Ligand switchable site selectivity in C–H alkenylation of thiophenes by turnover-limiting step control

The origin of switchable site selectivity during Pd-catalysed C–H alkenylation of heteroarenes has been examined through More O’Ferrall–Jencks, isotope effect, and DFT computational analyses, which indicate substitution of ionic thioether for pyridine dative ligands induces a change from selectivity-determining C–H cleavage to C–C bond formation, respectively.