Construction of Helical and Inherent Chirality by Brønsted Acid-Catalyzed Enantioselective Povarov Reaction of Alkynes

Povarov reaction is an efficient methodology toward N-heterocycles. Compared with the frequently investigated Povarov reaction of alkenes, the catalytic enantioselective Povarov reaction of alkynes remains challenging and has not been developed to date. Herein, we report a chiral Brønsted acid-catalyzed enantioselective Povarov reaction/oxidative aromatization of alkynes, providing a modular platform for the preparation of quindoline- and indenopyridine-type chiral helicenes with the simultaneous control of regioselectivity and enantioselectivity. Both electron-rich ynamides and unpolarized alkynes can undergo the transformation smoothly. Importantly, this strategy could be further extended to the synthesis of inherently chiral calix[4]arenes with effective enantiocontrol. Computational studies reveal the reaction mechanism and origin of regio- and enantioselectivity. Further derivatizations of chiral azahelicenes and investigations into the photophysical and chiroptical properties demonstrate the potential utility of this method. This protocol represents an important advancement in the enantioselective Povarov reaction of alkynes, as well as a rare example for the organocatalytic enantioselective transformation of unpolarized alkynes.