Scheme 5. Mild alternative for ligand synthesis. ^aReactions were run with heteroarene (1.0 equiv.), alkyltrifluoroborate (1.0 or 2.0 equiv.), MesAcr (5 mol%), K₂S₂O₈ (2.0 equiv.), trifluoroacetic acid (1.0 equiv.) in MeCN/H₂O (1 : 1) on 0.3 mmol scale.