Construction of Thiophenes and Selenophenes via Iron-Promoted [2+2+1] Cycloaddition of Alkynes with Elemental Chalcogens.

An iron-promoted [2+2+1] cycloaddition of alkynes with elemental sulfur and selenium enables the construction of thiophenes and selenophenes. Simple iron compounds, FeI2 and Fe(acac)3, enable these transformations using S8 and Se to afford multisubstituted heterocycles. A range of 1,6-diynes are tolerated, and a three-component variant using terminal and internal alkynes is also available. This protocol provides a practical approach to thiophenes and selenophenes utilizing earth-abundant iron and elemental chalcogens without additional additives.