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Review
. 2023 Apr 21;9(16):eadg3311.
doi: 10.1126/sciadv.adg3311. Epub 2023 Apr 21.

Transition metal-catalyzed remote C─H borylation: An emerging synthetic tool

Mirja Md Mahamudul Hassan  1 , Saikat Guria  1 , Sayan Dey  1 , Jaitri Das  1 , Buddhadeb Chattopadhyay  1
Affiliations
Review

Transition metal-catalyzed remote C─H borylation: An emerging synthetic tool

Mirja Md Mahamudul Hassan et al. Sci Adv. .

Abstract

Transition metal-catalyzed C─H bond activation and borylation is a powerful synthetic method that offers versatile synthetic transformation from organoboron compounds to virtually all other functional groups. Compared to the ortho-borylation, remote borylation remains more challenging owing to the inaccessibility of these C─H bonds. Enforcing the metal catalyst toward the remote C─H bonds needs well-judged catalyst design through proper ligand development. This review article aims to summarize the recent discoveries for the remote C─H borylation by the employment of new catalyst/ligand design with the help of steric of the ligand, noncovalent interactions. It has been found that C─H borylation now takes part in the total synthesis of natural products in a shorter route. Whereas, Ir-catalyzed C─H borylation is predominant, cobalt catalyst has also started to affect this field for sustainable and cost-effective development.

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Figures

Fig. 1.
Fig. 1.. Inception of CH borylation and journey toward Ir-catalyzed CH borylation.
(A) First arene C─H borylation (31). (B) Transition metal mediated photochemical borylation (32). (C) Mechanism of iron mediated photochemical borylation (33). (D) First catalytic C─H borylation (34). (E) Phosphine ligand-mediated borylation (35). (F) First bpy based ligand for arene C─H borylation (–38). (G) Ortho and remote C─H borylation (, , –41). (H) Pioneering reports of ortho-borylation (, , –45). m/z, mass/charge ratio.
Fig. 2.
Fig. 2.. Development of steric controlled remote meta-selective borylation.
(A) Ir/Rh catalyzed C─H borylation (46, 47). (B) Selective remote borylation by P-ligand (35). (C) Selective remote borylation by Bpy-ligand (36). (D) Synthetic diversification and origin of selectivity (23, 48, 49). (E) C6-borylation of indole derivatives (50, 51). (F) Steric controlled meta-borylation of mono substituted arenes (53).
Fig. 3.
Fig. 3.. Sterically controlled para-CH borylation.
(A) Itami's para-borylation using bulky phosphine ligand (57). (B) Para-selective borylation of 1,2-disubstituted arenes (60).
Fig. 4.
Fig. 4.. Sterically controlled para-CH borylation.
(A) Ligand-substrate distortion for para-selective borylation of twisted aromatic amides (bis-Boc) (61). (B) Steric and H-bonding controlled para-borylation of aniline (63).
Fig. 5.
Fig. 5.. Weak interaction approach for the remote meta-selective CH borylation.
(A) Variety of weak interactions in biological systems (65). (B) Design of remote C─H functionalization. (C) Meta-selective borylation of amide by weak interaction approach (67, 68). (D) Ligand controlled meta-borylation of benzaldehyde (70, 71). (E) Ion-pair controlled meta-borylation (72). (F) H-bonding assisted meta-borylation (73). (G) Ion-pair controlled meta-borylation (74). (H) L-shaped bifunctional ligand for meta-borylation (76).
Fig. 6.
Fig. 6.. Weak interaction approach for the remote meta-selective borylation.
(A) Meta-selective borylation of amide and pyridine (Lewis acid-base concept) (77). (B) Meta-selective borylation of amide and pyridine (Lewis acid-base concept) (78). (C) Meta-borylation of pyridine via Zn-N coordination (79). (D) Meta-borylation via electrostatic interaction (80, 81). (E) Meta-selective borylation of various arene systems (82, 83).
Fig. 7.
Fig. 7.. Weak interaction approach for the para-selective borylation.
(A) Lewis acid-base interaction for para-borylation (84). (B) O--K--O interaction for para borylation of esters by L-shaped bifunctional ligand (75). (C) Ion-pair controlled para-borylation (85, 86). (D) Ion-pair controlled para-borylation (87). (E) IMHB directed para-borylation (89). (F) Para-selective borylation of various arene systems (82, 83).
Fig. 8.
Fig. 8.. Development of Cobalt-catalyzed CH borylation.
(A) Initial Investigations for Co-pincer catalyzed C─H activation (91). (B) First Co-pincer catalyzed C─H borylation (–94). (C) Rational catalyst design (93).
Fig. 9.
Fig. 9.. Cobalt-catalyzed remote CH borylation.
(A) Ortho-borylation of fluoroarenes (95). (B) Para-selective borylation (96). (C) Meta-selective borylation (97).
Fig. 10.
Fig. 10.. Summary of pioneering concepts for the remote CH borylation.
Steric controlled remote borylation (35, 36, 53, 57, 60). Weak interaction approach for remote borylation: (A) Concepts of meta borylation using various weak interactions (, , –, , , , –81), (B) Concepts of para borylation using various weak interactions (, , –87, 89). Cobalt catalyzed remote borylation of arenes (–97).
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