Visible-Light Photoredox-Catalyzed Iminyl Radical Formation by N-H Cleavage with Hydrogen Release and Its Application in Synthesis of Isoquinolines

Article abstract of DOI:10.1021/acs.orglett.8b00193

An unprecedented visible-light photoredox-catalyzed iminyl radical formation by N-H cleavage with H₂ release has been developed. Its application in the synthesis of various isoquinolines and related polyaromatics in high atom economy at ambient temperature by applying a photosensitizer, Acr⁺-Mes ClO₄^-, and a new cobalt catalyst, Co(dmgH)₂(4-CONMe₂Py)Cl is reported. Mechanistic investigations indicated that the generated iminyl radical initiates the cascade C-N/C-C bonds formation and the catalytic cycle occurs by a simultaneous oxidative as well as reductive quenching pathway.

Full text of DOI:10.1021/acs.orglett.8b00193

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Visible-Light Photoredox-Catalyzed Iminyl Radical Formation by
N−H Cleavage with Hydrogen Release and Its Application in
Synthesis of Isoquinolines
Wan-Fa Tian,†,‡,§ Dang-Po Wang,†,‡,§ Shao-Feng Wang,†,‡ Ke-Han He,‡ Xiao-Ping Cao,†
and Yang Li*,‡
†State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering, Lanzhou University,
Lanzhou 730000, P. R. China
‡Center for Organic Chemistry, Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi’an, Shaanxi 710054, P. R.
China
S
* Supporting Information
ABSTRACT: An unprecedented visible-light photoredox-catalyzed iminyl radical formation by N−H cleavage with H2 release
has been developed. Its application in the synthesis of various isoquinolines and related polyaromatics in high atom economy at
ambient temperature by applying a photosensitizer, Acr+-Mes ClO4 , and a new cobalt catalyst, Co(dmgH)2(4-CONMe2Py)Cl is
−
reported. Mechanistic investigations indicated that the generated iminyl radical initiates the cascade C−N/C−C bonds formation
and the catalytic cycle occurs by a simultaneous oxidative as well as reductive quenching pathway.
Scheme 1. Strategies for the Iminyl Radicals’ Formation and
Their Application
-Heterocycle motifs prevalently exist in bioactive
1
Ncompounds and organic functional materials.
Con-
sequently, the development of atom-economical methods for
their synthesis has been pursued for a long time.1 Among these
methods, cyclization of active nitrogen-centered radicals, such
as amidyl, hydrazonyl, and iminyl radicals, is one of the
important strategies.2 In particular, generation of these radicals
by N−H bond cleavage without the requirement of
stoichiometric oxidants is highly desirable. In the case of
amidyl radicals3a−d,f and hydrazonyl radicals,3e,g some examples
have been developed. However, generation of iminyl radicals in
this manner is rare. Until now, iminyl radicals were generated
by the cleavage of N−Y (Y = OR, N2, X, etc.) (Scheme 1a,
condition A) via thermochemistry or photochemistry.4
Alternatively, they were formed by N−H cleavage in the
presence of stoichiometric oxidants (Scheme 1a, condition B).5
Only recently, the Xu group demonstrated an elegant oxidant-
free iminyl radical formation by electrochemical H2 release
through the cleavage of N−H bonds to directly undergo
intramolecular cyclization for the synthesis of benzimidazoles
and pyridoimidazoles (Scheme 1a, condition C).6
and electrochemistry.3c,6,9 However, to the best of our
knowledge, the cascade construction of more than one
chemical bond is rare among these transformations.3c,8f,9c,e
We developed a visible-light photoredox-catalyzed iminyl
radical formation by N−H cleavage with H2 release in the
presence of a new cobalt catalyst. Its application in the synthesis
of various isoquinolines and related polyaromatics in high
atom-economy at ambient temperature by a cascade C−N/C−
H2 release coupling reactions demonstrate a nearly 100%
atom-economic strategy for constructing various chemical
bonds by thermochemistry,7 visible-light photoredox catalysis,8
Received: January 18, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b00193
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
C bonds construction is accomplished (Scheme 1b, eq 2). In
comparison with classic methods,10 the transition-metal-
catalyzed oxidative-11 and acceptorless-dehydrogenation annu-
lation by thermochemistry,7a,c a concise and high atom-
economic route, is developed at ambient temperature. The
preactivation of N−H or stoichiometric oxidants is avoided. In
addition, a new regioselectivity was observed.7c
Scheme 3. Substrate Scope of Various Ketimines
Continuing on our research around H2 release and
isoquinoline synthesis,7c,12 bis(4-methylphenyl)methanimine
(1a) and 1,2-diphenylacetylene (2a) were selected as model
substrates for synthesis of isoquinolines by photoredox catalysis
with H2 release (Scheme 2). By applying a photosensitizer (PS)
a
Scheme 2. Investigation of Various Cobalt Catalysts
a
Reaction conditions: 1 (0.1 mmol), 2a (0.2 mmol), optimized
conditions, 12 h, isolated yields were reported; H2 was detected by GC
b
using CH4 as an internal standard. The structure of major
c
regioisomer is shown. The ratio of the isomers was determined by
1
crude H NMR spectrum.
