Question

Show how you would use the Robinson annulation to synthesize the following compounds.

Short answer

The starting reactants will be:

a)

b)

c)

Step-by-step solution

Robinson annulation 

Robinson annulation is a chemical reaction that results in a ring formation. Robinson annulations reaction forms unsaturated cyclic ketones from methyl vinyl ketones andaldehyde or ketones.

Robinson annulation has two reactions: First, Michael reaction and then intramolecular aldol condensation to give a new six-membered ring containing an alpha, beta-unsaturated ketone.

Process of Robinson annulation 

Robinson annulation begins with a Micheal addition followed by aldol condensation:

• Essential condition present, which removes - proton from ketone.
• In Micheal’s reaction, the enolate formed attacks enone.
• Enolate protonates to give ketone.
• Base removes- proton.
• In an aldol reaction, the enolate attacks the ketone.
• Alkoxide protonates to provide alcohol.
• The command removes -proton, and elimination of hydroxide occurs to give enone.

Steps of the process of Robinson Annulation

Robinson Annulation Retrosynthesis: 

As in the question, we are given the end product of Robinson Annulation instead of reactants so that it will work backwardly. We will first be seeing how the end product is synthesised from aldol condensation and then Michael’s reaction.

Hydration 

In Robinson, Annulation dehydration occurs at last, but here hydration is done.

a)

b)

c)

From six-membered ring to cyclic aldol formation 

In Robinson Annulation from cyclic aldol, a six-membered ring forms but here opposite occurs.

a)

b)

c)

Michael’s reaction 

Here Michael’s reaction is performed in the opposite direction.

a)

Reverse Michael reaction

All steps together are:

Robinson Annulation Retrosynthesis

b)

Reverse Michael reaction

All steps together are:

Robinson Annulation Retrosynthesis

c)

Reverse Michael reaction

All steps together are: