Advances in catalytic enantioselective synthesis of chiral helicenes and helicenoids

Abstract

Catalytic enantioselective synthesis of chiral helicenes and helicenoids has emerged as an important area of research. In the efforts toward efficient and enantioselective synthesis of chiral helicenes and helicenoids, chemists have developed several catalytic asymmetric reactions, primarily transition metal-catalyzed asymmetric intra- or intermolecular [2 + 2 + 2] cycloaddition, hydroarylation, olefin metathesis, and oxidative coupling reactions. In addition, asymmetric organocatalysis has shown potential for use in the enantioselective synthesis of chiral helicenes and helicenoids, including chiral phosphoric acid- and chiral amide-catalyzed enantioselective [3 + 2] and [4 + 2] cyclizations. In this review, advancements in the catalytic enantioselective synthesis of chiral helicenes and helicenoids from 1999 to the beginning of 2022 have been classified based on asymmetric transition metal catalysis and asymmetric organocatalysis. In addition, this review highlights the remaining challenges in this research field and sheds light on the future of this field. Chiral helicenes and helicenoids are a fascinating class of π-conjugated helical molecules comprising ortho-fused aromatic rings that have numerous applications in the fields of materials science and asymmetric catalysis. Therefore, catalytic enantioselective synthesis of chiral helicenes and helicenoids has become an important and emerging area of research. To provide a comprehensive summary and highlight the endeavors of chemists in this field, this review summarizes the advancements in catalytic enantioselective synthesis of chiral helicenes and helicenoids from 1999 (when the first catalytic asymmetric synthesis of chiral helicenes was achieved) to the beginning of 2022. Additionally, this review is divided into sections on asymmetric transition metal catalysis and asymmetric organocatalysis, in which reaction design and mechanism are discussed. Importantly, the remaining challenges in this field of research have been identified, which will encourage chemists to develop innovative solutions. This review summarizes the advancements in the catalytic enantioselective synthesis of chiral helicenes and helicenoids from 1999 to the beginning of 2022, which have been classified based on asymmetric transition metal catalysis and asymmetric organocatalysis. More importantly, this review highlights the remaining challenges in this research field and sheds light on the future of this field.