A facile access for multisubstituted trifluoromethyl olefins by visible light catalysis

Article abstract of DOI:10.1016/j.tetlet.2021.152829

Induced by visible light, a green approach for the highly substituted trifluoromethyl olefins has been developed by using alkyl boronic acid as a carbon radical precursor and the Boc-modified trifluoromethylated Baylis-Hillman adduct (BMTBHA) as an accept

Full text of DOI:10.1016/j.tetlet.2021.152829

Tetrahedron Letters 66 (2021) 152829
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
A facile access for multisubstituted trifluoromethyl olefins by visible
light catalysis
a,
a,
Shujian Ren a, Jiahui Fu a, Dongping Cheng b, , Xiaonian Li , Xiaoliang Xu
⇑
⇑
⇑
a College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, PR China
b College of Pharmaceutical Science, Zhejiang University of Technology, Hangzhou 310014, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Induced by visible light, a green approach for the highly substituted trifluoromethyl olefins has been
developed by using alkyl boronic acid as a carbon radical precursor and the Boc-modified trifluoromethy-
lated Baylis-Hillman adduct (BMTBHA) as an acceptor. This method starts from 1,1-disubstituted olefins
without the external stoichiometric oxidant.
Received 29 October 2020
Revised 20 December 2020
Accepted 4 January 2021
Available online 26 January 2021
Ó 2021 Elsevier Ltd. All rights reserved.
Keywords:
Visible light photocatalysis
Alkylboronic acids
Multisubstituted trifluoromethyl olefin
Introduction
which strongly limits its application in organic synthesis
(Scheme 1). Concerning the importance of trifluoromethyl olefins,
The introduction of fluorine atoms into the molecular skeleton
can greatly change the physical and chemical properties of organic
compounds and polymers [1]. The fluorinated molecules occupy an
increasingly important position in drug molecules due to their
excellent chemical stability and lipophilicity [2]. However, it’s rare
to find fluorinated molecules in natural products, and most of flu-
orine-containing drugs must be synthesized artificially. Trifluo-
romethyl olefins are not only a class of important drug structural
units, but also important substrates for C-F activation [3]. In the
past 10 years, the synthesis of trifluoromethyl olefins has aroused
great interest. Normally, cross-coupling is a major way for the con-
struction of vinyl-CF3 [4], which heavily relies on the use of pre-
functionalized olefins. And the commonly used trifluoromethyl
reagents such as Umemoto’s reagent, Togni’s reagent, CF3 surro-
gates and etc. have high price with poor atom economy [5].
Recently, some works have been focused on bifunctionalization
of alkynes and direct trifluoromethylation of olefinic CAH bonds to
form highly substituted trifluoromethyl olefins [6], in which both
transition metal catalysts and stoichiometric strong oxidants are
necessary. Debien et al. proposed the synthesis of multisubstituted
trifluoromethyl olefins by the carbon–oxygen bond homolysis in
2012 [7], however, the preparation of highly functional substrate
was troublesome and bulky leaving group led low atom economy,
developing greener and more easily operable method for accessing
such compound is still in urgent need.
Visible-light mediated photocatalysis has emerged as a power-
ful synthetic tool in organic chemistry for the last decade [8]. Its
unique performance has realized a variety of chemical transforma-
tions, and plays an irreplaceable role in the construction of special
organic compounds which could not be accomplished by tradi-
tional methods. The types of visible-light-catalyzed reactions
include amine oxidation [9], organic boron oxidation [10], reduc-
tion dehalogenation [11], double bond reduction [12], ATRP reac-
tion [13], and etc. Especially, the formation of
a-amino carbon
radical by visible light catalytic oxidation and the formation of
CAC and CAB bond by the visible light catalytic oxidation of
organic boron reagent are typical representatives. Recently we
published several results about the applications of Baylis-Hillman
adducts in the field of visible light catalysis [14]. With the contin-
uous interest in the photocatalysis and the importance of trifluo-
romethyl olefins, the Boc-modified trifluoromethylated Baylis-
Hillman adduct 1 (BMTBHA) was prepared and subjected for study.
