Rhodium-Catalyzed [4+2+1] Cycloaddition of In Situ Generated Ene/Yne-Ene-Allenes and CO.

Reported herein is the first rhodium-catalyzed [4+2+1] cycloaddition of in situ generated ene/yne-ene-allenes and CO to synthesize challenging seven-membered carbocycles fused with five-membered rings. This reaction is designed based on the 1,3-acyloxy migration of ene/yne-ene-propargyl esters to ene/yne-ene-allenes, followed by oxidative cyclization, CO insertion, and reductive elimination to form the final [4+2+1] cycloadducts. The possible competing [4+1], [4+2], and [2+2+1] cycloadditions were disfavored, making the present reaction an efficient way to access functionalized 5/7 rings.