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Different L-prolinamides 21, prepared from L-proline and chiral beta-amino alcohols are active bifunctional catalysts for the direct nitro-Michael addition of ketones to beta-nitrostyrenes. In particular, catalyst 21e, prepared from L-proline and (1S,2R?)-cis-1-amino-2-indanol, exhibits the highest catalytic performance working in polar aprotic solvents such as NMP, especially in the presence of 20 mol-% of acid additives such as p-nitrobenzoic acid or under microwave heating. High syn diastereoselectivities (up to 94 % de) and good enantioselectivities (up to 80 % ee) are obtained at room temp. Moreover, catalyst 21e can be easily recovered and reused. ESI-MS studies are used to characterize the intermediates assumed for the catalytic cycle. The stereochemical control attending Michael addition reactions between ketones and nitrostyrenes catalyzed by prolinamide derivatives 21 has been investigated with computational density functional methods. Transition-state energies for the rate-limiting C-C bond-forming step are calculated. Analysis of these structures indicates that hydrogen bonding plays an important role in catalysis, and that the energy barrier for Re-face attack to form syn-(4S,5R) products is lower than that for Si-face attack leading to syn-(4R,5S) products. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
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Reference：
Chiral nitrogen ligands in late transition metal-catalysed asymmetric synthesis—I. Addressing the problem of ligand lability in rhodium-catalysed hydrosilations,
Nitrogen-Containing Ligands for Asymmetric Homogeneous and Heterogeneous Catalysis