Selective Synthesis of 3‐(α‐Fluorovinyl)indoles and 3‐Acylindoles via the Cascade Reactions of 1‐Phenylpyrazolidinones with α,α‐Difluoromethylene Alkynes

Presented herein is a selective synthesis of 3‐(α‐fluorovinyl)indoles and 3‐acylindoles via the coupling of 1‐phenylpyrazolidinones with α,α‐difluoromethylene alkynes. Mechanistically, the formation of 3‐(α‐fluorovinyl)indoles is resulted from a cascade process including Rh(III)‐catalyzed ortho‐C−H bond cleavage, regioselective triple bond insertion, pyrazolidinone ring‐opening, indole ring‐formation and HF elimination. Interestingly, when this reaction was carried out in CH3OH/H2O instead of CH3CN, the in situ formed 3‐(α‐fluorovinyl)indoles readily undergo a hydration process to afford 3‐acylindole derivatives. This protocol features with controllable selectivity, simultaneous formation of both the heterocyclic scaffold and the monofluoroalkenyl moiety, atom‐economy, substrate diversity, good functional group tolerance and redox‐neutral reaction conditions. Anticancer screening of selected products against two human cancer cell lines demonstrated their potential as lead compounds for drug development. magnified image