Q.53. - Organic Chemistry

Question

Question: Draw a stepwise mechanism for the following Robinson annulation. This reaction was a key step in a synthesis of the steroid cortisone by R. B. Woodward and co-workers at Harvard University in 1951.

Step-by-Step Solution

Answer

Answer

Mechanism 

Step 1: Robinson Annulation

The combination reaction of the Michael Reaction and the Aldol Reaction named as the Robinson Annulation is useful in generating a structure containing a six-membered ring.

Step 2: Mechanism of Robinson Annulation Reaction

The carbonyl compound containing a more acidic  $\mathit{\alpha }$-hydrogen is attacked by the base and thus reacts with the other carbonyl compound to form an enolate. The enolate then undergoes reaction.

The obtained product undergoes tautomerization and hence intramolecular aldol reaction to form a six-membered ring.

Step 3: Mechanism of the given reaction

The mechanism of the given reaction is given hereunder. 

Stepwise mechanism of the given reaction