Base-controlled regioselectivity <i>via</i> distinct mechanisms during C–H thionation of azinium salts with elemental sulfur

Regioselective C-H-thionation of pyridine and quinoline rings can be achieved through the reaction of the corresponding quaternary azinium salts with sulfur and a base <i>via</i> a radical- or carbene-involved reaction pathway. The selectivity of CS group installation is determined by the reaction mechanism and affected by the base used.