Rhenium‐Catalyzed Synthesis of Stereodefined Cyclopentenes from β‐Ketoesters and Aliphatic Allenes

Come on allene : Commercially available [Re 2 (CO) 10 ] as a catalyst provides five‐membered carbocycles in moderate to excellent yields with high stereoselectivity (see scheme). The configuration at each of the three sp 3 carbon centers of the ring is defined. The reaction proceeds at the β, γ, and adjacent methylene positions of the allene; previously, similar reactions usually occurred at the α, β, and γ positions of the allene.