Iridium-Catalyzed Silylation of Five-Membered Heteroarenes: High Sterically Derived Selectivity from a Pyridyl-Imidazoline Ligand |
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| Authors: | Caleb Karmel Camille Z. Rubel Elena V. Kharitonova John F. Hartwig |
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| Affiliation: | 1. Department of Chemistry, University of California, Berkeley, CA, 94720 USA These authors contributed equally to this work.;2. Department of Chemistry, University of California, Berkeley, CA, 94720 USA |
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| Abstract: | The steric effects of substituents on five-membered rings are less pronounced than those on six-membered rings because of the difference in bond angles. Thus, the regioselectivities of reactions of five-membered heteroarenes that occur with selectivities dictated by steric effects, such as the borylation of C−H bonds, have been poor in many cases. We report that the silylation of five-membered-ring heteroarenes occurs with high sterically derived regioselectivity when catalyzed 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 yields of heteroarylsilanes from functionalization at the most sterically accessible C−H bonds of these rings under conditions that the borylation of C−H bonds with previously reported catalysts formed mixtures of products or products that are unstable. The heteroarylsilane products undergo cross-coupling reactions and substitution reactions with ipso selectivity to generate heteroarenes that bear halogen, aryl, and perfluoroalkyl substituents. |
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| Keywords: | C-H-Funktionalisierung Heteroarene Iridiumkatalyse Regioselektivität Silylierung |
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