© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Four new phosphorus dendrimeric phase-transfer catalysts are prepared that contain 12 (+)-cinchoninium salts on the surface obtained by the quaternisation of the quinuclidinic N atom. The asymmetric alkylation of a glycinate Schiff base with benzyl bromide is used as a benchmark reaction, and the dendrimeric catalyst that contains an allyl group on the O-9 hydroxy group of the cinchonine units is the most active. The recovery and reuse of the catalyst are possible for five consecutive runs without loss of activity and with only a slight decrease in enantioselectivity. If other electrophiles are used, substituted benzyl bromides give better results than other activated alkyl bromides to afford the corresponding R amino acid derivatives. A comparison of these results with those reported previously for similar cinchoninium salts shows that dendrimers could be a better support than other polymers for this type of organocatalysis.
- phase-transfer catalysis
Rull, J., Jara, J. J., Sebastián, R. M., Vallribera, A., Nájera, C., Majoral, J. P., & Caminade, A. M. (2016). Recoverable Dendritic Phase-Transfer Catalysts that Contain (+)-Cinchonine-Derived Ammonium Salts. ChemCatChem, 8(12), 2049-2056. https://doi.org/10.1002/cctc.201600283