Dimethylformamide, halogenation

Materials of these types have T s of some 290-300°C and some grades are claimed to be stable to about 400°C. Whilst resistant to hydrocarbons, halogenated hydrocarbons, ethers and acids the polymers are soluble in such materials as dimethylformamide, N-methylpyrrolidone and pyridine. Bases can cause stress cracking. These non-crystalline polymers are tough at temperatures as low as -46°C whilst at 260°C they have the strength shown by PTFE at room temperature. The polymers also exhibit excellent electrical insulation properties. 

Both 3-bromo- and 3-iodo-indoles have been selectively prepared by titrimetric addition to the heterocycle of the halogen dissolved in dimethylformamide. The mildly basic solvent is probably responsible for trapping the generated hydrogen halide (82S1096). 

The oxidation of n-butanal by CUCI2 in dimethylformamide showed simple second-order kinetics in the presence of lithium chloride . At 83 °C, 2 s 2x10 1.mole". sec". a-Monohalogenation occurs in 97% yield. Cu(Il)-catalysed enolisation followed by ligand-transfer is proposed. a-Halogenation of acetone is accomplished by CUCI2, viz. 

A New Improved Synthesis of Tricycle Thienobenzazepines Apphcation of chemistry recently developed by Knochel" combined with the well-described halogen dance (HD) reaction, allowed preparation of our key intermediate A in only three synthetic transformations (Scheme 6.4). In this respect, treatment of 2-bromo-5-methylthiophene with hthium diisopropylamide followed by dimethylformamide afforded aldehyde 11 in good yield, lodo-magnesium exchange with conunercial 4-iodo-3-nitro anisole followed by reaction with 11 afforded the thiophene catbinol 12. Dehydroxylation of 12 provided our key intermediate A which presented the requisite functionality to examine our approach to the construction of the seven-member ring system. 

The formyl group provides enough activation so that lithium fluoride will convert 5-bromofuran-2-carboxaldehyde into 5-fluorofuran-2-carboxalde-hyde, but only in dimethylformamide at 100°C. Other metal cations are ineffective. Replacement by other halogens is easy, the chloride-bromide displacement being reversible.180... 

Phosphorus, white Phosphoryl chloride Air, oxidants of all types, halogens, metals Carbon disulfide, AtA -dimethylformamide, 2,5-dimethylpyrrole, 2,6-dimethyl-pyridine 1-oxide, dimethylsulfoxide, water, zinc... 

Formation of carboxylic acids by reduction in dimethylformamide of the carbon-halogen bond in die presence of carbon dioxide and using sacrificial anodes. 

An attempt to directly convert hyellazole (245) to 6-chlorohyellazole (246) by reaction with N-chlorosuccinimide in the presence of a catalytic amount of hydrochloric acid led exclusively to 4-chlorohyellazole. On the other hand, bromination of 245 using NBS and a catalytic amount of hydrobromic acid gave only the expected 6-bromohyellazole (733). Alternatively, a direct one-pot transformation of the iron complex 725 to 6-bromohyellazole (733) was achieved by reaction with an excess of NBS and switching from oxidative cyclization conditions (basic reaction medium) to electrophilic substitution conditions (acidic reaction medium). Finally, a halogen exchange reaction with 4 equivalents of cuprous chloride in N,N-dimethylformamide (DMF) at reflux, transformed 6-bromohyellazole (733) into 6-chlorohyellazole (246) (602) (Scheme 5.73). 

Unsubstituierte Imidazole reagieren wie zahlreiche andere Nukleophile mit elektronenarmen Halogen-arenen unter nukleophiler Substitution des Halogen-Atoms zu 1 -Aryl-imidazolen. So wird z.B. aus Imidazol mit 4-Fluor-l,3-dinitro-benzol/ Dimethylformamid bei 20° in 91% Ausbeute l-(2,4-Dirtitro-phenyI)-imidazol erhalten769. 

Although the use of N,N-dimethylformamide permits satisfactory chlorination or bromination of primary positions at room temperature, side reactions can occur between carbon tetrahalides, triphenylphosphine, and JV,N-dimethylformamide that can, in some cases, result in low yields of halogenated products (see also, Section II, 2c p. 230). 

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