Mechanistic study on iodine-catalyzed aromatic bromination of aryl ethers by N -Bromosuccinimide

Pramanick, Pranab K.; Hou, Zhen-Lin; Yao, Bo

doi:10.1016/j.tet.2017.10.073

Cited by 16 publications

(9 citation statements)

References 84 publications

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“…0.2 mbar = 73–81 °C) afforded a yellow oil (39.8 g). It was a 91:9 (mol:mol) mixture of compounds 39 (37.4 g, 82 %; ref . 94 %) and 38 (2.4 g, 8 %).…”

Section: Methodsmentioning

confidence: 99%

“…The feasibility of the RCM/4‐electron oxidation route to the unsubstituted benzotropolone 5a led us to extend our strategy to a number of substituted benzotropolones 5b – 5d (Schemes and ). Striving for the methoxybenzotropolone 5b the methoxyacetophenone 38 was brominated with NBS following the literature (Scheme ). This provided 82 % of the desired bromide 39 .…”

Section: Synthesis Of a (Methoxybenzo)tropolonementioning

confidence: 99%

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6,7‐Benzotropolone Syntheses Based on Ring‐Closing Metatheses and Four‐Electron Oxidations

et al. 2020

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Four homoallyl ortho-vinylaryl ketones (10a-d) -1,8dienes of sorts -were prepared by several approaches. In the presence of 1-2 mol-% Grubbs-II catalyst, they ring-closed to give 6,7-dihydrobenzocyclohepten-5-ones (11a-d) in 90-96 % yield. With SeO 2 the parent compound (11a) delivered benzocyclohepten-5-one (13a) and/or selenium-containing compounds (18)(19)(20)(21)(22) but no more than traces of 6,7-benzotropolone (5a). However, 5a was accessible from compound 11a via the sodium enolate and allowing it to react with a stream of oxygen [a] Scheme 1. Top: our previously established ring-closing olefin metathesis ("RCM")/ketal hydrolysis route to type-5 6,7-benzotropolones. [9] Underneath: regiocomplementary processings of a type-4 RCM product via the dibromide 7 and the bromoolefins 7 or iso-7 by cross-couplings and hydrolyses giving type-8 or type-iso-8 6,7-benzotropolones, respectively. [10] The Arican routes of Scheme 1 have a major drawback, though, namely the harsh conditions required for hydrolyzing a type-4 ketal in the last step: Liberating the enol required refluxing with 10 equiv. of tosic acid and 100 equiv. of water in acetonitrile for 1 h -2 d. [9,10] These conditions were applicable to certain type-9 or type-iso-9-ketals, as well ( Figure 2). When their substituent R was Et, Ph, CO 2 Me or CO 2 Et, such hydrolyses also proceeded well. [9] However, when their substituent R was CH=CH-CO 2 iPr (in 9a or iso-9a), HC=CH 2 (in 9c or iso-9c) or C≡C-SiMe 3 (in iso-9c) the substrate vanished under hydrolysis conditions without delivering any benzotropolone. [9,10] The C≡C-SiMe 3 -containing ketal 9b was an in-between-case: Its hydrolysis released a benzotropolone as expected but the sidechain R had been converted into C(=O)-CH 3 . [10] Eur.2930 Scheme 2. Can 6,7-benzotropolones 5 be reached via an RCM/oxidation route rather than via the RCM/hydrolysis route of Scheme 1? A 4-e 2 oxidation 11 → 5 would be required overall, but two 2-e 2 oxidations 11 → 12 and 12 → 5 might be used as an alternative. 5.We wondered whether step 2 might be disadvantaged vs. a dehydration delivering the benzotropone 13. While 13 looks like a dead-end at first, it might be re-routable towards 5. This is because unsubstituted benzotropone (13, all R = H) gave unsubstituted benzotropolone (5, all R = H) by endoperoxide formation and an ensuing reduction with thiourea. [11] Consequently, benzotropones 13 appeared as conceivable intermediates of our Scheme-2 strategy towards benzotropolones. A Modified Synthesis of 6,7-BenzotropoloneOur proof-of-principle benzotropolone synthesis by the approach of Scheme 1 delivered the parent compound 5a and is shown in Scheme 3 and Scheme 5. Scheme 3 advances to the RCM product and Scheme 5 supplements its oxidation. Scheme 3. Reaching the RCM product 11a, our synthetic precursor of unsubstituted benzotropolone (5a).Our synthesis began by a salt-free Wittig methylidenation of ortho-bromobenzaldehyde (14, Scheme 3). [12] The resulting ortho-bromostyrene (15) was treated sucessively with nBuLi and the...

