Photoredox‐Enabled Manganese‐Catalyzed [2+2+2] Cycloaddition of Alkynes

Abstract Manganese (Mn) is the third most abundant transition metal on Earth and is known for its exceptional biocompatibility. The development of novel catalytic mode for Mn is of great significance to advancing organic synthesis. In this study, the first manganese (Mn)‐catalyzed [2+2+2] cycloaddition of alkynes is achieved with the aid of visible‐light photoredox catalysis. Photoredox catalysis is proposed to promote the transformation by in situ reduction of high‐valent Mn(II) complex to Mn(0) species, thereby initiating the reaction. Additionally, a photooxidation‐induced reductive ellimination step is also suggested. This system is further distinguished by its notable tolerance towards both terminal and internal alkynes as counterparts of diynes.