Cheng H.-G.
Miguélez J.
Miyamura H.
Yoo W.-J.
Kobayashi S.
* The University of Tokyo, Japan
Integration of Aerobic Oxidation and Intermolecular Asymmetric Aza-Friedel–Crafts
Reactions with a Chiral Bifunctional Heterogeneous Catalyst.
Chem. Sci. 2017;
8: 1356-1359
Key words
gold catalysis - palladium catalysis - platinum catalysis - aza-Friedel–Crafts reaction
- benzylic alcohols - aminoethylpyrroles
Significance
Chiral phosphoric acids immobilized on polymer/carbon black-entrapped Au/Pd or Au/Pt
nanoparticles (1 and 2, respectively) were prepared according to eq. 1. Catalysts 1 and 2 promoted an aerobic oxidation of benzyl alcohols and subsequent asymmetric aza-Friedel–Crafts
reaction with N-(2-aminoethyl)pyrroles in one pot to give the corresponding chiral piperazines in
≤91% yield and ≤95% ee (eq. 2).
Comment
Benzyl methyl sulfide prevents oxidation of the resulting piperazine products to their
imine forms. In the sequential reactions of benzyl alcohol and [2-(1H-pyrrol-1-yl)ethyl]amine, catalyst 1 was recovered by filtration and reused five times without significant loss of its
catalytic performance (first run: 92% yield, 89% ee, sixth run: 85% yield, 84% ee).
