Dibromo ether

Elimination of bromine and ethoxyl groups with zinc is much the same as the elimination of two adjacent halogen atoms. The /6-bromo ether is heated with a stirred suspension of powdered zinc or zinc-copper couple in 90-95% ethanol, n-propyl alcohol, or isopropyl alcohol. The preparation of 3 Octene fails in n-propyl alcohol. In several cases the products have been shown to be mixtures of cis and trans isomers. The yields for the first two steps of the synthesis are 70-90%. The coupling of the a,/S-dibromo ethers with primary Grignard reagents takes place in 50-80% yields, whereas with secondary Grignard reagents only 30-55% yields are obtained. 

Olefinic acetylenes of the general formula RCH= =CHC CR are prepared by coupling the a,/S-dibromo ethers with an acetylenic Grignard reagent followed by elimination of halogen and alkoxyl groups. Over-all yields are approximately 60%. ... 

A conjugated double bond system undergoes 1,4-addition (Thiele s rule) for example, butadiene and an equimolar quantity of bromine yield 1,4-dibromo-2-butene (90%). On the other hand, chlorination of butadiene in the liquid or vapor phase furnishes about equal amounts of 1,2-and 1,4-addition products. Other polyfunctional compounds resulting from this method of preparation include dihalogenated acids, esters, aldehydes, and ketones. < The addition of bromine to unsaturated ethers yields dibromo ethers which are used as intermediates in the synthesis of olefins (method 21) and olefinic alcohols (method 99) ... 

Dibromo ethers are obtained still more simply on mixing bromine with equivalent amounts of an aldehyde and an alcohol a 1-bromo ether is formed as intermediate by reaction of the aldehyde and alcohol with the HBr liberated in its bromination ... 

Claisen methodology for the elaboration of ,6-unsaturated acids and esters continues to be developed. The readily available dibromo-ether (281) is useful in the preparation of vinyl ether functions required for such rearrangements the e-bromine is displaced by an alkoxide derived from an allylic alcohol to give a... 

To a mixture of 0.40 mol of neohexene ( commercially available) and 200 ml of dry diethyl ether 0.35 mol of bromine was added with cooling between -40 and -50°C. The diethyl ether and excess of neohexene were then completely removed by evaporation in a water-pump vacuum.In the second flask was placed a solution of 90 g of commercial KO-tert.-C9H9 (see Chapter IV, Exp. 4, note 2) in 250 ml of DMSO. The dibromo compound was added in five portions during 15 min from the dropping funnel after the addition of each portion the flask was swirled gently in order to effect homogenization. Much heat was evolved and part of the tert.-butylacetylene passed over. After the addition the flask was heated for 30 min in a bath at B0-100°C. 

A solution of 2,3-dibromo-5-methoxyaniline (32 g, 0.17 mol) in CHjClj (300 ml) was stirred and cooled in an icc bath. Boron trichloride (1 M in CH2CI2, 180 ml, 0.18 mol), chloroacetonitrile (14.3 g, 0.19 mol) and TiC (1 M in CH CIj, 190ml, 0.19 mol) were added. The resulting mixture was refluxed for 1.5 h. The solution was cooled to room temperature and poured carefully on to a mixture of icc and 20% aq. HCl (700 ml). The organic layer was separated and the CH Clj removed by distillation. The residue was heated to 90°C on a water bath for 30 min. The solution was cooled and the solid collected by filtration. It was partitioned between ether (1.41) and 1 N NaOH (500 ml). The ether layer was washed with brine, dried over Na2S04 and evaporated. The residue was recrystallized from ethanol to give 2-amino-3,4-dibromo-6-methoxy-a-chloroacetophenone (55 g) in 90% yield. 

The above product (24 g, 0.067 mol) was dissolved in 90 10 dioxane-water (300 ml) and sodium borohydride (92.5 g, 0.067 mol) was added. The mixture was refluxed for 4h. The cooled solution was poured into 0.1 N HCl (1.11). A solid precipitated and was collected by filtration, dried and recrystallized from ether hexane to give 6,7-dibromo-4-methoxyindole (18.5 g, 90%). 

Acetylene is condensed with carbonyl compounds to give a wide variety of products, some of which are the substrates for the preparation of families of derivatives. The most commercially significant reaction is the condensation of acetylene with formaldehyde. The reaction does not proceed well with base catalysis which works well with other carbonyl compounds and it was discovered by Reppe (33) that acetylene under pressure (304 kPa (3 atm), or above) reacts smoothly with formaldehyde at 100°C in the presence of a copper acetyUde complex catalyst. The reaction can be controlled to give either propargyl alcohol or butynediol (see Acetylene-DERIVED chemicals). 2-Butyne-l,4-diol, its hydroxyethyl ethers, and propargyl alcohol are used as corrosion inhibitors. 2,3-Dibromo-2-butene-l,4-diol is used as a flame retardant in polyurethane and other polymer systems (see Bromine compounds Elame retardants). 

N,N-Dimethylaniline) Dimethylbenzene, see Xylene 1,3-Dimethylbutyl acetate Dimethyl carbamoyl chloride Dimethyl-1,2-dibromo-2,2-dichloroethyl phosphate, see Naled Dimethyl ether N-N-Dimethylethylamine Dimethylethoxy silane Dimethylformamide SK... 

Dibromo-2-(2-chlorojethoxyethane 640 g of bromine (4 mols) are added dropwise, with stirring, to 426 g (4 mols) of 2-chloroethylvinyl ether dissolved in 1,040 ml of chloroform maintained at -10 C. 

