The role of Zn2+ in enhancing the rate and stereoselectivity of the aldol reactions catalyzed by the simple prolinamide model
作者:Cecilia Andreu、Gregorio Asensio
DOI:10.1016/j.tet.2011.07.013
日期:2011.9
The aldol reaction between acetone and 4-nitrobenzaldehyde catalyzed by single L-prolinamide and its zinc complexes has been studied. An increase in the rate and the stereoselectivity of the reaction has been shown by using zinc derivatives. A mechanistic proposal, based on NMR and ESI studies, has been put forward to explain the experimental data: zinc prolinamide complexes catalyze the reaction following the general mechanism of stereoselective enamine nucleophilic addition to the acceptor aldehyde. Zn2+ prevents the nonspecific base-catalyzed reaction by diminishing the basicity of the amine nitrogen of prolinamide. (C) 2011 Elsevier Ltd. All rights reserved.
Inhibition of imidazolidinone intermediate formation in the aldol reactions catalyzed by zinc–prolinamide complexes
作者:Cecilia Andreu、Teresa Varea、Gregorio Asensio
DOI:10.1016/j.tet.2011.09.025
日期:2011.11
The use of zinc salts as cocatalysts in aldol condensations catalyzed by single prolinamide (and in the extension by other more complex prolinamides) can prevent the formation of the parasitic intermediate imidazolidinone, with faster and also more stereoselective reactions than those catalyzed by the free amine. This new finding, together with this ion's already known properties, make zinc salts highly suitable additives for aldol reactions catalyzed for prolinamide derivatives. (C) 2011 Elsevier Ltd. All rights reserved.