Photoredox autocatalysis: towards a library of generally applicable reductive photocatalysts

Dichotomous thinking dominates the field of synthetic photochemistry – either a reaction needs a photocatalyst or not. Herein, we report the discovery of photoredox autocatalytic pathway, a third mechanistic paradigm that is thus far overlooked, to access cyclic biaryl sulfonamides (BASNs). This reaction does not require exogenous catalyst as the visible light absorbing deprotonated product itself, with potent excited state reductive power, acts as the photocatalyst for its own synthesis. This finding implicated BASN as a novel organophotocatalyst architecture and allowed a rapid, modular, and low-cost combinatorial synthesis of a BASN library that expediated optimal photocatalyst screening. Furthermore, BASN was revealed as a general organophotocatalyst for a diverse set of transition metal-free transformations such as: intramolecular (spiro)-cyclizations, defunctionalizations, and C-C / C-heteroatom couplings.