Cyanoacetylene-driven base catalyzed synthesis of dihydropyrimidophenanthridinones from phenanthridine and water

3-Arylpropynenitriles are readily annulated with phenanthridine in the KOH/H₂O/MeCN system at room temperature to afford 4-aryl-1,13b dihydropyrimido[1,2-f]phenanthridin-2-ones. The moderate yield of the products can be rationalized by the anionic oligomerization of an intermediate zwitterion adduct of the reactants. The reaction represents a single-stage access to a new family of pharmaceutically prospective compounds.