Q19. - Organic Chemistry

Question

Question: Identify A, B, and C, intermediates in the synthesis of the five-membered ring called an $\alpha$ -methylene- $\gamma$-butyrolactone. This heterocyclic ring system is present in some antitumor agents.  

Step-by-Step Solution

Answer

Answer

 

The structures A, B, and C, intermediates in the synthesis of the five-membered ring formed are shown below:-

Representation of the reaction scheme for the formation of $\alpha$ -methylene- $\gamma$ -butyrolactone

Step 1: Stereoselectivity of LDA

LDA is a strong base and bulky base that abstracts protons from the least hindered side.

       Representation of the intermediate formed by LDA

Step 2: Use of alkylation

With alkylation, a methyl group adjacent to a carbonyl group is added where it replaces hydrogen.

Representation of the product formed by methylation

Step 3: Halogenation in acids

Halogenation is carried out by treating a carbonyl compound with a halogen in the presence of an acid.

  Representation of the product formed by halogenation in acid

Step 4: Use of lithium carbonate

Lithium carbonate is a strong base that abstracts the most acidic hydrogen via an elimination mechanism. The product obtained from the reaction is an elimination product.

Hence, considering the functions of the reagents, the structures A, B, and C, intermediates in the synthesis of the five-membered ring formed are shown below:-

 

Representation of the reaction scheme for the formation of $\alpha$ -methylene-  $\gamma$-butyrolactone