Acetylene dibromo

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). 

Independently Volpin17 synthesized diphenyl cyclopropenone from diphenyl-acetylene and dibromo carbene (CHBr3/K-tert.-butoxide). This reaction principle of (2 + 1) cycloaddition of dihalocarbenes or appropriate carbene sources ( caibenoids ) to acetylenic triple bonds followed by hydrolysis was developed to a general synthesis... 

Biedermann and Jacobson, who first prepared thieno[2,3-6]-thiophene (1) in 1886, characterized it as a 2,3,4,5-tetrabromo derivative with m.p. 172°. Later Capelle reported the isolation of a dibromo derivative of thienothiophene 1 with m.p. 122.5°, which was shown by Challenger and Harrison to be 2,3,5-tribromothieno[2,3-6]thiophene (m.p. 123°-124°). Capelle also obtained a tetrabromide, m.p. 223°, by bromination of the product of reaction of acetylene with sulfur. The tetrabromide seems to be identical with that prepared from the product of reaction of methane, acetylene, and hydrogen sulfide, m.p. 229°-230°, and is evidently 2,3,5,6-tetrabromothieno[3,2-6j-thiophene. ... 

A series of benzo[l,2- 4,5- ]dichalcogenophenes (X= S, Se, Te) have been synthesized from l,4-dibromo-2,5-bis(2-trimethylsilylethynyl)benzene using a cyclization reaction between the acetylene substituents and the chalcogenate anion in good yield (Equation 94) <2005JOC10569>. 

Several acetylenic derivatives are prepared by dehydrohalogenation of vicinal dibromo compounds, which are obtained by adding bromine to olefinic compounds. 

Elimination reactions are considered when simple, volatile haloacetylenes are to be prepared. Dichlaroacetylene. far example, has been prepared as an ethereal solution [124] (the undiluted compound is highly explosive) by treating CljC CHCl with KOH at 200 C. Dibromo-acetylene is formed under milder conditions, namely from Br2C=CHBr and ethanolic... 

Furane derivatives, like pyrroles, couple effectively with acetylenes. In case both the a-, and / -position are available for the reaction, like in the case of 4,5-dibromo-furfural in 6.45., the cross-coupling takes place preferentially in the former position65 The observed selectivity is in line with other palladium catalyzed transformations of dihalofuranes, such as their Stifle coupling.66... 

The second method of preparation (shown in Scheme 2) depends on treating dehydroepiandrosterone (prepared from cholestrol or sitosterol) with acetylene to form the 17a-ethnyl-17p-hydroxy derivative, which is carbonated to the 17a-propionic acid. Reduction of the unsaturated acid in alkaline solution yields the saturated acid, which cyclizes to the lactone on acidification. Bromination to the 5,6-dibromo-compound, followed by oxidation of the hydroxyl group to the ketone, and then dehydro-bromination to the 7a-hydroxyl derivative, produces spironolactone when esterified with thiolacetic acid. 

Dibromo acetylene Methyl nitrite Vinyl ether... 

AIBN = 2,2 -azobisisobutyronitrile 9-BBN = 9-borabicyclo [3.3.1]nonane Bn = benzyl BOC = f-butoxycarbonyl Bz = benzoyl CAN = ceric anunoninm nitrate Cp = cyclopenta-dienyl Cy = cyclohexyl DAST = diethylaminosnllur trifln-oride DBA = l,3-dibromo-5,5-dttnethylhydantoin DDQ = 2,3-dichloro-5,6-dicyano-l,4-benzoquinone DET = diethyl tartrate DIAD = diisopropyl acetylene dicarboxylate DIBAL-H = diisobutylalummum hydride DIPEA = diisopropyl ethyl amine DMDO = dimethyldioxirane HMPA = hexamethylphosphortriamide EDA = lithium diisopropy-lamide Ms = methylsulfonyl MOM = methoxymethyl NBS = iV-bromosuccmimide NMO = A-methylmorpholine iV-oxide PDC = pyridinium dichromate PMP = p-methoxyphenyl THP = tetrahydropyranyl TIPS = trisiso-propylsilyl TMANO = trimethylamine A-oxide TBDMS = t-butyldimethylsilyl Tf = trifluoromethanesulfonyl TMP = 2,2,6,6-tetramethylpiperidyl TMS = trimethylsilyl Ts = p-toluenesulfonyl. 

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%. ... 

Many acetylenic acids have been made by the dehydrohalogenation of the dibromo derivatives of olefinic acids. Aliphatic a,/3-acetylenic acids are often decarboxylated under the conditions of the reaction. However, phenylpropiolic acid, C,HsC = CC0,H, and acetylenedicarboxylic acid, HOaCC=CCO,H, are prepared in this way as well as acids having the triple bond in the / y-, y, S-, and more remote positions in the aliphatic chain. 

German chemists have used the method successfully for preparation of dichloro-cyclopropanes from olefins which yield little or no products when the dichlorocarbene is generaied from chloroform and potassium /-bntoxide. TTiey also generated dibromo-carbene in the same way. Cyclopropcnes are obtained in only low yields from acetylenes owing to side reactions. 

Other examples may be found among the mono- and di-halogenated acetylenes, such as diiodo- and dibromo-acetylene, CI2 = C and CBrj = C, which have more interesting physiopathological properties than the halogenated paraffin hydrocarbons. 

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