Copper-Mediated Annulation of Phosphorus-Containing Arenes with Alkynes: An Approach to Phosphindolium Salts.

A novel method for the synthesis of π-conjugated phosphindolium salts via copper-mediated C-H functionalization of trisubstituted phosphines with alkynes in a single step is reported. The reactions are highly regioselective with unsymmetrical aryl-alkyl-substituted alkynes. This protocol provides an unprecedented atom- and step-efficient access to valuable phosphindolium salts.