Electronically Driven Regioselective Iridium‐Catalyzed C−H Borylation of Donor‐π‐Acceptor Chromophores Containing Triarylboron Acceptors

Abstract

We observed a surprisingly high electronically driven regioselectivity for the iridium‐catalyzed C−H borylation of donor‐π‐acceptor (D‐π‐A) systems with diphenylamino (1) or carbazolyl (2) moieties as the donor, bis(2,6‐bis(trifluoromethyl)phenyl)boryl (B(FXyl)2) as the acceptor, and 1,4‐phenylene as the π‐bridge. Under our conditions, borylation was observed only at the sterically least encumbered para‐positions of the acceptor group. As boronate esters are versatile building blocks for organic synthesis (C−C coupling, functional group transformations) the C−H borylation represents a simple potential method for post‐functionalization by which electronic or other properties of D‐π‐A systems can be fine‐tuned for specific applications. The photophysical and electrochemical properties of the borylated (1‐(Bpin)2) and unborylated (1) diphenylamino‐substituted D‐π‐A systems were investigated. Interestingly, the borylated derivative exhibits coordination of THF to the boronate ester moieties, influencing the photophysical properties and exemplifying the non‐innocence of boronate esters.

(Hetero)arene-fused boroles: a broad spectrum of applications

“…2), which are much shorter than the sum of the van der Waals radii for boron and uorine (3.39 Å). 93 The s-donation from the uorine atom(s) of ortho-CF 3 group(s) to the vacant p z -orbital of boron was also observed in other boranes [94][95][96][97][98][99][100][101][102] and boroles. 45,68 The 2,4,6-tri-tert-butylphenyl (Mes*) group is the bulkiest substituent among these protecting groups and, thus, provides the most stable 9-borauorenes.…”

Synthesis of Highly Functionalizable Symmetrically and Unsymmetrically Substituted Triarylboranes from Bench‐Stable Boron Precursors

“…Overview of reported follow-up reactions, to which the BXyl 3 moiety (BAr 3 or BAr 2 Ar') is tolerant, and selected functional groups that have been attached. Examples of each path are given in the following references: a, [26][27][28][29][30] b, [27,[29][30][31][32][33] c, [34,35] d, [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] e, [52][53][54][55][56][57] f, [42,[58][59][60][61][62] g, [63][64][65][66][67] and h. [68][69][70][71]…”

“… Overview of reported follow‐up reactions, to which the BXyl 3 moiety (BAr 3 or BAr 2 Ar’) is tolerant, and selected functional groups that have been attached. Examples of each path are given in the following references: a,[ 26 , 27 , 28 , 29 , 30 ] b,[ 27 , 29 , 30 , 31 , 32 , 33 ] c,[ 34 , 35 ] d,[ 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ] e,[ 52 , 53 , 54 , 55 , 56 , 57 ] f,[ 42 , 58 , 59 , 60 , 61 , 62 ] g,[ 63 , 64 , 65 , 66 , 67 ] and h.[ 68 , …”

“…[ 76 , 77 ] The resulting boronate ester moieties can be employed in various functional group transformations as well as Suzuki‐Miyaura cross‐coupling reactions (Figure 2 b). [ 27 , 29 , 30 , 31 , 32 , 33 ] In this way, triarylboranes can also be attached to chromophores or stationary phases. Even deprotonation or lithium‐halide exchange reactions can be employed to functionalize triarylboranes due to their high tolerance towards different reaction conditions (Figure 2 d).…”

Photoinduced Borylation for the Synthesis of Organoboron Compounds

“…Organoboron compounds can be conveniently used in numerous transformations in organic synthesis and catalysis, drug discovery, materials science, and so on. − Not only can the boronate group in organoboronate esters be converted to virtually all functional groups but also the boronate esters themselves can be employed in various cross-coupling reactions to synthesize valuable organic compounds and can also be used to catalyze enantioselective Diels–Alder reactions and the selective activation of diols, carbohydrates, and so on. − Recently, organoboron compounds have emerged as useful components of and precursors to conjugated materials, − covalent organic frameworks, − and hydrogels. − Their low toxicity and easy handling make them widely applicable in the total synthesis of natural products with bioactivity. In addition, organoboronic acids can be directly utilized as therapeutic agents and biological probes. − For example, bortezomib and its derivatives (Scheme ), which are carboxylic bioisosteres, can replace motifs with similar chemical and physical properties and act as proteasome inhibitors …”