Iridium‐Catalyzed Silylation of Five‐Membered Heteroarenes: High Sterically Derived Selectivity from a Pyridyl‐Imidazoline Ligand
The steric effects of substituents on five-memberedrings are less pronounced than those on six-membered ringsbecause of the difference in bond angles. Thus, the regiose-lectivities of reactions of five-membered heteroarenes thatoccur with selectivities dictated by steric effects, such as theborylation of CH bonds, have been poor in many cases. Wereport that the silylation of five-membered-ring heteroarenesoccurs with high sterically derived regioselectivity whencatalyzed by the combination of [Ir(cod)(OMe)]2(cod=1,5-cyclooctadiene) and a phenanthroline ligand or a new pyridyl-imidazoline ligand that further increases the regioselectivity.The silylation reactions with these catalysts produce high yieldsof heteroarylsilanes from functionalization at the most steri-cally accessible CH bonds of these rings under conditions thatthe borylation of CH bonds with previously reported catalystsformed mixtures of products or products that are unstable. Theheteroarylsilane products undergo cross-coupling reactionsand substitution reactions with ipso selectivity to generateheteroarenes that bear halogen, aryl, and perfluoroalkylsubstituents.
Read more on publisher's site.