Abstract
Cinchona
alkaloid-derived chiral catalysts represent one of the
most widely applied classes of organocatalysts, which have been successfully
utilized in the promotion of a wide variety of asymmetric reactions.
Cinchona alkaloids exist in nature as pseudoenantiomers, which allow
cinchona alkaloid-catalyzed reactions to provide high enantioselectivities
and yields toward both enantiomers of interest in many reactions.
On the other hand, the subtle structural difference between pseudoenantiomeric
cinchona alkaloids could also lead to uneven efficiency that severely
limits the applicability of some cinchona alkaloid-catalyzed reactions.
We describe here the elucidation of the origin of and the consequent
development of novel modified cinchona alkaloids to address such a
problem in asymmetric imine umpolung reactions by cinchonium salts.