Acyl radical smiles rearrangement to construct hydroxybenzophenones by photoredox catalysis

Article abstract of DOI:10.1021/acs.orglett.9b00353

The first visible-light-induced acyl radical Smiles rearrangement to transform biaryl ethers to hydroxybenzophenones under mild and metal-free conditions is reported. Using the dual catalysis of hypervalent iodine(III) reagents and organophotocatalysts, ketoacids readily generate acyl radicals and undergo 1,5-ipso addition. This method can construct electron-deficient and electron-rich hydroxybenzophenones with excellent chemoselectivity and on gram scale. The performance of the reaction in neutral aqueous conditions holds potential for future biomolecule applications.

Full text of DOI:10.1021/acs.orglett.9b00353

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Acyl Radical Smiles Rearrangement To Construct
Hydroxybenzophenones by Photoredox Catalysis
Junzhao Li,† Zhengyi Liu,† Shuang Wu,†,‡ and Yiyun Chen*,†,‡
†State Key Laboratory of Bioorganic and Natural Products Chemistry, Center for Excellence in Molecular Synthesis, Shanghai
Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road,
Shanghai 200032 China
‡School of Physical Science and Technology, ShanghaiTech University, 100 Haike Road, Shanghai 201210 China
S
* Supporting Information
ABSTRACT: The first visible-light-induced acyl radical
Smiles rearrangement to transform biaryl ethers to hydrox-
ybenzophenones under mild and metal-free conditions is
reported. Using the dual catalysis of hypervalent iodine(III)
reagents and organophotocatalysts, ketoacids readily generate
acyl radicals and undergo 1,5-ipso addition. This method can
construct electron-deficient and electron-rich hydroxybenzo-
phenones with excellent chemoselectivity and on gram scale.
The performance of the reaction in neutral aqueous
conditions holds potential for future biomolecule applications.
and heating conditions, which are not chemoselective and
enzophenones are an important class of natural products,
Bamong which the hydroxybenzophenones present widely incompatible with many functional groups.2,3 In addition, the
migratory aryl groups are limited to electron-deficient arenes,
while the electron-rich hydroxybenzophenones are not
applicable due to the nucleophilic character of the reaction.4
In contrast to ionic Smiles rearrangements, the radical
Smiles rearrangement provides alternative reactivity, which
may enable synthetic routes for both electron-deficient and
electron-rich hydroxybenzophenones.5 However, there is only
one isolated example using di-tert-butyl peroxides in refluxing
chlorobenzene to generate acyl radicals from aldehydes, in
which harsh reaction conditions compromised the functional
group compatibility of the reaction and resulted in moderate
yields for most substrates.6 From the bond energy data, the
cleavage of the CAr−O bond (78.8 kcal/mol) should be
compensated by the formation of the CAr−C bond (90.7−98.7
kcal/mol), such that no strong heating or strong oxidants
should be required.7 In this paper, we report the first visible-
light-induced acyl radical Smiles rearrangement reaction by
dual hypervalent iodine(III)/photoredox catalysis under mild
conditions, which is chemoselective and suitable for both
electron-deficient and electron-rich aryl migratory groups to
construct various hydroxybenzophenones (Scheme 1b).
and carry various bioactivities such as kinase inhibition,
antifungal, and anticancer activity (Scheme 1a).1 Truce−
Smiles rearrangement represents an effective approach to
synthesize benzophenones; however, the nucleophilic Truce−
Smiles rearrangement reactions typically require strong base
Scheme 1. Construction of Hydroxybenzophenones by Acyl
Radical Smiles Rearrangement
α-Ketoacids are readily available acyl synthons in organic
synthesis; however, its reactivity for 1,5-ipso addition is
unknown.8,9 We started the investigation with the ketoacid-
substituted biarylether 1a, which is not applicable for ionic
Smiles rearrangement with an electron-rich trimethylbenzene
migratory group. With [Ru(bpy)3](PF6)2 (0.02 equiv) and the
Received: January 28, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b00353
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
catalytic amount of cyclic iodine(III) reagent acetoxybenzio-
doxole (BIOAc) (0.2 equiv), we gladly observed the formation
of the desired hydroxybenzophenone 2a, but in low 32% yield
(entry 1 in Table 1). The use of cesium carbonate as base to
Scheme 2. Substrates Scope
Table 1. Optimization of the Acyl Radical Smiles
Rearrangement Reaction
c
c
entry
photocatalyst
additive conv (%) yield of 2a (%)
1
2
3
4
5
6
7
8
9
[Ru(bpy)3](PF6)2
[Ru(bpy)3](PF6)2
[Ir(ppy)2(dtbbpy)]PF6
BIOAc
Cs2CO3
BIOAc
BIOAc
PIDA
48
<5
34
>95
>95
<5
75
6
<5
<5
32
<5
12
87 (84)
74
<5
33
5
0
0
Acr-Mes+ClO4
−
Acr-Mes+ClO4
−
Acr-Mes+ClO4
PIFA
Na2CO3
−
Acr-Mes+ClO4
Acr-Mes+ClO4
−
−
BIOAc
BIOAc
b
Acr-Mes+ClO4
−
10
a
Reaction conditions: 1 (0.10 mmol, 1 equiv), photocatalysts (0.002
mmol, 0.02 equiv), and additive (0.02 mmol, 0.2 equiv) in 2.0 mL of
acetone under nitrogen with 4 W blue LED irradiation at 25 °C for 12
b
c
h, unless otherwise noted. Dark treatment. Conversions and yields
were determined by 1H NMR analysis, and isolated yields are in
parentheses. BI = benziodoxole.
