Pyridinium bromide preparation

Amino-5-nitrosopyrimidines also condense with benzoylacetonitrile, phenacyl-pyridinium bromide and acetonylpyridinium chloride in the presence of sodium cyanide to produce. 7-amino-6-pteridinyl ketones (63JOC1197). Pteridine syntheses from pyridinium salts are not limited to the preparation of pteridyl ketones since pyridinium acetamide... 

Morishima et al. [42] prepared polyanions (A-x, 3) of various charge densities tagged with the merocyanine dye (Me) by terpolymerization of acrylic acid (AA), acrylamide (AAm), and a small mole fraction of l-(2-methacryloyloxyethyl)-4-(2-(4-hydroxyphenyl)ethenyl)pyridinium bromide (MA-Mc). Since these polyanions carry only 1 mol% of the MA-Mc units, they can practically be treated as copolymers of AA and AAm with a wide range of composition. 

The oxamate group has been incorporated into a vinyl polymer by Kirsh and Kabanov 41). These workers prepared a copolymer of 4-vinyl-A -(phenacyloxime)pyridinium bromide and vinylpyridine. For the hydrolysis of p-nitrophenyl acetate the oxamate polymer produced a significant rate enhancement over the monomeric analogs. 

N-dodecyl 3-carbamoyl pyridinium bromide (I) was prepared from vacuum-distilled n-dodecyl bromide (K K) and nicotinamide (Kodak) according to a published procedure (15) and identified... 

The majority of the recipes described in the literature are based on the anionic sodium dodecylsulfate (SDS) as a model system. The possibility of using cationic surfactants such as octadecyl pyridinium bromide for the preparation of miniemulsions was first exploited in 1976. However, the emulsions were prepared by stirring and the resulting emulsions showed broadly distributed droplet sizes [2,39,50]. Recent work on steady-state miniemulsions showed that cationic and nonionic surfactants form well-defined miniemulsions for further miniemulsion polymerization processes, resulting in narrow size distributed stable cationic and nonionic latex particles [51]. Similar molecular amounts of the simple cationic surfactant, cetyltrimethylammonium bromide or chloride... 

Tandem Michael addition/aldol condensation of l-(2-oxopropyl)pyridinium chloride (112) or l-(3-ethoxycarbonyl-2-oxopropyl)pyridinium bromide (113) with chalcones 111 forms diketones 114 or 115, respectively, which under condensation afford cyclohexanones that aromatize by the elimination of pyridinium chloride or bromide, respectively, to give 3,5-disubstituted phenols 116 and 4,6-disubstituted ethyl 2-hydroxybenzoates 117, respectively (equation 104) . This approach has been extended to solid-phase synthesis in order to prepare a phenol library (equation 105) . ... 

A simpler large scale method to obtain pyrantel, morantel (10a,b) and oxantel (11) involves condensation of 23 with an aryl aldehyde in presence of a base. Water is removed by azeotropic distillation or by using a chemical scavenger like methyl/ethyl formate, which reacts with water to push the reaction in the forward direction (Scheme 3). Other methods to prepare pyrantel and its derivatives are also reported [5,6,13-17]. The l-(2-arylvinyl)pyridium salts (18,19), structural congeners of pyrantel/moratel, are prepared by quaternisation of pyridine with the appropriate bromomethylaryl ketones (27) to afford 28. The latter is reduced with sodium boro-hydride to give the carbinol 29, which on dehydration leads to the formation of l-(2-arylvinyl)pyridinium bromides (18,19) [8]. 

Synthesis was carried out of the copolymers of 4-vinylpyridine (4VP), styrene (St) and divinylbenzene (DVB) with varied compositions, P(4VP-St-DVB), by suspensionpolymerisationusing 2,2 -azobisisobutyronitrile (AIBN) as an initiator. Preparation of the insoluble (crosslinked) pyridinium-type polymers in benzyl-pyridinium bromide form, which possess various macromolecular chain compositions, was performed by the reaction of eachP(4VP-St-DVB) with benzyl bromide (BzBr), respectively. By using different halohydrocarbon RX in the quatemisation of P(4VP-St-DVB), the insoluble pyridinium-type polymers with various pyridinium group stractures were obtained. FTIR was nsed to identify the stractures of P(4VP-St-DVB) and its quatemised product Q-P(4VP-St-DVB). The 4VP content in each copolymer P(4VP-St-DVB) was measured by non-aqueous titration and the pyridinium group content (Cq) in each Q-P(4 VP-St-DVB) sample was determined by means of the back titration manner in argentometiy and/or the elemental analysis method, respectively. Also, the particle structure... 

First attempts were directed to the ethoxybutyrylisothiazole 209 prepared from 3-cyano isothiazole with 3-ethoxypropylmagnesium bromide in poor yield (30%). Cleavage of the ether with hydrobromic acid, followed by evaporation to dryness of the acidic solution, gave in a nearly quantitative yield the 4,5,6,7-tetrahydro-4-oxoisothiazolo[2,3-a]pyridinium bromide 210 (97%) (69JCS(C)707, Scheme 74). 

Methyl[lS annulene (3). This monosubstituted annulene has been prepared from [18]annulene (1) in two steps. Monobromo[18]annulene (2) is prepared in 44% yield by bromination with ah equimolar amount of pyridinium bromide per-bromide. This reacts with a large excess of dimethylcopperlithium to give methyl-[18]annulene in 52% yield. It is imperative that no excess methyllithium be present in the reaction mixture.12... 

Improvements in the preparation and dehydrohalogenation of w o-stilbene dibromide [Org. Syntheses, Coll. Vol. 3, 350 (1955)] are as follows. ra 5-Stilbene (20 g.) is heated with 400 ml. of acetic acid on the steam bath until dissolved, 40 g. of pyridinium bromide perbromide is added, and the mixture is heated on the steam bath and swirled for 5 minutes, meso-Stilbene dibromide separates at once in pearly white plates. The mixture is cooled to room temperature, and the product is collected and washed with methanol. The yield of dibromide, m.p. 

The electronic nature of the coupling partners could be reversed by introducing a boronic acid fragment on the benzonitrile, such as boronic acid 22c, and affecting the coupling with an aryl triflate of pyridinium bromide. Because the aryl boronate could be prepared using the aryl lithium in the presence of triisopropyl borate, this would obviate the need for the expensive pinacol diborane. Reduction of the intermediate pyridine or tetrahydropyridines would provide the desired products (see Scheme 5.8). 

Naphthoic acid has been prepared similarly, 0.25 g being obtained from 0.5 g of the pyridinium bromide. 

The benzene-fused analogue (189) has also been prepared in 14% yield by a Wittig reaction <72JA7087>. This could be oxidized to the sulfoxide and sulfone by H2O2 in acetic acid. Neither the sulfoxide nor the sulfone showed any tendency to dimerize by a Diels-Alder mode. This is in contrast to simple thiophene 5-oxides, and is probably because any such dimerization would result in the formation of a benzocyclobutadiene structure. Photolysis of the sulfone leads to a head-to-head dimer. The thiophene ring in (189) is very reactive. Bromination with pyridinium bromide... 

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