Organic Letters
Letter
annulation is shown in Scheme 6. Initially, the reaction of
[IrCp*Cl2]2 with AgNTf2 affords a cationic iridium species,
and scale-up synthesis. The present protocol is expected to
provide opportunities for the exploration of novel optoelec-
tronic materials based on dibenzopyranone structures. Further
investigations on the reaction mechanism and extension of the
substrate scope are ongoing in our laboratory.
Scheme 6. Plausible Mechanism
ASSOCIATED CONTENT
* Supporting Information
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S
The Supporting Information is available free of charge on the
Experimental procedures and spectroscopic character-
AUTHOR INFORMATION
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Corresponding Author
ORCID
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We acknowledge financial support from the National NSF of
China (No. 21502123), the Fundamental Research Funds for
the Central Universities (2016SCU04A11), and the Compre-
hensive Training Platform of Specialized Laboratory, College of
Chemistry, Sichuan University.
which then coordinates to the carbonyl group of α-keto acid 1a
and induces the ortho C−H cleavage to deliver a cyclometalated
Ir(III) intermediate IM1.16 Following C−H activation
occurring at the α-position of 2a leads to IM2, which
subsequently undergoes a reductive elimination to afford IM3
and release the Ir(I) species. In the presence of Ag2O, the
bi(hetero)aryl α-keto acid IM3 would undergo decarboxylation
to give an acyl radical species IM4, which then undergoes
another Ag-mediated oxidation to give the cationic species
IM5. Following nucleophilic attack by H2O gives the
bi(hetero)aryl carboxylic acid 5a.17 Next, C−H iridation at
the β-position of the thiophene moiety of 5a with Ir(III)
delivers IM6, which then undergoes a reductive elimination to
provide the desired product 3a with the release of an Ir(I)
species. Finally, the Ir(I) species is oxidized by Ag2O to
regenerate the reactive Ir(III) species to complete the catalytic
cycle (path A). Alternatively, similar to the transformation
process from IM3 to 5a, the α-keto acid 1a could first undergo
a decarboxylation to deliver the benzoic acid. Then carbonyl-
directed C−H activation at the ortho position of the benzoic
acid gives IM7, which subsequently reacts with 2a to afford an
Ir(III) intermediate IM8. The following reductive elimination
of IM8 and intramolecular oxidative C−H lactonization
provide the desired product 3a (path B). Because the carboxylic
acid substrates showed lower efficiencies than the correspond-
ing α-keto carboxylic acids, this reaction might mainly proceed
via path A. However, the possibility of path B could not be
excluded at the current stage.
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In conclusion, we have demonstrated an Ir(III)-catalyzed
oxidative annulation of (hetero)aromatic α-keto carboxylic
acids with benzothiophenes for the construction of benzo-
thieno[3,2-c][2]benzopyranones via triple C−H activation and
C−C/C−O formations in one step. This reaction features a
relatively broad substrate scope, good functional group
tolerance, good regioselectivities, mild reaction conditions,
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