Three Carbons for Complexity! Recent Developments of Palladium-Catalyzed Reactions of Allenes

The three carbon atoms of allene moieties allow unique transformations and rapid generation of complexity. Not surprisingly, allenes became extremely versatile building blocks in organic synthesis. Transition-metal-catalyzed reactions of these cumulene pi-systems have been particularly successful, and many applications in the synthesis of complex products have been reported. This review summarizes the palladium-catalyzed transformation of allenes published during the last decade. Many of the examples presented are impressive multicomponent processes or cascade reactions involving two or more steps leading to molecular complexity in simple one-pot operations. Consequently, several reactions have been developed with the goal of delivering new synthetic routes to natural products.