a
Scheme 4. Substrate Scope of Various Alkynes
a
1H NMR yield of 3aa was reported using Cl2CHCHCl2 as an internal
standard.The yield of H2 was detected by GC using CH4 as an internal
b
standard. Isolated yield.
Acr+-Mes ClO4− (5 mol %) and a catalyst Co(dmgH)2PyCl (5
mol %), 3aa was obtained in 32% yield with 24% H2 under blue
LED irradiation at ambient temperature (Table S1, entry 1).
Photosensitizers TPT and PDI resulted in lower yields (Table
S1, entries 2−3, ≤ 14%). The influence of solvents was studied.
Methanol totally inhibited the transformation (Table S1, entry
4). Dichloroethane (DCE) induced 3aa in 33% yield with 1%
H2, which should be explained by the DCE acting as an oxidant
(Table S1, entry 5).13 When DCM was applied as the solvent,
3aa was obtained in 40% yield with 31% H2 (Table S1, entry
6). Dilution of the substrate concentration (0.02 M based on
1a) and further improving the loadings of PS and catalyst to 10
mol % (Scheme 2, condition A) resulted in 3aa in 60% yield
with 57% H2. The substituent on the para position of the
pyridine moiety of the cobalt catalyst should effect the reaction
efficiency.
Thus, different cobalt catalysts bearing various substituents,
such as dimethylaminyl (−NMe2), methyl ester (−CO2Me),
N,N-dimethylamidyl (−CONMe2), and N,N-diethylamidyl
(−CONEt2), were investigated (Scheme 2, conditions B−E).
To our delight, the catalyst Co(dmgH)2(4-CONMe2Py)Cl led
to 3aa in 92% yield with 89% H2 (Scheme 2, condition D).
Control experiments showed that blue LED irradiation, PS, and
the cobalt catalyst are essential (Table S1, entries 10−12).
The substrate scope was investigated under optimized
conditions (Schemes 3−5). The biaryl ketimines bearing
electron-donating and weak electron-withdrawing groups on
the para position of the phenyl rings, such as from methyl and
methoxy to chloro, afforded products 3aa−da in high yields
(83−92%). Stronger electron-withdrawing groups, such as
fluoro and trifluoromethyl, decreased the reaction efficiencies to
some extent (3ea, 78%; 3fa, 63%). The trifluoromethyl ether
resulted in good reactivity (3ga, 60%). The methyl and chloro
on the meta position led to good efficiency (3ha and 3ha′,
76%; 3ia and 3ia′, 73%). In comparison with the steric effect,
a
Reaction conditions: 1a (0.1 mmol), 2 (0.2 mmol), optimized
conditions, 12 h, isolated yields were reported; H2 was detected by GC
using CH4 as an internal standard. p-Methylphenyl is abbreviated as
b
c
PMeP. 1H NMR yield was reported. The ratio of the isomers was
1
determined by the crude H NMR spectrum.
the influence of the electronic effect on the m-methyl acted as a
dominant role (3ha:3ha′ = 2.0:1.0). The m-chloro of the biaryl
ketamine displayed some steric effect (3ia/3ia′ = 1.3:1.0). The
methyl on the ortho position led to a decreased yield (3ja,
63%). When n-butyl and tert-butyl were investigated as the alkyl
substituents of the alkyl aryl ketimines, the reaction showed
moderate yields (3ka, 57%; 3ia, 51%).