To the solution of the magnesium compound so obtained the following solution is added dropwise, with stirring so as to maintain a slight reflux of ether 1,2-dibromo-2-(2-chloro)-ethoxyethane 550 g. Anhydrous ether 300 ml. 

Cyclohexadiene has been prepared by dehydration of cyclohexen-3-ol,3 by pyrolysis at 540° of the diacetate of cyclohexane-1,2-diol,4 by dehydrobromination with quinoline of 3-hromocyclohexene,6 by treating the ethyl ether of cyclohexen-3-ol with potassium bisulfatc,6 7 by heating cyclohexene oxide with phthalic anhydride,8 by treating cyclohexane-1,2-diol with concentrated sulfuric acid,9 by treatment of 1,2-dibromocyclo-hexane with tributylamine,10 with sodium hydroxide in ethylene glycol,10 and with quinoline,6 and by treatment of 3,6-dibromo-cyclohexene with sodium.6... 

A solution of 10,ll-dibromo-10,l l-dihydrodibenzo[6,/]thiepin (5g, 13.5 mmol) and 1-methylpiperazine (6.5 g, 65 mmol) in benzene (70 mL) was allowed to stand at rt for 5 d. The benzene solution was washed with H20 and 3 M HC1, dried (Na2S04) and evaporated to dryness. The solidified residue (3.9 g) was recrystallized (petroleum ether, 15 mL) yield 2 g (51 %) mp 83-84°C (Note benzene should be replaced by organic solvents with lower toxicity). 

B. l,l-Diphenyl-2-bromo-Z-acetoxy- -j>ropene. A 250-ml. flask equipped with a condenser is charged with 17.6 g. (0.050 mole) of 1,1-dibromo-2,2-diphenylcyclopropane, 12.5g. (0.075 mole) of silver acetate [Acetic acid, silver(l +) salt] (Note 4), and 50 ml. of glacial acetic acid, then immersed in an oil bath at 100-120° for 24 hours (Note 5). After cooling, the mixture is diluted with 200 ml. of ether and filtered. The ethereal filtrate is washed with two 100-ml. portions of water, two 100-ml. portions of aqueous saturated sodium carbonate, and finally with two 100-ml. portions of water. After drying over anhydrous sodium sulfate, the ether is removed on a rotary evaporator. Distillation of the resulting residue under reduced pressure yields 12.0 g. (72%) of the product, b.p. 142-145° (0.15 mm.), 1.6020-1.6023 (Note 6). 

To a solution of hexamethyldisilane (2.5 mmol) in HMPA (CAUTION— CANCER SUSPECT AGENT) (3 ml) at 0-5 °C was added methyl lithium (2.5 mmol, 1.5 m MeLi.LiBr complex in ether) dropwise. After being stirred for 3 min, the red solution was treated with Cul (2.5 mmol) in Me2S (1 ml), the resulting black reaction mixture was stirred for 3 min. and 2,3-dibromo-propene (1 mmol) was added rapidly via a syringe. The reaction mixture was allowed to warm to room temperature, and was stirred for 1.5 h. It was then poured into pentane (25 ml) and saturated ammonium chloride solution (25 ml, buffered to pH 8 by the addition of ammonium hydroxide), and the mixture was stirred vigorously for 1 h. The aqueous phase was re-extracted with pentane, and the combined organic extracts were dried. Removal of... 

This procedure, in contrast to previous methods, comprises only one step and is readily adapted to large-scale preparative work. Furthermore dibromination is very slow in methanol and hence the crude reaction products contain only traces of dibromo ketones. This contrasts with the behavior in other solvents such as ether or carbon tetrachloride, where larger amounts of dibromo ketones are always present, even when one equivalent of bromine is used. Methanol is thus recommended as a brominating solvent even when no orientation problem is involved. It should be noted that a-bromomethyl ketals are formed along with x-bromoketones and must be hydrolyzed during the workup (Note 8).7... 

When a,a -dibromo ketones (117) are treated with Me2CuLi in ether at —78°C and the mixture quenched with methanol, monomethylation takes place (no dimethyla-tion is observed). It has been suggested that the reaction involves cyclization (10-... 

Longifolene has also been synthesized from ( ) Wieland-Miescher ketone by a series of reactions that feature an intramolecular enolate alkylation and ring expansion, as shown in Scheme 13.26. The starting material was converted to a dibromo ketone via the Mr-silyl enol ether in the first sequence of reactions. This intermediate underwent an intramolecular enolate alkylation to form the C(7)—C(10) bond. The ring expansion was then done by conversion of the ketone to a silyl enol ether, cyclopropanation, and treatment of the siloxycyclopropane with FeCl3. 

Johnson, C. R. el. al, Tetrahedron Lett., 1964, 45,3327 Preparation of the 4-bromo compound by partial debromination of crude 3,5-dibromo-cyclopentene by addition of its ethereal solution to the aluminate in ice-cold ether is hazardous. Explosions have occurred on 2 occasions about 1 h after addition of dibromide. 

An improved synthesis of dithieno[3,2-A2, 3 -<7]thiophene 15a has been achieved from 2,3-dibromothiophene 304 (Scheme 57). Lithiation of 2,3-dibromothiophene 304 using -butyllithium followed by oxidative coupling with cupric chloride provided 3,3 -dibromo-2,2 -bithiophene 305 in 79% yield. Treatment of 305 with 2 equiv of -butyllithium in ether at —78 °C under nitrogen for 40 min and then adding benzenesulfonic acid thioanhydride and leaving the reaction mixture to reach room temperature afforded dithieno[3,2-A2, 3 -<7]thiophene 15a in 70% yield <2002TL1553>. 

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