Reconstructive Synthesis of Fluorinated Dihydropyrido[1,2-a] indolones by a Cyclohexadione Cut-to-Fuse Strategy

We describe a fluorinative ring-cleavage reaction that breaks C−C bonds in cyclic β-diketones bearing an aryl moiety by using N-fluorobenzenesulfonimide (NFSI) in the presence of inorganic carbonates (Cs₂CO₃ or K₂CO₃) in methanol at room temperature within one hour. The generated fluorinated keto acid esters bearing ortho-nitro aryl groups were transformed into fluorinated dihydropyrido[1,2-a]indolones (DHPIs) via reductive cyclization using B₂(OH)₄ followed by amidation in the presence of K₂CO₃. This “cut-to-fuse” strategy enables the reconstructive synthesis of valuable fused heterocycles from relatively simple cyclohexadiones.