Construction of Tricyclic Nitrogen Heterocycles by Gold(I)-Catalyzed Cascade Cyclization of Allenynes and Its Application to Polycyclic π-Electron Systems.

A novel approach to the direct construction of tricyclic nitrogen heterocycles based on gold-catalyzed cascade cyclization of aminoallenynes is described. The expected bis-cyclization reaction of hydroxyisobutyryl-protected aminoallenynes was efficiently promoted by a catalytic amount of BrettPhosAuNTf 2 in the presence of i PrOH, producing 1,2-dihydrobenzo[ cd ]indole derivatives in good yields. Combined with Friedel-Crafts acylation or palladium-catalyzed N -arylation, the resulting tricyclic products were efficiently converted to nitrogen-containing polycyclic aromatic compounds (N-PACs) with highly conjugated π-electron systems. The newly obtained hexacyclic indolium salts showed characteristic concentration-dependent absorption and emission properties.