Asymmetric counteranion-directed photoredox catalysis.

Photoredox catalysis enables unique and broadly applicable chemical reactions but controlling their selectivity has proven to be difficult. The pursuit of enantioselectivity is a particularly daunting challenge, arguably due to the high energy of the activated radical (ion) intermediates, and previous approaches have invariably required pairing of the photoredox catalytic cycle with an additional activation mode for asymmetric induction. A potential solution for photoredox reactions proceeding via radical ions would be catalytic pairing with enantiopure counterions. However, while attempts toward this approach have been described, high selectivity has not yet been accomplished. Here we report a potentially general solution to radical cation-based asymmetric photoredox catalysis. We describe organic salts, featuring confined IDPi counteranions that catalyze highly enantioselective [2+2]-cross cycloadditions of styrenes.