Novel bromination reagents · hexabromocyclopentadiene: bromination of activated saturated sites

Magen, S.; Oren, Jakob; Fuchs, Benzion

doi:10.1016/s0040-4039(01)81387-3

Cited by 24 publications

(6 citation statements)

References 17 publications

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“…These include commercially available tribromide salts such as tetrabutylammonium tribromide (1), 3 or pyridinium tribromide (2), 4 and several variations as ionic liquids such as 3-7 [ Figure 1 (a)]. 5 Commercially available N-bromosuccinimide (NBS, 8) 6 and 1,3-dibromo-5-5-dimethylhydantoin (9), 7 hexabromocyclopentadiene (10), 8 and 4,4-dibromo-2,6-di-tert-butylcyclohexa-2,5-dienone (11) 9 are non-Br 2containing Br + sources, for example, that have been found useful for brominations of aromatic compounds and αcarbons of activated carbonyls [ Figure 1 (b)]. However, since these reagents transfer only one bromine equivalent to the target molecule, a large amount of waste is generated.…”

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Brominations with Pr4NBr9 as a Solid Reagent with High Reactivity and Selectivity

et al. 2014

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Tetrapropylammonium nonabromide (Pr 4 NBr 9 ) is introduced as a room-temperature solid reagent for rapid bromination reactions of various substrates. The reagent exhibits reactivity similar to that of elemental bromine, but shows higher selectivity and it is easier and safer to store and to handle.Brominated organics are valuable precursors for transition-metal-catalyzed cross-couplings, 1 and numerous other transformations for the synthesis of specialty chemicals and pharmaceutical products. 2 Therefore, reagents for the selective bromination of organic compounds are highly demanded tools for synthetic chemistry. Elemental bromine has been used in the past as a readily available electrophilic bromination reagent, but it is an undesirable chemical to work with because of its disadvantages: high vapor pressure, toxicity, and corrosiveness. Hence, other bromination reagents that are more user-friendly have been developed and used frequently. These include commercially available tribromide salts such as tetrabutylammonium tribromide (1), 3 or pyridinium tribromide (2), 4 and several variations as ionic liquids such as 3-7 [ Figure 1 (a)]. 5 Commercially available N-bromosuccinimide (NBS, 8) 6 and 1,3-dibromo-5-5-dimethylhydantoin (9), 7 hexabromocyclopentadiene (10), 8 and 4,4-dibromo-2,6-di-tert-butylcyclohexa-2,5-dienone (11) 9 are non-Br 2 -containing Br + sources, for example, that have been found useful for brominations of aromatic compounds and α-carbons of activated carbonyls [ Figure 1 (b)]. However, since these reagents transfer only one bromine equivalent to the target molecule, a large amount of waste is generated. Although some of these compounds showed a significant increase in chemo-and regioselectivity, elemental bromine remained the most efficient brominating agent. In addition, the reactivity was often much lower than that of Br 2 , which in return required longer reaction times or heating of the reaction mixture. A second approach has been the use of bromide salts or hydrogen bromide in combination with strong oxidants to generate the electrophilic bromination reagent in situ. However, this often led to undesired side reactions and in many cases produced a similar amount of waste. 10 We herein introduce tetrapropylammonium nonabromide (Pr 4 NBr 9 , 12), which we discussed in an earlier communication, 11 as a bromination reagent that overcomes most of the aforementioned limitations ( Figure 2). Quaternary ammonium nonabromides and other perbromides have been known in the literature for a long time, 12 and they were, in part, even applied in bromination reactions. 13 However, only recently has further structural evidence of higher polybromides been established, 11,14 and this report represents the first application and study of a solid nonabromide as a bromination agent for organic synthesis. The nonabromide 12 is a dark-red solid that can be handled under air, weighed on a balance, and only slowly releases bromine, which greatly reduces hazards to the user compared to Br 2 . It can be conveniently ...

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Brominations with Pr4NBr9 as a Solid Reagent with High Reactivity and Selectivity

et al. 2014

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“…The use of a larger amount of H 2 O 2 did not lead to a considerable increase in the conversion of acetophenone 1 to tribromoketone 4. Alternative procedures for the synthesis of tribromoketone 4 are based on bromination of acetophenone in acetic acid in the presence of bases, 39,40 bromination of dibromoacetophenone with hexabromocyclopentadiene in acetonitrile, 41 or the reaction of phenylpropiolic acid in the presence of mercury salts. 42 The experimental conditions, which provided a high yield of dibromoketone 3, were used in bromination of ketones 5a-n containing various substituents in the aromatic moiety ( Table 2).…”

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A Convenient Synthesis of 2,2-Dibromo-1-arylethanones by Bromination of 1-Arylethanones with the H₂O₂-HBr System

