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Asymmetric Conjugate Addition of Ketones to β‐Nitrostyrenes by Means of 1,2‐Amino‐Alcohol‐Derived Prolinamides as Bifunctional Catalysts
Author(s) -
Almaşi Diana,
Alonso Diego A.,
GómezBengoa Enrique,
Nagel Yvonne,
Nájera Carmen
Publication year - 2007
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200700031
Subject(s) - chemistry , bifunctional , catalysis , hydrogen bond , bifunctional catalyst , alcohol , amino acid , medicinal chemistry , organic chemistry , molecule , biochemistry
Different L ‐prolinamides 21 , prepared from L ‐proline and chiral β‐amino alcohols are active bifunctional catalysts for the direct nitro‐Michael addition of ketones to β‐nitrostyrenes. In particular, catalyst 21e , prepared from L ‐proline and (1 S ,2 R )‐ 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 ‐(4 S ,5 R ) products is lower than that for Si ‐face attack leading to syn ‐(4 R ,5 S ) products. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)