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The first sequential acid-catalyzed propargylation/base-mediated aza -cycloisomerization between indolyl-benzimidazoles and propargylic alcohols is described. This protocol enables the one-pot construction of N -fused benzimidazo-β-carbolines in good yields. The synthetic utility of this approach is demonstrated by the assembly of an aza -helicene and also by a gram-scale reaction.