Tandem Reactions involving 1,4-Palladium Migrations.

Transition-metal-catalyzed tandem reactions have become a mainstay in organic chemistry owing to their high atom- and step-economies. Metal-migration-based tandem reactions allow the engagement of simple starting materials for incorporating functional groups into certain positions and constructing complex scaffolds, which provide novel means that are complementary to traditional cross-coupling or C-H activation processes. In light of the broad utility of the 1,4-Pd migration reaction, this paper reviews its progress in the past two decades, summarizing the tandem process and classifying it based on insertion, elimination, transmetalation, and C-H bond activation. Special emphasis is placed on the driving force of Pd migration and different migration mechanisms. Moreover, this review also attempts to summarize common strategies for improving the regio- and site-selectivities of the migration process.