Substituent Effect in the Synthesis of α,α‐Dibromoketones, 1,2‐Dibromalkenes, and 1,2‐Diketones from the Reaction of Alkynes and Dibromoisocyanuric Acid

Alkyne Oxidation by a Vitamin B2-Based Photocatalytic System with Both H2O and O2 as the Oxygen Source

The employment of readily available photocatalysts and green oxygen atom sources is recognized as a promising strategy to develop sustainable catalysis for oxidation reactions. We herein reported a sacrificial reagent-free system consisting of riboflavin tetraacetate (RFT), an ester of natural vitamin B2 as the photocatalyst, and Sc(OTf)3 and NaCl as the cocatalysts for alkyne oxidation under blue light or even sunlight irradiation to produce 1,2-diketone in which the oxygen atoms were from both water and molecular oxygen, respectively. A major Cl-/Cl• cycle was proposed to be involved and achieved by the excited [RFT-2Sc3+]* complex via single electron transfer for the first time, distinguished from the OCl- active species by a two-electron process in previous flavin-halide photo-oxidation systems.

FeIII -Based Eutectic Mixtures as Multi-task and Reusable Reaction Media for Efficient and Selective Conversion of Alkynes into Carbonyl Compounds

An efficient, simple and general protocol for the selective hydration of terminal alkynes into the corresponding methyl ketones has been developed by using a cheap, easy-to-synthesise and sustainable FeIII -based eutectic mixture [FeCl3  ⋅ 6H2 O/Gly (3 : 1)] as both promoter and solvent for the hydration reaction, working: i) under mild (45 °C) and bench-type reaction conditions (air); and ii) in the absence of ligands, co-catalysts, co-solvents or toxic, non-abundant and expensive noble transition metals (Au, Ru, Pd). When the final methyl ketones are solid/insoluble in the eutectic mixture, the hydration reaction takes place in 30 min, and the obtained methyl ketones can be isolated by simply decanting the liquid FeIII -DES, allowing the direct isolation of the desired ketones without VOC solvents. By using this straightforward and simple isolation protocol, we have been able to recycle the FeIII -based eutectic mixture system up to eight consecutive times. Furthermore, the FeIII -eutectic mixture is able to promote the selective and efficient formal oxidation of internal alkynes into 1,2-diketones, with the possibility of recycling this system up to three consecutive times. Preliminary investigations into a possible mechanism for the oxidation of the internal alkynes seem to indicate that it proceeds through the formation of the corresponding methyl ketones and α-chloroketones.

Catalyst-Free and Transition-Metal-Free Approach to 1,2-Diketones via Aerobic Alkyne Oxidation

A catalyst-free and transition-metal-free method for the synthesis of 1,2-diketones from aerobic alkyne oxidation was reported. The oxidation of various internal alkynes, especially more challenging aryl-alkyl acetylenes, proceeded smoothly with inexpensive, easily handled, and commercially available potassium persulfate and an ambient air balloon, achieving the corresponding 1,2-diketones with up to 85% yields. Meanwhile, mechanistic studies indicated a radical process, and the two oxygen atoms in the 1,2-diketons were most likely from persulfate salts and molecular oxygen, respectively, rather than water.

Synthetic Routes Towards the Synthesis of Geminal α-Difunctionalized Ketones

The importance of gem-difunctionalized ketones is represented by their broad applications across chemical boundaries over recent years. The interesting reactivities that this class of compounds possess have made them ideal building blocks to access high-value organic molecules. Furthermore, the gem-difunctionalized ketone moiety has featured in numerous bioactive molecules. For these reasons, a plethora of routes to access such significant molecules have been developed by research groups worldwide - this account looks at delineating the synthesis of gem-difunctionalized ketones from carbonyl substrates, diazo compounds, sulfur ylides and alkynyl reactants.

Csp–Csp bond cleavage and fragment coupling: a transition metal-free “extrusion and recombination” approach towards synthesis of 1,2-diketones

A metal-free strategy for C–C bond activation of 1,3-diynes has been established via an “extrusion and recombination” approach to derive structurally important 1,2-diketones in good yields with excellent selectivity.

Facile one-pot synthesis of ketones from primary alcohols under mild conditions

One-pot transformation of primary alcohols to ketones was achieved by using dibromoisocyanuric acid and Fe₂O₃. This synthetic method provides a variety of ketones in high yield under mild reaction conditions.

Visible-light-promoted oxidative halogenation of alkynes

In nature, halogenation promotes the biological activity of secondary metabolites, especially geminal dihalogenation.