Enantioselective Synthesis of Dithia[5]helicenes and their Postsynthetic Functionalization to Access Dithia[9]helicenes

• Published in: Angewandte Chemie International Edition Vol. 61; no. 6; pp. e202114577 - n/a
• Main Authors: Pelliccioli, Valentina, Hartung, Thierry, Simon, Martin, Golz, Christopher, Licandro, Emanuela, Cauteruccio, Silvia, Alcarazo, Manuel
• Format: Journal Article
• Language: English
• Published: Germany John Wiley and Sons Inc 01.02.2022
• Subjects: Alkyne hydroarylation; Asymmetric catalysis; Au-catalysis; Communication; Communications; Dithiahelicenes; π-Extension; Dithiahelicenes; Alkyne hydroarylation; Au-catalysis; π-Extension; Asymmetric catalysis
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202114577

A highly enantioselective synthesis of 5,13‐disubstituted dibenzo[d,d′]benzo[1,2‐b:4,3‐b′]dithiophenes is reported. Key for the successful assembly of these helical architectures is the last two successive Au‐catalyzed intramolecular alkyne hydroarylation events. Specifically, the second cyclization is the enantiodetermining step of the whole process and provides the desired helicenes with excellent ee values when a TADDOL‐derived 1,2,3‐(triazolium)phosphonite moiety (TADDOL: α,α,α′,α′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanol) is employed as an ancillary ligand. The absolute stereochemistry of the newly prepared structures has been determined by X‐ray crystallography to be P; the optical properties of these heterohelicenes are also reported. A three‐step procedure was subsequently developed that allows the transformation of the initially obtained dithia[5]helicenes into dithia[9]helicenes without erosion of the enantiopurity. The use of a chiral Au catalyst bearing an α‐cationic phosphonite as an ancillary ligand and two successive alkyne hydroarylation events allows the assembly of dithia[5]helicenes with excellent enantioselectivity. Moreover, regioselective postsynthetic bromination of the dithia[5]helicene products generates starting materials for the efficient preparation of even more π‐expanded systems, such as dithia[9]helicenes.