Metal-free One-pot Nenitzescu Synthesis of 5-Hydroxy-[1H]-benzo[g]indole Derivatives

A catalyst-free one-pot synthesis of 5-hydroxy-[1H]-benzo[g]indole derivatives has been developed via a modified Nenitzescu reaction using 1,4-naphthoquinones, β-ketoesters/β-dicarbonyl compounds, and ammonium acetate. The transformation proceeds through in situ enamine formation followed by 5-exo-trig C–N cyclization. The protocol affords diverse 5-hydroxyindoles in good to excellent yields. DFT calculations and TEMPO experiments suggest that the reaction yielded the product via a polar mechanistic pathway.