Palladium-Catalyzed Double Cyclization Processes Leading to Polycyclic Heterocycles: Recent Advances

In this minireview, we discuss some recently reported methods for the synthesis of polycyclic heterocycles by palladium-catalyzed double cyclization processes. Paradigmatic examples taken by the most recent literature (from 2014 to the beginning of 2019) are presented. Only transformations in which palladium is involved in at least one cyclization stage are taken into consideration. The first part deals will Pd(0)-catalyzed processes. Double cyclizations initiated by the oxidative addition of an Ar-X bond or other functional groups are treated first, followed by processes beginning with carbopalladation by Pd(0) attack to unsaturated bonds. The second part concerns Pd(II)-catalyzed reactions, and begins with double cyclizations initiated by intramolecular nucleophilic attack to unsaturated bonds coordinated to Pd(II), followed by processes initiated by aromatic palladation.