Rh(iii)-Catalyzed [3 + 2]/[4 + 2] annulation of acetophenone oxime ethers with 3-acetoxy-1,4-enynes involving C–H activation

A novel, synthetically simple, selective rhodium(iii)-catalyzed [3 + 2]/[4 + 2] annulation cascade reaction to construct complex azafluorenone frameworks has been developed. We herein report a rhodium(iii)-catalyzed [3 + 2]/[4 + 2] annulation of acetophenone oxime ethers with 3-acetoxy-1,4-enynes involving activation of both the C-H bond and the C-N pi-bond for producing trans-2,9b-dihydro-1H-indeno[1,2-b]pyridines with excellent chemoselectivity, regioselectivity and diastereoselectivity. Mechanistic studies show that the allyl-Rh intermediate may be formed to control chemoselectivity toward the [3 + 2]/[4 + 2] annulation reaction, enabling acetophenone oxime ethers as a three-atom/two-atom unit to construct two cycles, a five-membered carbocycle and a six-membered N-heterocycle, in a single reaction.