An annulation is a reaction that forms a ring or a cyclic compound. The Robinson annulation uses two reactions we have already learned, the Michael addition followed by an Aldol condensation to give a ring.
The first step of a Robinson annulation is a Michael addition.
Following the Michael addition, an aldol condensation forms the ring. An alpha proton is removed and a carbonyl is attacked giving the ring. Following dehydration, a conjugated carbonyl ring system is produced.
The Robinson annulation is an important reaction because the conjugated six-membered rings it can produce. These rings are are a part of steroids like testosterone.
