Photoredox radical borylation of electron-deficient alkenes with NHC-boranes

Zhu, Congjun; Gao, Shan; Li, Weipeng; Zhu, Chengjian

doi:10.1039/d0cc06966c

Cited by 20 publications

(5 citation statements)

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“…Curran’s group realized the formal 1,4-hydroboration of electron-deficient arenes, which provided a practical approach to borylated 1,4-cyclohexadiene . Zhu and Li disclosed the photocatalyzed reaction of NHC–BH 3 and Morita–Baylis–Hillman adducts, affording functionalized allyl boron compounds . Very recently, Chen and Liu described a novel approach for generation of NHC–boryl radicals with thiol catalyst, in which boryl radicals were produced by B–S bond homolytic cleavage of in situ formed boryl sulfides under light irradiation .…”

Section: Lewis Base–boryl Radical Mediated C–b Bond Formationmentioning

confidence: 99%

“…65 Zhu and Li disclosed the photocatalyzed reaction of NHC−BH 3 and Morita−Baylis−Hillman adducts, affording functionalized allyl boron compounds. 66 Very recently, Chen and Liu described a novel approach for generation of NHC−boryl radicals with thiol catalyst, in which boryl radicals were produced by B−S bond homolytic cleavage of in situ formed boryl sulfides under light irradiation. 34 Ye also developed a photoredox protocol for single electron oxidation of an amine−borane complex to generate the corresponding boryl radical.…”

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confidence: 99%

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Lewis Base–Boryl Radicals Enabled Borylation Reactions and Selective Activation of Carbon–Heteroatom Bonds

2022

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Metrics & MoreArticle Recommendations CONSPECTUS:The past decades have witnessed tremendous progress on radical reactions. However, in comparison with carbon, nitrogen, oxygen, and other main group element centered radicals, the synthetic chemistry of boron centered radicals was less studied, mainly due to the high electron-deficiency and instability of such 3-center−5-electron species. In the 1980s, Roberts and co-workers found that the coordination of a Lewis base (amines or phosphines) with the boron center could form 4-center−7-electron boryl radicals (Lewis base−boryl radicals, LBRs) that are found to be more stable. However, only limited synthetic applications were developed. In 2008, Curran and co-workers achieved a breakthrough with the discovery of N-heterocyclic carbene (NHC) boryl radicals, which could enable a range of radical reduction and polymerization reactions. Despite these exciting findings, more powerful and valuable synthetic applications of LBRs would be expected, given that the structures and reactivities of LBRs could be easily modulated, which would provide ample opportunities to discover new reactions. In this Account, a summary of our key contributions in LBR-enabled radical borylation reactions and selective activation of inert carbon−heteroatom bonds will be presented. Organoboron compounds have shown versatile applications in chemical society, and their syntheses rely principally on ionic borylation reactions. The development of mechanistically different radical borylation reactions allows synthesizing products that are inaccessible by traditional methods. For this purpose, we progressively developed a series of NHC−boryl radical mediated chemo-, regio-, and stereoselective radical borylation reactions of alkenes and alkynes, by which a wide variety of structurally diverse organoboron molecules were successfully prepared. The synthetic utility of these borylated products was also demonstrated. Furthermore, we disclosed a photoredox protocol for oxidative generation of NHC−boryl radicals, which enabled useful defluoroborylation and arylboration reactions. Selective bond activation is an ideal way to convert simple starting materials to value-added products, while the cleavage of inert chemical bonds, in particular the chemoselectivity control when multiple identical bonds are present in similar chemical environments, remains a long-standing challenge. We envisaged that finely tuning the properties of LBRs might provide a new solution to address this challenge. Recently, we disclosed a 4-dimethylaminopyridine (DMAP)−boryl radical promoted sequential C−F bond functionalization of trifluoroacetic acid derivatives, in which the α-C−F bonds were selectively snipped via a spin-center shift mechanism. This strategy enables facile conversion of abundantly available trifluoroacetic acid to highly valuable mono-and difluorinated molecules. Encouraged by this finding, we further developed a boryl radical enabled three-step sequence to construct all-carbon quaternary centers from a range of trich...

