Switchable regioselection of C-H thiolation of indoles using different TMS counterions

A switchable regioselectivity in C-H thiolation reaction by simply swapping the counteranions of TMS is reported here for the first time. An exclusive C3-H thiolation of indoles with sodium arylsulfinates was achieved in the presence of TMSCl as a promoter. In contrast, with the use of TMSOTf instead of TMSCl under otherwise identical conditions, a regiospecific C2-H thiolation of indoles was realized with the same set of substrates.