Sequential Nucleophilic Addition and Regioselective Ring‐Expansion Reactions of α‐Diazophosphonates with Isatins: Access to 4‐Phosphonylated‐3‐hydroxyquinolin‐2(1H)‐ones

Abstract A sequential protocol of α ‐diazophosphonates with isatins to access a series of α ‐diazo‐ β ‐hydroxyphosphonate derivatives via the inorganic base catalysis was reported. The resulting α ‐diazo‐ β ‐hydroxyphosphonates could then be readily transformed to 4‐phosphonylated‐3‐hydroxyquinolin‐2(1 H )‐ones with moderate to excellent yields through a catalyst‐free regioselective ring‐expansion rearrangement. Control experiment demonstrates that intramolecular cyclization pathway is more reasonable for the ring‐expansion process. In addition, a benzo[ b ]thiophene‐derived isatin featured with the inhibition of SARS‐CoV M pro was also suitable for this transformation and generated the corresponding scaffolds with potential anti‐virus activities for further development.