Scalable, Metal- and Additive-Free, Photoinduced Borylation of Haloarenes and Quaternary Arylammonium Salts

Mfuh, Adelphe; Doyle, John; Chhetri, Bhuwan; Arman, Hadi D.; Larionov, Oleg V.

doi:10.1021/jacs.6b01376

Cited by 260 publications

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“…We recently reported that haloarenes, including electron-rich fluoroarenes, as well as quaternary arylammonium salts readily react with diboron compounds to produce aromatic boronic acids and esters (Fig. 1a-c) under photochemical activation conditions 29 . A similar photoinduced borylation method was also developed by Li 30,31 .…”

Section: Introductionmentioning

confidence: 99%

Metal- and additive-free photoinduced borylation of haloarenes

et al. 2017

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Boronic acids and esters have crucial roles in the areas of synthetic organic chemistry, molecular sensors, materials science, drug discovery, and catalysis. Many of the current applications of boronic acids and esters require materials with very low levels of transition metal contamination. Most of the current methods for the synthesis of boronic acids require, however, transition metal catalysts and ligands that have to be removed via additional purification procedures. This protocol describes a simple, metal- and additive-free method of conversion of haloarenes directly to boronic acids and esters. This photoinduced borylation protocol does not require expensive and toxic metal catalysts and ligands and produces innocuous and easy-to-remove by-products. Furthermore, the reaction can be carried out on multigram scales in common grade solvents without the need for reaction mixtures to be deoxygenated. The setup and purification steps are typically accomplished within 1–3 h. The reactions can be run overnight, and the protocol can be completed within 13–16 h. Two representative procedures that are described in this protocol provide details for preparation of a boronic acid (3-cyanopheylboronic acid) and a boronic ester (1,-benzenediboronic acid bis(pinacol)ester). We also discuss additional details of the method that will be helpful in the application of the protocol to other haloarene substrates.

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Metal- and additive-free photoinduced borylation of haloarenes

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“…19,20 Homolytic and heterolytic cleavage of the Ar–X bond followed by the homolytic substitution at boron 21 in B 2 (OR) 4 were proposed as key steps in this process.…”

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“…The experimental and computational data available for the photoinduced Ar–X monoborylation, 19,22 point to a solvent-cage-assisted radical pathway (Scheme 2) for the dual 1,2-C–H/C–X borylation reaction in isopropanol. Photoinduced homolysis is very efficient for bromo- and iodoarenes in low- and medium polarity solvents.…”

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“…Photoinduced homolysis is very efficient for bromo- and iodoarenes in low- and medium polarity solvents. 13,14 Following the initial homolytic substitution at B 2 pin 2 with the photogenerated aryl radical, 19,22 addition of the Bpin radical to PhBpin may be enabled by the cage effect of the more confining medium (e.g. compare viscosities of acetonitrile 0.377 cP, 23 and isopropanol 2.859 cP, 24 at 15 °C).…”

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“…It is possible that heterolytic cleavage of the C–X bond in the very polar HFIP leads to the generation of the triplet aryl cation 6 that can react with the sp 2 - sp 3 diboron anion 7 . 19,22,28 Subsequent recombination of the intermediates ( 8 and 9 ) will favor the 1,3-addition ( 10 ), since the 1,2- and 1,4-addition will produce cationic intermediates that are destabilized by the π-acceptor boryl group 29 (e.g. as in 11 ).…”

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Additive- and Metal-Free, Predictably 1,2- and 1,3-Regioselective, Photoinduced Dual C–H/C–X Borylation of Haloarenes

et al. 2016

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Boron‐Mediated Radical Reactions

André‐Joyaux¹,

Gnägi²,

Gnägi‐Lux³

et al. 2022

Patai's Chemistry of Functional Groups

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This chapter focuses on the use of boron‐containing reagents in radical reactions. In all reactions presented here, boron is playing a key role in the radical process either by being part of the radical process or by influencing the reactivity of the radical and nonradical species. The diversity of radical chemistry involving organoboron species is spectacular. They represent a unique source of radicals for chain reactions allowing for instance efficient radical initiation at low temperature and generation of a broad range of functionalized alkyl radicals from easily prepared organoboranes. Recent developments in redox chemistry including photoredox catalysis, electrochemistry, and single‐electron‐transfer processes have allowed the generation of alkyl and aryl radicals from stable organoboron derivatives such as alkyl‐ and aryl‐trifluoroborates. A broad range of synthetic applications such as radical cascade processes, multicomponent reactions, and cross‐coupling reactions in the presence of suitable metals are possible. Besides radical generation, boron‐containing radical precursors and radical traps are becoming of increasing importance to prepare building blocks enclosing a boron moiety suitable for further functionalization. Merging radical processes with classical boron chemistry including Suzuki–Miyaura‐type cross‐coupling processes; homologation via 1,2‐metallate rearrangement; and conversions to alcohols, amines, and related compounds offers unique opportunities for applications in organic synthesis.

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Scalable, Metal- and Additive-Free, Photoinduced Borylation of Haloarenes and Quaternary Arylammonium Salts

Cited by 260 publications

References 116 publications

Metal- and additive-free photoinduced borylation of haloarenes

Metal- and additive-free photoinduced borylation of haloarenes

Additive- and Metal-Free, Predictably 1,2- and 1,3-Regioselective, Photoinduced Dual C–H/C–X Borylation of Haloarenes

Boron‐Mediated Radical Reactions

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