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A method for the synthesis of 1,2-diketones through the mild and metal-free catalytic photooxygenation of alkynes is described. This reaction, using 9,10-dicyanoanthracene as a catalytic sensitizer with/without biphenyl as a co-sensitizer, readily furnished a variety of desired products upon visible-light irradiation. Mechanistic studies indicated that a radical cation process might have been involved. This report provides the first examples of the transformation of alkynes via acetenyl radical cation intermediates, which have thus far not been explored in organic synthesis.

A redox-neutral, mild, and simple protocol is developed for the synthesis of α-trifluoromethylated ketones from vinyl azides under transition-metal-free conditions. In the presence of organic photoredox catalyst N-methyl-9-mesityl acridinium and sodium trifluoromethanesulfinate, a broad range of substituted vinyl azides were found to react smoothly upon visible-light irradiation, readily furnishing the corresponding products in satisfied yields.

The direct functionalization of an aliphatic C–H bond within a complex molecule through a free-radical pathway is a valuable tool in synthetic chemistry. Herein, we developed an efficient transition-metal-free approach to generate Δ2-isoxazolines from oximes by radical-mediated C(sp3)–H oxidation. Investigation of the mechanism suggested that in the presence of Selectfluor and Bu4NI, the homolysis of the in situ formed O–I bond generated an iminoxyl radical that facilitated subsequent 1,5-H transfer and C(sp3)–H oxidation.

A wide range of chlorinated and brominated isoxazolines is prepared through Pd-catalyzed cyclization of oxime substrates in the presence of CuCl2 or CuBr2.

A palladium-catalyzed efficient synthesis of 5-methylisoxazoles via oxime-mediated functionalization of unactivated olefins is described. The reaction affords a variety of 5-methylisoxazoles in moderate to good yields. To further demonstrate the utility of the method, the rapid synthesis of valdecoxib and oxacillin is reported.