Ruthenium-Catalyzed C−C Bond Cleavage of 2H-Azirines: A Formal [3+2+2] Cycloaddition to Fused Azepine Skeletons

2H‐azirines can serve as three‐atom synthons by C−C bond cleavage, however, it involves a high energy barrier under thermal conditions (>50.0 kcal mol−1). Reported is a ruthenium‐catalyzed [3+2+2] cycloaddition reaction of 2H‐azirines with diynes, thus leading to the formation of fused azepine skeletons. This approach features an unprecedented metal‐catalyzed C−C bond cleavage of 2H‐azirines at room temperature, and the challenging construction of aza‐seven‐membered rings from diynes. The results of this study provide a new reaction pattern for constructing nitrogen‐containing seven‐membered rings and may find applications in the synthesis of other complex heterocycles. Fusion rings: The ruthenium‐catalyzed [3+2+2] cycloaddition of 2H‐azirines with diynes has been established. This approach features an unprecedented metal‐catalyzed C−C bond cleavage of 2H‐azirines at room temperature, and achieves the challenging construction of aza‐seven‐membered rings from diynes.