Organic Letters
Letter
isatin 6v (eq 15) tolerated Cu(II) salts in DMSO under
heating,14 which ruled out a mechanism via the Cu(II)-
mediated cleavage of the C2−C3 bond of 6 and subsequent
annulation to 3.
Screening of reaction conditions, experimental proce-
dures, X-ray diffraction data, 1H and 13C NMR spectra of
Based on previous literature and all controlled results
described above, a possible mechanism for the copper-mediated
cascade reactions is proposed in Scheme 6. Initially, 1a and 2a
AUTHOR INFORMATION
Corresponding Authors
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ORCID
Scheme 6. Proposed Mechanism
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We thank the NSFC (U1604285, 21772032 and 21702051),
PCSIRT (IRT1061), the 111 Project (D17007), Science &
Technology Innovation Talents in Universities of Henan
Province (17HASTIT002), and Outstanding Young Talent
Cultivation Project Funding of Henan Normal University
(14YR002). We thank Simon Partridge, PhD, from Liwen
Bianji, Edanz Editing China, for editing the English text of a
draft of this manuscript.
react to afford 4a through a cross-coupling process with copper
as the catalyst under basic conditions (provided by pyridine).11
Then, 4a-A is expected to be formed by 4a in the presence of
Cu(II) and oxygen under heat.14a,15 Subsequently, intra-
molecular addition of the amino group to the aldehyde group
of glyoxal 4a-A results in the formation of 2-hydroxyindolin-3-
one derivative 4a-B, which is further oxidized to form key
intermediate isatin 6a.9,14a,15c,16 Product 3a is finally formed by
rearrangement of 6a.17 The transformation from 6a to 3a might
occur via three processes, as follows: C−H activation of 6a by
Cu complex 6a-A to afford metallacycle 6a-B via SEAr,17a−c
direct intramolecular nucleophilic attack at the ketone to form
tricyclic intermediate 6a-C, and then conversion of 6a-C to 3a
after carbon monoxide extrusion.17d,e
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