Synthesis of 1,2-Diketones via a Metal-Free, Visible-Light-Induced Aerobic Photooxidation of Alkynes

Abstract

1,2-Diketones were synthesized by the oxidation of corresponding alkynes using air as the oxidant under metal-free conditions upon irradiation of blue light. A cheap and readily available organic dye, eosin Y, was used as the photocatalyst. For various substituents on the aryl ring, the reaction proceeded smoothly to give the dicarbonylation products in moderate to good yields. Some oxidation-sensitive groups, such as formyl and the carbon-carbon double bond, were tolerated under the developed reaction conditions.

Eosin Y catalysed photoredox synthesis: a review

“…50 The plausible reaction mechanism is described in Scheme 11. 51 Initially, eosin Y was converted to excited state eosin Y* upon irradiation of visible light, and this eosin Y* underwent reductive quenching by thiophenol to afford the radical cation A and form an eosin Y radical anion. The eosin Y radical anion was oxidized to the ground state by aerobic oxygen to complete the photoredox cycle and a superoxide radical anion (O 2 À c) was generated simultaneously.…”

Visible‐Light‐Mediated Oxygenation Reactions using Molecular Oxygen

“…[31] Recently,S un and co-workersd escribed an EY-catalyzed methodf or the synthesis of 1,2-diketones by oxidation of alkynes using air as the oxidant under metal-free conditions upon blue-light irradiation (Scheme 15). [32] Various substituents on the aryl rings including someo xidation-sensitive groups such as formyl and carbonÀcarbon double bonds were compatible, and the product was formedi nm oderate to good yields.…”

Eosin‐Y‐Catalyzed Photoredox C−S Bond Formation: Easy Access to Thioethers

“…The reduced Eosin Y radical anion subsequently undergoes aerial oxidation to regenerate the neutral Eosin Y for the next catalytic cycle, along with the generation of superoxide radical anion (O 2 − ) which deprotonates the thiyl radical cation to form the thiyl radical and a hydroperoxyl radical (HO 2 . ) . Hydrazone ( 1 ) acts as a precursor to the diazo compound, which on addition with the thiyl radical affords the intermediate I , followed by dediazotization to generate the intermediate II .…”