Dehydrohalogenation acetylene derivs

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

Dehydrohalogenation with fluoride ion Acetylene derivs. and allenes from a,/ -ethylenehalides... 

The reactions of halogenomethylpyridines Table 6.13) with nucleophilic reagents are normal and require no comment is. The familiar reaction of dehydrohalogenation to produce acetylene derivatives is of considerable value in its application to side-chain halogen derivatives of the pyridine series. Its value arises from the possibility of carrying out the sequence of reactions, 2(or 4)-picoline 2(or 4)-styrylpyridine (p. 334) -> 2 (or 4)-styrylpyridine dihalide (p. 349) 2-(or 4)-tolazole. The dehydrohalogena-... 

Subsequent dehydrohalogenation afforded exclusively the desired (Z)-olefin of the PGI2 methyl ester. Conversion to the sodium salt was achieved by treatment with sodium hydroxide. The sodium salt is crystalline and, when protected from atmospheric moisture and carbon dioxide, is indefinitely stable. A variation of this synthesis started with a C-5 acetylenic PGF derivative and used a mercury salt cataly2ed cyclization reaction (219). Although natural PGI has not been identified, the syntheses of both (6R)- and (65)-PGl2, [62777-90-6] and [62770-60-7], respectively, have been described, as has that of PGI3 (104,216). 

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. 

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