Next, various biaryl alkynes were studied. When the
symmetric disubstituents on the para position of phenyl rings
of the diarylacetylenes were varied from methyls to fluoros,
obviously decreased reactivities were observed (3ab−ae, 85%−
46%). 1,2-Bis(4-(trifluoromethyl)phenyl)ethyne totally in-
hibited the transformation. Interestingly, applying a methyl
instead of one of the trifluoromethyls, the product was obtained
in excellent yield (3af, 90%). The observation of one
regioisomer should be explained by the distinctly biased
electronic property on the triple bond of the alkyne. Similar
results were observed for products 3ag and 3ag′, 3ah and 3ah′,
and 3ai and 3ai′. The disubstituents on the phenyl rings of the
diarylacetylenes were −CF3 with −H, −F with −CH3, and −Cl
B
DOI: 10.1021/acs.orglett.8b00193
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Letter
a
reaction mixture confirmed that only Acr+-Mes ClO4− acts as a
visible-light photosensitizer (Figure S1). Then, radical-trap
experiments were conducted by introducing 2,2,6,6-tetrameth-
yl-1-piperidinyloxy (TEMPO) as a radical capture reagent (eq
S2). Compound 3aa was obtained in 70% yield without
observation of radical capture and H2 release. This should be
attributed that the generated radicals are too active. TEMPO is
acted as the terminal oxidant in this transformation. To our
delight, when 1,2-diphenylethene was used instead, the desired
TEMPO captured compound 5, N-(1,2-diphenyl-2-((2,2,6,6-
tetramethylpiperidin-1-yl)oxy)ethyl)-1,1-di-p-tolylmethani-
mine, was obtained in 60% yield with a trace amount of H2 (eq
S3). Its formation should originate from the capture of the
benzyl radical, possiblely generated by the iminyl radical
addition to the double bond of 1,2-diphenylethene, by
TEMPO. This result indicates the possibility of iminyl radical
generation by N−H cleavage in the demonstrated conversion.
In addition, the quantum yield, Φ,15 was calculated to be 0.19.
At this stage, the data are inconclusive on whether the reaction
proceeded via a photoredox-catalytic pathway or a radical-chain
pathway.
Scheme 5. Substrate Scope of Polycyclic ketimines
a
Reaction conditions: 1 (0.1 mmol), 2 (0.2 mmol), optimized
conditions, 12 h, isolated yields were reported; H2 was detected by GC
using CH4 as an internal standard; the ratios of isomers were
b
determined by the isolated yields. Thermal ellipsoids are drawn at
30% probability with H atoms omitted for clarity.
The emission-quenching experiments showed that Co-
(dmgH)2(4-CONMe2Py)Cl, 1a, and 2a could quench the
excited photosensitizer Acr•-Mes•+ ClO4 (Figure S7). Mean-
−
with −Me, respectively. Regioselectivity was also observed on
products 3aj and 3aj′ (4.9:1.0) with the disubstituents of −H
and −CH3. The m-methyls on the phenyl rings of the
diarylacetylene resulted 3ak in excellent yield. However, the
o-methyls inhibited the reactivity by steric effect. The
trimethylsilane-substituted arylacetylene led to moderate yield
(3al, 48%).
