Chiral quaternary ammonium cinchonidine salts

Figure 4.14 Polymeric chiral quaternary ammonium cinchonidine salts for asymmetric allylation.

Asymmetric Michael additions can also be performed under phase-transfer conditions with an achiral base in the presence of a chiral quaternary ammonium salt as a phase-transfer agent. Conn and coworkers conducted the Michael addition of 2-propyl-l-indanone (13) to methyl vinyl ketone under biphasic conditions (aq 50% NaOH/toluene) using the cinchonine/cinchonidine-derived chiral phase-transfer catalysts (PTCs), 14a and 14b, as a catalyst (Scheme 9.5). However, only low to... 

Fluorine substituents on the aromatic ring in chiral quaternary ammonium salts also play an important role for the improvement of enantioselectivity in asymmetric alkylations of the Schiff base of glycine esters in an aqueous biphase system. Dolling first demonstrated asymmetric methylation of indanone (44) by cinchonidine ammonium salt (43) (Scheme 5.12) [18]. 

Wang M, Gao LX, Mai WP, Xia AX, Wang F, Zhang SB. Enantioselective iodolactonization catalyzed hy chiral quaternary ammonium salts derived from cinchonidine. J. Org. Chem. 2004 69(8) 2874-2876. 

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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