C3-Symmetrical Cinchonine-Squaramide as New Highly Efficient, and Recyclable Organocatalyst for Enantioselective Michael Addition

A novel and recyclable catalyst, a C-3-symmetrical cinchonine-squaramide, has been developed for the asymmetric Michael addition of 1,3-dicarbonyl compounds to nitroalkenes. When using only 1 mol% of catalyst 1a for the reaction, high reaction yields with excellent enantioselectivities and diastereoselectivities (up to 96% yield, >99% ee, >99:1 dr) were achieved, in which the results for cyclic keto esters are the best ever achieved. Moreover, 1a can be easily recovered by simple precipitation and was used for six cycles without losing any selectivity and activity.