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.)

Short answer

Answer

Mechanism of formation of X

Step-by-step solution

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.

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