Q.63. - Organic Chemistry

Question

Question: Devise a synthesis of 2-methylcyclopentanone from cyclohexene. You may also use any required reagents

Step-by-Step Solution

Answer

Answer

Cyclohexene on ozonolysis followed by oxidation gives a dicarboxylic acid. This is followed by esterification with ethanol and transesterification to form ethyl-2-oxocyclopentane carboxylate. Substitution in the second position gives 2-methylcyclopentanone.

Step 1: Ring contraction reactions

A series of reactions that leads to a decrease in the number of carbon atoms in a chain are called ring contraction reactions.

These reactions are used to produce strained rings which are not easily synthesized by cyclization.

Step 2: Ozonolysis reaction

The addition of ozone to an alkene to cleave the double bond to form two carbonyl compounds is called ozonolysis.

This reaction is mainly used to identify the position of unsaturation in a compound.

Ozonolysis can also be used for ring-opening in cycloalkenes.

Step 3: Synthesis of 2-methylcyclopentanone from cyclohexene

The cyclohexene ring is opened by ozonolysis forming hexane-1,6- dial.

Ozonolysis of cyclohexene

 

The dialdehyde formed is oxidized to dicarboxylic acid using chromium trioxide which forms diester with ethanol.

Transesterification causes the formation of ethyl-2-oxocyclopentane carboxylate.

Oxidation followed esterification

 

Ethyl-2-oxocyclopentane carboxylate undergoes substitution reaction to form 2-methyl cyclopentanone.

Synthesis of 2-methylcyclopentanone