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L ‐Prolinamides Derived from Chiral and Achiral 1,2‐Diamines as Useful Bifunctional Organocatalysts for Direct Diastereo‐ and Enantioselective Aldol Reaction
Author(s) -
Pedrosa Rafael,
Andrés José M.,
Manzano Rubén,
Rodríguez Paula
Publication year - 2010
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.201000616
Subject(s) - stereocenter , enantioselective synthesis , chemistry , aldol reaction , diastereomer , diamine , bifunctional , cyclohexanone , organocatalysis , catalysis , organic chemistry , stereochemistry
Diastereomeric catalysts 5 and epi ‐ 5 , which differ in the configuration of the stereocenter at the amino component, have been prepared from L ‐proline and ( S )‐ N 2 , N 2 ‐dibenzyl‐3‐methylbutane‐1,2‐diamine or ( R )‐ N 1 , N 1 ‐dibenzyl‐3‐methylbutane‐1,2‐diamine, respectively. Diastereomeric prolinamides 10 and epi ‐ 10 , which are regioisomers of 5 and epi ‐ 5 , respectively, were obtained from the same starting compounds. All of the catalysts promoted high diastereo‐ and enantioselectivity in the cross‐aldol reaction between aromatic aldehydes and cyclohexanone using acetic acid as co‐catalyst. A small match/mismatch effect over the stereoselection was observed, depending on the configuration of thestereocenters at the proline and diamine components. In general, the best results were obtained with catalyst 5 , which has the same configuration at both stereocenters. Under the same reaction conditions, prolinamide 20 , which was synthesized from L ‐proline and ethylene diamine, withoutstereocenters at the diamine component, behaved as an excellent enantioselective organocatalyst, giving the aldol products in very high diastereo‐ and enantioselectivity.