Alkyne bromination-double-dehydrobromination

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... 

Acetaldehyde is available as in part (a). Alkynes such as acetylene are available from the corresponding alkene by bromination followed by double dehydrobromination. Using ethylene, prepared in part (b), the sequence becomes... 

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