TADDOL-Derived Cationic Phosphonites: Toward an Effective Enantioselective Synthesis of [6]Helicenes via Au-Catalyzed Alkyne Hydroarylation

A series of cationic phosphonites, all sharing a TADDOL skeleton but decorated with different positively charged substituents at phosphorus, were synthesized and tested as chiral ancillary ligands on the Au-catalyzed intramolecular hydroarylation of appropriate diynes toward carbo[6]helicenes with different substitution patterns. Our studies showed that the Au complexes derived from phosphonites bearing 1,3-dimesityl-1,2,3-triazolium and 1,4-dimesityl-1,2,4-triazolium substituents are the best precatalysts for the desired cyclization in terms of regio- and enantioselectivity of the products obtained. In contrast, all of our attempts to prepare Au complexes from cationic phosphonites derived from CAACs failed, and only ligand decomposition products could be isolated