while, no reactivity of 1,2-bis(4-methoxyphenyl)acetylene (6)
under optimized conditions as well as a larger quenching rate
than that of 1a and 2a were observed (Figure S7). These
phenomena suggest that generation of the corresponding
diarylacetylene radical cation inhibits iminyl radical formation,
while the diarylacetylene radical cation does not initiate the
catalytic cycle. This deduction is also supported by the
oxidation potentials of 1a, 2a, and 6 (E1a•+/1a = +1.62 V vs
SCE, E2a•+/2a = +1.86 V vs SCE, E6•+/6 = +1.28 V vs SCE, see
the SI) and the reported reduction potential of
EAcr•‑Mes•+ClO4−/Acr•‑MesClO4− as +2.06 V vs SCE.16 Obviously,
1a could undergo singe-electron transfer (SET) to the excited
Thus, naphthaleneyl- and phenanthryl-substituted ketimines
were further explored. The phenylnaphthalenyl ketimines
resulted in cyclization exclusively on the phenyl ring (3ma,
87%; 3na, 82%). When phenylphenanthryl-substituted keti-
mines were studied, besides the products of the cyclization on
the phenyl ring (3oa−oe), new regioselective products of the
cyclization on the phenanthryl rings (3oa′−oe′) were also
obtained in considerable amounts.7c The structure of 3oa′was
further confirmed by X-ray crystallography. Electron-donating
and weak electron-withdrawing groups on the phenyl rings of
the ketimines, as well as methyl and fluoro on the phenylrings
of 1,2-diphenylacetylenes, resulted in good reaction efficiency
(3oa, 3oa′−oe, 3oe′, 64−85%). A rough tendency was
observed that the ratio of the cyclized products on the
phenanthryl rings was increased (3oa′−ua′) when the
substituents on the phenyl rings varied from methyl and
methoxy to trifluoromethyl. This method affords a concise
route for synthesis of polycyclic aromatic compounds under
mild conditions.14
−
photosensitizer Acr•-Mes•+ ClO4 . The oxidation potential of
EAcr•‑MesClO4−/ Acr+‑MesClO4− was detected as −0.55 V vs SCE.16
The reduction potentials EIII/II and EII/I of the cobalt catalyst
were determined as −0.77 V vs SCE and −1.04 V vs SCE,
respectively. Thus, the SET between Acr•-Mes ClO4− and CoIII
or CoII is not favorable. On the other hand, based on the
reduction of O2 to O2 by the excite state of Acr•-Mes•+
•−
ClO4− (EO2•−/O2 = −0.87 V vs SCE),17 and the high quenching
−
rate of Acr•-Mes•+ ClO4 by Co(dmgH)2(4-CONMe2Py)Cl,
the SET from Acr•-Mes•+ ClO4 to the Co(III) is possible.
−
On the basis of the above results, a plausible reaction
mechanism is proposed in Scheme 7. Under blue LED
irradiation, Acr+-Mes ClO4 is excited to the state Acr•-Mes•+
−
−
To demonstrate the potential synthetic application, a gram-
scale reaction of 1a with 2a was performed with a lower
concentration (0.01 M based on 1a). Compound 3aa (1.65 g)
was achieved in 85% yield with 83% H2 using 5 mol % of Acr+-
ClO4 . The Mes•+ moiety is reductively quenched by 1a, and
the acridinyl radical moiety is oxidatively quenched by the CoIII
Scheme 7. Proposed Mechanism
−
Mes ClO4 and Co(dmgH)2(4-CONMe2Py)Cl (Scheme 6).
Subsequently, a series of experiments were conducted to give
insight into the reaction mechanism. First, the detection of the
UV−vis absorption spectrum of each component and the
Scheme 6. Gram-Scale Synthesis of 3aa
C
DOI: 10.1021/acs.orglett.8b00193
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Letter
simultaneously by two SETs to regenerate the ground-state
REFERENCES
■
Acr+-Mes ClO4 . Meanwhile, the iminyl radical 7, H+, and the
−
(1) Eicher, T.; Hauptmann, S.; Speicher, A. The Chemistry of
Heterocycles; Wiley-VCH: Weinheim, 2012.
(2) For selected reviews, see: (a) Fallis, A. G.; Brinza, I. M.
Tetrahedron 1997, 53, 17543. (b) Zard, S. Z. Chem. Soc. Rev. 2008, 37,
1603. (c) Chen, J.-R.; Hu, X.-Q.; Lu, L.-Q.; Xiao, W.-J. Chem. Soc. Rev.
