Pyridinium Dichlorobromate: A New Stable Brominating Agent for Aromatic Compounds

Muathen, Hussni A.

doi:10.1055/s-2002-19794

Cited by 14 publications

(11 citation statements)

References 13 publications

(13 reference statements)

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“…Instead, post-assembly rotaxane modification was attempted. Electrophilic aromatic bromination using pyridinium dichlorobromate [41] was envisaged as a way to introduce bromine at the 3-and 3 0 -positions of the stilbene of the rotaxane 1 ,based on the chemistry explored by Dumanski et al [42] However,s uch reactions yieldedc omplex mixtures of products. When components were separateda nd analyzed using 1 HNMR spectroscopy,inmost cases there was no evidence of olefinic proton resonances, indicating that addition had occurred across the double bond.…”

Section: Resultsa Nd Discussionmentioning

confidence: 99%

Centrosymmetric and Non-centrosymmetric Packing of Aligned Molecular Fibers in the Solid State Self Assemblies of Cyclodextrin-based Rotaxanes

Cieslinski

Steel

Lincoln

et al. 2006

Supramolecular Chemistry

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Two[ 2]-rotaxanes each comprising a -cyclodextrin as the rotor, andw ithe ither3 ,3 0 -difluoro-o r3 ,3 0 -dichlorostilbene as the axle and trinitrophenylamino substituents as the blocking groups at the 4-and 4 0 -positions, were prepared and their structures analyzed in solution and the solid state using 1 HN MR spectroscopy and X-ray crystallography, respectively.W ithe achr otaxane,i n solution the stilbene rotates freely within the cyclodextrin annulus. In the solid state the 3,3 0 -dichlorostilbene-based rotaxane adopts two very similar conformations, each having the chlorines in the anti,anti-orientation. By comparison, the3 ,3 0 -difluorostilbene-based rotaxane adopts anti,anti-, anti,syn-a nd syn,syn-orientations of the substituents. The crystal packing of each rotaxane displays aligned molecular fibers, which are centrosymmetrically orientated in the case of the difluoride due to the head-to-head/tail-to-tail alignment of the cyclodextrins. By contrast, all of the cyclodextrins in the dichloride are aligned head-to-tail along as ingle axis to give apolar,non-centrosymmetric crystal.

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Section: Resultsa Nd Discussionmentioning

confidence: 99%

Centrosymmetric and Non-centrosymmetric Packing of Aligned Molecular Fibers in the Solid State Self Assemblies of Cyclodextrin-based Rotaxanes

Cieslinski

Steel

Lincoln

et al. 2006

Supramolecular Chemistry

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“…Pyridinium dichlorobromate was prepared by the literature method [15]. Alkaloids used in the reactions were isolated from plant material: (-)-anabasine [(2S)-3-(2-piperidinyl)-pyridine] (10), mp 104-105°C (2 Torr), lit.…”

