Organic Letters
Letter
Scheme 6. Deuterium-Labeling Experiments: Rh(I) versus
Ru(II)
AUTHOR INFORMATION
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Corresponding Author
ORCID
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This work was supported by the JST Strategic Basic Research
Program “Advanced Catalytic Transformation Program for
Carbon Utilization (ACT-C)” (JPMJCR12YS) and a Grant in
Aid for Specially Promoted Research from MEXT (17H06091).
REFERENCES
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additive (Scheme 6b). No deuterium atom was incorporated at
either the α- or β-position of the product 2a, suggesting that a
different mechanism is operative in this systems. As proposed
by Prabhu,5c the mechanism of the Ru(II)-catalyzed system
involves the insertion of maleimide into the C−Ru bond in a
ruthenacycle (carboruthenation) followed by protonation of
the resulting C−Ru bond by a carboxylic acid. This mechanism
explains the deuterium-labeling results in which no deuterium
atom was incorporated into the product 2a (Scheme 6b). In
contrast, in the mechanism responsible for the Rh(I)-catalyzed
reaction, more complicated paths appear to be involved.
In summary, we have reported the development of a direct
rhodium-catalyzed alkylation of C(sp2)−H bonds in aromatic
amides with maleimides using an 8-aminoquinoline bidentate
chelation system. In the case of the Cu(II) catalyst in an 8-
aminoquinoline bidentate chelation system reported by Hirano
and Miura,4 oxidative cyclization took place to give spriocyclic
products. In addition, the use of a Ru(II) catalyst gave the same
products as the Rh(I) system, but the mechanism was clearly
different. The reaction is highly regioselective at the less
hindered ortho-C−H bonds in the case of meta-substituted
aromatic amides.
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