Tapping Water as an Oxygen Source: Visible-Light-Driven Synthesis of 4H-Pyrans from 5-Alkynyl Ketones and Sulfonyl Chlorides.

4H-Pyrans are privileged bioactive scaffolds, yet their oxygen is invariably sourced intramolecularly from carbonyl derivatives, restricting structural diversity accessible through established paradigms. Herein, we report a visible light-driven strategy that repurposes water as an extrinsic oxygen source to enable divergent access to two classes of tetrasubstituted 4H-pyrans from readily available 5-alkynyl ketones and sulfonyl chlorides. Using inexpensive 4CzIPN, this protocol delivers over 40 examples in up to 72% yield. Mechanistic studies (X-ray corroborated) reveal photoinduced water-mediated oxysulfonylation of unactivated alkynes as the pivotal branching step. Synthetic utility is demonstrated through late-stage functionalization, gram-scale operation, and facile conversion to structurally diverse 6- and 7-membered heterocycles.