Site‐Selective Functionalization of Cysteine Units in Peptides Through Meerwein Arylation Reactions Under Mild Conditions

α‐Methylstyrenes are known as highly reactive scavengers for aryl radicals. By developing a novel bifunctional reagent, which combines a 2‐bromoacyl unit for coupling to thiols with a styrene moiety for further functionalization via aryl radicals, a broadly applicable tool became available. Given that the two‐step functionalizations can be carried out under particularly mild conditions, the novel methods also enable the selective modification of peptidic substrates at their cysteine units.