Enantioselective Au‐Catalyzed Synthesis of Thia[5]‐ and Thia[6]helicenes and Their Transformation into Bowl‐shaped Pleiadenes

Abstract

A series of helically shaped benzo[b]chryseno[4,3‐d]thiophenes, naphtho[1,2‐b]phenanthro[4,3‐d]thiophenes, and chryseno[3,4‐b]naphtho[1,2‐d]thiophenes is synthesized via a highly enantioselective Au‐catalyzed intramolecular alkyne hydroarylation reaction. The inversion barriers of the structures obtained are determined both theoretically and experimentally, and their chiroptical properties are reported. Preliminary studies on the post‐synthetic functionalization of these thiahelicenes and their transformation into azahelicenes are also presented. In addition, a straightforward one‐step protocol is developed, which wraps the initially obtained chryseno[3,4‐b]naphtho[1,2‐d]thiophenes into bowl‐shaped pleiadene derivatives without erosion of the enantiopurity. The number of structurally related products that are obtained with high enantioselectivity enables the establishment of comprehensive correlations between the structure and conformational stability or (chir)optical properties.

Der richtige Dreh: Helicene enantioselektiv synthetisieren

“…Des Weiteren dirigiert der Schwefel nachträgliche synthetische Modifikationen, wie zum Beispiel aromatische Substitution. 12) Alcarazo veröffentlichte im Jahr 2023 eine Synthese von Thia [6]helicen. Die Reaktion geht vom substituierten Alkin (15) aus, das mit Silberhexafluoroantimonat und dem Goldkatalysator (17) in einem Schritt zu dem Thiahelicen (16) umgesetzt wurde (Abbildung 6).…”

“…6 Enantioselektive goldkatalysierte Synthese von Thia [5]helicenen durch Alcarazo aus dem Jahr 2023. 12) 4Chem Award 2024…”

Impact of Truncation on Optoelectronic Properties of Azaborole Helicenes

“…Thus, the presence of an additional substituent at a sterically hindered position in dioxa[6]helicene ( C , Figure 1) converted a flexible molecule (17.0 kcal mol −1 ) into a configurationally stable derivative (32.7 kcal mol −1 ) [11] . In another study, the position of a thiophene ring in singly‐truncated isomeric thiahelicenes had a strong impact on their enantiomerization barriers [12] …”

“…[11] In another study, the position of a thiophene ring in singly-truncated isomeric thiahelicenes had a strong impact on their enantiomerization barriers. [12] The remote steric effect of an aryl substituent was also utilized by Longhi, Pischel, Ros and co-workers [13] to produce a set of three configurationally stable azabora [5]helicenes differing in the electronic nature of the pendant group (D1-D3, Figure 1). Interestingly, the substituent type at the para-position of the phenyl ring (H, OMe, NMe 2 ) determined the sign of the lowest energy electronic circular dichroism (ECD) band (rotatory strength) of the given enantiomers.…”

Substitution Effects on the Photophysical and Photoredox Properties of Tetraaza[7]helicenes

“…The research interest in helicenes has grown in recent years, driven by the increasing number of synthetic approaches [1][2][3][4][5][6][7][8] and the desire to exploit the unique properties of this class of compounds, which originate from their helical structure in combination with the extended aromatic system. Helicenes find a wide variety of applications, such as synthetic use in the preparation of chiral catalysts, often in the form of ligands, or more exotic applications including the construction of molecular machines.…”