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“…0.2 mbar = 73–81 °C) afforded a yellow oil (39.8 g). It was a 91:9 (mol:mol) mixture of compounds 39 (37.4 g, 82 %; ref . 94 %) and 38 (2.4 g, 8 %).…”

Section: Methodsmentioning

confidence: 99%

Section: Synthesis Of a (Methoxybenzo)tropolonementioning

confidence: 99%

6,7‐Benzotropolone Syntheses Based on Ring‐Closing Metatheses and Four‐Electron Oxidations

et al. 2020

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“…4 In 1997, Majetich's group showed that bromodimethylsulfonium bromide was a milder and more selective reagent than Br 2 . 5 Many reagents have been used including NBS, 6 1,3-dibromomethylhydantoin, 7 benzyltrimethylammonium tribromide, 8 pyridinium bromide perbromide, 9 and NaBrO 3 10 among others. The use of hypervalent reagents for aromatic bromination is of current interest.…”

Section: ■ Introductionmentioning

confidence: 99%

Stepwise Mechanism for the Bromination of Arenes by a Hypervalent Iodine Reagent

Granados

Shafir²,

Arrieta

et al. 2020

J. Org. Chem.

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A mild, metal-free bromination method of arenes has been developed using the combination of bis(trifluoroacetoxy)iodobencene and trimethylsilyl bromide. In situ-formed dibromo(phenyl)-λ3-iodane (PhIBr2) is proposed as the reactive intermediate. This methodology using PIFA/TMSBr has been applied with success to a great number of substrates (25 examples). The treatment of mono-substituted activated arenes led to para-brominated products (2u–z) in excellent 83–96% yields. Density functional theory calculations indicate a stepwise mechanism involving a double bromine addition followed by a type II dyotropic reaction with concomitant re-aromatization of the six-membered ring.

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“…The century-old classical method of using hazardous and corrosive reagents X 2 (X = Br, Cl) suffers from low atom economy (<50%), formation of corrosive byproducts (e.g., HBr) [15,16], which cause serious environmental issues. To mitigate the problem, several mild and operationally safe halogenating agents have been successfully introduced to replace X 2 [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. Among them, the use of N-halosuccinimides has turned out to be a viable alternative to X 2 because of their low-cost, ease of handling, and possible recycling of the byproduct succinimide [24][25][26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Automated grindstone chemistry: a simple and facile way for PEG-assisted stoichiometry-controlled halogenation of phenols and anilines using N-halosuccinimides

Das

Bhosle

Chatterjee

et al. 2022

Beilstein J. Org. Chem.

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A simple electrical mortar–pestle was used for the development of a green and facile mechanochemical route for the catalyst-free halogenation of phenols and anilines via liquid-assisted grinding using PEG-400 as the grinding auxiliary. A series of mono-, di-, and tri-halogenated phenols and anilines was synthesized in good to excellent yields within 10–15 min in a chemoselective manner by controlling the stoichiometry of N-halosuccinimides (NXS, X = Br, I, and Cl). It was observed that PEG-400 plays a key role in controlling the reactivity of the substrates and to afford better regioselectivity. Almost exclusive para-selectivity was observed for the aromatic substrates with free o- and p-positions for mono- and dihalogenations. As known, the decarboxylation (or desulfonation) was observed in the case of salicylic acids and anthranilic acids (or sulfanilic acids) leading to 2,4,6-trihalogenated products when 3 equiv of NXS was used. Simple instrumentation, metal-free approach, cost-effectiveness, atom economy, short reaction time, and mild reaction conditions are a few noticeable merits of this environmentally sustainable mechanochemical protocol.

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Mechanistic study on iodine-catalyzed aromatic bromination of aryl ethers by N -Bromosuccinimide

Cited by 16 publications

References 84 publications

6,7‐Benzotropolone Syntheses Based on Ring‐Closing Metatheses and Four‐Electron Oxidations

6,7‐Benzotropolone Syntheses Based on Ring‐Closing Metatheses and Four‐Electron Oxidations

Stepwise Mechanism for the Bromination of Arenes by a Hypervalent Iodine Reagent

Automated grindstone chemistry: a simple and facile way for PEG-assisted stoichiometry-controlled halogenation of phenols and anilines using N-halosuccinimides

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