Urea as a Redox-Active Directing Group under Asymmetric Photocatalysis of Iridium-Chiral Borate Ion Pairs

The development of a photoinduced, highly diastereo- and enantioselective [3 + 2]-cycloaddition of N-cyclopropylurea with α-alkylstyrenes is reported. This asymmetric radical cycloaddition relies on the strategic placement of urea on cyclopropylamine as a redox-active directing group (DG) with anion-binding ability and the use of an ion pair, comprising an iridium polypyridyl complex and a weakly coordinating chiral borate ion, as a photocatalyst. The structure of the anion component of the catalyst governs reactivity, and pertinent structural modification of the borate ion enables high levels of catalytic activity and stereocontrol. This system tolerates a range of α-alkylstyrenes and hence offers rapid access to various aminocyclopentanes with contiguous tertiary and quaternary stereocenters, as the urea DG is readily removable.