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Synthesis 2010(13): 2171-2178  
DOI: 10.1055/s-0029-1218792
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

Catalytic Asymmetric 6π-Electrocyclization: Accessing Highly Substituted Optically Active 2-Pyrazolines via Diastereoselective Alkylations

Steffen Müller, Benjamin List*
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
Fax: +49(208)3062999; e-Mail: list@mpi-muelheim.mpg.de;
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Publication History

Received 29 April 2010
Publication Date:
20 May 2010 (online)

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Abstract

The chiral phosphoric acid catalyzed asymmetric electrocyclization of α,β-unsaturated hydrazones has been studied. This reaction is one of the first catalytic asymmetric 6π-electrocyclizations reported, and enables the synthesis of 2-pyrazolines in high yields and enantiomeric ratios. The obtained products are not only interesting because of their pharmaceutical properties, but can be manipulated in highly diastereoselective fashion, as shown for alkylation reactions. Thus, the combination of catalytic asymmetric 6π-electrocyclization followed by diastereoselective alkylation can provide interesting synthetic building blocks in optically active form.

Key words

electrocyclic reactions - enantioselective organocatalysis - heterocycles - diastereoselectivity - 2-pyrazolines

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