Metal-free photoredox-catalysed formal C–H/C–H coupling of arenes enabled by interrupted Pummerer activation

Abstract

Aryl–aryl cross-coupling constitutes one of the most widely used procedures for the synthesis of high-value materials that range from pharmaceuticals to organic electronics and conducting polymers. The assembly of (hetero)biaryl scaffolds generally requires multiple steps; coupling partners must be functionalized before the key bond-forming event is considered. The development of selective C–H arylation processes in arenes—which sidestep the need for prefunctionalized partners—is thus crucial for streamlining the construction of these key architectures. Here we report an expedient, one-pot assembly of (hetero)biaryl motifs using photocatalysis and two non-prefunctionalized arene partners. The approach is underpinned by the functionalization of a C–H bond in an arene coupling partner using the interrupted Pummerer reaction. A unique pairing of the organic photoredox catalyst and the intermediate dibenzothiophenium salts enables highly selective reduction in the presence of sensitive functionalities. The utility of the metal-free, one-pot strategy is exemplified by the synthesis of a bioactive natural product and the modification of complex molecules of societal importance. Forming carbon–carbon bonds at the expense of two C–H bonds is difficult, but attractive, as it reduces the number of chemical steps during synthesis by avoiding prefunctionalization. Here such a method is reported, involving an interrupted Pummerer reaction and a photoredox-catalysed coupling.