Photoredox Autocatalysis: Towards a Library of Generally Applicable Sulfonamide Reductive Photocatalysts.

Dichotomous thinking dominates the field of synthetic photochemistry-either a reaction needs a photocatalyst or not. Herein, we report the identification of a photoredox autocatalytic pathway - an alternative to the existing mechanistic paradigms - to access cyclic biaryl sulfonamides (BASNs). This reaction does not require exogenous catalyst as the visible light absorbing deprotonated product - 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 expedited optimal photocatalyst screening. Furthermore, BASN was revealed as a widely applicable organophotocatalyst for diverse transition metal-free transformations such as: intramolecular (spiro)-cyclizations, defunctionalizations, and C-C / C-heteroatom couplings.