Aryne Relay-Triggered Three-Component Cascade via <i>In Situ</i> <i>o</i> -QDM Generation: Synthesis of <i>N,O</i> -Spiroheterocycles and Benzo[ <i>f</i> ]isoindole-1,3(2 <i>H</i> )-diones

The synthesis of spiroheterocycles via the controllable in situ generation of o -quinodimethanes ( o -QDMs) bearing a tetrasubstituted exocyclic C═C bond remains a long-standing synthetic challenge. Herein, we report an aryne relay-triggered three-component (four-molecule) cascade reaction that enables the transition-metal-free assembly of N,O -spiroheterocycles (32 examples, up to 94% yield, mostly d.r . > 20:1) and benzo[ f ]isoindole-1,3(2 H )-diones (27 examples, up to 84% yield). This transformation uses readily available 2-benzyl oxazolines, aryne precursors, and electron-deficient alkenes as starting materials, proceeding through the in situ generation and selective trapping of the aforementioned o -QDM intermediates. The protocol exhibits a broad substrate scope, and its synthetic utility is further validated by gram-scale synthesis and versatile product derivatization.