Dehydrobromination of 10,11-dibromo

Dehydrobromination of 10,11-dibromo hendecanoic acid with sodium amide, 32,104... 

We have recently converted the ethenyl group of the cinchona alkaloid into an ethynyl group by a bromination-double-dehydrobromination sequence [17, 18]. Bromina-tion of the natural products 1, 2 in CC14 provided the corresponding 10,11-dibromo-cinchona alkaloids in quantitative yield as a yellowish precipitate. The double dehydrobromination to afford alkynes 26 and 27 was studied under a variety of... 

Acetyl-lO,11-dibromo-5//-dibenz[7>,/]azepine (49), formed by addition of bromine to 5-acetyl-5/7-dibenz[7>,/]azepine, undergoes dehydrobromination to the 5-acetyldibenz[7>,/]-azepinc 50a on treatment with ethanolic potassium hydroxide.121-132 In contrast, on heating the dibromo compound under reflux with sodium methoxide in methanol, amide hydrolysis and methoxy denomination occur to give the 10-methoxy derivative 50b.132,1 33 Dehydrobromination of the dibromo compound 49, without hydrolysis or replacement of bromine, can be accomplished in hot dibutylamine.118... 

Lie Ken Jie et al. (10,11) developed a new method for the synthesis of all four geometric isomers of 9,11-octadecadienoic acid. Starting from methyl ricinoleate, the double bond was first brominated to form 9,10-dibromo-12-hydroxyoctadecanoate. Ultrasound-assisted dehydrobromination yielded 12-hydroxyoctadeca-9-ynoic acid. After esterification with methanol and mesylation to methyl 12-mesyloxyoctadeca-9-ynoate the mesylate was eliminated with aqueous KOH under ultrasonication. The obtained mixture of santalbic acid (40%) and its Z-isomer (60%) was separated by repeated urea fractionation. This method has the advantage, that after elimination of the mesylate only two isomers must be separated, and the triple bond can be selectively hydrogenated to form the Z-double bond. 

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