Ion-Tagged Prolinamide Organocatalysts for the Direct Aldol Reaction On-Water
Environment for funding. We acknowledge the Institute for Frontier
Materials for the postgraduate scholarship to DE.
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3 Conclusion
Presented herein is a concise and high yielding synthesis of
two ionic liquid supported organocatalysts 3 and 4,
accessed in three synthetic steps. Variation of the anionic
component of the cationic imidazolium partner, CF3CCO-
-
(catalyst 3) and PF6 (catalyst 4) had a pronounced effect
on both the physical properties and catalytic behaviour of
these compounds. The latter catalyst (4) being technically
classified as a chiral ionic liquid, possessing a melting
point below 100 °C and exhibiting no evaporation phe-
nomena by isothermal TGA and a Tg of 14.5 °C. Evalua-
tion of these catalysts in the direct asymmetric aldol
reaction revealed a significant contrast in catalytic perfor-
mance between 3 and 4, with the former giving good
reaction conversion but very poor stereochemical outcome
for both dr and er, attributed to the presence of the triflu-
oroacetate anion in solution. We have proposed that the
unsuitability of the trifluoroacetate anion is a result of
encouraging epimerisation of the aldol products. Con-
versely, catalyst 4 performed well in the direct aldol
reaction and showed excellent application across a range of
ketones and aldehydes.
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Acknowledgments The authors acknowledge the Institute for
Frontier Materials, Strategic Research Centre for Chemistry and
Biotechnology, and the Faculty of Science, Engineering, and Built
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123