PROBLEM7.64 - Organic Chemistry

Question

Question: Fluticasone, the chapter-opening molecule, can be prepared by the following reaction. Draw a stepwise mechanism for this reaction.

Step-by-Step Solution

Answer

ANSWER 

Formation of the fluticasone by the S_N1 mechanism

Preparation of fluticasone

Fluticasone is used for the treatment of cold-like nasal symptoms. 

It is prepared by the reaction of compound A with BrCH₂F and  K₂CO₃ by using DMF as a solvent. The reaction proceeds by the  S_N2 mechanism.

The role of the potassium carbonate is to abstract a proton from the thioacetic acid group. The alkyl halide then attacks the thioacetate, and the bromo group acts as a leaving group. 

Stepwise mechanism for the preparation of fluticasone

The first step involves the attack of potassium carbonate on the thioacetate group. This results in the loss of the proton and causes the attack of the alkyl halide BrCH₂F . The bromide group acts as leaving group. 

Formation of the fluticasone by the S_N1  mechanism