Analysis of the mechanism of asymmetric amplification by chiral auxili trans-1,2-diaminocyclohexane bistriflamide

Kouichi Asakura, Yuuki Isoda, Dilip K. Kondepudi, Tomohiko Yamaguchi

Research output: Contribution to journalArticle

Abstract

Asymmetric amplification is a phenomenon in which the enantiomeric excess (ee) of a product is higher than that of a chiral auxiliary for a catalyst. We analyzed the mechanism of asymmetric amplification observed in the addition of diethyizinc (Et2Zn) to benzaldehyde (PhCHO) to synthesize 1-phenyl-1-propanol in the presence of trans-1,2-diaminocyclohexane bistriflamide (DCBF) and titanium tetraisopropoxide (TIOP). In a manner similar to the reaction in which 1-piperidino-3,3-dimethyl-2-butanol is a chiral auxiliary for the catalyst, when asymmetric amplification was observed, the ee of the product varied as the reaction progressed. The mechanisms of variation in ee in the two reactions, however, were different. No asymmetric amplification was observed when TIOP and PhCHO were added to a mixture of DCBF and Et2Zn, while the ee of the product was always higher than that of DCBF when PhCHO and Et2Zn were added to a mixture of DCBF and TIOP. In the latter case, the product ee decreased as the reaction progressed. The results indicate that DCBF forms inactive heterochiral complex causing an increase in the ee of DCBF in the solution, which is the chiral auxiliary for the catalyst. But the complex is not very stable and gradually dissociates due to the reaction with Et2Zn. As a result, the asymmetric amplification decreases as the reaction progresses.

Original languageEnglish
Pages (from-to)919-923
Number of pages5
JournalChirality
Volume20
Issue number8
DOIs
Publication statusPublished - 2008 Aug

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Keywords

  • Asymmetric amplification
  • Benzaldehyde
  • Diethyl-zinc
  • Enantiomeric excess
  • Reservoir model
  • Titanium tetraisopropoxide
  • Trans-1,2-diaminocyclohexane bistriflamide

ASJC Scopus subject areas

  • Analytical Chemistry
  • Drug Discovery
  • Organic Chemistry
  • Pharmacology

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