Robinson annulation through the Stork enamine

The Robinson annulation builds a six-membered ring bearing an enone. Stork showed that the pyrrolidine enamine of cyclohexanone undergoes Michael addition to methyl vinyl ketone under neutral conditions, without the polymerization of the unsaturated ketone or the polyalkylation caused by strong bases.

After hydrolysis, 2-(3-oxobutyl)cyclohexanone cyclizes under basic conditions (intramolecular aldol condensation) and dehydrates to the octalone, a classic intermediate in the synthesis of steroids and terpenes. The Robinson annulation is studied in topic 7.