The Role of Achiral Pyrazolidinone Templates in Enantioselective Diels−Alder Reactions: Scope, Limitations, and Conformational Insights
作者:Mukund P. Sibi、Levi M. Stanley、Xiaoping Nie、Lakshmanan Venkatraman、Mei Liu、Craig P. Jasperse
DOI:10.1021/ja066425o
日期:2007.1.1
were also observed in reactions of 7d with chiralLewis acids derived from relatively small chiralligands, 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
We have developed a novel method for accessing exo adducts with high enantioselectivity in nitrone cycloadditions to enoates. Pyrazolidinones proved to be effective achiral templates in the cycloadditions, providing exo adducts typically in >15:1 selectivity and 90-98% ee. The use of Lewis acids that form square planar complexes, such as copper triflate, was important for obtaining high exo selectivity.
Enantioselective Conjugate Addition of Hydroxylamines to Pyrazolidinone Acrylamides
作者:Mukund P. Sibi、Mei Liu
DOI:10.1021/ol016807t
日期:2001.12.1
[GRAPHICS]Chiral relay templates provide amplification of selectivity in conjugate addition reactions. Reversal of stereochemistry of the product isoxazolidinones has also been demonstrated by a simple change of the Lewis acid.
A New Approach to Enantiocontrol and Enantioselectivity Amplification: Chiral Relay in Diels−Alder Reactions
作者:Mukund P. Sibi、Lakshmanan Venkatraman、Mei Liu、Craig P. Jasperse
DOI:10.1021/ja016396b
日期:2001.8.1
Chiral Lewis Acid Catalysis in Nitrile Oxide Cycloadditions
作者:Mukund P. Sibi、Kennosuke Itoh、Craig P. Jasperse
DOI:10.1021/ja0318636
日期:2004.5.1
examples of highly regio- and enantioselective nitrileoxidecycloadditions to unsaturated alkenes using substoichiometric amounts of a chiral Lewis acid. Pyrazolidinones proved to be effective achiral templates in the cycloadditions providing C-adducts typically in >30:1 selectivity and 80-99% ee. To avoid potential problems involving coordination of the Lewis acid by amine bases, we have devised a novel