BMTBHA could be obtained easily from a stable and commonly
used industrial feedstock 2-bromo-3,3,3-trifluoroprop-1-ene
(BTP) and aldehyde promoted by zinc powder [15] and then pro-
tected by (Boc)2O. Considering the particularity of trifluoromethyl
group and its stronger electron withdrawing capacity, we proposed
that 1 is more vulnerable to be competitive nucleophilic attacked
between leaving group and coupling partner than traditional
Baylis-Hillman adducts. And the selectivity of defluorination and
⇑
Corresponding authors.
E-mail addresses: chengdp@zjut.edu.cn (D. Cheng), xnli@zjut.edu.cn (X. Li),
xuxiaoliang@zjut.edu.cn (X. Xu).
https://doi.org/10.1016/j.tetlet.2021.152829
0040-4039/Ó 2021 Elsevier Ltd. All rights reserved.

S. Ren, J. Fu, D. Cheng et al.
Tetrahedron Letters 66 (2021) 152829
leaving group’s removal is unclear because of the formation of
trifluoromethyl carbanion [16]. Recently, our group has explored
the coupling -trifluoromethyl aryl olefins with boronic acid
a-
a
through photocatalysis/Lewis base dual catalysis [17]. Upon check-
ing the literatures, there were few researches [18] on the synthesis
of trifluoromethyl olefins via double bond transfer, and there have
no literatures reporting the synthesis of highly substituted trifluo-
romethyl olefins by photocatalysis (Scheme 2).
Result and discussion
In order to realize the viability of the reaction, a model reaction
employing tert-butyl (1-phenyl-2-(trifluoromethyl)allyl) carbonate
(1a, 0.5 mmol), cyclohexylboronic acid (2a, 0.75 mmol), DABCO
(0.125 mmol), PC1 (1.0 mol %), and DCE (6 mL) was carried out
in a Schlenk tube with 7 W blue LED. Delightfully, the desired 3a
was isolated in 49% yield within 5 h (Table 1, entry 1). Inspired
by this result, photocatalyst, solvent, and Lewis base were then
investigated. Only activated alkyl boronic acid could be oxidized
by excited PC1. The solvents such as DCM, THF, DMF, NMP, and
DMSO were tried and the results were negative, compared with
that of DCE (entries 4–9). A brief screen of bases revealed that
DMAP, DBU, DBN, PPh3 (entries 10–13) are not as effective as that
of DABCO, although there was still more than 39% of 1a left (entry
1). Considering that boronic acid could be transformed to borate
ether or borate ester in methanol [19], which were easily combined
with Lewis base, different volumes of methanol were added into
Scheme 1. General ways for trifluoromethyl olefins.
Scheme 2. Two possible reaction paths of 1.
Table 1
Optimization of the reaction conditions.a
Entry
Catalyst
Lewis base
Additive
Solvent
Yield(%)a
1
2
3
4
5
6
7
8
PC1
PC2
PC3
PC1
PC1
PC1
PC1
PC1
PC1
PC1
PC1
PC1
PC1
PC1
PC1
PC1
PC1
PC1
PC1
–
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DMAP
DBU
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
DCE
DCE
DCE
DCM
THF
MeCN
NMP
DMF
DMSO
DCE
DCE
DCE
DCE
DCE:MeOH(1:1)
DCE:MeOH(4:1)
DCE:MeOH(9:1)
49(30:19)
0
0
24(15:19)
25(16:9)
7(5:2)
23(13:10)
11(7:4)
19(13:6)
0
17(10:7)
14(8:6)
0
9
10
11
12
13
14
15
16
17b
18b
19b
20
21
22d
DBN
PPh3
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
–
Trace
Trace
Trace
50(31:19)
Na2CO3
K2CO3
Cs2CO3
–
–
–
DCE
DCE
DCE
DCE
DCE
DCE
73(45:28)
82(54:28)(74)c(2.16:1)
0
0
0
PC1
PC1
DABCO
a
General condition: 1a (0.5 mmol), 2a (0.75 mmol), PC1(1 mol%), Lewis base (0.125 mmol), solvent (6 mL), 7 W blue LED, N2 atmosphere, PC1 = Ir(dFCF3ppy)2(dtbbpy)PF6,
PC2 = Ir(ppy)2(dtbbpy)PF6 PC3 = Ir(ppy)3, the E/Z ratio was determined by GC.
b
0.125 mmol (0.25 eq) of additive.
