Borrowing Hydrogen and Acceptorless Dehydrogenative Coupling in the Multicomponent Synthesis of N‐Heterocycles: A Comparison between Base and Noble Metal Catalysis

Abstract Acceptorless dehydrogenative coupling reactions (ADC) and hydrogen transfer strategies (HT) provide a powerful tool in the multicomponent formation of N ‐ heterocycles. A broad variety of complex products can be obtained starting from simple, cheap and commercially available reagents. The protocols are highly atom‐efficient, as water, dihydrogen, or in some cases hydrogen peroxide, are the only by‐products. Moreover, neither further reducing or oxidizing agents, nor external hydrogen are in general required. Especially base metal‐catalyzed strategies become ever more important. Therefore, in recent years, various different manganese, iron, cobalt, nickel and copper catalysts have been developed. This Minireview highlights the progress that has been made by using abundant metal complexes to promote multicomponent cyclizations for the formation of N ‐ heterocycles and compares their performance with available noble metal catalyst systems.