2016, 45, 2044. (d) Xiong, T.; Zhang, Q. Chem. Soc. Rev. 2016, 45,
CoII are generated. 7 reacts with 2a to construct the C−N bond
to afford intermediate 8. 8 undergoes radical cyclization to
construct the C−C bond to give 3aa by intermediate 9 with the
release of an electron (e−) and the second H+. The CoII is
reduced to CoI by the released e−. The reaction of CoI with H+
gives CoIII−H, which further reacts with the second H+ to
release H2 to close the cobalt catalyst cycle. The reduction of
CoIII−H to CoII−H followed by protonation to release H2 and
produce CoII or the homolytic cleavage involving two CoIII−H
to evolve H2 can not be ruled out.18
In summary, we have developed the first visible-light
photoredox-catalyzed iminyl radical formation by N−H bond
cleavage with H2 release and its application in the synthesis of
isoquinolines and related polyaromatics in high atom economy
under ambient temperature. During the transformation, the
generated iminyl radical initiates cascade C−N/C−C bond
construction. The new cobalt catalyst Co(dmgH)2(4-CON-
Me2Py)Cl plays an important role in achieving the high
reaction efficiency and wide substrate scope. The advantages of
the established method will inspire the utilization of the iminyl
radical by visible light irradiation with H2 release for various N-
heterocycle synthesis.
3069. (e) Karkas, M. D. ACS Catal. 2017, 7, 4999.
̈
̈
(3) For selected samples by electrochemistry, see: (a) Xu, H.-C.;
Moeller, K. D. J. Am. Chem. Soc. 2010, 132, 2839. (b) Gieshoff, T.;
Schollmeyer, D.; Waldvogel, S. R. Angew. Chem., Int. Ed. 2016, 55,
9437. (c) Hou, Z.-W.; Mao, Z.-Y.; Zhao, H.-B.; Melcamu, Y. Y.; Lu, X.;
Song, J.; Xu, H.-C. Angew. Chem., Int. Ed. 2016, 55, 9168. (d) Xiong,
P.; Xu, H. H.; Xu, H.-C. J. Am. Chem. Soc. 2017, 139, 2956. For
selected samples by visible-light photoredox catalysis, see: (e) Hu, X.-
Q.; Chen, J.-R.; Wei, Q.; Liu, F.-L.; Deng, Q.-H.; Beauchemin, A. M.;
Xiao, W.-J. Angew. Chem., Int. Ed. 2014, 53, 12163. (f) Choi, G. J.;
Knowles, R. R. J. Am. Chem. Soc. 2015, 137, 9226. (g) Brachet, E.;
Marzo, L.; Selkti, M.; Konig, B.; Belmont, P. Chem. Sci. 2016, 7, 5002.
̈
(4) For selected samples about thermochemistry, see: (a) Forrester,
A. R.; Gill, M.; Sadd, J. S.; Thomson, R. H. J. Chem. Soc., Perkin Trans.
1 1979, 1, 612. (b) Uchiyama, K.; Hayashi, Y.; Narasaka, K. Chem. Lett.
1998, 27, 1261. (c) Lin, X.; Stien, D.; Weinreb, S. M. Org. Lett. 1999,
1, 637. For selected samples by photochemistry, see: (d) Boivin, J.;
Fouquet, E.; Zard, S. Z. Tetrahedron Lett. 1991, 32, 4299. (e) Jiang, H.;
An, X.; Tong, K.; Zheng, T.; Zhang, Y.; Yu, S. Angew. Chem., Int. Ed.
2015, 54, 4055. (f) Davies, J.; Booth, S. G.; Essafi, S.; Dryfe, R. A.;
Leonori, D. Angew. Chem., Int. Ed. 2015, 54, 14017. (g) Sun, X.; Yu, S.
Chem. Commun. 2016, 52, 10898. (h) Shu, W.; Nevado, C. Angew.
Chem., Int. Ed. 2017, 56, 1881. (i) Jiang, H.; Studer, A. Angew. Chem.,
Int. Ed. 2017, 56, 12273. (j) Davies, J.; Sheikh, N. S.; Leonori, D.
