Organic & Biomolecular Chemistry
Communication
Notes and references
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Fig. 4 Plausible reaction mechanism.
counter cation exchange with a chiral phase-transfer catalyst to
give intermediate B. Then, the Michael addition of B with
enone proceeded to give the chiral enolate C. This was fol-
lowed by protonation to give the corresponding product 4,
along with the regeneration of the catalyst. In this mechanism,
the conversion of intermediate B to C is the enantioselective
carbon–carbon bond forming step. Therefore, the structure of
B is crucial for both the enantioselectivity of the product and
reactivity with the unactivated reactant such as methyl acrylate.
The tert-butylthio moiety behaved as a strong electron-donat-
ing group, thereby increasing the electron density and nucleo-
philicity of
reactants.11
B and enabling the reaction with various
In conclusion, the phase-transfer catalysed asymmetric syn-
thesis of α-chiral tetrasubstituted α-aminothioesters was
achieved using various enones. The corresponding products
were obtained in high yields with up to 81% ee. Mechanistic
studies revealed that the negative charges of the ionic inter-
mediates for the present reaction were not delocalised on the
imine moiety but were delocalised only on the thioester part.
The derivatisation reactions demonstrated the wide applica-
bility of the products for the synthesis of more functionalised
molecules. Further investigations on the application of chiral
products in asymmetric catalysis are ongoing.
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Conflicts of interest
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There are no conflicts to declare.
Acknowledgements
We are grateful for financial support from a Grant-in-Aid for
Early-Career Scientists (no. 20K15271) from the JSPS, and the
Leading Research Promotion Program ‘Soft Molecular
Activation’ of Chiba University, Japan.
This journal is © The Royal Society of Chemistry 2021
Org. Biomol. Chem., 2021, 19, 6402–6406 | 6405