Terent’ev¹,

Khodykin²,

Krylov³

et al. 2006

Synthesis

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S y n t h e s i s o f 2 , 2 -D i b r o m o -1 -a r y l e t h a n o n e s Alexander O. Terent'ev,* Abstract: 1-Arylethanones and related compounds are brominated in dioxane with the H 2 O 2 -HBr aq system, resulting in the replacement of two hydrogen atoms in the methyl group with bromine. The reaction is also accompanied by bromination of the aromatic ring provided that the latter contains electron-donating substituents. The reaction proceeds rapidly (20 min) and results in complete conversion of ketones to give 2,2-dibromo-1-arylethanones in yields up to 86%.2,2-Dibromo-1-arylethanones are used in organic synthesis primarily for the construction of heterocyclic structures 1-3 and small rings, 4-6 for the preparation of compounds with a double 7-9 or triple 10 bond, and in reactions with phosphorous esters 11,12 and thiols. 13,14 Most of the known methods for the synthesis of 2,2-dibromo-1-arylethanones are based on bromination of acetophenones with molecular bromine 8,11,15-18 and its complex compounds. 19,20 In the last two decades, chlorination and bromination of organic compounds with HCl or HBr combined with peroxides have developed extensively. 21-38 These methods are most actively used for halogenation of arenes, 22-26,28-36 alkenes, 21,23 and ketones. 37,38 As part of our continuing studies on the use of hydrogen peroxide in organic synthesis, in particular the halogenation of ketones, 38 we report the results of bromination of 1-arylethanones with the H 2 O 2 -HBr system. The influence of experimental conditions on the selectivity of bromination and the yield of 2,2-dibromo-1-phenylethanone was revealed using acetophenone (1) as an example (Scheme 1, Table 1). The reaction was carried out by adding 35% aqueous hydrogen peroxide to a refluxing solution of ketone 1 in dioxane (acetic acid) and 48% hydrobromic acid for one minute. Then the mixture was refluxed with stirring for 20 minutes. The reaction afforded dibromoketone 3 as the major product and mono-(2) and tribromoketones (4) as by-products.Our study demonstrated that the highest yield (84%) of dibromoketone 3 was achieved in the presence of a fourfold molar excess of H 2 O 2 (run 1). In the presence of a threefold molar excess of H 2 O 2 (run 2), the yield of 3 decreased to 78%, and monobromoketone 2 remained unconsumed. A decrease in the amount of HBr (run 3), a decrease in the reaction time to 8 min (run 4), or lowering of the reaction temperature to 50 °C (run 5) also lead to a decrease in the yield of dibromoketone 3.Bromination of ketone 1 in acetic acid in the presence of sulfuric acid afforded dibromoketone 3 in 43% yield and tribromoketone 4 in 48% yield. The formation of product 4 is the first example of the preparation of 2,2,2-tribromo-1-phenylethanone in an acidic medium in a satisfactory yield. The use of a larger amount of H 2 O 2 did not lead to a considerable increase in the conversion of acetophenone 1 to tribromoketone 4. Alternative procedures for the synthesis of tribromoketone 4 are based on bromination of acetophenone in ac...

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“…Potentially fluxional hexabromocyclopentadiene 1 (R = M = Br) is also able to undergo the intermolecular transfer of the bromine atom to the nucleophilic carbon centres. 221,222 This reagent brominates smoothly aromatic amines and alcohols, furans, thiophenes and ketones activated at the a-carbon atoms, the electrophilic substitution of aromatic compounds proceeding selectively at the para position due to formation of intermediate p complexes.…”

Section: Fluxional Compounds As Efficient Carriers Of Groups and Prec...mentioning

confidence: 99%

Circumambulatory rearrangements of cyclopolyenes containing element-centred migrants

Михайлов¹,

Душенко²,

Zschunke³

2003

Russ. Chem. Rev.

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PACS. 73.20.At -Surface states, band structure, electron density of states. PACS. 73.23.Ad -Ballistic transport. PACS. 73.50.-h -Electronic transport phenomena in thin films.Abstract. -We present fully quantum-mechanical magnetotransport calculations for shortperiod lateral superlattices with one-dimensional electrostatic modulation. A non-perturbative treatment of both magnetic field and modulation potential proves to be necessary to reproduce novel quantum oscillations in the magnetoresistance found in recent experiments in the resistance component parallel to the modulation potential. In addition, we predict oscillations of opposite phase in the resistance component perpendicular to the modulation not yet observed experimentally. We show that the new oscillations originate from the magnetic miniband structure in the regime of overlapping minibands.

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Novel bromination reagents · hexabromocyclopentadiene: bromination of activated saturated sites

Cited by 24 publications

References 17 publications

Brominations with Pr4NBr9 as a Solid Reagent with High Reactivity and Selectivity

Brominations with Pr4NBr9 as a Solid Reagent with High Reactivity and Selectivity

A Convenient Synthesis of 2,2-Dibromo-1-arylethanones by Bromination of 1-Arylethanones with the H₂O₂-HBr System

Circumambulatory rearrangements of cyclopolyenes containing element-centred migrants

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Novel bromination reagents · hexabromocyclopentadiene: bromination of activated saturated sites

Cited by 24 publications

References 17 publications

Brominations with Pr4NBr9 as a Solid Reagent with High Reactivity and Selectivity­

Brominations with Pr4NBr9 as a Solid Reagent with High Reactivity and Selectivity­

A Convenient Synthesis of 2,2-Dibromo-1-arylethanones by Bromination of 1-Arylethanones with the H2O2-HBr System

Circumambulatory rearrangements of cyclopolyenes containing element-centred migrants

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Brominations with Pr4NBr9 as a Solid Reagent with High Reactivity and Selectivity

Brominations with Pr4NBr9 as a Solid Reagent with High Reactivity and Selectivity

A Convenient Synthesis of 2,2-Dibromo-1-arylethanones by Bromination of 1-Arylethanones with the H₂O₂-HBr System