Bromination dioxane dibromide

Furan reacts vigorously with chlorine and bromine at room temperature to give poly-halogenated products. Low temperature (-40 °C) reaction of furan with chlorine in dichloromethane yields mainly 2-chlorofuran and reaction of furan with dioxane dibromide at 0 °C affords 2-bromofuran in good yield. 2-Iodofuran is obtained by treatment of 2-furoic acid with iodine and potassium iodide in aqueous sodium hydroxide. 

A French patent claims the successful use of methanol for the 21-bromination of 17a-hydroxy-20-ketopregnanes as well as 21-bromination of 17-desoxy-20-ketopregnanes. This solvent has been successfully employed with dioxane dibromide as the brominating agent. 

Procedures have been worked out which increased the yield of 2-bromothiophene to 78% on direct bromination in acetic acid-ether mixtures and to 67% in carbon tetraehlorided With the mild brominating agent, dioxane dibromide, quantitative yields of 2-bromothiophene are obtained. A very convenient procedure for the iodination of thiophenes consists of the acid-catalyzed (HzSOi) reaction with iodine and HIO3, giving 2-iodothiophene in 75% yieldd In contrast to the HgO method, all the iodine is utilized. 

Further papers in this section include the hydrosilylation of a-pinene and of j8-pinene, ° thiocyanation and selenocyanation of a-pinene, ° cationic polymerization of a- and /3-pinene epoxides,bromination of ( )-c/s-pinonic acid with dioxan dibromide, and straightforward myrtenol (224 R=CH20H) ° and tetrahydroperillyl alcohol syntheses from -pinene epoxide. 

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. ... 

Although bromination of thiophene in acetic acid gives good yields of 2-bromothiophene, quantitative yields are reported with dioxane dibromide (63AHC(l)l). Treatment of... 

Monobromination of these oxy compounds is difficult to achieve even at low temperatures and with low molar proportions of bromine. At - 10°C, bromine converted l-methyl-2-pyridone into a mixture of 3- and 5-bromo derivatives (1 2), but with 18% 3,5-dibromination as well. Reagents such as NBS at 10°C and dioxan dibromide were more effective giving a 1 4 ratio of 3- 5-bromo in a total yield of 56%, and a 1 1.3 ratio (with 8% dibromination) in a total yield of 81%, respectively (82CHE1284). 

Thus, 5-nitro-2-acetylselenophene is readily brominated by dioxane dibromide, while introduction of bromine into the 4-nitro isomer requires the more drastic conditions of bromine in glacial acetic acid.114... 

Dioxane, as solvent in preparation, of 2,4-dialkylthiazoles, 184, 191 Dioxane dibromide, as bromination agent,... 

Bromination Boron tribromide. Bromotrifluoromethane. N-Bromosuccinamide. n-Butyla-mine. Cupric bromide. Dibromoisocyanuric acid. Dioxane dibromide. Iodine monobromide. Iron. Pyridine. 

Bromination. Monobromination of the highly reactive resorcinol dimethyl ether (la) and 2-methylresorcinol dimethyl ether (lb) can be effected in 80-90% yield with dioxane dibromide. ... 

N-Bromophthalimide and dioxane dibromide have been found less effective for bromination 307 oxidation reactions predominate. Chlorination of 2-methyl-4,5-diphenyloxazole in chloroform at room temperature after 14 days results in the formation of 4,5-dichloro-2-trichloromethyl-4,5-diphenyl-2-oxazoline, which is basically an addition compound.307... 

Dioxane dibromide, C4H802 Br2, is also a mild brominating agent. 

Aromatic amines are usually polybrominated on treatment with bromine. Several mild brominating agents have been introduced in attempts to achieve partial bromination without the necessity of protecting the amino group and subsequent hydrolysis, but these give variable results when applied to a large variety of amines. Dioxane dibromide monobrominates tertiary aromatic amines, but gives poor yields with primary and secondary aryl amines. The use of A-bromo-succinimide (l-bromo-2,5-pyrrolidinedione) leads to monobrominated compounds that are frequently contaminated with decomposition products. 

Treatment with phosphorus pentachloride results in the formation of 4-chlorobutyl acetate <73JOCll73>. 4-Bromobutyl esters are also produced by bromination of 1,3-dioxepane and 2-mono-substituted 1,3-dioxepanes with Af -bromosuccinimide at 70°C. Bromination in the side chain occurs only at lower temperatures, or when both 2-positions are substituted <81KGS174>. Use of dioxane-dibromide in dioxane as brominating agent at ambient temperatures predominantly leads to a-bromoalkyl derivatives <77DOK(237)338,78KGS131>. 

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