5.18 The Nazarov Cyclization

Although well established as a reliable method for forming new cyclopentenone rings from acyclic precursors, the Nazarov reaction has been the subject of substantial recent work. The effect of substituents on 1,4-dien-3-one precursors is discussed. Asymmetric methods are presented, including chirality transfer, chiral Lewis acids, and asymmetric organocatalysis. An overview is given of various ‘interrupted’ variants, in which cyclized intermediates undergo domino trapping reactions with either nucleophilic or electrophilic reagents. Finally, cyclization via alternative and unconventional precursors is described, including the vinylogous and iso-Nazarov reactions, transition metal activation of alkyne-containing substrates, and the aza-Nazarov reaction.