Skip to main content
Article
The Role of Achiral Pyrazolidinone Templates in Enantioselective Diels−Alder Reactions:  Scope, Limitations, and Conformational Insights
Journal of the American Chemical Society (2007)
  • Mukund P. Sibi
  • Levi M. Stanley
  • Xiaoping Nie
  • Lakshmanan Venkatraman
  • Mei Liu
  • Craig P. Jasperse
Abstract

We have evaluated the role of achiral pyrazolidinone templates in conjunction with chiral Lewis acids in room temperature, enantioselective Diels−Alder cycloadditions. The role of the fluxional N(1) substituent was examined, with the bulky 1-naphthylmethyl group providing enantioselectivities up to 99% ee, while templates with smaller fluxional groups gave lower selectivities. High selectivities were also observed in reactions of 7d with chiral Lewis acids derived from relatively small chiral ligands, suggesting the pyrazolidinone templates are capable of relaying stereochemical information from the ligand to the reaction center. Lewis acids capable of adapting square planar geometries, such as Cu(OTf)2, Cu(ClO4)2, and Pd(ClO4)2, were found to be particularly effective at providing high selectivities. Additionally, substitution at the C-5 position of the pyrazolidinone templates has been shown to be critical for optimal selectivity. Reactions of the optimal pyrazolidinone appended with a number of common dienophiles and various dienes demonstrate the utility of this achiral template. Furthermore, catalytic loadings could be lowered to 2.5 mol % with essentially no loss in selectivity. π−π interactions were evaluated as a means to explain the unusually high selectivity observed at room temperature. Finally, non-C2-symmetric ligands were employed as a test to determine if chiral relay was operative.

Disciplines
Publication Date
2007
Publisher Statement
Reprinted (adapted) with permission from Journal of the American Chemical Society 129 (2007): 395, doi:10.1021/ja066425o. Copyright 2007 American Chemical Society.
Citation Information
Mukund P. Sibi, Levi M. Stanley, Xiaoping Nie, Lakshmanan Venkatraman, et al.. "The Role of Achiral Pyrazolidinone Templates in Enantioselective Diels−Alder Reactions:  Scope, Limitations, and Conformational Insights" Journal of the American Chemical Society Vol. 129 Iss. 2 (2007)
Available at: http://works.bepress.com/levi_stanley/9/