Brønsted Acid-Catalyzed Multicomponent Phosphonylation/Cyclization Strategy for the Synthesis of Phosphinylated 2 <i>H</i> -Isoindoles

A Brønsted acid-catalyzed three-component modular phosphonylation/cyclization protocol has been established for the efficient synthesis of phosphinylated 2<i>H</i>-isoindoles, employing <i>o</i>-propargyl alcohol benzaldehydes, diarylphosphine oxides, and arylamines as starting materials. This metal-free cascade transformation is characterized by mild conditions, broad substrate compatibility, gram-scale synthesis, and one-pot construction of C-P, C-N, and CC bonds. Mechanistic studies revealed that this chemistry involves Kabachnik-Fields reaction, 5-<i>exo</i>-<i>dig</i> cyclization, and aromatization. Interestingly, these isoindole-substituted phosphine oxides emit bright fluorescence in the aggregated states under UV irradiation.