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Synthesis of indoles from alkynes and a nitrogen source under metal-free conditions.

Indoles are an important nucleus of N-heterocycles found in many natural products, active pharmaceuticals, and functional materials. In addition, indoles have various reactive positions, each one with a different reactivity, which may be susceptible to different reactions. This characteristic makes them important substrates for further transformations. This paper deals with the methodologies published in the last ten years, which used metal-free conditions to prepare indoles starting from alkynes and nitrogen compounds.