentanol}$ is shown as follows:

Synthesis of $\text{trans-2-phenylcyclopentanol}$ from cyclopentanol.

The structure for cyclopentanol and $\text{trans-2-phenylcyclopentanol}$ is as follows:

In $\text{trans-2-phenylcyclopentanol}$, one phenyl ring is attached trans to the hydroxyl group in cyclopentanol. Cyclopentene can be prepared by acid catalyzed dehydration of cyclopentanol at ${200}^{0}C$. This cyclopentene is then converted to an epoxide using mCPBA. This epoxide, when treated with phenyl magnesium bromide in presence of dimethyl ether in acidic workup, opens the epoxide ring such that the hydroxyl group on the cyclopentane ring and the phenyl ring are trans to each other.

The sequence of reactions starting from cyclopentanol to yield the final given product $\text{trans-2-phenylcyclopentanol}$ is shown below.

Synthesis of $2-phenylcyclopentanone$ from cyclopentanol.

The structure for cyclopentanol and $2-phenylcyclopentanone$ is as follows:

In $2-phenylcyclopentanone$, one phenyl ring is attached to the cyclopentanone on the carbon atom adjacent to the carbonyl group. Cyclopentene can be prepared by acid catalyzed dehydration of cyclopentanol at ${200}^{0}C$. This cyclopentene is then converted to an epoxide using mCPBA. This epoxide, when treated with phenyl magnesium bromide in presence of dimethyl ether in acidic workup, opens the epoxide ring such that the hydroxyl group and the phenyl ring are on adjacent carbon atoms. When this $\text{2-phenylcyclopentanol}$ is treated with a mild oxidizing agent such as pyridinium chlorochromate in dichloromethane, it results in $2-phenylcyclopentanone$.

The sequence of reactions starting from cyclopentanol to yield the final given product $2-phenylcyclopentanone$ is shown below.

Synthesis of the given diol from cyclopentanol.

The structure for the given diol is as follows:

In the given diol, one phenyl ring and one hydroxyl group are attached to the same carbon of cyclopentane ring. The other hydroxyl group is attached to C2 position of cyclopentane ring.

Oxidation of the cyclopentanol will produce cyclopentanone. Reaction of this cyclopentanone with phenyl magnesium bromide will form a tertiary alcohol. Acid catalyzed dehydration of this tertiary alcohol will produce $1-phenylcyclopentene$. This can be converted to the required diol using osmium tetraoxide in the presence of tertiary butyl hydroperoxide. The diol produced will have two hydroxyl groups cis to each other.

The sequence of reactions starting from cyclopentanol to yield the final given product $\text{2-phenylcyclopentanol}$ is shown below.

Synthesis of $\text{1-phenyl-1,5-pentanediol}$ from cyclopentanol.

The structure for cyclopentanol and $\text{1-phenyl-1,5-pentanediol}$ is as follows:

Cyclopentanol, when undergoes oxidation in presence of a mild oxidizing agent such as pyridinium chlorochromate in dichlormethane, the hydroxyl group turns to a carbonyl group and forms cyclopentanone. Cyclopentanone, when treated with Grignard reagent (PhMgBr) in the presence of diethyl ether with acidic workup, forms $\text{1-phenylcyclopentanol}$. This new alcohol after dehydration in the presence of sulfuric acid at $200{}^{0}C$ forms $\text{1-phenylcyclopentene}$. This $\text{1-phenylcyclopentene}$ undergoes ozonolysis reaction with reductive work up in the presence of Zn to get two carbonyl compounds within the same molecule. These carbonyl groups can be reduced to alcohols using $NaB{H}_4.$

The sequence of reactions is shown below.