replace BIOAc or the change to [Ir(ppy)2(dtbbby)]PF6
photocatalyst did not improve the reaction (entries 2 and
3).10 In contrast, the organic photocatalyst 9-mesityl-10-
a
b
c
d
e
Entry 4, Table 1. 16 h. 24 h. Acetone/HFIP = 1:1 as solvent. 0.4
f
equiv of BIOAc. 5.5 mmol scale.
−
methylacridinium perchlorate (Acr-Mes+ClO4 ) gave the
optimal 87% yield of 2a (84% isolated yield, entry 4).11 The
noncyclic iodine(III) phenyliodine(III) diacetate (PIDA) gave
slightly decreased 74% yield of 2a, while the phenyliodine
bis(trifluoroacetate) (PIFA) was ineffective (entries 5 and
of 2m due to the side products from decomposition. The
ketoacid scope was next explored, and various electron-rich or
electron-deficient aryl substitutions including methyl, methox-
yl, phenyl, halide, cyanide, alkynyl, and trifluoromethyl groups
were all tolerated to give 2n−u in 57−81% yields. We also
performed the gram-scale reaction with 1r, and the 2-
hydroxychlorobenzophenone 2r was obtained in 80% yield in
1.21 g.
6).12 The combination of Acr-Mes+ClO4 with sodium
−
carbonates for carboxylate anion formation only gave 2a in
33% yield, suggesting the unique role of hypervalent
iodine(III) for the transformation of ketoacids (entry
7).9c,d,13 The photocatalyst, cyclic iodine(III), and light are
all essential for the reaction (entries 8−10).
We next explored the scope of migratory aryl groups in
different substrates (Scheme 2). The ortho-substituted halides
1b−d gave fluoro-, chloro-, and bromo-substituted 2-
hydroxybenzophenones 2b−d smoothly in 72−87% yields.4
The para-substituted cyanide 1e and ester 1f gave the
corresponding products 2e,f in 73−77% yields. Significantly,
the reactive aldehyde group in NHC catalysis method was not
affected in this reaction condition to give 2g in 76% yield,14
and the nitro group is also tolerated to give 2h in 71% yield.15
The highly electron-rich 1i with dimethoxyl substitutions gave
2i in 76% yield, which widely presents in many bioactive
natural products but remains inaccessible with nucleophilic
Smiles rearrangement reactions.1,2b,c,3 The sterically hindered
diisopropyl substitution did not inhibit the reaction to give the
hindered 2j in 77% yield,16 which is very difficult to prepare
from cross-coupling reactions.17 The 2,4-dimethyl substitution
gave 58% yield of 2k.18 The bicyclic naphthalene 1l resulted in
56% yield of 2l, and quinolone 1m gave a decreased 26% yield
The reaction mechanism was then investigated by testing the
reaction of the preformed benziodoxole−ketoacid complex 3
(Scheme 3a).19 The formation of 2a in 60% yield without the
addition of BIOAc confirmed the critical role of the BI−
ketoacid complex for the reaction.9c,d,20 In addition, the
combination of the preformed benziodoxole−ketoacid com-
plex 3 (0.2 equiv) and the ketoacid 1a (0.8 equiv) afforded 2a
in 79% yield, which suggested the catalytic turnover of the
benziodoxole−ketoacid complex 3. We also measured the
cyclic voltammetry of the benziodoxole−ketoacid complex 3
and obtained the oxidation potential at 0.82 V, which was well
below the photoexcited Acr-Mes+* (E*red = 2.06 V).9c,21 The
cyclic voltammetry of benziodoxole−ketoacid complexes from
ketoacids 1f, 1h, and 1i were also measured, which were in the
range of 0.83−1.02 V. In contrast, the corresponding ketoacids
did not show peak anodic currents at these oxidation
potentials, which confirmed the benziodoxole coordination is
critical for the ketoacid oxidation.19
B
DOI: 10.1021/acs.orglett.9b00353
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
