Helical Multi-Coordination Anion-Binding Catalysts for the Highly Enantioselective Dearomatization of Pyrylium Derivatives.

A general and highly enantioselective synthesis of oxygen heterocycles from readily available in situ generated pyrylium derivatives has been realized by embracing a multi-coordination approach with helical anion-binding tetrakistriazole catalysts. The high activity of the tetrakistriazole (TetraTri) catalysts, with distinct confined anion-binding pockets, allows for remarkably low catalyst loadings (down to 0.05 mol %), while providing a simple access to chiral chromanones and dihydropyrones in high enantioselectivities (up to 98:2 e.r.). Moreover, experimental and theoretical studies provide new insights into the hydrogen-donor ability and key binding interactions of the TetraTri catalysts and its host:guest complexes, suggesting the formation of a 1:3 species.