Site-selective aromatic C-H functionalization yielding triarylsulfonium salts, and subsequent transformations

Aromatic C–H functionalization, the exchange of hydrogen atoms which are bound to carbon atoms for functional groups, is a powerful strategy to increase complexity of aromatic molecules. The high abundance of C–H bonds in biologically relevant organic molecules combined with the typically low reactivity of C–H bonds causes two major challenges for C–H functionalization chemistry, the positional selectivity and the tolerance of other, more reactive, functional groups. Unselective reactions produce mixtures of products, which decreases the yield of the desired product, and may lead to additional purification steps. In order for C–H functionalization to be synthetically useful, the introduced functional group needs to engage in many subsequent reactions to give access to a broad range of different products. The aromatic C–H functionalization reaction presented here uses sulfoxide reagents to introduce thianthrenium or dibenzothiophenium groups to complex molecules. The reaction proceeds with exquisite site-selectivity and tolerates many functional groups. Many new tranformations were here developed to allow conversion of the sulfonium group into useful functional groups. Those new transformations include transition metal catalyzed cross coupling as well as a novel photoredox catalyzed process, which both enable the synthesis of a broad range of useful structures. This new method, in contrast to established methods, is unique in providing site selectivity as well as synthetic versatility