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Electrophotocatalytic diamination of vicinal C–H bonds

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Science  05 Feb 2021:
Vol. 371, Issue 6529, pp. 620-626
DOI: 10.1126/science.abf2798

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Double C–H amination

The conversion of C–H bonds into C–N bonds is broadly useful in producing pharmaceutically important compounds from simple, readily available feedstocks. Shen and Lambert report a method to induce this reaction twice in a row at benzylic and neighboring alkyl carbon centers, using acetonitrile solvent as a convenient source of nitrogen. The method relies on successive electrochemical and photochemical activation of a cyclopropenium catalyst and yields hydrogen gas as a clean co-product.

Science, this issue p. 620

Abstract

The conversion of unactivated carbon-hydrogen (C–H) bonds to carbon–nitrogen (C–N) bonds is a highly valued transformation. Existing strategies typically accomplish such reactions at only a single C–H site because the first derivatization diminishes the reactivity of surrounding C–H bonds. Here, we show that alkylated arenes can undergo vicinal C–H diamination reactions to form 1,2-diamine derivatives through an electrophotocatalytic strategy, using acetonitrile as both solvent and nitrogen source. The reaction is catalyzed by a trisaminocyclopropenium (TAC) ion, which undergoes anodic oxidation to furnish a stable radical dication while the cathodic reaction reduces protons to molecular hydrogen. Irradiation of the TAC radical dication (wavelength of maximum absorption of 450 to 550 nanometers) with a white-light compact fluorescent light generates a strongly oxidizing photoexcited intermediate. Depending on the electrolyte used, either 3,4-dihydroimidazole or 2-oxazoline products are obtained.

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