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Polymer‐Supported Enantioselective Bifunctional Catalysts for Nitro‐Michael Addition of Ketones and Aldehydes
Author(s) -
TuchmanShukron Lital,
Miller Scott J.,
Portnoy Moshe
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201102474
Subject(s) - bifunctional , chemistry , catalysis , moiety , enantioselective synthesis , enamine , amine gas treating , michael reaction , organic chemistry , cyclopentanone , nitro , organocatalysis , diamine , reactivity (psychology) , polymer chemistry , addition reaction , combinatorial chemistry , medicine , alternative medicine , pathology , alkyl
of an L ‐amino acid as a spacer and a urea‐forming moiety in a polymer‐supported bifunctional urea–primary amine catalyst, based on (1 R , 2 R )‐(+)‐1,2‐diphenylethylenediamine, significantly improves the catalyst’s activity and stereoselectivity in the asymmetric addition of ketones and aldehydes to nitroolefins. Yields and enantioselectivities, unprecedented for immobilized catalysts, were obtained with such challenging donors as acetone, cyclopentanone, and α,α‐disubstituted aldehydes, which usually perform inadequately in this reaction (particularly when a secondary‐amine‐based catalyst is used). Remarkably, though in the examined catalysts the D ‐amino acids as spacers were significantly inferior to the L isomers, for the chosen configuration of the diamine (match–mismatch pairs) the size of the side chain of the amino acid hardly influenced the enantioselectivity of the catalyst. These results, combined with the reactivity profile of the catalysts with substrates bearing two electron‐withdrawing groups and the behavior of the catalysts’ analogues based on tertiary (rather than primary) amine, suggest an enamine‐involving addition mechanism and a particular ordered CC bond‐forming transition state as being responsible for the catalytic reactions with high enantioselectivity.