Metal‐Free One‐Pot Tandem Construction of C4‐Phosphorylated Phthalazin‐1(2H)‐ones under Visible‐Light Photoredox Catalysis

Abstract Visible‐light photoredox‐catalyzed metal‐free one‐pot tandem regioselective synthesis of C4‐phosphorylated phthalazin‐1(2 H )‐ones from arylhydrazines, 2‐formylbenzoic acids with diarylphosphine oxides is described. This three‐component transformation occurs smoothly under mild conditions, providing regiospecific access to various phosphorylated products in 73–91% yield. The efficacy of the current catalysis arises from the use of organic 1,2,3,5‐tetrakis(carbazol‐9‐yl)‐4,6‐dicyanobenzene (4CzIPN) as the photocatalyst and cheap K 2 S 2 O 8 as the oxidant.