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 π-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.