Pyridinium Hydrobromide Perbromide Research Articles

ChemInform Abstract: Pyridinium Tribromide Catalyzed Condensation of Indoles and Aldehydes to Form Bisindolylalkanes.

Abstract An efficient synthetic method for bis(indol-3-yl)alkane derivatives has been developed. In the presence of 5 mol% of pyridinium tribromide (PTB), the condensation of indoles and aldehydes proceeded smoothly under mild conditions, giving rise to the corresponding bis(indol-3-yl)alkanes in good to excellent yields.

Pyridinium tribromide catalyzed condensation of indoles and aldehydes to form bisindolylalkanes

Abstract An efficient synthetic method for bis(indol-3-yl)alkane derivatives has been developed. In the presence of 5 mol% of pyridinium tribromide (PTB), the condensation of indoles and aldehydes proceeded smoothly under mild conditions, giving rise to the corresponding bis(indol-3-yl)alkanes in good to excellent yields.

Transition-Metal-Free, Chemoselective Aerobic Oxidations of Sulfides and Alcohols with Potassium Nitrate and Pyridinium Tribromide or Bromine

An efficient oxidation of sulfides with air catalyzed by the combination of potassium nitrate with pyridinium tribromide under transition-metal-free conditions was reported. By replacing pyridinium tribromide with bromine, the reaction system was also useful in the oxidation of alcohols. All reactions afforded the corresponding products in good to excellent yields with high chemoselectivities.

Regioselective Mono-, Di-, and Trifunctionalization of Iridabenzofurans through Electrophilic Substitution Reactions

Reaction between the cationic iridacyclopentadiene complex [Ir(C4H4)(NCMe)(CO)(PPh3)2][CF3SO3] (1) and methylpropiolate produces the cationic iridabenzofuran [Ir(C7H5O{OMe-7})(CO)(PPh3)2][CF3SO3] (2) in high yield. On treatment of 2 with chloride, the carbonyl ligand is displaced and the corresponding neutral iridabenzofuran Ir(C7H5O{OMe-7})Cl(PPh3)2 (3) is formed. The fused metallacyclic rings of the iridabenzofurans 2 and 3 bear only one substituent (OMe), and therefore these compounds are well suited for studies of electrophilic aromatic substitution reactions. Bromination of cationic 2 with pyridinium tribromide proceeds to give the monobrominated iridabenzofuran [Ir(C7H5O{OMe-7}{Br-6})(CO)(PPh3)2][CF3SO3] (4) exclusively. Bromination of neutral 3 with the same reagent gives the dibrominated iridabenzofuran Ir(C7H5O{OMe-7}{Br-6}{Br-2})Br(PPh3)2 (5) exclusively. Treatment of compound 3 with mercury(II) trifluoroacetate followed by excess bromide (to displace coordinated trifluoroacetate) produces the trimercurated iridabenzofuran Ir(C7H5O{OMe-7}{HgBr-6}{HgBr-4}{HgBr-2})Br(PPh3)2 (6). The three Hg−C bonds in 6 are readily cleaved on addition of pyridinium tribromide, and the resulting product is the tribrominated iridabenzofuran Ir(C7H5O{OMe-7}{Br-6}{Br-4}{Br-2})Br(PPh3)2 (7). These regioselective mono-, di-, and trifunctionalization reactions of iridabenzofurans have been studied by DFT calculations, and the derived condensed Fukui functions have been used to rationalize the preferred sites for electrophilic attack. The crystal structures of 2−7 have been obtained.

ChemInform Abstract: Utilization of o-Xylylene N,N-Diethylphosphoramidite for the Synthesis of Phosphoric Diesters.

Abstract o-Xylylene alkyl phosphites which were derived by the reaction of alcohols with o-xylylene N,N-diethylphosphoramidite in the presence of 1H-tetrazole were reacted with second alcohols in the presence of pyridinium bromide perbromide, and a tert-amine, to give the corresponding triesters involving phospholipids. The esters were deprotected to phosphoric diesters by hydrogenolysis or the reaction with disodium disulfide.

Redetermination of 4-(dimethylamino)pyridinium tribromide

In the title salt, C7H11N2 +·Br3 −, the essentially planar cation (r.m.s. deviation = 0.006 Å) forms an N—H⋯Br hydrogen bond to one of the Br atoms of the almost linear anion [Br—Br—Br = 179.31 (2)°]. The crystal studied was found to be a racemic twin. The whole-mol­ecule disorder of the cation and anion about a twofold rotation axis described earlier [Ng (2009). Acta Cryst. E65, o1276] is an artifact of halving one of the axes of the ortho­rhom­bic unit cell.

ChemInform Abstract: Three-Step Synthesis of an Array of Substituted Benzofurans Using Polymer-Supported Reagents.

An efficient combinatorial route to substituted 3-phenylbenzofurans, is achieved by the bromination of acetophenones to α-bromoacetophenones by polymer-supported pyridinium bromide perbromide (PSPBP). The subsequent clean substitution of the obtained bromides by phenols using 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD-P) and cyclodehydration of the resulting α-phenoxyacetophenones using Amberlyst 15, affords pure products without the need for any chromatographic purification step.

