Transition‐Metal Catalyzed [4+2]‐Cycloaddition Reactions: A Sexennial Update

Abstract Cycloaddition reactions serve as exceptionally useful strategy to provide atom‐economical, efficient and practical access to complex molecules from simple starting materials. The [4+2]‐cycloaddition reaction allows for the stereospecific construction of six‐membered carbo‐/heterocycles. Cycloaddition reactions catalyzed by transition metals are potent methods for the rapid construction of highly functionalized molecular frameworks. This review article summarizes the different reports on transition‐metal catalyzed [4+2]‐cycloaddition reactions involving various transition metals such as Pd, Cu, Rh, Au, Fe, Ni, Sc, Sn, Hf, Ag, Mn, Dy, Co etc. for the straightforward construction of pharmaceutically active six‐membered heterocycles. An emphasis is laid on the mechanistic insights to highlight the unique application of novel processes of transition‐metals in these transformations to build intricate polycyclic structures.