Angew. Chem., Int. Ed. 2017, 56, 13361. (k) Yu, X.-Y.; Chen, J.-R.;
Wang, P.-Z.; Yang, M.-N.; Liang, D.; Xiao, W.-J. Angew. Chem., Int. Ed.
2018, 57, 738. For selected reviews, see: (l) Walton, J. C. Molecules
2016, 21, 63. (m) Walton, J. C. Molecules 2016, 21, 660. (n) Jackman,
M.; Cai, Y.; Castle, S. Synthesis 2017, 49, 1785.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b00193.
Experimental procedure, product characterization, and
spectral data (PDF)
(5) (a) Zhang, L.; Ang, G. Y.; Chiba, S. Org. Lett. 2010, 12, 3682.
(b) Li, D.; Yang, T.; Su, H.; Yu, W. Adv. Synth. Catal. 2015, 357, 2529.
(6) Zhao, H.-B.; Hou, Z.-W.; Liu, Z.-J.; Zhou, Z.-F.; Song, J.; Xu, H.-
C. Angew. Chem., Int. Ed. 2017, 56, 587.
Accession Codes
CCDC 1576204 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_
request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: +44 1223 336033.
(7) For selected samples, see: (a) He, R.; Huang, Z.-T.; Zheng, Q.-Y.;
Wang, C. Angew. Chem., Int. Ed. 2014, 53, 4950. (b) Zhou, A.-X.; Mao,
L.-L.; Wang, G.-W.; Yang, S.-D. Chem. Commun. 2014, 50, 8529.
(c) He, K.-H.; Zhang, W.-D.; Yang, M.-Y.; Tang, K.-L.; Qu, M.; Ding,
Y.-S.; Li, Y. Org. Lett. 2016, 18, 2840. (d) Li, W.-H.; Wu, L.; Li, S.-S.;
Liu, C.-F.; Zhang, G.-T.; Dong, L. Chem. - Eur. J. 2016, 22, 17926.
(e) Manikandan, R.; Madasamy, P.; Jeganmohan, M. ACS Catal. 2016,
6, 230. (f) Chen, C.; Chen, X.; Zhao, H.; Jiang, H.; Zhang, M. Org.
Lett. 2017, 19, 3390. (g) Lv, N.; Liu, Y.; Xiong, C.; Liu, Z.; Zhang, Y.
Org. Lett. 2017, 19, 4640.
(8) For selected samples and reviews, see: (a) Mitkina, T.;
Stanglmair, C.; Setzer, W.; Gruber, M.; Kisch, H.; Konig, B. Org.
Biomol. Chem. 2012, 10, 3556. (b) Meng, Q.-Y.; Zhong, J.-J.; Liu, Q.;
Gao, X.-W.; Zhang, H.-H.; Lei, T.; Li, Z.-J.; Feng, K.; Chen, B.; Tung,
C.-H.; Wu, L.-Z. J. Am. Chem. Soc. 2013, 135, 19052. (c) Li, X.-B.; Li,
Z.-J.; Gao, Y.-J.; Meng, Q.-Y.; Yu, S.; Weiss, R. G.; Tung, C.-H.; Wu,
L.-Z. Angew. Chem., Int. Ed. 2014, 53, 2085. (d) Zhang, G.; Liu, C.; Yi,
H.; Meng, Q.; Bian, C.; Chen, H.; Jian, J.-X.; Wu, L.-Z.; Lei, A. J. Am.
Chem. Soc. 2015, 137, 9273. (e) Zhang, G.; Hu, X.; Chiang, C.-W.; Yi,
H.; Pei, P.; Singh, A. K.; Lei, A. J. Am. Chem. Soc. 2016, 138, 12037.
(f) Zhao, Q.-Q.; Hu, X.-Q.; Yang, M.-N.; Chen, J.-R.; Xiao, W.-J.
Chem. Commun. 2016, 52, 12749. (g) Lin, J.; Li, Z.; Kan, J.; Huang, S.;
Su, W.; Li, Y. Nat. Commun. 2017, 8, 14353. (h) Zhong, J.-J.; Meng,
Q.-Y.; Chen, B.; Tung, C.-H.; Wu, L.-Z. Huaxue Xuebao 2017, 75, 34.
