Phosphine-Catalyzed [3 + 2] Annulations of Indole N-Alkynamides with Ynones: Direct Synthesis of Arylidene Spiro-Cyclopentanone Pyrroloquinolinediones.

We report a phosphine-catalyzed [3 + 2] annulation of indole N-alkynamides with ynones, providing efficient access to arylidene spiro-cyclopentanone pyrroloquinolinediones. The reaction proceeds through the in situ generation of a reactive enedione intermediate and exhibits broad substrate scope, high regioselectivity, and gram-scale applicability. Mechanistic studies support the involvement of transient enedione and phosphine-derived zwitterionic intermediates. This strategy unveils a previously unexplored reactivity of indole N-alkynamides and enables rapid construction of structurally unique spirocyclic frameworks.