Ir-Catalyzed ortho-Borylation of Phenols Directed by Substrate-Ligand Electrostatic Interactions: A Combined Experimental/in Silico Strategy for Optimizing Weak Interactions.

A strategy for affecting ortho versus meta/para selectivity in Ir-catalyzed C-H borylations (CHBs) of phenols is described. From selectivity observations with ArylOBpin (pin = pinacolate), it is hypothesized that an electrostatic interaction between the partial negatively charged OBpin group and the partial positively charged bipyridine ligand of the catalyst favors ortho selectivity. Experimental and computational studies designed to test this hypothesis support it. From further computational work a second generation, in silico designed catalyst emerged, where replacing Bpin with Beg (eg = ethylene glycolate) was predicted to significantly improve ortho selectivity. Experimentally, reactions employing B2eg2 gave ortho selectivities > 99%. Adding triethylamine significantly improved conversions. This ligand-substrate electrostatic interaction provides a unique control element for selective C-H functionalization.

Harnessing C-H Borylation/Deborylation for Selective Deuteration, Synthesis of Boronate Esters, and Late Stage Functionalization.

Ir-catalyzed deborylation can be used to selectively deuterate aromatic and heteroaromatic substrates. Combined with the selectivities of Ir-catalyzed C-H borylations, uniquely labeled compounds can be prepared. In addition, diborylation/deborylation reactions provide monoborylated regioisomers that complement those prepared by C-H borylation. Comparisons between Ir-catalyzed deborylations and Pd-catalyzed deborylations of diborylated indoles described by Movassaghi are made. The Ir-catalyzed process is more effective for deborylating aromatics and is generally more effective in the monodeborylation of diborylated thiophenes. These processes can be applied to complex molecules such as clopidogrel.