Alkyne cinchona alkaloids

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... 

Figure 12.3 X-ray crystal structure of alkynes derived from cinchona alkaloids. Torsion angles defining twist sense, cf. Scheme 12.19.

Further extension of this strategy to the asymmetric functionalization of cyclic a,(3-unsaturated ketones was later reported by the same group [107], 9- z-amino cinchona alkaloid salt 57 proved to be the optimal catalyst to afford the key intermediates 104, which are useful precursors for a series of important building blocks including alkynes, alkenes, 1,3-diketone, and bicyclic compounds (Scheme 5.50). 

The enantioselective Lewis-acid-promoted 2 -t- 2-cycloaddition of trifluoropyruvate with various alkynes produced stable oxetene derivatives for use in the synthesis of pharmaceuticals and agrochemicals. l,4-diazabicyclo[2.2.2]octane (DABCO)-catalysed 2- -2-cycloaddition of allenoates and trifluoromethylketones produced 2-alkyleneoxetanes in good yields and with good diastereo-selectivities dr > 20 1). A cinchona alkaloid (20) catalysed the 2- -2-cycloaddition between tV-sulfonylimines and alkyl 2,3-butadienoates to form / -configured 2,4-disubstituted azetidines in high yields and with high enantioselectivities. ... 

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