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Section: Lewis Base–boryl Radical Mediated C–b Bond Formationmentioning

confidence: 99%

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confidence: 99%

Lewis Base–Boryl Radicals Enabled Borylation Reactions and Selective Activation of Carbon–Heteroatom Bonds

2022

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“…Significantly, MBH adducts can be served as an excellent radical acceptor in organic synthesis since their distinctive structures incorporate an activated CC bond connected to electron-withdrawing groups. A great deal of radical donors, such as Langlois’ reagent, N -hydroxyphthalimide esters (NHPI esters), potassium organotrifluoroborates, tertiary amines, ethers, α-bromo ketones, or NHC-boranes have been proved to be ideal C or B-radical precursors under photoredox catalysis or electrocatalysis to provide numerous trisubstituted olefins (Scheme a). In addition, the aryl sulfonylation of MBH adducts has been identified as an efficient method to obtain allylic sulfones by exploiting various sulfonyl reactants .…”

Section: Introductionmentioning

confidence: 99%

Photoinduced Alkylsulfonylation and Cyanoalkylsulfonylation of Morita–Baylis–Hillman Adducts via Multicomponent Insertion of Sulfur Dioxide

Song,

Bao,

Sun

et al. 2024

J. Org. Chem.

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General and convenient visible-light-promoted alkylsulfonylation and cyanoalkylsulfonylation of MBH adducts have been developed through the multicomponent insertion of sulfur dioxide, enabling the assembly of two C−S bonds to generate structurally diverse allylic alkylsulfones (43 examples in total). The reaction of MBH adducts with potassium alkyltrifluoroborates and 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct afforded sulfones with generally good yields. Notably, the addition of N,N,N′,N′-tetramethylethylenediamine as a base into the photocatalytic system led to yielding an alkyl sulfonyl unit and cyano group-anchored trisubstituted alkenes by utilizing cycloketone oxime esters as C-radical precursors. Both of these reactions have constructed two C−S bonds, and all desired products were obtained in moderate to excellent yields with complete stereospecificity.

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“…Concomitantly, photoredox-mediated SET with NHC-boranes was also disclosed by Curran for the elegant 1,4hydroboration of electron-rich arenes. [21] Finally, borylation of MBH adducts, [22] and regioselective borylation of diverse Michael acceptors [23] were also possible under similar conditions. Finally, the SET event to generate a boryl radical can also occur upon light irradiation of an EDA complex formed between the borane and a N-methoxy pyridinium acceptor, as shown by Lin and Quan in a very recent report.…”

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Photocatalytic and Electrochemical Borylation and Silylation Reactions

Biremond

Riomet

Jubault

et al. 2023

The Chemical Record

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Due to their high versatility borylated and silylated compounds are inevitable synthons for organic chemists. To escape the classical hydroboration/hydrosilylation paradigm, chemists turned their attention to more modern and green methods such as photoredox chemistry and electrosynthesis. This account focuses on novel methods for the generation of boryl and silyl radicals to forge C−B and C−Si bonds from our group.

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Photoredox radical borylation of electron-deficient alkenes with NHC-boranes

Abstract: An efficient photoredox radical borylation of electron-deficient Morita–Baylis–Hillman type alkenes is achieved to afford multi-functionalized allylic boranes. The reaction demonstrates a wide substrate scope and showcases excellent functional group tolerance....

Cited by 20 publications

References 33 publications

Lewis Base–Boryl Radicals Enabled Borylation Reactions and Selective Activation of Carbon–Heteroatom Bonds

Lewis Base–Boryl Radicals Enabled Borylation Reactions and Selective Activation of Carbon–Heteroatom Bonds

Photoinduced Alkylsulfonylation and Cyanoalkylsulfonylation of Morita–Baylis–Hillman Adducts via Multicomponent Insertion of Sulfur Dioxide

Photocatalytic and Electrochemical Borylation and Silylation Reactions

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