Diverse Enantioselective Synthesis of Hetero[7]helicenes via an Organocatalyzed Double Annulation Strategy

Abstract

A highly efficient catalytic enantioselective double annulation protocol has been developed for the asymmetric synthesis of hetero[7]helicenes. This method involves a sequential chiral phosphoric acid (CPA)-catalyzed three-component double Povarov reaction with a pentacyclic diamine followed by aromatization, which yielded various bispyridine-containing hetero[7]helicenes with good yields and excellent enantioselectivity. Notably, two distinct oxidative aromatization methods have been developed to selectively afford hetero[7]helicenes with either mono-amido or bis-amido substitutions at the peri-positions. Extensive derivatizations of these chiral heterohelicene products, along with detailed studies of their photophysical and chiroptical properties, underscore the significance of this method.