Organic Letters
Letter
substituted polyhydroquinolines 4e was also formed as a racemic
product (entry 3). Recently, Natale and co-workers applied the
title method to a few oxazole-4-carbaldehydes using TRIP
catalyst III.19 Once again, HPLC traces presented in this
publication are not fully convincing since there are discrepancies
between retention times on chromatograms of the racemic
product and the one obtained with the chiral phosphoric acid
catalyst.12 Moreover, the authors claim enantiomeric excesses
higher than 90%, but without giving precise values. When trying
to reproduce these results, we observed the formation of the
expected product 4f in moderate yield and with marginal
enantioselectivity (7% ee, entry 4).
As a summary, a careful survey on the multicomponent
phosphoric-acid-catalyzed synthesis of polyhydroquinolines10
was conducted. Contrary to the initial report, our study shed a
new light on this transformation, where the organocatalyst
actually seems to have no decisive influence either on the
reaction rate or on the enantiodetermining step. As a more
general conclusion, the present study along with similar ones20
should be seen as a reminder for both authors working in
enantioselective catalysis and reviewers that very careful
attention should be placed on the evaluation of the solidity of
experimental evidence proposed to determine enantiomeric
excess values.
Thierry Constantieux − Aix Marseille Univ, CNRS, Centrale
Marseille, iSm2, Marseille 13397, France
Complete contact information is available at:
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We warmly thank Roselyne Rosas (Aix Marseille Univ, CNRS,
Centrale Marseille, FSCM, Spectropole, Marseille, France) for
1H NMR kinetic experiments, the whole team of the Spectropole
(Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille,
France) for the preparation of substrates and precursors of
catalysts. Financial support from Aix Marseille Université,
Centrale Marseille, the CNRS, and the Agence Nationale de la
Recherche (ANR-13-BS07-0005, PhD scholarship for O.Q.) is
acknowledged. Moreover, the project leading to this publication
has received funding from Excellence Initiative of Aix-Marseille
UniversityA*MIDEX, a French “Investissements d’Avenir”
programme (scholarship for C.L.).
REFERENCES
ASSOCIATED CONTENT
* Supporting Information
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sı
The Supporting Information is available free of charge at
NMR spectra and HPLC chromatograms along with
complementary experimental details (PDF)
FAIR data, including the primary NMR FID files, for
compounds I, II, III, 4a−4f, and S3−S7 (ZIP)
AUTHOR INFORMATION
Corresponding Authors
■
Cyril Bressy − Aix Marseille Univ, CNRS, Centrale Marseille,
Xavier Bugaut − Aix Marseille Univ, CNRS, Centrale Marseille,
Jean Rodriguez − Aix Marseille Univ, CNRS, Centrale
Marseille, iSm2, Marseille 13397, France;
Authors
Ophélie Quinonero − Aix Marseille Univ, CNRS, Centrale
Marseille, iSm2, Marseille 13397, France
Clément Lemaitre − Aix Marseille Univ, CNRS, Centrale
Marseille, iSm2, Marseille 13397, France
Marion Jean − Aix Marseille Univ, CNRS, Centrale Marseille,
Nicolas Vanthuyne − Aix Marseille Univ, CNRS, Centrale
Christian Roussel − Aix Marseille Univ, CNRS, Centrale
Marseille, iSm2, Marseille 13397, France
Damien Bonne − Aix Marseille Univ, CNRS, Centrale
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J. E. Chem. Commun. 2011, 47, 529.
(11) The partial salification of catalyst during chromatography can
sometimes account for discrepancies in the reactivity and selectivity:
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Org. Lett. 2021, 23, 3394−3398