Q12P - Organic Chemistry (Mcmurry)

Question

How might you carry out the following transformation? More than one step 

is needed.

Step-by-Step Solution

Answer

The below transformation is used to prepare 2-cyclopentyl-1-ethanol form 

cyclopentylmethanol.

Step 1: Preparation of (bromomethyl)cyclopentane from cyclopentylmethanol.

In the first step, the given starting material cyclopentylmethanol is treated with ${\mathrm{PBr}}_3$to form a P-O bond by displacing bromide ion. In the complex cation, the oxygen atom in the alcohol group bears a positive on it and making it as a good leaving group. This process is known as activation. The bromide ion attacks the carbon atom through${\mathrm{S}}_{\mathrm{N}}2$mechanism to form a new carbon-bromine bond as shown below.

Step 2: Conversion of (bromomethyl)cyclopentane into 2-cyclopentylacetic acid.

In the second step, (bromomethyl)cyclopentane reacts with$\mathrm{NaCH}$to give 2-

cyclopentylacetonitrile through an${\mathrm{S}}_{\mathrm{N}}2$nucleophilic substitution pathway. In the third

step, the hydrolysis of 2- cyclopentylacetonitrile in the presence of aqueous acid

$\left({\mathrm{H}}_3{\mathrm{O}}^{+}\right)$to produce 2-cyclopentylacetic acid as shown below

Step 3: Conversion of 2-cyclopentylacetic acid into 2-cyclopentyl-1-ethanol.

In the fourth step, 2-cyclopentylacetic acid is successfully converted to 2-

cyclopentyl-1-ethanol by using the strong reducing agent,${\mathrm{LiAIH}}_4$This above

said reaction is drawn as follows.