Chelation-assisted transition metal-catalysed C–H chalcogenylations
The development of convenient and mild chalcogenylation reactions for the preparation of unsymmetrical diaryl sulfides and diaryl selenides has received significant attention in recent years due to their prevalence in natural products, organic molecular syntheses, catalysis, drug candidates and functional materials. In contrast with conventional organic transformations which largely rely on the inherent reactivity of functional groups, transition metal-catalysed direct C–H functionalizations have emerged as a powerful strategy that eliminates prefunctionalised starting materials and thus leads to more atom- and step-economical processes. This review summarizes the recent advances in C–S and C–Se formations via transition metal-catalyzed C–H functionalization utilizing directing groups to control the site-selectivity until autumn 2019. Typical examples are listed and mechanistic aspects are discussed in detail.