Transition‐Metal‐Catalyzed Convergent Synthesis of Heterocyclic Compounds via CH Activation/Cyclization: An Overview and Summary Toward Terminal Alkynes

The development of one-step transformations to heterocyclic compounds would considerably boost the synthetic efficiency in organic chemistry. In recent years, numerous examples of the transition-metal-catalyzed (TMC) CH activation/annulation strategy have been reported. Despite remarkable progress achieved with internal alkynes, allenes, and alkyne surrogates, terminal alkynes remain challenging substrates. Due to their relatively acidic terminal protons, terminal alkynes easily undergo alternative homocoupling reactions under commonly used oxidative conditions, exhibiting significant difficulties in CH functionalizations. To date, the CH activation involving terminal alkynes remains one of the most promising and appealing areas in organic synthesis. This review provides a comprehensive overview of the current progress in tandem CH activation reactions with terminal alkynes. With a strong emphasis on the catalysis of Rh and Co transition metals, it predominantly covers the synthesis of five-, six-membered heterocycles, and fused heterocycles. In this protocol, specific topics, such as purely chemical synthesis, electrochemical synthesis, and enantioselective synthesis, mechanistic details associated with the documented reactions are discussed. In addition, a tactical user guidance for terminal alkynes-participated CH activation is also put forward.