As originally described , the Nazarov cyclization involves the activation of a divinyl ketone using a stoichiometric Lewis acid or protic acid promoter . The key step of the reaction mechanism involves a cationic 4π @-@ electrocyclic ring closure which forms the cyclopentenone product ( See Mechanism below ) . As the reaction has been developed , variants involving substrates other than divinyl ketones and promoters other than Lewis acids have been subsumed under the name Nazarov cyclization provided that they follow a similar mechanistic pathway .