Regioselective Bromination of Organic Substrates by Tetrabutylammonium Bromide Promoted by V2O5−H2O2:  An Environmentally Favorable Synthetic Protocol

Bora, Upasana; Bose, Gopal; Chaudhuri, Mihir K.; Dhar, Siddhartha Sankar; Gopinath, Rangam; Khan, and Abu T.; Patel, Bhisma K.

doi:10.1021/ol9902935

Cited by 195 publications

(48 citation statements)

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“…[39] When a sufficiently large amount of vanadium(V) oxide is used (50 mol %), no additional acid is required to ensure complete halogenation, since V 2 O 5 itself ensures an acidic media (pH 2.1). [40,41] Similar results were obtained when flavone and aurone derivatives were brominated. The bromination of ketones in the presence of V 2 O 5 leads to enolization through chelation of a 1,3-dicarbonyl compound.…”

Section: Vanadium and Molybdenum Complexes As Functional Mimics Of Vasupporting

confidence: 66%

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Oxidative Halogenation with “Green” Oxidants: Oxygen and Hydrogen Peroxide

2009

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It is difficult to imagine organic chemistry without organo-halogen compounds and the molecular halogens needed for their preparation. The halogens have very different reactivity, with iodine usually requiring some form of activation, while others are reactive and hazardous chemicals. To avoid their use, various modified reagents have been discovered (N-bromo- and N-chlorosuccinimide, Selectfluor..), but halogens are used to prepare these reagents and when they are used the atom economy is poor. A better approach, which is based on biomimetric research on oxidative halogenation in nature, consists of generating the halogenating reagent in situ under acidic conditions from a halide salt. The result of such a reaction has been halogenation with 100 % halogen atom economy. Suitable oxidants for the oxidation of halides are hydrogen peroxide and oxygen.

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Section: Vanadium and Molybdenum Complexes As Functional Mimics Of Vasupporting

confidence: 66%

“…H 2 O 2 can also act as a nucleophile, and it was reported that peroxides are formed together with iodohydrines in the iodination of cyclohexene (40). [110] Vicinal iodoperoxyalkanes were isolated together with some iodohydrines when different alkyl hydroperoxides-and even H 2 O 2 -were used for the oxidative iodination (Scheme 29).…”

Section: Angewandte Chemiementioning

confidence: 99%

Oxidative Halogenation with “Green” Oxidants: Oxygen and Hydrogen Peroxide

2009

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“…Product 16a is an important precursor for flavonoids (cf. vitexin) (30). a-bromination of acetophenone 17, a deactivated aromatic compound, to the corresponding a-bromo acetophenone 17a in high yield has also been successful.…”

Section: Screening Of Reaction Conditionsmentioning

confidence: 99%

“…Our earlier work on peroxoborate (29) and oxidative bromination of aromatics (30) suggested that the peroxoborate intermediate generated in situ would enable bromide oxidation in presence of an acid. The fact, that Br 3 is formed in this process has been ascertained from an independent experiment wherein Br was oxidized by the present methodology in the absence of any organic substrate but in the presence of tetrabutylammonium chloride and three equivalents of KBr leading to nearly quantitative isolation of tetrabutylammonium tribromide (TBATB) (98% yield) (Scheme 2).…”

Section: Introductionmentioning

confidence: 99%

Boric acid catalyzed bromination of a variety of organic substrates: an eco-friendly and practical protocol

Nath

Chaudhuri

2008

Green Chemistry Letters and Reviews

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An environmentally benign, easy to operate, and practical protocol for the regioselective bromination of aromatic compounds using boric acid as a recyclable catalyst, KBr as the source of bromide and hydrogen peroxide as the oxidant is described. Peroxoborate generated in solution, from the reaction of boric acid and H 2 O 2 , very effectively catalyses the bromination of organic substrates at room temperature in a selective manner. The catalyst used is inexpensive, eco-friendly, safe to handle, and recyclable. The methodology is chemoselective for dibenzylidineacetone and regioselective for the other substrates. High yields of the products, mild reaction conditions, high selectivity, use of H 2 O or C 2 H 5 OH as solvent, and redundancy of bromine are some of the major advantages of the synthetic protocol.Keywords: arenes; aryl ketone; alkenes; bromination; hydrogen peroxide; boric acid IntroductionOwing to their increasing commercial use, brominated aromatic compounds are very important in synthetic organic chemistry. They are key intermediates in the preparation of many organometallic reagents (1Á4) and play vital roles in transition metal mediated coupling reactions such as Stille (5), Suzuki (6), Heck (7,8), and Sonogashira reactions (9,10). Many pesticides, insecticides, herbicides, pharmaceutically and medicinally active molecules, and fire retardants carry bromo functionality (11).The need for isomerically pure bromoaromatic compounds has led to develop selective brominating agents or bromination protocols (12). Most of the processes currently practiced for the bromination of aryl compounds employ toxic, corrosive, and rather expensive molecular bromine, resulting in the formation of large amount of HBr waste, thereby reducing the atom efficiency by 50% (11). In large scale operations this causes environmental problems in addition to being expensive. Bromination using HBr with either H 2 O 2 (11,13Á15) or O 2 (16Á18) as an oxidant was thought to be a possible solution. This, however, met with partial success. In addition, HBr is highly toxic and corrosive, and is as harmful as molecular bromine. These problems enhanced the appeal of bromination protocols based on oxidation of bromide salt by H 2 O 2 with better bromide atom economy (13Á16,19,20). The systems reported so far require metal or other catalysts and volatile organic solvents (16,19,21Á24 ( as the active brominating agent, and finally (iii), site-selective bromination of organic substrates to afford bromoorganic compounds (Scheme 1).Our earlier work on peroxoborate (29) and oxidative bromination of aromatics (30) suggested that the peroxoborate intermediate generated in situ would enable bromide oxidation in presence of an acid. The fact, that Br 3 is formed in this process has been ascertained from an independent experiment wherein Br was oxidized by the present methodology in the absence of any organic substrate but in the presence of tetrabutylammonium chloride and three equivalents of KBr leading to nearly quantitative isolation of tetrabut...

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“…1 Organic tribromide salts as mild reagents are good candidates for this selective conversion, because they are not only stable, crystalline solids, and relatively soluble in most organic solvents but also can be handled more conveniently than liquid bromine and can be used successfully for this purpose. Although they are used as brominating agents of aromatic rings, 2 α-bromination of ketones, [3][4][5][6] and ketals, 3,7 electrophilic addition, 3,4,[8][9][10][11][12][13][14] and substitution, 4,13,[15][16][17][18][19] they are also used as catalyst for the oxidation of aromatic aldehydes to carboxylic acids 20 or ω-bromoesters, 21 and dialkyl and alkyl aryl sulfides to sulfoxides, 22 protection of carbonyl, 23 and hydroxyl groups, 24 cleavage of ethers and dithioacetals 25 and conversion of thioamides into amides. 26 They can also be applied in the synthesis of heterocyclic ring systems such as aziridines 27 and benzothiazoles.…”

Section: Introductionmentioning

confidence: 99%