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Green Chemistry
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Journal Name
ARTICLE
▪−
radical anion O2 reacts with intermediate A to generate
benzyl radical (B) and HOO▪ followed by radical-radical
coupling, or directly produced the peroxide C17 which has
been detected by HRMS analysis of the reaction mixture.
Protonation of C leads to the formation of the benzyl cation
(C) and H2O2.18 On the other hand, 2-acylimidazole (1)
undergoes fast ligand exchange with the copper(II) catalyst to
form enolate complex (E), which proceeds via a nucleophilic
attack on the electrophilic intermediate (D). The further ligand
exchange between neutral complex (F) and substrate 1 leads
to the formation of 3 in an enantioselective fashion and
regeneration of intermediate E.
Conflicts of interest
DOI: 10.1039/D0GC00262C
There are no conflicts to declare.
Acknowledgements
We gratefully acknowledge funding from the National Natural
Science Foundation of China (grant no. 21572184, 21671164),
the Natural Science Foundation of Fujian Province of China
(grant no. 2017J06006), and the Fundamental Research Funds
for the Central Universities (grant no. 20720190048).
Notes and references
O2
O2
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[CuI]
[CuII]
R2
photocatalysis
O2
HOO
R1
R2
R2
R1
R1
O
O
O
A
B
2
HOO
H
O
(R1 = R2 = H) detected
HRMS (ESI, m/z)
calcd for
C
H+
H2O2
O
R1
R2
R2
R1
C13H11O3 (M+H)+: 215.0703,
O
O
found: 215.0705
D
C
[CuII]
[CuII]
O
R4
O
O
N
asymmetric
catalysis
R4
[CuII]
R4
R2
N
N
NR3
R1
N
N
R3
R3
H+
O
E
F
1
- H+
1
3
Scheme 6 Plausible mechanism.
Conclusions
3 S. A. Girard, T. Knauber and C. Li, Angew. Chem. Int. Ed., 2014, 53, 74–100.
4 For selected examples of direct cross-dehydrogenative coupling of two C(sp3)−H
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Am. Chem. Soc., 2006, 128, 56–57; (d) R. Rocaroy, I. Anastasiou and O. Baudoin,
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Chen, C. Liu, W. Wu and H. Jiang, Angew. Chem. Int. Ed., 2017, 56, 13324–13328;
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Commun., 2019, 55, 7402–7405; (g) M. V. Leskinen, Á. Madarász, K-T Yip, A.
Vuorinen, I. Pápai, A. J. Neuvonen and P. M. Pihko, J. Am. Chem. Soc., 2014, 134,
6453–2507; (h) T. Tanaka, K. Hashiguchi, T. Tanaka, R. Yazaki and T. Ohshima,
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We have developed an effective and green strategy for
aerobic cross-dehydrogenative coupling reaction between
two C(sp3)−H bonds via copper-based asymmetric
photocatalysis. Good to excellent yields, enantioselectivity
and modest diastereoselectivity have been achieved.
Mechanistic studies reveal that the copper catalyst provides
both photoactivation to initiate the CDC reaction between
carbonyl compounds and xanthene derivatives, as well as
powerful asymmetric induction. This work demonstrates
potential applications of chiral copper catalysts in challenging
asymmetric photochemical transformations, and offers an
economic and easily-handled approach to stereoselective C−C
bond formation.
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