Question

What is the product of the following sequence of reactions?

A)
      

B)
     

C)
      

D)
     

Answer 1

Hint: The answer to this question involves the fact that sodium borohydride reduces the compound which is followed by bromination which is followed by oxidation at final stage.

Complete Solution :
We are about the various reactions which are used in organic chemistry to convert one compound to another.
_ Reactions like oxidation, reduction, halogenations, alkylation, acylation etc., are associated with several named reactions invented by scientists which are given by their name.
- Basic reactions include conversion from one compound completely to another or even it may be a slight modification of the original reactant.
Therefore based on these categories, the reactions are given several names and some compounds are used as catalysts which help for these conversions.
Now, in the above question the compound given is the cyclopentanone which is treated with several reagents and the conversions are done.

Let us see these conversions stepwise.
- For the first step, cyclopentanone is treated with sodium borohydride and an alcohol. $NaB{{H}_{4}}$ acts as good reducing agents and efficiently reduces aldehydes and ketones into alcohols.
Thus, cyclopentanone on treatment with $NaB{{H}_{4}}$ converts into cyclopentanol.
- Furthermore, in the second step this product is subjected to bromination with the help of $HBr$ that acts as brominating agent and thus cyclopentanol converts into bromocyclopentane.
- The third step is treatment of obtained product with magnesium in ether which converts bromo cyclopentane into cyclopentyl magnesium bromide that is Grignard reagent which is converted to cyclopentyl methanol by attacking formaldehyde and subsequent hydrolysis.
The final step involves oxidation reaction where PCC which is an oxidising agent in combination with dichloromethane converts cyclopentyl methanol to cyclopentane carbaldehyde.
The overall reaction is as shown below:

So, the correct answer is “Option D”.

Note: The main thing to note while solving conversion reactions is to be thorough with named reactions and the reagents used for basic conversions. This guides you to the correct answer.