Acetylene, dibromo derivatives

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. ... 

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. 

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). 

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

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. 

Quaternization of quinoxaline is neatly avoided by the synthesis of the azirino[l,2-a]quinoxalines 71 from o-phenylenediamine and the dibromo ketones 70. The azirino compound apparently acts as a 1,3 dipole and undergoes addition with a variety of dipolarophiles to give fused quinox-alines containing a bridgehead nitrogen atom. " Thus the acetylene derivatives 72 give the pyrrolo derivatives 73. The yields are much improved by the use of chloranil in situ to oxidize the presumed dihydro intermediates 74. 

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