The Pd(II)-Initiated Catellani-type Reactions.

The Catellani reaction is known as a powerful strategy for the expeditious synthesis of highly substituted arenes and benzo-fused rings, which are usually difficult to access through traditional cross-coupling strategies. It utilizes the synergistic interplay of palladium and norbornene catalysis to facilitate sequential ortho C-H functionalization and ipso termination of aryl halides in a single operation. In classical Catellani-type reactions, aryl halides are mainly used as the substrates, and a Pd-0 catalyst is required to initiate the reaction. Nevertheless, recent advances showcase that Catellani-type reactions can also be initiated by a Pd-II catalyst with different starting materials instead of aryl halides via different reaction mechanisms and under different conditions. This emerging concept of Pd-II/norbornene cooperative catalysis has significantly advanced Catellani-type reactions, thus enabling future developments of this field. In this Minireview, Pd-II-initiated Catellani-type reactions and their application in the synthesis of bioactive molecules are summarized.