Robinson annulation: practice and mechanism
First a Michael addition to methyl vinyl ketone, then an intramolecular aldol condensation: a new six-membered ring containing an enone is built onto the ketone.
Example
Two steps in a row: first the ketone enolate attacks methyl vinyl ketone in a Michael addition. Then the new methyl ketone group reacts with the original carbonyl group in an intramolecular aldol condensation. A new six-membered ring with a cyclohexenone forms.
Mechanism step by step
- 1
The ketone enolate adds to methyl vinyl ketone (Michael addition): a 1,5-dicarbonyl compound forms.
- 2
A new enolate at the methyl group of the former MVK attacks the ring ketone (intramolecular aldol reaction), closing a six-membered ring.
- 3
On warming water is eliminated: a bicyclic enone forms (e.g. an octalone).
Practice tasks
Which product forms, which reagent is needed? After each answer you see the explanation.
Which main product forms?
Typical mistakes
Often confused with: Michael addition · Aldol condensation
Frequently asked questions
What is the Robinson annulation used for?
For six-membered rings with an enone, e.g. in building steroids and terpenes (Wieland–Miescher ketone).
How do I recognise a Robinson annulation in the product?
A cyclohexenone fused to an existing ring. Working backwards: disconnect the C=C bond (aldol), then the Michael bond.