Synthesis of Amino-Substituted α- and δ-Carbolines via Metal-Free [2 + 2 + 2] Cycloaddition of Functionalized Alkyne-Nitriles with Ynamides.

A metal-free [2 + 2 + 2] cycloaddition of alkyne-cyanamides or ynamide-nitriles with ynamides is described for the efficient synthesis of amino-substituted α- and δ-carbolines. This novel methodology is environmentally friendly and allows for highly regioselective access to carboline derivatives in good to excellent yields with wide functional group tolerance.