Highly Regioselective Isoquinoline Synthesis via Nickel-Catalyzed Iminoannulation of Alkynes at Room Temperature

A simple and cost-efficient nickel catalytic system for the annulation of 2-haloaldimines with alkynes to synthesize 3,4-disubstituted and 3-substituted isoquinolines at room temperature has been developed. The air-stable and inexpensive Ni(dppe)Cl-2 was employed as a precatalyst, and Et3N was found to be an essential additive for obtaining high yields. By using this nickel catalytic system one-pot three-component direct synthesis of isoquinolines starting with simple 2-halobenzaldehydes, tert-butylamine, and alkynes were also achieved. These reactions occur in moderate to excellent yields with complete regioselectivity. Moreover, these reactions feature a broad substrate scope, easy scalability, operational simplicity, and excellent practicality.