With the mild and metal-free reaction conditions, we next
tested the reaction under neutral aqueous conditions for
potential future biomolecule applications.9c,20d,25 In pH 7.4
phosphate-buffered saline (PBS) solutions with 1.0 equiv of
BI-OAc, the ketoacid-substituted biarylether 1a in 10 mM
concentration readily underwent the structure rearrangement
to give hydroxybenzophenone 2a in 66% yield, which will be
very valuable for the photomanipulation of bioactive molecule
in biological studies (eq 1).26
Scheme 3. Mechanistic Investigations of the Acyl Smiles
Rearrangement
In conclusion, we have developed the first acyl radical Smiles
rearrangement by dual hypervalent iodine(III)/photoredox
catalysis to transform various biarylethers to hydroxybenzo-
phenones. The metal-free reaction conditions are mild and
tolerate various functional groups, working with both electron-
deficient and electron-rich migratory aryl groups. The reaction
is suitable for gram-scale synthesis and works in neutral
aqueous reaction conditions, suggesting future preparative and
biomolecule applications.
The TEMPO was next added to the reaction conditions
(Scheme 3b). The complete inhibition of the reaction with the
acyl-TEMPO adduct 4 formation in 26% yield suggested the
acyl radical intermediate.21 The crossover experiment with 1j
and 1q resulted in the unscrambled products 2j and 2q, which
suggested the intramolecular acyl radical addition reactions
rather than the intermolecular reactions (Scheme 3c). The
quantum yield of the reaction was measured as 50% by the
standard ferrioxalate actinometry, which indicated the radical-
chain mechanism was unlikely.22
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.9b00353.
■
S
Mechanistic experiments, optimization tables, exper-
imental methods, and additional experimental data-
(PDF)
NMR spectra (PDF)
Based on the mechanistic investigations above, we propose
the reaction is initiated by the BI-ketoacid complex formation
in situ, which can be oxidized readily by the photoexcited Acr-
Mes+* to the ketoacid radical (Scheme 4).11a,23 The ketoacid
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: yiyunchen@sioc.ac.cn.
ORCID
Scheme 4. Mechanistic Proposals
Yiyun Chen: 0000-0003-0916-0994
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support was provided by National Natural Science
Foundation of China (21622207, 21472230, 91753126) and
the Strategic Priority Research Program of the Chinese
Academy of Sciences XDB20020200.
REFERENCES
■
(1) (a) Kulanthaivel, P.; Hallock, Y. F.; Boros, C.; Hamilton, S. M.;
Janzen, W. P.; Ballas, L. M.; Loomis, C. R.; Jiang, J. B.; Katz, B. J. Am.
Chem. Soc. 1993, 115, 6452−6453. (b) Whyte, A. C.; Gloer, J. B.;
Scott, J. A.; Malloch, D. J. Nat. Prod. 1996, 59, 765−769. (c) Krick,
A.; Kehraus, S.; Gerhauser, C.; Klimo, K.; Nieger, M.; Maier, A.;
Fiebig, H.-H.; Atodiresei, I.; Raabe, G.; Fleischhauer, J.; Konig, G. M.
radical then eliminates the carbon dioxide to form the acyl
radical I, and BI-OAc is released for the next catalytic
activation of ketoacids. The acyl radical I next undergoes 1,5-
ipso addition to form the dearomatized radical intermediate II,
which is in equilibrium with the CAr−O bond-cleaved phenoxyl
radical III. The radical intermediate II or III (phenoxyl radical
Ered ∼ 0.9 V) then undergoes single-electron reduction by the
Acr-Mes radical (Ered = −0.57 V) to form the hydroxybenzo-
phenone with the turnover of the Acr-Mes+ catalyst.11a,23,24
̈
̈
J. Nat. Prod. 2007, 70, 353−360.
(2) (a) Truce, W. E.; Ray, W. J.; Norman, O. L.; Eickemeyer, D. B. J.
