Taming transient radical couplings by preassembling organophotocatalytic dyads

We report two organophotocatalytic dyads with distinct mechanisms that enable metal-free generation-and tame couplings of-transient carbon-centered radical partners. After forming their planar charge transfer or charge separated states, the dyads assemble non-covalently with radical precursors where electron transfer reactivity is triggered by photoexcitation. Modulating the dyad's donor substituent diverts the mechanism from (i) consecutive photoinduced electron transfer via a radical anion catalyst/electron acceptor substrate binary assembly to (ii) a ternary assembly of charge-separated catalyst and both partner substates. In both cases, reductively-generated alkenyl and alkynyl radicals couple with oxidatively activated trialkylamines in high efficiency, exquisite chemoselectivity and excellent atom economy without need of any transition metal co-catalyst-improving sustainability of cross-couplings. Key to success was the intra-assembly generation and stabilization of transient radicals, preventing homocoupling/decomposition and furnishing a broad scope of products including late-stage functionalized drug molecules.