Site-Selective Thiolation of (Multi)halogenated Heteroarenes.

A general and simple strategy for the site-selective thiolation of various pharmaceutically relevant electron-rich heteroarenes with thiols is reported. This mild and reliable photocatalytic protocol enables C-S coupling at the most electron-rich position of the (multi)halogenated substrates, complementing established methodologies. Experimental and computational studies suggest a radical chain mechanism with the key step being a homolytic aromatic substitution of the heteroaryl halide by an electrophilic thiyl radical, highlighting an underdeveloped reactivity mode.