Cinchona alkaloid-based catalysts nucleophilic substitution

Addition of CH2(CN)2 to -substituted 2-enoylpyridines RCH=CHCO(2-Py), catalysed by the cinchona alkaloid-based bifunctional ureas, such as (345) (10mol%), has been reported to proceed with <97% ee in m-xylene at room temperature. Squaramide (346) proved to be even more efficient for the addition of the same nucleophile to enones R CH=CHCOR, which required only 0.5 mol% catalyst loading to attain <96% ee (in CHCI3 at room temperature), ... 

Aldol reactions using a quaternary chinchona alkaloid-based ammonium salt as orga-nocatalyst Several quaternary ammonium salts derived from cinchona alkaloids have proven to be excellent organocatalysts for asymmetric nucleophilic substitutions, Michael reactions and other syntheses. As described in more detail in, e.g., Chapters 3 and 4, those salts act as chiral phase-transfer catalysts. It is, therefore, not surprising that catalysts of type 31 have been also applied in the asymmetric aldol reaction [65, 66], The aldol reactions were performed with the aromatic enolate 30a and benzaldehyde in the presence of ammonium fluoride salts derived from cinchonidine and cinchonine, respectively, as a phase-transfer catalyst (10 mol%). For example, in the presence of the cinchonine-derived catalyst 31 the desired product (S)-32a was formed in 65% yield (Scheme 6.16). The enantioselectivity, however, was low (39% ee) [65],... 

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