Alkyne Cinchona Alkaloids, Their Derivatives, and Basic Transformations

Alkyne Cinchona Alkaloids, Their Derivatives, and Basic Transformations 

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 

Simple 10,11-didehydro QCD and 10,11-didehydro QCI are also accessible using this reliable two-step procedure. Thus, QCI, which solidifies at room temperature when pure, forms alkyne 28 with a change of chirality descriptor from R to S at carbon C5. QCI-derived alkyne 28 crystallizes readily and also sublimes on warming, forming beautiful colorless needles, reaching from wall to wall of the reaction vessel [17]. 

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