Angewandte Chemie International Edition
10.1002/anie.201809820
COMMUNICATION
suitable for six-membered substrates. All of our efforts to attempt
the asymmetric variant met failure.
In summary, we have developed the first visible light-driven
copper-catalyzed radical cross-coupling of oxime esters,
styrenes, and boronic acids. The reaction features broad
substrate scope, simple procedure and inexpensive copper
[
16]
catalyst, providing
a
practical access to valuable
1,1-diarylmethane-containing alkylnitriles. This work has also
established a platform to employ alkyl radicals derived from
addition of cyanoalkyl radical to alkenes in cross-coupling
chemistry as proxies for alkyl halides. Many exciting extensions
3
3
3
of this strategy can be envisaged such as C(SP )-C(SP ), C(SP )-N,
3
Scheme 2. Mechanistic studies.
and C(SP )-O bond forming couplings; current investigations into
these subjects are underway in our laboratory.
To obtain some insight into the mechanism, we carried out
several control experiments using the model substrates of 1a, 2a,
and 3a (Scheme 2). Upon addition of stoichiometric TEMPO or
PhSeSePh, complete inhibition of the target reaction was indeed
observed; and the corresponding radical trapping products 7 and
Acknowledgements
8
could be detected, suggesting the involvement of cyanoalkyl
We are grateful to the NNSFC (21472058, 21472057, 21622201
and 21232003), the Science and Technology Department of
Hubei Province (2016CFA050 and 2017AHB047), and the
Program of Introducing Talents of Discipline to Universities of
China (111 Program, B17019) for support of this research.
radical 1a-A. Moreover, small amounts of 1,6-ketonitrile 4a’
could also be detected, which might result from radical
intermediate 1a-B in the presence of adventitious of oxygen.
To indentify the redox states of the copper catalyst that might be
involved in the reaction, we also employed EPR spectroscopy to
explore the redox process between Cu(I) complex and O-acyl
oxime ester 1a (Supporting Information, Figure S3). With addtion
[
8a]
Conflict of interest
of the 1a, the solution of Cu(CH
3 4 6
CN) PF /dtbbpy in DMF showed
obvious Cu(II) singals, which is in good agreement with the
[
19]
literature.
These results support the SET process between
The authors declare no conflict of interest.
Cu(I) complex and 1a.
According to these experimental results and previous
Keywords: visible light • copper catalysis • iminyl radicals •
[
7,8]
reports,
we proposed a Cu(I)/Cu(II)/Cu(III)-based catalytic
nitriles • radical cross-coupling
cycle with the model reaction as an example (Scheme 3). The
reaction begins with a SET-mediated reduction of O-acyl oxime
[
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1] a) F. Diederich, P. J. Stang, Eds.; Metal-catalyzed Cross-coupling
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1
a by both of the photoexcited LCu(II)* (path a) and ground state
LCu(II) species (path b), followed by fragmentation to give iminyl
radical 1a’, and oxidized LCu(II) species. As observed during the
optimization studies, visible light irradiation and ligand have
played an important role in accelerating the reaction. Then, iminyl
radical 1a’ undergoes the selective β-scission to generate
cyanoalkyl radical 1a-A that can be further trapped by
2
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elimination to give final product 4a. Notably, the whole process is
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1
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Scheme 3. Proposed reaction pathway.
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