Asymmetric conjugate addition of α-keto esters to nitroolefins catalyzed by chiral CuII hydroxo complexes

As a part of our research project on hard anion-late transition metal complexes as mild acid–base catalysts, we describe herein that CuII hydroxo complexes having chiral N-substituted-diaminocyclohexanes are mild and selective catalysts, which are applicable to the catalytic asymmetric conjugate addition of α-keto esters to nitroolefins. The reaction proceeded diastereoselectively without the detectable formation of self-aldol products, affording the corresponding coupling products with anti-stereochemistry in an enantioselective manner.

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(1R,2R)-N,N′-Bis[(2,4,6-triisopropylphenyl)methyl]-1,2-diaminocyclohexaneC38H62N2[α]D27=-56.5 (c 1.01, CHCl3)Source of chirality: chiral poolAbsolute configuration: (1R,2R)

(3S,4S)-tert-Butyl 4-(3′,4′-methylenedioxyphenyl)-3-benzyl-5-nitro-2-oxopentanoateC23H25NO7Ee = 71%[α]D29=-16.1 (c 0.63, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (3S,4S)