Reaction rate differences between organotrifluoroborates and boronic acids in BINOL-catalyzed conjugate addition to enones

[Display omitted] Enantioselective organocatalysis has been successfully employed in combination with trifluoroborate reagents for novel organic transformations over the last decade. However, no experimental rate studies of these reactions have been reported. Herein we report Hammett plot analysis o...

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Bibliographic Details
Published in:Tetrahedron letters 2021-10, Vol.83, p.153412, Article 153412
Main Authors: Brooks, Bailey, Hiller, Noemi, May, Jeremy A.
Format: Article
Language:English
Subjects:
Conjugate Addition
Hammett plot
Organoboronate
Organocatalysis
Trifluoroborate
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Summary:[Display omitted] Enantioselective organocatalysis has been successfully employed in combination with trifluoroborate reagents for novel organic transformations over the last decade. However, no experimental rate studies of these reactions have been reported. Herein we report Hammett plot analysis of the organocatalyzed enantioselective conjugate addition of alkenyl, aryl, and heteroaryl trifluoroborate salts to chalcone derivatives with substitution at both the β-aryl and keto-aryl positions. The rate trend for keto-aryl substitution diverges from that of boronic acid nucleophiles in that the keto-aryl substituent for trifluoroborate salts does not measurably impact reaction rate in a manner consistent with charge stabilization. In addition, variable temperature NMR in combination with quantitative thin-layer chromatography (TLC) analysis suggests that the reaction is impacted by the low solubility of the trifluoroborate salts, so particle size and stirring speed affect reaction rates.
ISSN:0040-4039
1873-3581
DOI:10.1016/j.tetlet.2021.153412