Visible light-induced aerobic dioxygenation of α,β-unsaturated amides/alkenes toward selective synthesis of β-oxy alcohols using rose bengal as a photosensitizer

The first visible light-induced dioxygenation of α,β-unsaturated amides with N-hydroxy compounds under air was developed with the use of the non-toxic organic dye rose bengal as the photoredox catalyst. This metal-free reaction is highly chemoselective, producing the corresponding β-oxy alcohols rather than the competitive cyclized products through aminooxyarylation. Other aromatic alkenes, dihydrofurans and dienes, were also applicable to this reaction. Compared with the established radical dioxygenation methods to construct β-oxy alcohols, the present photochemical protocol avoids the use of (over)stoichiometric amounts of hazardous/poisonous oxidants, transition metals and additional reducing reagents, yielding the desired dioxygenated products in a safe and eco-friendly fashion. Moreover, the practical application of this methodology is highlighted by a concise two-step synthesis of 1,4-dioxane-2-carboxamides, a framework for building Mcl-1 inhibitors.