We next studied the effect of various parameters on the Fe–Cu borylation,(14) with particular attention to the selectivity (borylation/PDB ratio). 2-Bromonaphthalene 2b was chosen as the model substrate since it is moderately prone to PDB in related Pd-catalyzed reactions.(6c) The effect of ligands was first considered: we found that in THF at 20 °C, TMEDA favorably improved the selectivity, up to 50% with 0.2 equiv ligand. Increasing the amount of TMEDA was ...