Transition-Metal-Free Oxidative Homocoupling of Aryl, Alkenyl, and Alkynyl Grignard Reagents with TEMPO

Maji, Modhu Sudan; Studer, Armido

doi:10.1055/s-0029-1216859

Cited by 16 publications

(4 citation statements)

References 7 publications

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“…To enable the Sonogashira cross coupling of the corresponding aryldibromide central units (structures 14–23 32–39 in SI) at elevated temperatures, desilylation of 4-((trimethylsilyl)ethynyl)pyridine 40 with TBAF (1 M in THF) was performed in 1,4-dioxane (room temperature for 30 min). Since the light-sensitive 4-ethynylpyridine is not stable in air, the mixture was directly subjected to the aryldibromide in the presence of PdCl 2 (PhCN) 2 , CuI, t -Bu 3 P, and ( i -Pr) 2 NH, to give the target structures 1–10 in very good yields (Supplementary Note 1).…”

Section: Resultsmentioning

confidence: 99%

Quantum interference and heteroaromaticity of para- and meta-linked bridged biphenyl units in single molecular conductance measurements

Gantenbein

Wang

Al-Jobory

et al. 2017

Sci Rep

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Is there a correlation between the (hetero)aromaticity of the core of a molecule and its conductance in a single molecular junction? To address this question, which is of fundamental interest in molecular electronics, oligo(arylene-ethynylene) (OAE) molecular wires have been synthesized with core units comprising dibenzothiophene, carbazole, dibenzofuran and fluorene. The biphenyl core has been studied for comparison. Two isomeric series have been obtained with 4-ethynylpyridine units linked to the core either at para-para positions (para series 1–5) or meta-meta positions (meta series 6–10). A combined experimental and computational study, using mechanically controlled break junction measurements and density functional theory calculations, demonstrates consistently higher conductance in the para series compared to the meta series: this is in agreement with increased conjugation of the π–system in the para series. Within the para series conductance increases in the order of decreasing heteroaromaticity (dibenzothiophene < carbazole < dibenzofuran). However, the sequence is very different in the meta series, where dibenzothiophene ≈ dibenzofuran < carbazole. Excellent agreement between theoretical and experimental conductance values is obtained. Our study establishes that both quantum interference and heteroaromaticity in the molecular core units play important and inter-related roles in determining the conductance of single molecular junctions.

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Section: Resultsmentioning

confidence: 99%

Quantum interference and heteroaromaticity of para- and meta-linked bridged biphenyl units in single molecular conductance measurements

Gantenbein

Wang

Al-Jobory

et al. 2017

Sci Rep

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“…TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy, 1.0 equiv) suppressed the coupling reaction of 1a and 2a but not to a complete extent, and 3aa was isolated in 45% yield (Figure b). Possibly, TEMPO was consumed as an oxidant for the PhMgBr homocoupling reaction . The results of light on/off experiments indicated that constant irradiation was required for product formation, while radical chain processes could not be excluded (Figure c) .…”

Section: Resultsmentioning

confidence: 99%

Purple Light-Promoted Coupling of Bromopyridines with Grignard Reagents via SET

Lei,

Wang,

et al. 2024

J. Org. Chem.

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Alkyl- and arylpyridines and 2,2′-bipyridines are conventionally prepared by Minisci reactions of pyridines and transition metal-catalyzed coupling reactions of halopyridines. Herein, purple light-promoted radical coupling reactions of 2- or 4-bromopyridines with Grignard reagents in Et2O or a mixture of Et2O and tetrahydrofuran in regular glassware without the need for a transition metal catalyst were disclosed for the first time. Methyl, primary and secondary alkyl, cycloalkyl, aryl, heteroaryl, pyridyl, and alkynyl Grignard reagents were compatible with the protocol. As a result, alkyl- and arylpyridines and 2,2′-bipyridines were easily prepared. Single electron transfer from the Grignard reagent to bromopyridine was stimulated by purple light. An electron extruded from the dimerization of the Grignard reagent worked as the catalyst. Light on/off experiments indicated that constant irradiation was required for product formation. Studies of radical clock substrates verified the involvement of a pyridyl radical from bromopyridine and the noninvolvement of an alkyl or aryl radical from the Grignard reagent. The available proof supports a photoinduced SRN mechanism for the new coupling reactions.

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“…described transition‐metal‐free homocoupling of aryl, alkenyl, and alkynyl Grignard reagents by using the 2,2,6,6‐tetramethyl‐piperidine 1‐oxyl radical (TEMPO) as oxidant. The described reaction has produced high yields for homocoupling reactions for synthesis of polyfluorenes,poly(fluorenylenebutadiynylenes), and poly(fluorenylenebutadienylenes) . Another study presented by Cai et al.…”

Section: Introductionmentioning

confidence: 99%

“…The described reaction has produced high yields for homocoupling reactions for synthesis of polyfluorenes,poly(fluorenylenebutadiynylenes), and poly (fluorenylenebutadienylenes). [22][23][24][25] Another study presented by Cai et al described a method to synthesize of π-conjugated polymers containing 1,3-butadiene units by polycondensation using an organic base as the catalyst instead of toxic transition metal-based catalysts. [26] Their synthetic strategy was based on the reaction of α,β-unsaturated compounds containing γ-H with aldehyde compounds, where electron-withdrawing groups such as ester and nitrile are incorporated as side groups.…”

Section: Introductionmentioning

confidence: 99%

Transition‐Metal‐Free Direct C‐H Arylation of Thiophene in Aqueous Media via Potassium Peroxymonosulfate

et al. 2019

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This study covers the use of potassium peroxymonosulfate (PPS) which, is a mild and inexpensive catalyst, for direct coupling of C–H/C–H for water soluble thiophene. The 3‐(4‐methyl‐3′‐ thienyloxy)propyltriethylammonium bromide (M1) has been selected as model monomer that reacted PPS in 2.0, 0.20 and 0.020 monomer to PPS ratio. The reaction has been monitored via NMR spectroscopy revealing the monomer consumption and formation of dimers to tetramers as well as completion of reaction within 15 minutes. Resultant product is easily collected without tedious work up steps. The computational calculation has optimized the regularity of the coupling as head to tail, tail to tail, head to tail (HT‐TT‐HT) for tetramer. The regularity of tetramer which is further satisfied via NMR analysis showing emergence of new peaks at 3.56 and 4.48. The shifts in the UV maximum of reactive species have been monitored by absorbance spectroscopy showing time dependent red shift corresponds to growing from monomer to tetramers. The reaction has self‐stopped due to low solubility of moderate condensates (higher than trimer), however further experiments have performed in water‐organic mixtures showed great promises to obtain higher condensates.

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Transition-Metal-Free Oxidative Homocoupling of Aryl, Alkenyl, and Alkynyl Grignard Reagents with TEMPO

Abstract: Oxidative homocoupling of aryl, alkenyl, and alkynyl Grignard reagents by using commercially available TEMPO as an organic oxidant is described. These coupling reactions occur highly efficiently without the presence of any transition metal.

Cited by 16 publications

References 7 publications

Quantum interference and heteroaromaticity of para- and meta-linked bridged biphenyl units in single molecular conductance measurements

Quantum interference and heteroaromaticity of para- and meta-linked bridged biphenyl units in single molecular conductance measurements

Purple Light-Promoted Coupling of Bromopyridines with Grignard Reagents via SET

Transition‐Metal‐Free Direct C‐H Arylation of Thiophene in Aqueous Media via Potassium Peroxymonosulfate

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