Catalysis Letters

, Volume 134, Issue 3, pp 264–269

Novel Evidence on the Role of the Nucleophilic Intermediate Complex in the Orito-Reaction: Unexpected Inversion in the Enantioselective Hydrogenation of 2,2,2-Trifluoroacetophenone on Pt-Cinchona Chiral Catalyst Using Continuous-Flow Fixed-Bed Reactor

  • György Szőllősi
  • Szabolcs Cserényi
  • Mihály Bartók
Article

DOI: 10.1007/s10562-009-0242-2

Cite this article as:
Szőllősi, G., Cserényi, S. & Bartók, M. Catal Lett (2010) 134: 264. doi:10.1007/s10562-009-0242-2

Abstract

The enantioselective hydrogenation of 2,2,2,-trifluoroacetophenone over Pt/Al2O3 catalysts modified by cinchona alkaloids was investigated for the first time using continuous-flow fixed-bed reactor system in toluene/AcOH 9/1 solvent mixture in absence and presence of 0.1 v/v% trifluoroacetic acid (TFA). The enantioselective hydrogenations yielded the (R)-product in excess on Pt–CD, Pt–CN, Pt–QN and Pt–QD catalysts in toluene/AcOH mixture; consequently, unexpected inversion took place on the Pt–CN and Pt–QD catalysts. Hydrogenation in the presence of 0.1% (v/v) TFA follows the general rule of the Orito reaction, according to which the products formed in excess are (R)-alcohols on Pt–CD and Pt–QN and (S)-alcohols on Pt–CN and Pt–QD. Since there is no inversion in the presence of TFA, the observed unexpected inversion can be interpreted on the basis of the nucleophilic intermediate complex.

Graphical Abstract

Keywords

Asymmetric hydrogenation Platinum Cinchona alkaloids Trifluoroacetophenone Continuous-flow fixed-bed reactor Unexpected inversion 

Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • György Szőllősi
    • 1
  • Szabolcs Cserényi
    • 2
  • Mihály Bartók
    • 1
    • 2
  1. 1.Stereochemistry Research Group of the Hungarian Academy of SciencesSzegedHungary
  2. 2.Department of Organic ChemistryUniversity of SzegedSzegedHungary