Question

Identify X and Y, two of the intermediates in a synthesis of the antidepressant venlafaxine (trade name Effexor), in the following reaction scheme. Write a mechanism for the formation of X from W.

Short answer

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

Step-by-step solution

Robinson annulation

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

Mechanism of Robinson annulation reaction

The carbonyl compound containing a more acidic -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 an intramolecular aldol reaction to form a six-membered ring.

Mechanism of the given reaction

The mechanism of the given reaction is given hereunder:

Stepwise mechanism of the given reaction