Synthesis of 1,2-Fused Benzimidazoles by Amine-Initiated [3 + 3] Annulations of β′-Acetoxy Allenoates with 1C,3N-Bisnucleophiles

The amine-catalyzed [3 + 3] annulations of β′-acetoxy allenoates with 1C,3N-bisnucleophiles have been established. Under the optimal reaction conditions, this operationally simple synthetic process works well with a wide substrate scope, delivering novel 1,2-fused benzimidazole derivatives in moderate to good yields. In addition, preliminary attempts on the asymmetric version of this reaction have been explored by using cinchona alkaloid-based tertiary amines.