Isolated yield.
In the dark.
c
d
2

S. Ren, J. Fu, D. Cheng et al.
Tetrahedron Letters 66 (2021) 152829
Table 2
Scope of the present photocatalytic method for multisubstituted trifluoromethyl
olefins.a
Scheme 3. A plausible reaction mechanism.
ever, BMTBHA bearing p-CF3 group on the aromatic ring (3q) was
unreactive under the standard condition. The presence of elec-
tron-donating groups on the aromatic ring of BMTBHA were bene-
fit for the reaction and gave moderate yields. Only trace amount of
product was obtained from the substrate containing naphthyl (3p).
The yield of aliphatic BMTBHA substrate (3o) was moderate. Then
different substituted boronic acids were explored. The yields were
slight lower when primary alkyl boronic acids were selected as
candidates (3r-3s), which has great relationship with the stability
of the primary carbon radical. When the cyclic alkyl boronic acids
such as cyclobutyl, cyclopentyl, cyclohexyl boronic acid (3a,3u-3v)
were used, the yields of corresponding products were increased.
Tetrahydropyrrole 2-borate protected by N-Boc (3w) was suitable
for the reaction and only E-isomer was produced, which could be
the result of steric effect and the stabilization effect of nitrogen
atom on ortho carbon radicals. Unfortunately, aromatic boronic
acid was unreactive under the standard conditions, and the addi-
tion of methanol also could not change the result.
In order to further understand the reaction mechanism, 3 eq of
Tempo was added into the reaction system. No product was
detected by TLC, and the peak of tempo-cyclohexyl couldn’t be
found in GC–MS, which may be contributed to the inhibition of cat-
alytic cycle in the presence of excessive Tempo. Based on the liter-
atures [10,19] and our above experiments, the reaction mechanism
is hypothesized. Firstly, boronic acid is activated by Lewis base and
oxidized by the excited PC1 under the irradiation of blue LEDs.
Then the generated free radical goes through the nucleophilic addi-
tion to BMTBHA, and the radical intermediate is further reduced by
the PC1. Finally, the product generates after leaving the OBoc group
(Scheme 3).
aGeneral condition: 1a (0.5 mmol), 2a (0.75 mmol), PC (1 mol%), Lewis base
(0.125 mmol), solvent (6 mL), 7 W blue LED, N2 atmosphere, the E/Z ratio was
determined by NMR analysis of the product.
DCE. Unexpectedly, the reaction was inhibited by even a very small
amount of methanol (entries 14–16), which was quite different
from the literature’s report. We inferred the possibility is that
tert-butoxide anion on the one hand combined with boronic acid
to regenerate DABCO, and on the other hand was protonated by
the residual water in the system to form tert-butyl alcohol after
CO2 removal from BocO-. No further improvement was achieved
with increased equivalent of DABCO and boronic acid. Further-
more, the inorganic bases carbonates were surveyed. 1a could be
totally transformed to 3a in 74% yield when 0.25 eq Cs2CO3 was
added. since Cs2CO3 is almost insoluble in DCE, the reactions with
Cs2CO3 in other solvents were studied and it can be concluded that
the reaction results in larger polar solvents such as DMSO, DMF,
NMP, MeCN, acetone were not as good as it in DCE. The presence
of photocatalyst, visible light and Lewis base was essential to the
reaction (entries 20–22). The by-product of defluorination or the
competitive nucleophilic attack of tert-butoxide anion was not
observed. The acetyl instead of Boc-modified trifluoromethylated
Baylis-Hillman adduct was not effective in this reaction. Based on
this and the previous reports, [14] it can conclude that BMTBHA
is completely different from conventional Baylis-Hillman adducts
from the reaction characteristics and activity. The Z/E configura-
tion was determined by 2D NOE spectrum (See the Supporting
Information for details).
