Synthesis of indol-3-yl-benzofurans and carbazoles via Cu(OTf)2-catalyzed [3 + 2] and [4 + 2] cycloaddition.

An efficient Cu(OTf)2-catalyzed [3 + 2] cycloaddition of indole-3-acrylate with p-benzoquinone has been developed to construct two distinct indole-tethered benzofuran scaffolds, offering the first-ever selective access to these scaffolds. Moreover, the [4 + 2] cycloaddition reaction of indole-3-acrylate with vinyl ketone derivatives was used to synthesize carbazoles in a one-pot manner. The disclosed strategies provided a series of selective transformations under low-catalyst loading, with a broad substrate scope featuring diverse applicability and practical simplicity of the developed protocol with easily available substrates.