Organic Letters 2011-05-20

Primary amine/CSA ion pair: a powerful catalytic system for the asymmetric enamine catalysis.

Chen Liu, Qiang Zhu, Kuo-Wei Huang, Yixin Lu

Index: Org. Lett. 13(10) , 2638-41, (2011)

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Abstract

A novel ion pair catalyst containing a chiral counteranion can be readily derived by simply mixing cinchona alkaloid-derived diamine with chiral camphorsulfonic acid (CSA). A mixture of 9-amino(9-deoxy)epi-quinine 8 and (-)-CSA was found to be the best catalyst with matching chirality, enabling the direct amination of α-branched aldehydes to proceed in quantitative yields and with nearly perfect enantioselectivities. A 0.5 mol % catalyst loading was sufficient to catalyze the reaction, and a gram scale enantioselective synthesis of biologically important α-methyl phenylglycine has been successfully demonstrated.