Enantioselective Synthesis of 1, 12‐Disubstituted [4]Helicenes. Issue 14 (20th February 2020) - Hartung, Thierry
Abstract: A highly enantioselective synthesis of 1, 12‐disubstituted [4]carbohelicenes is reported. The key step for the developed synthetic route is a Au‐catalyzed intramolecular alkyne hydroarylation, which is achieved with good to excellent regio‐ and enantioselectivity by employing TADDOL‐derived (TADDOL=α, α, α, α‐tetraaryl‐1, 3‐dioxolane‐4, 5‐dimethanol) α‐cationic phosphonites as ancillary ligands. Moreover, an appropriate design of the substrate makes the assembly of [4]helicenes of different substitution patterns possible, thus demonstrating the synthetic utility of the method. The absolute stereochemistry of the newly prepared structures was determined by X‐ray crystallography and characterization of their photophysical properties is also reported. Abstract : Minimalistic helicenes : The use of a chiral gold catalyst bearing an α‐cationic TADDOL‐derived phosphonite as an ancillary ligand allows the enantioselective assembly of 1, 12‐disubstituted [4]helicenes—one of the smallest helical polyarene architectures.