A redox neutral, highly enantioselective coupling between N-arylaminomethanes and N-sulfonyl aldimines was developed by harnessing the efficient catalysis of P-spiro chiral arylaminophosphonium barfate and a transition-metal photosensitizer under visible light irradiation. This mode of synergistic catalysis provides a powerful strategy for controlling the bond-forming processes of reactive radical intermediates.

A catalytic cycle initiated by the oxidative quenching of the excited photosensitizer (Ir*(ppy)3) is established for the enantioselective coupling between (N-arylamino)methanes and (N-methanesulfonyl)aldimines catalyzed by Ir-based photosensitizer and a chiral (arylamino)phosphonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate under visible light irradiation. This achievement clearly demonstrates the insensitivity of this redox-neutral asymmetric reaction to the sequence of the key redox events involved in the synergistic catalysis.

Catalysis by chiral weakly-coordinating anions (WCAs) remains underdeveloped due to the lack of a molecular design strategy for exploiting their characteristics, such as the non-nucleophilic nature. Here, we report the development of a chiral borate ion comprising an O,N,N,O-tetradentate backbone, which ensures hitherto unattainable structural robustness. Upon pairing with a proton, the hydrogen borate acts as an effective catalyst for the asymmetric Prins-type cyclization of vinyl ethers, providing access to structurally and stereochemically defined dihydropyrans. The key to selectivity control is the distinct ability of the borate ion to discriminate the prochiral faces of the acyclic oxonium ion intermediate and dictate the regiochemical outcome. We anticipate that this study paves the way for exploring the untapped potential of WCA catalysis for selective chemical synthesis.

Highly enantioselective protonation of α-halo and alkoxy carboxylic acid-derived ketene disilyl acetals is achieved by using P-spiro chiral diaminodioxaphosphonium barfate as a Brønsted acid catalyst, where the enantiofacial discrimination by the catalyst mainly stems from the recognition of the electronic difference between two substituents on the ketene disilyl acetal.