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Abstract
The asymmetric alkylation of Schiff bases under basic conditions in a ball mill was performed. The starting Schiff bases of glycine were prepared beforehand by milling protected glycine hydrochloride and benzophenone imine, in the absence of solvent. The Schiff base was then reacted with a halogenated derivative in a ball mill in the presence of KOH. By adding a chiral ammonium salt derived from cinchonidine, the reaction proceeded asymmetrically under phase‐transfer catalysis conditions, giving excellent yields and enantiomeric excesses up to 75 %. Because an equimolar amount of starting material was used, purification was greatly simplified.
Grinding on one side! Ball milling under solvent‐free conditions is presented herein for the synthesis of glycine Schiff bases and their subsequent asymmetric alkylation to prepare chiral natural and unnatural amino acids (see scheme). The use of a cinchona‐derived catalyst provided good enantiomeric excesses up to 75 %.
<!--Unmatched element: w:blockFixed-->| Authors: | Nun, Pierrick; Pérez, Violaine; Calmès, Monique; Martinez, Jean; Lamaty, Frédéric | |
| Journal: | Chemistry - A European Journal | |
| Year: | 2012 | |
| Pages: | n/a | |
| DOI: | 10.1002/chem.201102885 | |
| Publication date: | 09-02-2012 |
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