(i) Pei, P.; Zhang, F.; Yi, H.; Lei, A. Huaxue Xuebao 2017, 75, 15. For
selected reviews of visible-light photoredox catalysis, see: (j) Prier, C.
K.; Rankic, D. A.; MacMillan, D. W. Chem. Rev. 2013, 113, 5322.
(9) For selected samples, see: (a) Qian, X.-Y.; Li, S.-Q.; Song, J.; Xu,
H.-C. ACS Catal. 2017, 7, 2730. (b) Wang, P.; Tang, S.; Huang, P.;
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: liyang79@mail.xjtu.edu.cn.
ORCID
Xiao-Ping Cao: 0000-0001-8340-1122
Yang Li: 0000-0003-4724-4785
Author Contributions
§W.-F.T. and D.-P.W. contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the NSFC (Nos. 21472145 and
21572085), the Fundamental Research Funds for the Central
Universities (xjj2015099), and the 111 Project of MOE (111-2-
17). We thank Prof. Ya-Ping Du and Prof. Gang He, Xi’an
Jiaotong University, for support on related experiments.
D
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Lei, A. Angew. Chem., Int. Ed. 2017, 56, 3009. (c) Wang, P.; Tang, S.;
Lei, A. Green Chem. 2017, 19, 2092. (d) Wu, Z.-J.; Xu, H.-C. Angew.
Chem., Int. Ed. 2017, 56, 4734. (e) Liu, K.; Tang, S.; Huang, P.; Lei, A.
Nat. Commun. 2017, 8, 775. (f) Hou, Z.-W.; Mao, Z.-Y.; Song, J.; Xu,
H.-C. ACS Catal. 2017, 7, 5810. (g) Tang, S.; Liu, Y.; Lei, A. Chem.
2018, 4, 27.
(10) Li, J.-J.; Corey, E. J. In Name Reactions in Heterocyclic Chemistry;
John Wiley & Sons: Hoboken, NJ, 2005; p 375.
(11) For selected reviews, see: (a) He, R.; Huang, Z.-T.; Zheng, Q.-
Y.; Wang, C. Tetrahedron Lett. 2014, 55, 5705. (b) Huang, H.; Ji, X.;
Wu, W.; Jiang, H. Chem. Soc. Rev. 2015, 44, 1155.
(12) (a) He, K.-H.; Li, Y. ChemSusChem 2014, 7, 2788. (b) He, K.
H.; Tan, F.-F.; Zhou, C.-Z.; Zhou, G.-J.; Yang, X.-L.; Li, Y. Angew.
Chem., Int. Ed. 2017, 56, 3080.
(13) Nagano, T.; Hayashi, T. Org. Lett. 2005, 7, 491.
(14) Stepien, M.; Gonka, E.; Zyla, M.; Sprutta, N. Chem. Rev. 2017,
117, 3479.
(15) (a) Cismesia, M. A.; Yoon, T. P. Chem. Sci. 2015, 6, 5426.
(b) Majek, M.; Jacobi von Wangelin, A. Acc. Chem. Res. 2016, 49,
2316.
(16) (a) Fukuzumi, S.; Ohkubo, K.; Suenobu, T. Acc. Chem. Res.
2014, 47, 1455. (b) Margrey, K. A.; Nicewicz, D. A. Acc. Chem. Res.
2016, 49, 1997.
(17) (a) Sawyer, D. T.; Calderwood, T. S.; Yamaguchi, K.; Angelis, C.
T. Inorg. Chem. 1983, 22, 2577. (b) Fukuzumi, S.; Ohkubo, K. Chem.
Sci. 2013, 4, 561.
(18) (a) Dempsey, J. L.; Brunschwig, B. S.; Winkler, J. R.; Gray, H. B.
Acc. Chem. Res. 2009, 42, 1995. (b) Lazarides, T.; McCormick, T.; Du,
P.; Luo, G.; Lindley, B.; Eisenberg, R. J. Am. Chem. Soc. 2009, 131,
9192.
E
DOI: 10.1021/acs.orglett.8b00193
Org. Lett. XXXX, XXX, XXX−XXX