Q.58. - Organic Chemistry

Question

Question: One step in a recent short synthesis of a prostaglandin (Section 19.6) involves the conversion of succinaldehyde to the bicyclic hemiacetal X. Draw a stepwise mechanism for this process. (Hint: The mechanism begins with an intermolecular aldol reaction.)

Step-by-Step Solution

Answer

Answer

 

Mechanism of formation of X

Step 1: Aldol reaction in acidic medium

Aldol condensation can be both acid-catalyzed and base-catalyzed. The mechanism is similar for both, but in case of acid-catalyzed aldol condensation, instead of abstraction of alpha hydrogen, protonation of oxygen occurs. The enol tautomer acts as a nucleophile in this case.

Step 2: Mechanism for the formation of X

The starting material, succinic aldehyde is redrawn as shown below:

Structure of succinaldehyde

 

Two molecules of succinic aldehyde undergo an intermolecular aldol reaction in presence of an acid, the mechanism of which is given below:

Mechanism of formation of X