High-Throughput Optimization of Ir-Catalyzed C–H Borylation: A Tutorial for Practical Applications

With the aid of high-throughput screening, the efficiency of Ir-catalyzed C–H borylations has been assessed as functions of precatalyst, boron reagent, ligand, order of addition, temperature, solvent, and substrate. This study not only validated some accepted practices but also uncovered unconventional conditions that were key to substrate performance. We anticipate that insights drawn from these findings will be used to design reaction conditions for substrates whose borylations are difficult to impossible using standard catalytic conditions

Cobalt-Catalyzed C–H Borylation of Alkyl Arenes and Heteroarenes Including the First Selective Borylations of Secondary Benzylic C–H Bonds

A cobalt di-<i>tert</i>-butoxide complex bearing N-heterocyclic carbene (NHC) ligands has been synthesized and characterized. This complex is effective at catalyzing the selective monoborylation of the benzylic position of alkyl arenes using pinacolborane (HBpin) as the boron source. This same cobalt complex enables selective monoborylation of <i>N</i>-methylpyrrole, <i>N</i>-methylpyrazole, and <i>N</i>-methylindole. Catalysis can be achieved with as little as 2–3 mol % of the cobalt precatalyst at 80 °C

Bismuth Acetate as a Catalyst for the Sequential Protodeboronation of Di- and Triborylated Indoles

Bismuth­(III) acetate is a safe, inexpensive, and selective facilitator of sequential protodeboronations, which when used in conjunction with Ir-catalyzed borylations allows access to a diversity of borylated indoles. The versatility of combining Ir-catalyzed borylations with Bi­(III)-catalyzed protodeboronation is demonstrated by selectively converting 6-fluoroindole into products with Bpin groups at the 4-, 5-, 7-, 2,7-, 4,7-, 3,5-, and 2,4,7-positions and the late-stage functionalization of sumatriptan

Outer-Sphere Direction in Iridium C–H Borylation

The NHBoc group affords ortho selective C–H borylations in arenes and alkenes. Experimental and computational studies support an outer sphere mechanism where the N–H proton hydrogen bonds to a boryl ligand oxygen. The regioselectivities are unique and complement those of directed ortho metalations