Convenient One-Step Synthesis of Benzo[c]phenanthridines by Three-Component Reactions of Isochromenylium Tetrafluoroborates and Stilbenes in Acetonitrile

A new type of three-component reaction of air-stable isochromenylium tetrafluoroborates with electron-rich stilbenes in acetonitrile has been developed under catalyst-free conditions in this work. This cascade multibond-formation reaction is initiated by an intermolecular oxa [4 + 2]-cycloaddition, relayed with a nucleophilic addition of acetonitrile, and terminated by an intramolecular Friedel–Crafts reaction, affording the corresponding benzo­[c]­phenanthridine analogues in one step.