Iridium-Catalyzed Borylation of Secondary C-H Bonds in Cyclic Ethers

The borylation of secondary C-H bonds, specifically secondary C-H bonds of cyclic ethers, with a catalyst generated from tetramethylphenanthroline and an iridium precursor is reported. This borylation occurs with unique selectivity for the C-H bonds located beta to the oxygen atoms over the weaker C-H bonds located alpha to oxygen atoms. Mechanistic studies imply that the C-H bond cleavage occurs directly at the beta position rather than at the alpha position followed by isomerization of a reaction intermediate.