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Letter
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reaction optimization showed that the reaction was not
sensitive to water, it was most likely that radical C combined
with atmospheric oxygen to result in the formation of peroxy
radical D. Cleavage of the peroxy radical by Ce(IV)14 then
ensued to produce dihydrofuran intermediate E, which then
underwent oxidative aromatization to yield the desired furan 2.
In summary, catalytic Pd(PPh3)2Cl2 could immensely
enhance the reactivity of CAN in the oxidative cyclization of
2-propargylic 1,3-ketoesters to furnish 2-ketofuran-4-carbox-
ylate esters. A wide range of substrates were converted to furan
products in mostly moderate to good yields within an
extremely short reaction time (less than 5 min) under mild
conditions. With a slight change of conditions, 1,2-diary-
ldiketones could be prepared via oxidation of diarylalkynes in
moderate to good yields. Studies of the catalytic species as well
as roles of Pd(II) species in the reaction are ongoing in our
laboratory.
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reactions were carried out on larger than 1 mmol scales.
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ASSOCIATED CONTENT
* Supporting Information
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S
The Supporting Information is available free of charge on the
̈
Shibasaki, M., Yamamoto, Y., Eds.; Wiley-VCH: Morlenbach, 2004.
Optimization, time−conversion studies, experimental
procedures, spectroscopic data, and NMR spectra of
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AUTHOR INFORMATION
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Corresponding Author
ORCID
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This research work was supported by grants from Chulabhorn
Research Institute (CRI), Chulabhorn Graduate Institute
(CGI), Mahidol University, the Center of Excellence on
Environmental Health and Toxicology, Science & Technology
Postgraduate Education and Research Development Office
(PERDO), Ministry of Education, and a Thailand Research
Fund (TRF) Grant (RSA6180045). N.C. is also grateful for
support from the Royal Golden Jubilee (RGJ) scholarship
program (PHD/0139/2560). Assistance by Ms. Kanokkan
Sriwaiyaphram (2017 summer intern from Chulalongkorn
University) and Mr. Jesada Maneewong (2018 summer intern
from Burapha University) is gratefully acknowledged.
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