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Theoretical studies of stereoselectivities in the directanti- andsyn-aldol reactions catalyzed by different amino acid derivatives

Authors
Journal
Tetrahedron Asymmetry
0957-4166
Publisher
Elsevier
Publication Date
Volume
19
Issue
11
Identifiers
DOI: 10.1016/j.tetasy.2008.05.012
Disciplines
  • Physics

Abstract

Abstract Quantum mechanics calculations have been performed to study the stereoselectivities in the direct anti- and syn-aldol reactions catalyzed by different amino acid derivatives. The effects of two kinds of catalysts, l-proline amino alcohol amides and l-leucine amino alcohol amides, on the diastereoselectivity and enantioselectivity of the direct intermolecular aldol reactions between α-substituted ketones and 4-nitrobenzaldehyde have been studied. Transition states of the crucial C–C bond-forming step with the enamine intermediate addition to the aldehyde for the subject reactions are reported. These theoretical calculations provide a good explanation for the opposite syn versus anti diastereoselectivities of these two kinds of catalysts ( anti-selectivity for the proline derivative, syn-selectivity for the leucine derivative). Calculated and observed diastereomeric ratios and enantiomeric excess values are in good agreement.

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