Synthesis of Trisubstituted Alkenes Bearing a Quaternary Carbon by Lewis-Acid Catalyzed Regioselective Reaction of Internal Alkynols with 2-Pyrrolylanilines

Substituted alkenes, crucial in organic chemistry, are typically accessed from internal alkynes by using transition-metal catalysis. Herein, we report a novel approach to the Lewis acid-catalyzed synthesis of trisubstituted alkenes bearing a quaternary carbon from internal alkynols and 2-pyrrolyl arylamines. This method involves allene formation followed by intramolecular [5 + 1] annulation to furnish a diverse range of trisubstituted alkenes with excellent regioselectivity and poor diastereoselectivity. Further, we demonstrated the gram-scale synthesis and synthetic transformations and proposed the reaction mechanism based on the isolation of intermediates.