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Synfacts 2010(2): 0225-0225
DOI: 10.1055/s-0029-1219131
DOI: 10.1055/s-0029-1219131
Organo- and Biocatalysis
© Georg Thieme Verlag
Stuttgart ˙ New York
Catalytic Asymmetric 6π-Electrocyclizations
first article: S. Müller, B. List*, second article: E. E. Maciver, S. Thompson, M. D. Smith*
Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, Germany and University of Oxford, UK
Further Information
Publication History
Publication Date:
21 January 2010 (online)
![](https://www.thieme-connect.de/media/synfacts/201002/lookinside/thumbnails/10.1055-s-0029-1219131-1.jpg)
Significance
The groups of List and Smith independently report catalytic asymmetric
6π-electrocyclizations. List’s strategy is based
on the isoelectronicity of the pentadienyl anion and the
α,β-unsaturated
hydrazonium cation. The cation is generated by protonation of α,β-unsaturated
hydrazones with a chiral Brønsted acid 1.
After electrocyclization to protonated 3-pyrazolines, subsequent
isomerization and deprotonation yield the thermodynamically more
stable 2-pyrazolines. Smith’s group reports that under
phase-transfer conditions N-aryl imines
generate a 2-aza-pentadienyl anion system which cylizes to functionalized
indolines in the presence of 10 mol% of
N-benzyl
cinchonidinium chloride (2).