Section: Methodsmentioning

confidence: 99%

Plant coumarins. 4.* Synthesis of N-containing derivatives of oreoselone

et al. 2009

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dione were found. Several 2-aminofuranocoumarins were synthesized by reaction of 2-bromoreoselone with derivatives of pyrrolidine, piperidine, and piperazine. The new compounds were interesting as potential biologically active compounds.Linear dihydrofuranocoumarins are widely distributed plant metabolites with pronounced biological activity [2][3][4]. Thus, marmesin (1) is an effective c-AMP synthetase [5] and acetylcholinesterase [6] inhibitor. Propanediol (2) is used as an antidote to snake venom [7]. The potential of coumarins for creating new antioxidants has recently been actively discussed owing to their specific activity as selective MAO inhibitors [8]. Thus, the development of methods for modifying furanocoumarins is of definite interest in medicinal chemistry.An accessible source of furanocoumarins is Peucedanum morisonii Bess., which is widely distributed in western Siberia. Its main metabolite peucedanin (3) can be isolated from roots of the plant in yields up to 4% of the dry raw material mass [9]. The preparation of several derivatives of peucedanin and its hydrolysis product oreoselone (4) through modification of the furan ring has been reported [10,11]. Herein we describe the synthesis of new oreoselone derivatives.The starting material for the transformations was 2-bromoreoselone (5), which was formed by bromination of 3 with Br 2 in CHCl 3 , as previously reported [10]. We found that 5 was also the only product from bromination of peucedanin by Br 2 in formic acid (98% yield), by dioxanedibromide in CCl 4 (94-98% yield), by N-bromosuccinimide in CCl 4 (97-98% yield), and by pyridine dichlorobromate (PyHBrCl 2 ) in CH 3 OH (94% yield). Subsequent bromination of 5 by NBS (3 equiv.) in the presence of benzoyl peroxide in CCl 4 formed 2-(1,3-dibromopropan-2-ylidene)-2H-furo[3,2-g][1]benzopyran-3,7-dione (6) (73% yield). Obviously benzoyl peroxide enhances dehydrobromination of 2-bromoreoselone and subsequent allylic bromination. This was confirmed by the fact that 6 was formed by bromination of known 2-(1-methylethylidene)-7H-furo[3,2-g][1]benzopyran-3,7-dione (7) under these conditions [10, 12] (51% yield).

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“…Pyridinium dichlorobromate was prepared as described by Muathen. [18] Anisole (3a) was purified by distillation (bp 153-154 • C) before use. 3-Methylacetanilide (7b) was prepared by acetylating m-toluidine.…”

Section: Methodsmentioning

confidence: 99%

“…Instead, they retarded the reaction rate, due to inclusion of both the substrate and the brominating agent. In light of the lack of regiocontrol in this system, the recent account of the use of pyridinium dichlorobromate for aromatic bromination in aqueous methanol [18] prompted us to investigate the effect of employing cyclodextrins with this reagent. As reactants for the study, we chose anisole (3a) and acetanilide (3b), in order to make direct comparisons with the chlorination of those compounds.…”

Section: Introductionmentioning

confidence: 99%

Effect of Cyclodextrins on Electrophilic Aromatic Bromination in Aqueous Solution

Dumanski¹,

Easton

Lincoln³

et al. 2003

Aust. J. Chem.

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Cyclodextrins act as molecular reactors to change the ratios of the products of reactions of anisole, acetanilide, 3methylanisole, and 3-methylacetanilide with pyridinium dichlorobromate. With anisole and acetanilide, bromination at the para position is favoured over ortho substitution, and the effect is greatest with α-cyclodextrin. In the reactions of the methylanisole and methylacetanilide, the cyclodextrins afford higher yields of monobrominated products and less of the di-and tribromides, and β-cyclodextrin has the greatest effect. These outcomes can be attributed to inclusion of the substrates within the cyclodextrins restricting access of the reagent adjacent to the methoxy and acetamido groups. The yields of 4-bromoanisole, 4-bromoacetanilide, 4-bromo-3-methylanisole, and 4-bromo-3methylacetanilide are thus increased from 73 to 94, 55 to 98, 37 to 86, and 39 to 72%, respectively. Perhaps more significantly, the quantities of the corresponding by-products are substantially reduced, from 27 to 6, 45 to 2, 63 to 14, and 61 to 28%. Since the reactions occur readily in water at ambient temperature, the cyclodextrins make them very efficient.

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Pyridinium Dichlorobromate: A New Stable Brominating Agent for Aromatic Compounds

Cited by 14 publications

References 13 publications

Centrosymmetric and Non-centrosymmetric Packing of Aligned Molecular Fibers in the Solid State Self Assemblies of Cyclodextrin-based Rotaxanes

Centrosymmetric and Non-centrosymmetric Packing of Aligned Molecular Fibers in the Solid State Self Assemblies of Cyclodextrin-based Rotaxanes

Plant coumarins. 4.* Synthesis of N-containing derivatives of oreoselone

Effect of Cyclodextrins on Electrophilic Aromatic Bromination in Aqueous Solution

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