Biphilic Organophosphorus Catalysis: Regioselective Reductive Transposition of Allylic Bromides via P^III/P^V Redox Cycling

We report that a regioselective reductive transposition of primary allylic bromides is catalyzed by a biphilic organophosphorus (phosphetane) catalyst. Spectroscopic evidence supports the formation of a pentacoordinate (σ⁵-P) hydridophosphorane as a key reactive intermediate. Kinetics experiments and computational modeling are consistent with a unimolecular decomposition of the σ⁵-P hydridophosphorane via a concerted cyclic transition structure that delivers the observed allylic transposition and completes a novel P^III/P^V redox catalytic cycle. These results broaden the growing repertoire of reactions catalyzed within the P^III/P^V redox couple and suggest additional opportunities for organophosphorus catalysis in a biphilic mode