4-(Dimethyl-amino)pyridinium tribromide: whole mol-ecule disorder of cation and anion.

In the title salt, C7H11N2 +·Br3 −, the cation and the near-linear anion [Br—Br—Br = 179.41 (8)°] both show whole-mol­ecule disorder about crystallographic twofold rotation axes. The cation is weakly hydrogen-bonded to the anion by an N—H⋯Br inter­action. The crystal studied was found to be a racemic twin, with a twin component of nearly 50%.

Pyridinium Hydrobromide Perbromide: A Versatile Reagent in Organic Synthesis

Pyridinium hydrobromide perbromide (PHPB) has been extensively used in organic synthesis as a selective brominating reagent for alkenes, [¹-5] alkanes, [6] arenes, [7] ketones, [7] [8] anilines, [9] aromatic ethers, [¹0] N-heterocycles, [¹¹] and oxidi­zing reagents. [¹²] [¹³] PHPB forms red prismatic crystals and its melting point is at 134 ˚C. Further, it is easy to handle, stable and environmentally safe. [¹4] PHPB has been used for regioselective heterocyclization of ortho-cyclohexenyl phenols [¹5] and ipsobromodeformylation in o-hydroxy and o-methoxy substituted aromatic aldehydes. [¹6] It was also found to be a useful catalyst for the chemoselective deprotection of primary TBS and TES ethers, [¹7] hydrolysis of thioacetals, [¹8] and hydroamination of activated styrenes. [¹9]

Concise bromodecarboxylation of cinnamic acids to β-bromostyrenes

A convenient salt-free approach to the halodecarboxylation of cinnamic acid analogs to β-bromostyrene was reported. This conversion was conducted at 0 °C in CH 2Cl 2 with only 10% of acetic acid. This protocol can be used for cinnamic acids with a variety of substituents, including β-methyl cinnamic acid ( 1d) in 60–81% yield, but not for hydroxyl- and p-methyl-cinnamic acids. Meanwhile, pyridine hydrobromide perbromide was used as bromide source to convert 1a– 2a in 59% yield.

Chemoselective TBS deprotection of primary alcohols by means of pyridinium tribromide (Py·Br 3) in MeOH

A catalytic amount of pyridinium tribromide (Py·Br 3) in MeOH chemoselectively deprotects primary TBS ethers in the presence of a variety of other protecting and common functional groups in modest to excellent yields when performed at 0 °C.

Carboxy Pyridinium Bromide Perbromide Reagents, Part I: Selective Oxidation of Thiols and Sulfides

Efficient and convenient oxidation of aliphatic and aromatic thiols to disulfides and of sulfides to sulfoxides with pyridinium hydrobromide perbromide (PHBP), nicotinic acid hydrobromide perbromide (NAHBP), and 2,6-dicarboxy pyridinium hydrobromide perbromide (DCPHBP) in a solvent or under solvent free conditions and at ambient temperature is introduced.

A facile and convenient method for the conversion of thioamides into amides using pyridinium hydrobromide perbromide

Selective transformation of thioamides to their corresponding carbonyl compounds are performed in high to excellent yields under mild conditions using pyridinium hydrobromide perbromide (PHBP) as a mild and efficient reagent.

A Facile Synthetic Method for Conversion of Chlorophyll-ato Bacteriochlorophyll-c

A simple synthetic route for converting chlorophyll(Chl)-a to bacteriochlorophyll(BChl)-c is described. Methyl bacteriopheophorbide(MBPhe)-d, easily obtained from Chl-a, was selectively brominated at the 20-position with pyridinium tribromide, and the following Suzuki-coupling with methylboronic acid afforded ca. a 4:1 mixture of desired MBPhe-c (20-Me) and debrominated MBPhe-d (20-H) in quantitative yield. Separation of MBPhe-c, transesterification of the 17-propionate group (Me --> farnesyl), and magnesium insertion successfully led to naturally occurring BChl-c.

Immunoaffinity Column Cleanup with Liquid Chromatography for Determination of Aflatoxin B1 in Corn Samples: Interlaboratory Study