Conclusions
In conclusion, we have developed a facile method for the syn-
thesis of trifluoromethyl olefins by visible light catalysis. Com-
pared with other methods, this method has the following
advantages: (1) it can react at normal temperature and pressure
with good substrate tolerance, and the driving power of reaction
is green and easily available visible light. (2) Only small amounts
of Lewis base and inorganic base are needed.
Under the optimized conditions, the generality and scope of
substrates were subjected to this reaction. Various Structurally dif-
ferent BMTBHA could react smoothly with cyclohexyl boronic acid
to afford the target products (3b-3e) in high yields (Table 2). How-
3

S. Ren, J. Fu, D. Cheng et al.
Tetrahedron Letters 66 (2021) 152829
(f) H. Tang, Y. Kuang, J. Zeng, X. Li, W. Zhou, Y. Lu, RSC Adv. 9 (2019) 31474;
(g) T. Shang, J. Zhang, Y. Zhang, F. Zhang, X. Li, G. Zhu, Org. Lett. 22 (2020)
3667;
(h) G. Liu, X. Zhang, G. Kuang, N. Lu, Y. Fu, Y. Peng, Q. Xiao, Y. Zhou, ACS Omega
5 (2020) 4158;
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
(i) S. Tanaka, Y. Nakayama, Y. Konishi, T. Koike, M. Akita, Org. Lett. 22 (2020)
2801;
(j) S. Qi, S. Gao, X. Xie, J. Yang, J. Zhang, Org. Lett. 22 (2020) 5229;
(k) R. Tomita, Y. Yasu, T. Koike, M. Akita, Beilstein J. Org. Chem. 10 (2014)
1099;
Acknowledgments
(l) L. Wu, K. Zhao, Z. Shen, T.P. Loh, Org. Chem. Front. 4 (2017) 1872;
(m) C. Yang, A. Hassanpour, K. Ghorbanpour, S. Abdolmohammadi, E. Vessally,
RSC Adv. 9 (2019) 27625.
This work was supported by Natural Science Foundation of Zhe-
jiang Province (No. LY18B020018) and National Natural Science
Foundation of China (No. 21602197).
[7] L. Debien, B. Quiclet-Sire, S.S. Zard, Org. Lett. 14 (2012) 5118.
[8] (a) F. Teply´, Collect. Czech. Chem. Commun. 76 (2011) 859;
(b) J.W. Tucker, C.R. Stephenson, J. Org. Chem. 77 (2012) 1617;
(c) C.K. Prier, D.A. Rankic, D.W. MacMillan, Chem. Rev. 113 (2013) 5322;
(d) I. Ghosh, M.L. Das, A., Shaikh, R., König, B, Acc. Chem. Res. 49 (2016) 1566;
(e) X. Pan, H. Xia, J. Wu, Org. Chem. Front. 3 (2016) 1163;
(f) K.L. Skubi, T.R. Blum, T.P. Yoon, Chem. Rev. 116 (2016) 10035;
(g) A. Savateev, M. Antonietti, ACS Catal. 8 (2018) 9790;
(h) Y. Chen, L. Lu, D. Yu, C. Zhu, W. Xiao, Sci. China Chem. 62 (2019) 24;
(i) J. Chen, J. Cen, X. Xu, X. Li, Catal. Sci. Technol. 6 (2016) 349;
(j) X. Yu, J. Chen, W. Xiao, Chem. Rev. (2020), https://doi.org/10.1021/acs.
chemrev.0c00030;
Appendix A. Supplementary data
Supplementary data (copies of 1H NMR, 13C NMR spectra of all
products) to this article can be found online at https://doi.org/10.
1016/j.tetlet.2021.152829.
References
(k) H. Yi, G. Zhang, H. Wang, Z. Huang, J. Wang, A.K. Singh, A. Lei, Chem. Rev.
117 (2017) 9016.
