Highly Active CH Bond Borylation of Aromatics With Pyridine as Convenient, Low-Cost Ligand Under Iridium Catalysis

Although iridium-catalyzed CH bond borylation represents the archetypical example of step- and atom-economy transformation, the utilization of sophisticated and expensive ligands, which are typically prepared via extensive chemical manipulations raises questions about its overall sustainability in the synthetic arena. For instance, N,N-chelating ligands derived from 1,10-phenanthroline (phen) or 2,2'-bipyridine (bpy) scaffolds, whose synthesis relies on multistep transformations including the use of strong acids and oxidants, or costly palladium-catalyzed cross-coupling chemistry, respectively, dominate the field while affording high E-factor values and leading to an important carbon footprint. Herein we show that it is possible to replace these ligands by simple, unfunctionalized pyridine (pyr) ligand in the iridium-catalyzed CH bond borylation of aromatic substrates that feature CH bonds that are relatively acidic such as phthalimides and related 1,2-disubstituted aromatics. As a result, turnover numbers superior to 500 with catalyst loading as low as 0.1 mol% were disclosed for the CH bond borylation of compounds relevant for biology and materials sciences. In addition, the catalytic system was found to be compatible with 2-MeTHF as a green solvent.