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Synfacts 2010(2): 0225-0225  
DOI: 10.1055/s-0029-1219131
Organo- and Biocatalysis
© Georg Thieme Verlag Stuttgart ˙ New York

Catalytic Asymmetric 6π-Electrocyclizations

Contributor(s): Benjamin List, Frank Lay
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
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Publication History

Publication Date:
21 January 2010 (online)

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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).