[9] (a) A. McNally, C.K. Prier, D.W. MacMillan, Science 334 (2011) 1114;
(b) A. Noble, D.W. MacMillan, J. Am. Chem. Soc. 136 (2014) 11602;
(c) J. Xuan, T. Zeng, Z. Feng, Q. Deng, J. Chen, L. Lu, W. Xiao, H. Alper, Angew.
Chem. Int. Ed. 54 (2015) 1625;
[1] (a) M. Schlosser, Angew. Chem. Int. Ed. 45 (2006) 5432;
(b) D. O’Hagan, Chem. Soc. Rev. 37 (2008) 308;
(c) F. Meyer, Chem. Commun. 52 (2016) 3077;
(d) Y. Zhou, J. Wang, Z. Gu, S. Wang, W. Zhu, J.L. Aceña, V.A. Soloshonok, K.
Izawa, H. Liu, Chem. Rev. 116 (2016) 422.
(d) J. Xie, S. Shi, T. Zhang, N. Mehrkens, M. Rudolph, A.S.K. Hashmi, Angew.
Chem. Int. Ed. 54 (2015) 6046;
(e) K. Nakajima, Y. Miyake, Y. Nishibayashi, Acc. Chem. Res. 49 (2016) 1946;
(f) W. Zhou, G. Cao, G. Shen, X. Zhu, Y. Gui, J. Ye, L. Sun, Li Liao, J. Li, D. Yu,
Angew. Chem. Int. Ed. 56 (2017) 15683;
(g) J. Li, Z. Gu, X. Zhao, B. Qiao, Z. Jiang, Chem. Commun. 55 (2019) 12916;
(h) J. Hou, A. Ee, H. Cao, H.W. Ong, J. Xu, J. Wu, Angew. Chem. Int. Ed. 57 (2018)
17220;
[2] (a) W.K. Hagmann, J. Med. Chem. 51 (2008) 4359;
(b) S. Purser, P.R. Moore, S. Swallow, V. Gouverneur, Chem. Soc. Rev. 37 (2008)
320;
(c) W. Zhu, J. Wang, S. Wang, Z. Gu, J.L. Acena, K. Izawa, H. Liu, V.A. Soloshonok,
J. Fluor. Chem. 167 (2014) 37.
[3] (a) H. Amii, K. Uneyama, Chem. Rev. 109 (2009) 2119;
(b) G. Chelucci, Chem. Rev. 112 (2012) 1344;
(i) A. Trowbridge, D. Reich, M.J. Gaunt, Nature. 561 (2018) 522;
(j) Y. Kong, W. Xu, X. Liu, J. Weng, Chin. Chem. Lett. doi: 10.1016/j.
cclet.2020.05.022..
(c) T. Ahrens, J. Kohlmann, M. Ahrens, T. Braun, Chem. Rev. 115 (2015) 931;
(d) F. Tian, G. Yan, J. Yu, Chem. Commun. 55 (2019) 13486;
(e) X. Lu, X. Wang, T. Gong, J. Pi, S. He, Y. Fu, Chem. Sci. 10 (2019) 809;
(f) R.J. Wiles, J.P. Phelan, G.A. Molander, Chem. Commun. 55 (2019) 7599;
(g) H. Chen, D. Anand, L. Zhou, J. Asian, Org. Chem. 8 (2019) 661;
(h) D. Anand, Z. Sun, L. Zhou, Org. Lett. 22 (2020) 2371;
(i) C. Yao, S. Wang, J. Norton, M. Hammond, J. Am. Chem. Soc. 142 (2020) 4793;
(j) F. Chen, X. Xu, Y. He, G. Huang, S. Zhu, Angew. Chem. Int. Ed. 59 (2020)
5398.
[10] (a) J.C. Tellis, D.N. Primer, G.A. Molander, Science 345 (2014) 433;
(b) Y. Yasu, T. Koike, M. Akita, Adv. Synth. Catal. 354 (2012) 3414;
(c) H. Huang, G. Zhang, L. Gong, S. Zhang, Y. Chen, J. Am. Chem. Soc. 136 (2014)
2280;
(d) H. Huang, K. Jia, Y. Chen, Angew. Chem. Int. Ed. 54 (2015) 1881;
(e) F. Lima, M.A. Kabeshov, D.N. Tran, C. Battilocchio, J. Sedelmeier, G.
