Robinson annulation template

Cyclohexanone enolate adds to methyl vinyl ketone; the 1,5-diketone closes by aldol condensation to the bicyclic enone (octalone).

Mechanism step by step

Michael addition then intramolecular aldol condensation: a new six-membered ring

1. Enolate – Hydroxide removes an α-H
2. Michael addition – The enolate adds to the end of the enone
3. Protonation – A 1,5-diketone
4. Second enolate – The methyl ketone is deprotonated
5. Ring closure – Intramolecular aldol: a six-membered ring
6. Protonation – The β-hydroxy ketone
7. Enolate – The CH₂ next to C=O is deprotonated
8. Dehydration (E1cB) – OH⁻ leaves: the conjugated enone

Key points

• Builds the steroid and terpene ring skeleton (Wieland–Miescher ketone).
• Michael first, aldol second: the 1,5-diketone closes to a six-membered ring.
• Dehydration is driven by conjugation of C=C with C=O.
• Asymmetric versions use proline as catalyst (Hajos–Parrish).

Drawn with 221 atoms, 29 arrows, 10 shapes – every one editable in MolDraw.

Sources

• Rapson & Robinson, J. Chem. Soc. 1935, 1285 Original paper
• Kürti & Czakó, Strategic Applications of Named Reactions in Organic Synthesis, Elsevier 2005 Textbook
• Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012 Textbook