Am. Chem. Soc. 1958, 80, 3625−3629. (b) Snape, T. J. Chem. Soc. Rev.
2008, 37, 2452−8. (c) Holden, C. M.; Greaney, M. F. Chem. - Eur. J.
2017, 23, 8992−9008.
C
DOI: 10.1021/acs.orglett.9b00353
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(3) Janssen-Muller, D.; Singha, S.; Lied, F.; Gottschalk, K.; Glorius,
2016, 6, 4983−4988. (c) Zuo, Z.; Ahneman, D. T.; Chu, L.; Terrett,
J. A.; Doyle, A. G.; MacMillan, D. W. C. Science 2014, 345, 437−440.
(d) Cassani, C.; Bergonzini, G.; Wallentin, C.-J. Org. Lett. 2014, 16,
4228−4231. (e) Griffin, J. D.; Zeller, M. A.; Nicewicz, D. A. J. Am.
Chem. Soc. 2015, 137, 11340−8. (f) Zhou, Q.-Q.; Guo, W.; Ding, W.;
Wu, X.; Chen, X.; Lu, L.-Q.; Xiao, W.-J. Angew. Chem., Int. Ed. 2015,
54, 11196−11199. (g) Le Vaillant, F.; Courant, T.; Waser, J. Angew.
Chem., Int. Ed. 2015, 54, 11200−11204.
F. Angew. Chem., Int. Ed. 2017, 56, 6276−6279.
́
(4) (a) Terrier, F. Chem. Rev. 1982, 82, 77−152. (b) Fernandez, I.;
Frenking, G.; Uggerud, E. J. Org. Chem. 2010, 75, 2971−2980.
(c) Jones, G. O.; Al Somaa, A.; O’Brien, J. M.; Albishi, H.; Al-Megren,
H. A.; Alabdulrahman, A. M.; Alsewailem, F. D.; Hedrick, J. L.; Rice,
J. E.; Horn, H. W. J. Org. Chem. 2013, 78, 5436−5443.
(5) (a) Studer, A.; Bossart, M. Tetrahedron 2001, 57, 9649−9667.
(b) Chen, Z. M.; Zhang, X. M.; Tu, Y. Q. Chem. Soc. Rev. 2015, 44,
5220−45. (c) Allart-Simon, I.; Gerard, S.; Sapi, J. Molecules 2016, 21,
878. (d) Li, W.; Xu, W.; Xie, J.; Yu, S.; Zhu, C. Chem. Soc. Rev. 2018,
47, 654−667. (e) Loven, R.; Speckamp, W. N. Tetrahedron Lett. 1972,
13, 1567−1570. (f) Motherwell, W. B.; Pennell, A. M. K. J. Chem. Soc.,
(14) (a) Flanigan, D. M.; Romanov-Michailidis, F.; White, N. A.;
Rovis, T. Chem. Rev. 2015, 115, 9307−9387. (b) Menon, R. S.; Biju,
A. T.; Nair, V. Chem. Soc. Rev. 2015, 44, 5040−5052.
(15) (a) Garrera, H. A.; Cosa, J. J.; Previtali, C. M. J. Photochem.
Photobiol., A 1991, 56, 267−274. (b) Wakasa, M.; Sakaguchi, Y.;
Nakamura, J.; Hayashi, H. J. Phys. Chem. 1992, 96, 9651−9656.
(c) Davies, J.; Booth, S. G.; Essafi, S.; Dryfe, R. A. W.; Leonori, D.
Angew. Chem., Int. Ed. 2015, 54, 14017−14021.
(16) The 1,6-ipso addition adduct was observed in 16% yield; see
the Supporting Information for details.
(17) (a) Chuzel, O.; Roesch, A.; Genet, J.-P.; Darses, S. J. Org. Chem.
2008, 73, 7800−7802. (b) Li, X.; Zou, G. Chem. Commun. 2015, 51,
5089−5092.
(18) The 1,6-epso addition adduct was obtained in 24% yield; see
the Supporting Information for details.
̈
Chem. Commun. 1991, 877−879. (g) Bossart, M.; Fassler, R.;
Schoenberger, J.; Studer, A. Eur. J. Org. Chem. 2002, 2002, 2742−
2757. (h) Gao, P.; Shen, Y. W.; Fang, R.; Hao, X. H.; Qiu, Z. H.;
Yang, F.; Yan, X. B.; Wang, Q.; Gong, X. J.; Liu, X. Y.; Liang, Y. M.
