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Synlett 2008(17): 2655-2658  
DOI: 10.1055/s-0028-1083438
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

exo- and Enantioselective Diels-Alder Reactions: Pyrazolidinone Auxiliaries as a Means to Enhanced exo Selectivity

Mukund P. Sibi*, Xiaoping Nie, Jessica P. Shackleford, Levi M. Stanley, Frances Bouret
Department of Chemistry and Molecular Biology, North Dakota State University, Fargo, ND 58105, USA
Fax: +1(701)2311057; e-Mail: Mukund.Sibi@ndsu.edu;
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Publication History

Received 21 May 2008
Publication Date:
01 October 2008 (online)

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Abstract

Achiral pyrazolidinone auxiliaries have been investigated in exo- and enantioselective Diels-Alder reactions. The effect of pyrazolidinone N-1 substitution and chiral ligand identity were studied in Yb(OTf)3-catalyzed exo-selective Diels-Alder reactions. An appropriate choice of pyrazolidinone auxiliary and Yb(OTf)3/Pybox chiral Lewis acid led to moderate exo selectivity and high enantioselectivity for the exo-cycloadduct.

Key words

Diels-Alder - exo-selective - enantioselective - pyrazolidinone - chiral Lewis acid

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The identity of the exo and endo adducts was established by NMR spectroscopy. Additionally, the products were converted into known benzyl esters.