Enantioselective Construction of Chiral Azahelicenes through Catalytic Asymmetric Povarov-Type Cycloaddition Involving Alkynes.

A new class of 3-alkynylindoles bearing a terminal alkynyl group as highly reactive two-carbon (2C) building blocks has been designed and applied in chiral phosphoric-acid-catalyzed enantioselective Povarov-type cycloaddition with fused arylamines and benzaldehydes. Thus, a series of chiral azahelicenes have been synthesized in moderate to good yields with overall excellent enantioselectivities, which exhibit switchable photophysical properties under acidic or basic conditions. This work represents the first use of terminal alkynes in an asymmetric Povarov-type cycloaddition and provides a powerful strategy for the construction of helically chiral scaffolds.