An immobilized monophosphine-Ir system, which was prepared in situ from [Ir(OMe)(cod)](2) and a silica-supported, compact phosphine, showed high activities and selectivities for the borylation of aromatic C-H bonds with bis(pinacolato)diboron. This system was effective not only for the borylation of benzene but also for the ortho borylation of arenes with directing groups, such as ester, amide, sulfonate, acetal, alkoxymethyl, and chloro groups, under mild reaction conditions.

No abstract

Supported phosphine-Rh systems, prepared in situ from silica-supported bridgehead monophosphines and [Rh(OH)(cod)](2), have enabled ortho-selective C-H borylation for a range of arenes containing nitrogen-based directing groups. The regioselectivity was excellent with various N-directing groups, including saturated and unsaturated N-heterocycles, tert-aminoalkyl groups, and imine-type C-N double bonds. The reaction showed significant tolerance toward steric repulsion around the reacting C-H bond. This Rh catalysis complements the Ir-catalyzed ortho-borylation, which is effective for arenes with oxygen-based directing groups.

Direct C(sp(3))-H borylation of amides, ureas, and 2-aminopyridine derivatives at the position α to the N atom, which gives the corresponding α-aminoalkylboronates, has been achieved with a heterogeneous catalyst system consisting of [Rh(OMe)(cod)]2 and a silica-supported triarylphosphine ligand (Silica-TRIP) that features an immobilized triptycene-type cage structure with a bridgehead P atom. The reaction occurs not only at terminal C-H bonds but also at internal secondary C-H bonds under mild reaction conditions (25-100 °C, 0.1-0.5 mol % Rh).

The directed ortho borylation of phenol derivatives protected with an N,N-diethylcarbamoyl group was efficiently catalyzed by an immobilized monophosphine-Ir system, which was prepared in situ from [Ir(OMe)(cod)](2) and a silica-supported, compact phosphine. The utility of the carbamoyloxy group as a leaving group for metal-catalyzed cross-coupling reactions was demonstrated by its utilization in the synthesis of a terphenyl derivative.

The ester-directed regioselective borylation of arenes catalyzed by a silica-supported monophosphine-Ir complex displayed a significantly broad substrate scope toward heteroaromatic compounds, including thiophene, pyrrole, furan, benzothiophene, benzofuran, indole, and carbazole derivatives. The regioselectivity is complementary to the selectivities observed in the heteroarene C-H borylation with the dtbpy-Ir catalyst system.

Site-selective C-H borylation of quinoline derivatives at the C8 position has been achieved by using a heterogeneous Ir catalyst system based on a silica-supported cage-type monophosphane ligand SMAP. The efficient synthesis of a corticotropin-releasing factor1 (CRF1) receptor antagonist based on a late-stage C-H borylation strategy demonstrates the utility of the C8 borylation reaction.

The site-selective activation and borylation of unactivated C(sp(3))-H bonds in 2-alkylpyridines to form primary and secondary alkylboronates was achieved using silica-supported monophosphine-Ir catalysts. This borylation occurs selectively at C-H bonds located γ to the pyridine nitrogen atom. The site-selectivity of this reaction suggests that the C-H bond cleavage occurs with the assistance of a proximity effect due to N-to-Ir coordination.