Enantioselective synthesis of chiral quinohelicenes through sequential organocatalyzed Povarov reaction and oxidative aromatization

Abstract

Heterohelicenes are of increasing importance in the fields of materials science, molecular recognition, and asymmetric catalysis. However, enantioselective construction of these molecules, especially by organocatalytic methods, is challenging, and few methods are available. In this study, we synthesize enantioenriched 1-(3-indol)-quino[n]helicenes through chiral phosphoric acid-catalyzed Povarov reaction followed by oxidative aromatization. The method has a broad substrate scope and offers rapid access to an array of chiral quinohelicenes with enantioselectivities up to 99%. Additionally, the photochemical and electrochemical properties of selected quinohelicenes are explored.

Padlocking dihydrofurannulation for the control of small degree of helicity built on a fused-tetracyclic core

“…In 2023, Yang and Li's groups independently reported an enantioselective Povarov reaction leading to centrally and helically chiral scaffolds, precursors of azahelicene after oxidation. 12 Contemporaneously, the group of Wang managed the control of both central and helical stereogenic elements via enantioselective phospha-Michael addition under phosphonium salt organocatalysis. 13 Therefore, the development of efficient methodologies to address the control of new small helically shaped chiral scaffolds built on a fused-tetracyclic core is timely and highly desirable.…”

Catalytic asymmetric construction of helicenes via transformation of biaryls

“…To overcome these synthetic challenges, new strategies such as asymmetric cascade reactions of biaryls with multiple reactivities, asymmetric multicomponent reactions, multifunctional catalysis, and dual catalysis are highly desirable. 75,76…”

Helicoselective Synthesis of Indolohelicenoids through Organocatalytic Central‐to‐Helical Chirality Conversion

“…Yan and co‐workers developed chiral bifunctional amide catalyzed intramolecular cyclization of 1‐alkynylnaphthalen‐2‐ol derivatives for the enantioselective synthesis of helicenes via vinylidene ortho ‐quinone methide intermediates [17] . Recently, Li and Yang independently reported a stepwise method for preparing enantiomerically pure quinohelicenes by construction of the terminal pyridine ring [18a,b] . Additionally, Wang reported a peptide‐mimic phosphonium salt catalyzed dynamic kinetic resolution and oxidative aromatization method for synthesizing phosphorus‐containing chiral helicenes [18c] …”