Efficient Rh-catalyzed C–H borylation of arene derivatives under photochemical conditions

Abstract

Photocatalysis allows innovations in organic synthesis. Among the various catalytic reactions, CH-functionalizations offer valuable possibilities for the refinement of easily available building blocks. In this respect, catalytic borylation is of interest, too. So far, most of the catalytic borylation reactions are performed under thermal conditions at comparably high temperatures. Here, we describe a new synthetic route for efficient borylation reactions of arenes using a photocatalytic pathway. This novel approach allows the synthesis of a broad variety of borylated arenes and heteroarenes under mild conditions. Applying trans-[Rh(PMe3)2(CO)Cl] as an active photocatalyst and HBPin as an boron source, we achieved high TON. A catalytic cycle that relies on a Rh(I)-Rh(III) interconversion is proposed.

Iridium‐Catalysed C−H Borylation of Heteroarenes: Balancing Steric and Electronic Regiocontrol

“…Of these, iridium trisboryl complexes have become the catalyst system of choice and this review will focus on the application of these systems in the borylation of heterocyclic substrates. Whilst other transition metal complexes including those containing Pd, Co, Fe, Zn, Ru, Ni, Pt, Rh, and Mn also promote similar transformations, these will only be discussed when they offer a distinct advantage in regiocontrol [38–46] …”

Increasing Catalyst Efficiency in C−H Activation Catalysis

“…This system was used to prepare PhBpin with aTON of 700. [64,65] Angewandte Chemie of this reaction is perhaps enhanced through the use of light irradiation as opposed to more forcing thermal conditions. Ir I -catalyzed CÀHborylationo fbenzene.…”

“…One example was performed on a gram‐scale to afford the product in 85 % yield with a TON of 425. Other notable Rh I ‐catalyzed borylation reactions include the work of Beller and co‐workers, who used UV light irradiation to activate the precatalyst [Rh(PMe 3 ) 2 (CO)Cl] via the extrusion of CO (Scheme ). This system was used to prepare PhBpin with a TON of 700.…”

Iridium-Catalyzed Regioselective Borylation of Substituted Biaryls

“…Accurate mass determinations (HRMS) were obtained using an Orbitrap mass spectrometer or MALDI-TOF/TOF mass spectrometer. 1 H, 13 C, and 19 F NMR spectra were recorded at 700.130 MHz, 176.048 MHz, and 376.696 MHz, respectively, at ambient temperature. The chemical shifts in 1 H NMR spectra are reported using TMS as internal standard and were referenced with the residual proton resonances of the corresponding deutrated solvent (CDCl 3 : 7.26 ppm).…”

“…Moreover, photocatalytic borylation has also been reported. 19 Catalytic C-H borylation has been used to functionalize a large variety of aromatic and heteroaromatic systems 20 including medicinally active compounds, 21 symmetrical polyaromatics, 22 and polymers. 23 There are handful examples of applications of this methodology to prepare biarylboronic esters.…”