N-Bromosuccinimide reaction

Direct bromination of toluene and ethylbenzene form the corresponding benzyl bromides in high yield. The observed selectivity in SC-CO2 is similar to that observed in conventional organic solvents. Also, SC-CO2 is an effective alternative to carbon tetrachloride for use in the classical Ziegler bromination with N-bromosuccinimide. Reaction yields are high, side products are minimized, and bromine-atom selectivities are observed. Thus, SC-CO2 must be useful as a viable, environmentally benign substitute for many of the solvents typically used for free-radical reactions (Tanko and Blackert, 1994). 

Although the oxidation pathway is determined mainly by the nature of the azole nucleus, the conditions and the oxidants also have great significance. In the first experiments, the oxidant most used was lead tetraacetate. It still dominates, but many other oxidants have appeared, and they frequently give better results, for instance, nickel peroxide, manganese dioxide, potassium periodide, bromine water, and N-bromosuccinimide. Reactions with LTA are usually carried out in absolute methylene chloride at about 0-20°C, and for neutralization of the released... 

Tosyl cholesteryl acetate (V) (Akhtar and Barton, 1964) was first converted to the corresponding 19-iodide (VI) by treatment with sodium iodide in boiling ethyl methyl ketone. Reduction of the iodide with zinc and acid in the presenee of tritiated water provided cholesteryl acetate-19-H (VII) which was then converted to 7-dehydro-cholesterol-19-H (VIII), presxunably via the N-bromosuccinimide reaction. Ultraviolet irradiation and thermal rearrangement of the provitamin yielded cholecalciferol-9,19-H (IX). 

The addition of N-bromosuccinimide (1.1equiv) to a dichlo-romethane solution containing the alkene (1 equiv) and cyana-mide (4 equiv). The solution was maintained at room temperature (3 days) and then washed with water, dried, and concentrated in vacuo. Treatment of the bromocyanamide [intermediate] with 1% palladium on charcoal in methanol (1h) led to reduction of the for-madine. Addition of base to the reaction mixture (50% aqueous KOH, reflux 6h) followed by extraction with ether gave monoamine. (Yield is 48-64% final amine from alkenes analogous to safrole)... 

The iacreased chemical stabiUty of the 6-deoxytetracyclines allows chemical modification with retention of biological activity electrophilic substitutions have been carried out at C-7 and C-9 under strongly acidic conditions (46—53). Reactions of 6-deoxy-6-demethyltetracycline [808-26-4] (16), C21H22N2O7, with electrophiles, such as nitrate ion (49), bromomium ion (46,47) (from N-bromosuccinimide), or N-hydroxymethylphthalimide (53), yielded 7-substituted tetracyclines. In the case of the nitration reaction, both the 7- and 9-nitro isomers (17, X = NO2, Y = H) and (17, X = H, Y = NO2) were obtained. 

The isoxazole nucleus is also halogenated in the 4-position by N-bromosuccinimide provided there is no substituent in this position. This reaction does not proceed homolytically, as might have been expected, and appears to represent a simple electrophilic substitution by the bromine cation. Similar cases have been previously described for the bromination of certain aromatic compounds with A -bromo-succinimide. ... 

Olefins react with bromine by addition of the latter to the carbon-carbon double bond. In contrast the Wohl-Ziegler bromination reaction using N-bromosuccinimide (NBS) permits the selective substitution of an allylic hydrogen of an olefinic substrate 1 by a bromine atom to yield an allylic bromide 2. 

The allylic bromination of an olefin with NBS proceeds by a free-radical chain mechanism. The chain reaction initiated by thermal decomposition of a free-radical initiator substance that is added to the reaction mixture in small amounts. The decomposing free-radical initiator generates reactive bromine radicals by reaction with the N-bromosuccinimide. A bromine radical abstracts an allylic hydrogen atom from the olefinic subsfrate to give hydrogen bromide and an allylic radical 3 ... 

In order to induce the free-radical chain reaction, a starter compound such as dibenzoyl diperoxide, azo-Zj -(isobutyronitrile) or tcrt-butyl hydroperoxide or UV-light is used. The commercially available, technical grade N-bromosuccinimide contains traces of bromine, and therefore is of slight red-brown color. Since a small amount of elemental bromine is necessary for the radical... 

A solution of 3.4 grams of N-bromosuccinimide in 60 cc of absolute dioxane is added drop wise in the dark, during the course of 5 minutes, to a stirred solution, heated to 60°C, of 9.2 grams of ergocryptine in 180 cc of absolute dioxane. The reaction mixture is stirred at this temperature for 70 minutes and is concentrated to a syrup-like consistency in a rotary evaporator at a bath temperature of 50°C. The reaction mixture is subsequently diluted with 300 cc of methylene chloride, is covered with a layer of about 200 cc of a 2N sodium carbonate solution in a separating funnel and is shaken thoroughly. The aqueous phase is extracted thrice with 100 cc amounts of methylene chloride. The combined... 

Cyclization of /V-carbethoxyhydrazone 57 and ALformylhydrazone 58 of pyrrole-2-carbaldehyde gave 59 (73CC35 80JHC631) by base-catalyzed cyclodehydration. The expected substitution product at 6-position was obtained from the reaction of 58 with N-bromosuccinimide (Scheme 15). 

Usually, a-bromo-substituted arenes have been prepared through the reaction of arenes with bromine under ultraviolet irradiation. In the presence of benzoyl peroxide, N-bromosuccinimide can also be used for this purpose. 

When electron-withdrawing groups are attached to the double bond, the reaction is strongly inhibited and may fail completely. In such cases, the bromide anion, produced by the reaction of dimethyl sulfoxide with N-bromosuccinimide, competes with the dimethyl sulfoxide for the bromonium (or bromo carbonium) ion, an intermediate of the reaction. Thus, dibromide may accompany recovered alkene or any bromohydrin formed. Similarly, exogenous anions often compete with dimethyl sulfoxide for the cation. ... 

The suspension may be warmed to dissolve the alkene more rapidly. (E)-Stilbene dissolves completely at ca. 65°. If the suspension is warmed, it must be cooled below 30° before proceeding further to prevent a vigorous reaction when the N-bromo-succinimide is added. The submitters recommend that the warm suspension be cooled under an atmosphere of nitrogen. If a volatile alkene is used, the mixture should be cooled prior to and during the addition of N-bromosuccinimide to prevent losses by evaporation. 

N-chloro- or N-bromosuccinimide gives rise to a halogenation reaction of phen-ylamine or benzylamine that is very violent ... 

Verdet and Stille1 employed brominated poly(phenylene oxide) intermediates in an effort to synthesize more stable catalyst supports containing (cyclopentadienyl)metal complexes. Treatment of poly(oxy-2,6-dimethyl-l,4-phenylene) with N-bromosuccinimide under photolytic conditions produced only the bromomethyl derivative if the D.F. did not exceed 0.35. Subsequent treatment of the bromomethylated polymer with sodium cyclopentadienide afforded the cyclopentadienyl functionalized polymer, 5, but the reaction was accompanied by crosslinking and it was not possible to remove the bromomethyl substituents quantitatively. 

The preparation reported here is based on the method of Christie and Rapoport.4 9-Bromo-9-phenylfluorene has also been prepared by a light-initiated reaction of bromine and 9-phenylfluorene in carbon disulfide,2 by addition of phenylmagnesium bromide to fluorene36 followed by treatment with acetyl bromide,5 and by treatment of 9-phenylfluorene with N-bromosuccinimide.6... 

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