An interlaboratory study was conducted to evaluate the effectiveness of an immunoaffinity column cleanup liquid chromatography (LC) method for the determination of aflatoxin B1 levels in corn samples, enforced by European Union legislation. A test portion was extracted with methanol-water (80 + 20); the extract was filtered, diluted with phosphate-buffered saline solution, filtered on a microfiber glass filter, and applied to an immunoaffinity column. The column was washed with deionized water to remove interfering compounds, and the purified aflatoxin B1 was eluted with methanol. Aflatoxin B1 was separated and determined by reversed-phase LC with fluorescence detection after either pre- or postcolumn derivatization. Precolumn derivatization was achieved by generating the trifluoroacetic acid derivative, used by 8 laboratories. The postcolumn derivatization was achieved either with pyridinium hydrobromide perbromide, used by 16 laboratories, or with an electrochemical cell by the addition of bromide to the mobile phase, used by 5 laboratories. The derivatization techniques used were not significantly different when compared by the Student's t-test; the method was statistically evaluated for all the laboratories. Five corn sample materials, both spiked and naturally contaminated, were sent to 29 laboratories (22 Italian and 7 European). Test portions were spiked with aflatoxin B1 at levels of 2.00 and 5.00 ng/g. The mean values for recovery were 82% for the low level and 84% for the high contamination level. Based on results for spiked samples (blind pairs at 2 levels) as well as naturally contaminated samples (blind pairs at 3 levels), the values for relative standard deviation for repeatability (RSDr) ranged from 9.9 to 28.7%. The values for relative standard deviation for reproducibility (RSDR) ranged from 18.6 to 36.8%. The method demonstrated acceptable within- and between-laboratory precision for this matrix, as evidenced by the HorRat values.

Kinetics and mechanistic study of pyridinium hydrobromide perbromide-induced carbon–carbon bond scission

The title investigation shows that pyridinium hydrobromide perbromide (PHPB) induced electron transfer reaction in pentaamminecobalt(III) complexes of α-hydroxy acids $${{\begin{aligned} &\hbox{O}&\\ &\Vert&\\ [\hbox{R}-\hbox{CHOH}-&\hbox{C}&-\hbox{O}-\hbox{Co}^{\rm III}(\hbox{NH}_3)_5]^{2+} ({\hbox{ClO}_4})_2 \end{aligned}}}$$ such as mandelic, lactic and glycolic acids (R = C6H5), (R = CH3) and (R = H). Towards these complexes, PHPB acts as a two equivalent oxidising agent, yielding CoII and carbon–carbon bond cleavage products. Addition of pyridinium hydrobromide does not affect the rate indicating that PHPB itself is the reactive oxidising species. The rate decreases with an increase in acetic acid content in the solvent mixture. The observed experimental data have been rationalised in terms of a hydride ion transfer in the rate determining step. This oxidation acts as a diagnostic tool to find out the fraction proceeding by synchronous cleavages of C–H and C–C bonds.

Synthesis of 1,3‐ and 1,2‐Diphosphatidylglycerol

A novel phosphonium salt methodology was utilized for the first time to synthesize 1,3-, and 1,2-diphosphatidylglycerol. Optically active 1,2-di-O-acyl-sn-glyceryl phosphate was coupled with unprotected glycerol in the presence of pyridiniumbromide perbromide and triethylamine to yield, after final removal of phosphate protecting group, the title compounds. The 1,2-diphosphatidylglycerol (1,2-isomer of cardiolipin) may be a member of a new class of phospholipids for industrial applications similar to other phosphocholines.

Effect of Chiral and Achiral Perturbations on the Crystallization of 4,4‘-Dimethylchalcone from Ethyl Acetate

4,4‘-Dimethylchalcone is an achiral molecule that crystallizes from ethyl acetate in the chiral space group P212121. Herein we report the effect of beta radiolysis and circularly and linearly polarized light on the crystallization of 4,4‘-dimethylchalcone from ethyl acetate. Exposure of the evaporating solution to energetic beta particles from a Sr-90 source generated a random distribution of (+) and (−) crystals. Irradiation of the evaporating solution by intense right- or left-circularly polarized light (1064 nm) from a Nd:YAG laser afforded results that were comparable to the results of the beta radiolysis experiments. Linearly polarized light (LPL), on the other hand, had a profound influence on the distribution of crystals, yielding in this instance a large bifurcation of (+) and (−) crystals. A likely cause of this outcome may be due to the optical Kerr effect. The anisotropic polarizability of the chalcone molecule causes a preferential alignment in the direction of the E field when using LPL. This molecular alignment results in a sizable enantiomeric excess. Circularly polarized light does not produce the alignment of the chalcone and thus has no effect on the asymmetric induction. This alignment offers an opportunity for chirally autocatalytic secondary nucleation to occur, which is then able to amplify small initial asymmetry in the number of (+) and (−) crystals. The chirality of the chalcone crystals was determined via their reaction in water with pyridinium tribromide to yield the chiral compound erythro 1,2-dibromo-4,4‘-dimethylchalcone, thus allowing the chirality of the crystal to be propagated to molecular chirality.

A Convenient Synthesis of Oxazolines and Imidazolines from Aromatic Aldehydes with Pyridinium Hydrobromide Perbromide in Water.

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S-Adenosylhomocysteine Analogues with the Carbon-5‘ and Sulfur Atoms Replaced by a Vinyl Unit

Cross-metathesis of suitably protected 5'-deoxy-5'-methyleneadenosines with racemic and chiral N-Boc-protected six-carbon amino acids bearing a terminal double bond in the presence of the Hoveyda-Grubbs catalyst gave adenosylhomocysteine analogues with the C5'-C6' double bond. Bromination with pyridinium tribromide and dehydrobromination with DBU followed by standard deprotections yielded the 5'-(bromo)vinyl analogue. [structure: see text]