N-Bromosuccinimide in brominations

N-Bromosuccinimide in bromination of o-nitrotoluene to form u-nitro-benzyl bromide, 46, 81 -Bromotoluene, conversion to Grignard reagent, 47,108... 

Bromination has been described using brominating agents such as N-bromosuccinimide in carbon tetrachloride (418. 420) bromine in either chloroform, acetic acid, or hydrochloric acid (414. 418, 421-423) bromine in sulfuric acid (415-417) and enzymatic catalysis (424, 425). 

The bromination with N-bromOsuccinimide in CCU can be accomplished yielding to 2-brOmothiazole (12.5% yield) (27). 

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 ... 

So do anhydrides and many compounds that enolize easily (e.g., malonic ester and aliphatic nitro compounds). The mechanism is usually regarded as proceeding through the enol as in 12-4. If chlorosulfuric acid (CISO2OH) is used as a catalyst, carboxylic acids can be ot-iodinated, as well as chlorinated or brominated. N-Bromosuccinimide in a mixture of sulfuric acid-trifluoroacetic acid can mono-brominate simple carboxylic acids. ... 

N-Bromosuccinimide purchased from Arapahoe Chemical Company was used without purification. If the purity of the N-bromosuccinimide is in doubt, it should be titrated before use by the standard iodide-thiosulfate method and purified, if necessary, by recrystallization from 10 times its weight of water. Solutions of N-bromosuccinimide in dimethyl sulfoxide cannot be stored, since the solvent is oxidized by the brominating reagent. 

Figure 27.4 Reaction of guanine bases with N-bromosuccinimide causes bromination at the C-8 position of the ring. Amine nucleophiles can be coupled to this active derivative by nucleophilic displacement. Reaction of diamine compounds results in amine-terminal spacers that can be further modified to contain detectable components.

Et3N-3HF as a fluorinating agent [285, 286] or with other reagents [475, 476], Benzylic brominations with N-bromosuccinimide in the presence of a radical initiator have been investigated by van Koten [287]. 

Bromocriptine base is manufactured by bromination of a-ergocryptine with N-bromosuccinimide in dioxane solution. 

Halogenation of dibenzofuran produces the 2-halo compounds. Bromina-tion can be achieved in good yield with bromine in acetic acid " or with N-bromosuccinimide in boiling carbon tetrachloride. The 2,8-dibromo compound has been made, using dioxane dibromide. Chlorination of dibenzofuran in acetic acid in the presence of iron powder can be controlled to yield the 2-chloro or the 2,8-dichloro compounds. 2-Chlorodi-benzofuran is best prepared by reaction of dibenzofuran with phosphorus pentachloride. 2-Iododibenzofuran (45%) results from treatment of dibenzofuran with iodine in boiling chloroform in the presence of nitric acid. 2,8-Diododibenzofuran is best prepared by reaction of dibenzofuran with iodine and iodic acid in aqueous acetic acid. ... 

In delineating the scope of the bromination-nucleophilic sulfur reaction, two difficulties have been encountered. Bromination with bromine is not successful with tertiary hydrogens such as those present in prolyl derivatives (72CB625). Bromination can be accomplished by means of N-bromosuccinimide in presence of 2,2 -azobisisobutyronitrile however, in this case, 3,6-dialkylpiperazine-2,5-diones yield tetrabromo derivatives. These could be successfully utilized for the required purpose, as shown in Scheme 37. The trick consisted of displacing the bromine atoms attached to the ring by methoxy groups, followed by debromination and thiolation (75BCJ605). 

Quinoxalines substituted in the 5- or 6-position generally follow the pattern of reactions expected for substituted benzene derivatives, although recently there have been reports of interesting and unexpected reactions with nucleophiles (see Section III, A,2 and references 85-90). 6-Methylquinoxaline is brominated in the side chain when treated with N-bromosuccinimide in carbon tetrachloride in the presence of azobisiso-butyronitrile, to form 6-bromomethylquinoxaline.182... 

Rather specific thermal or photochemical bromination of allylic positions is, however, possible by using N-bromosuccinimide as brominating agent. Both procedures produce, however, variable quantities of Br2 depending on reaction conditions [32]. In thermal procedures, the concentration of intermediate Br2, and, hence, the importance of secondary addition products, can be controlled by the relative quantity of radical initiator (e.g., A1BN) and by reaction temperature. The appearance of addition products in a photochemical procedure would be evidence for the mechanism proposed by Adam et al. [2, 3, 33] which includes the intermediate production of Br2 (Eq. 21). 

The bromination of complexes of the type (131) with N-bromosuccinimide in acetonitrile produces substances with two bromine atoms per molecule.576 The bromi-nated complexes are planar, diamagnetic non-electrolytes, and n.m.r. spectra are consistent with the substitution having occurred at the positions marked. The free ligands, R = H, can be brominated and on reaction with nickel(n) acetate the same complex results.576... 

Now the alkene is converted into an epoxide by a slightly unusual sequence. Bromination with NBS (N-bromosuccinimide) in water gives a mixture of bromohydrins by electrophilic addition to the... 

Bromination of 1-alkynes with N-bromosuccinimide in the presence of catalytic amounts of silver nitrate, was used first for the bromination of 17-ethynyl steroids.7 Similarly, N-iodosuccinimide led to 17-iodoethynyl steroids, lodination of propiolates in this way has not been studied. A recent method of preparation of 1-iodoalk-l-ynes under phase-transfer conditions involves molecular iodine and copper(l) iodide as catalyst, in the presence of potassium or sodium carbonate as a base. Ethyl 3-iodopropiolate was prepared by this route in 80% yield.8... 

In the present procedure, indole is protected with a tert-butyldimethylsilyl group and further brominated with N-bromosuccinimide in a one-pot reaction. 3-Bromo-1-(tert-butyldimethylsilyl)indole readily undergoes halogen-lithium exchange with tert-... 

N,N -dicyclohexylcarbodiimide is also obtained in good yield in the bromination of N,N -dicyclohexylfomiamidine with N-bromosuccinimide, in the presence of pyridine or with bromine in the presence of NaOH. The bromoformamidine is an intermediate in this conversion. 

The substitution of a hydrogen atom in the benzylic position by a bromine atom on reaction with N-bromosuccinimide in the presence of catalytic amounts of AIBN (2.37) is known as the Wohl-Ziegler process k... 

Diphenylcyclopropenone has been brominated using N-bromosuccinimide in aqueous sulfuric acid to give a product in which both phenyl groups are brominated at the meta position A similar reaction was observed when the cyclopropenone was subjected to nitration (equation 53). ... 

Mol. wt. 285.95, m.p. 195°, dec. Suppliers Arapahoe, A, B, MCB. A useful reagent comparable to N-bromosuccinimide, it effects allylic bromination, dehydrogenation, substitution of active hydrogen, and oxidation of secondary alcohols. Review. Attempted side-chain bromination of 2,4-dibenzoylamino-6-methylquinazoline with bromine in chloroform led instead to elimination of the 4-benzoyl group, and reaction with N-bromosuccinimide in chloroform or carbon tetrachloride was... 

Hydrolysis of gem-dihalides. Cram and Helgeson" brominated [2.2]paracyclo-phane (II ) with N-bromosuccinimide in refluxing carbon tetrachloride in the presence NBS... 

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