Angew. Chem., Int. Ed. 2014, 53, 7629−33. (i) Kong, W.; Merino, E.;
Nevado, C. Angew. Chem., Int. Ed. 2014, 53, 5078−82. (j) Ni, S.;
Zhang, Y.; Xie, C.; Mei, H.; Han, J.; Pan, Y. Org. Lett. 2015, 17,
5524−7. (k) Zheng, G.; Li, Y.; Han, J.; Xiong, T.; Zhang, Q. Nat.
Commun. 2015, 6, 7011. (l) Zhou, T.; Luo, F. X.; Yang, M. Y.; Shi, Z.
J. J. Am. Chem. Soc. 2015, 137, 14586−9. (m) Hossian, A.; Jana, R.
Org. Biomol. Chem. 2016, 14, 9768−9779. (n) Chen, S.; Li, D. Y.;
Jiang, L. L.; Liu, K.; Liu, P. N. Org. Lett. 2017, 19, 2014−2017.
(o) Wu, Z.; Wang, D.; Liu, Y.; Huan, L.; Zhu, C. J. Am. Chem. Soc.
2017, 139, 1388−1391. (p) Douglas, J. J.; Albright, H.; Sevrin, M. J.;
Cole, K. P.; Stephenson, C. R. J. Angew. Chem., Int. Ed. 2015, 54,
14898−14902. (q) Brachet, E.; Marzo, L.; Selkti, M.; Konig, B.;
Belmont, P. Chem. Sci. 2016, 7, 5002−5006. (r) Shu, W.; Genoux, A.;
Li, Z.; Nevado, C. Angew. Chem., Int. Ed. 2017, 56, 10521−10524.
(s) Wang, S. F.; Cao, X. P.; Li, Y. Angew. Chem., Int. Ed. 2017, 56,
13809−13813. (t) Monos, T. M.; McAtee, R. C.; Stephenson, C. R. J.
Science 2018, 361, 1369. (u) Wang, N.; Gu, Q.-S.; Li, Z.-L.; Li, Z.;
Guo, Y.-L.; Guo, Z.; Liu, X.-Y. Angew. Chem., Int. Ed. 2018, 57,
14225−14229.
(19) See the Supporting Information for details.
(20) (a) Togo, H.; Katohgi, M. Synlett 2001, 2001, 0565−0581.
(b) Xie, J.; Xu, P.; Li, H.; Xue, Q.; Jin, H.; Cheng, Y.; Zhu, C. Chem.
Commun. 2013, 49, 5672−5674. (c) He, Z.; Bae, M.; Wu, J.; Jamison,
T. F. Angew. Chem., Int. Ed. 2014, 53, 14451−14455. (d) Huang, H.;
Jia, K.; Chen, Y. Angew. Chem., Int. Ed. 2015, 54, 1881−4. (e) Yang,
B.; Xu, X. H.; Qing, F. L. Org. Lett. 2016, 18, 5956−5959. (f) Tang,
W. K.; Feng, Y. S.; Xu, Z. W.; Cheng, Z. F.; Xu, J.; Dai, J. J.; Xu, H. J.
Org. Lett. 2017, 19, 5501−5504. (g) Wang, D.; Zhang, L.; Luo, S. Org.
Lett. 2017, 19, 4924−4927. (h) Zhang, J.-J.; Cheng, Y.-B.; Duan, X.-
H. Chin. J. Chem. 2017, 35, 311−315. (i) Wang, J.; Li, G.-X.; He, G.;
Chen, G. Asian J. Org. Chem. 2018, 7, 1307−1310.
(21) Vogler, T.; Studer, A. Synthesis 2008, 2008, 1979−1993.
(22) Cismesia, M. A.; Yoon, T. P. Chem. Sci. 2015, 6, 5426−5434.
(23) Fukuzumi, S.; Kotani, H.; Ohkubo, K.; Ogo, S.; Tkachenko, N.
V.; Lemmetyinen, H. J. Am. Chem. Soc. 2004, 126, 1600−1601.
(24) Bordwell, F. G.; Cheng, J. J. Am. Chem. Soc. 1991, 113, 1736−
1743.
(6) Motherwell, W. B.; Vazquez, S. Tetrahedron Lett. 2000, 41,
9667−9671.
