Metal-Free [2+2+2] Cycloaddition of Ynamides and Nitriles: Mild and Regioselective Synthesis of Fully Substituted Pyridines.

A metal-free trimolecular [2+2+2] cycloaddition of internal ynamides and nitriles for de novo synthesis of fully substituted pyridines is disclosed. With the versatile Brønsted acid catalyst HNTf2 , the mild intermolecular cyclotrimerization process proceeds with complementary chemoselectivity and excellent regioselectivity.