(7) (a) van Scheppingen, W.; Dorrestijn, E.; Arends, I.; Mulder, P.;
Korth, H.-G. J. Phys. Chem. A 1997, 101, 5404−5411. (b) Lias, S. G.;
Bartmess, J. E.; Liebman, J. F.; Holmes, J. L.; Levin, R. D.; Mallard, W.
G. J. Phys. Chem. Ref. Data 1988, 17, 1−861.
(8) (a) Rodríguez, N.; Goossen, L. J. Chem. Soc. Rev. 2011, 40,
5030−5048. (b) Gooßen, L. J.; Rudolphi, F.; Oppel, C.; Rodríguez,
N. Angew. Chem., Int. Ed. 2008, 47, 3043−3045. (c) Miao, J.; Ge, H.
Synlett 2014, 25, 911−919.
(25) (a) Hu, C.; Chen, Y. Tetrahedron Lett. 2015, 56, 884−888.
(b) Huang, H.; Zhang, G.; Gong, L.; Zhang, S.; Chen, Y. J. Am. Chem.
Soc. 2014, 136, 2280−2283. (c) Yang, J.; Zhang, J.; Qi, L.; Hu, C.;
Chen, Y. Chem. Commun. 2015, 51, 5275−5278. (d) Bloom, S.; Liu,
̈
C.; Kolmel, D. K.; Qiao, J. X.; Zhang, Y.; Poss, M. A.; Ewing, W. R.;
MacMillan, D. W. C. Nat. Chem. 2017, 10, 205. (e) Teders, M.;
(9) (a) Liu, J.; Liu, Q.; Yi, H.; Qin, C.; Bai, R.; Qi, X.; Lan, Y.; Lei, A.
Angew. Chem., Int. Ed. 2014, 53, 502−506. (b) Chu, L.; Lipshultz, J.
M.; MacMillan, D. W. C. Angew. Chem., Int. Ed. 2015, 54, 7929−
7933. (c) Huang, H.; Zhang, G.; Chen, Y. Angew. Chem., Int. Ed.
2015, 54, 7872−6. (d) Tan, H.; Li, H.; Ji, W.; Wang, L. Angew. Chem.,
Int. Ed. 2015, 54, 8374−8377. (e) Jia, K.; Pan, Y.; Chen, Y. Angew.
Chem., Int. Ed. 2017, 56, 2478−2481. (f) Mukherjee, S.; Garza-
Sanchez, R. A.; Tlahuext-Aca, A.; Glorius, F. Angew. Chem., Int. Ed.
2017, 56, 14723−14726. (g) Xu, S.-M.; Chen, J.-Q.; Liu, D.; Bao, Y.;
Liang, Y.-M.; Xu, P.-F. Org. Chem. Front. 2017, 4, 1331−1335.
(h) Zhang, X.; MacMillan, D. W. C. J. Am. Chem. Soc. 2017, 139,
11353−11356. (i) Zhang, M.; Xie, J.; Zhu, C. Nat. Commun. 2018, 9,
3517.
́
́
̈
Henkel, C.; Anhauser, L.; Strieth-Kalthoff, F.; Gomez-Suarez, A.;
Kleinmans, R.; Kahnt, A.; Rentmeister, A.; Guldi, D.; Glorius, F. Nat.
Chem. 2018, 10, 981−988. (f) The cosolvent (acetone or
acetonitrile) is used for the solubility of organic compounds.
(26) Wang, H.; Li, W.-G.; Zeng, K.; Wu, Y.-J.; Zhang, Y.; Xu, T.-L.;
Chen, Y. Angew. Chem., Int. Ed. 2019, 58, 561−565.
(10) Liu, M. S.; Huang, H. C.; Chen, Y. Y. Chin. J. Chem. 2018, 36,
1209−1212.
(11) (a) Romero, N. A.; Nicewicz, D. A. Chem. Rev. 2016, 116,
10075−10166. (b) Marzo, L.; Pagire, S. K.; Reiser, O.; Konig, B.
Angew. Chem., Int. Ed. 2018, 57, 10034−10072.
(12) Entries 4 and 5 of Table 1 with 0.4 equiv trifluoroacetic gave
significantly decreased 22% and 10% yields, respectively. See the
Supporting Information for details.
(13) (a) Xuan, J.; Zhang, Z.-G.; Xiao, W.-J. Angew. Chem., Int. Ed.
2015, 54, 15632−15641. (b) Huang, H.; Jia, K.; Chen, Y. ACS Catal.
D
DOI: 10.1021/acs.orglett.9b00353
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