Sedelmeier, B. Schenkel, S.V. Ley, Angew. Chem. Int. Ed. 55 (2016) 14085;
(f) B.A. Vara, N.R. Patel, G.A. Molander, ACS Catal. 7 (2017) 3955;
(g) X. Yu, Q. Zhou, P. Wang, C. Liao, J. Chen, W. Xiao, Org. Lett. 20 (2018) 421;
(h) T. Liu, Y. Li, L. Lai, J. Cheng, J. Sun, J. Wu, Org. Lett. 20 (2018) 3605;
(i) P. Renaud, E. André-Joyaux, A. Kuzovlev, N.D. Tappin, Angew. Chem. Int. Ed.
59 (2020) 13859.
[4] (a) L. Chu, F. Qing, Org. Lett. 12 (2010) 5060;
(b) O.A. Tomashenko, V.V. Grushin, Chem. Rev. 111 (2011) 4475;
(c) Z. He, T. Luo, M. Hu, Y. Cao, J. Hu, Angew. Chem. Int. Ed. 51 (2012) 3944;
(d) A. Hafner, T.S. Fischer, S. Bräse, Eur. J. Org. Chem. (2013) 7996;
(e) P. Xu, A. Abdukader, K. Hu, Y. Cheng, C. Zhu, Chem. Commun. 50 (2014)
2308;
[11] (a) J.M. Narayanam, J.W. Tucker, C.R. Stephenson, J. Am. Chem. Soc. 131 (2009)
8756;
(f) X. Zhang, J. Wang, Z. Wan, Org. Lett. 17 (2015) 2086;
(g) X. Lin, Z. Li, X. Han, Z. Weng, RSC Adv. 6 (2016) 75465;
(h) N. Sharma, N. Kumari, T.S. Chundawat, S. Kumar, S. Bhagat, RSC Adv. 7
(2017) 10150;
(i) S. Zhao, Y. Guo, E. Han, J. Luo, H. Liu, C. Liu, W. Xie, W. Zhang, M. Wang, Org.
Chem. Front. 5 (2018) 1143;
(j) S. Zhang, C. Xiao, H. Wan, Dalton Trans. 47 (2018) 4779;
(k) J.A. Kautzky, T. Wang, R.W. Evans, D.W.C. MacMillan, J. Am. Chem. Soc. 140
(2018) 6522;
(l) Y. Chen, Y. You, Z. Weng, Org. Chem. Front. 6 (2019) 213;
(m) S. Wu, J. Shi, C. Zhang, Org. Biomol. Chem. 17 (2019) 7468;
(n) C. Yang, A. Hassanpour, K. Ghorbanpour, S. Abdolmohammadi, E. Vessally,
RSC Adv. 9 (2019) 27625;
(b) S.M. Senaweera, A. Singh, J.D. Weaver, J. Am. Chem. Soc. 136 (2014) 3002;
(c) J.J. Devery III, J.D. Nguyen, C. Dai, C.R. Stephenson, ACS Catal. 6 (2016)
5962;
(d) K. Shimomaki, K. Murata, R. Martin, N. Iwasawa, J. Am. Chem. Soc. 139
(2017) 9467;
(e) S.K. Pagire, O. Reiser, Green Chem. 19 (2017) 1721;
(f) X. Luo, Z. Fan, B. Zhang, C. Chen, C. Xi, Chem. Commun. 55 (2019) 10980;
(g) X. Zhu, Y. Lin, Y. Sun, M.C. Beard, Y. Yan, J. Am. Chem. Soc. 141 (2019) 733.
[12] (a) T. Courant, G. Masson, J. Org. Chem. 81 (2016) 6945;
(b) O. Reiser, Acc. Chem. Res. 49 (2016) 1990;
(c) A. Hossain, S. Engl, E. Lutsker, O. Reiser, ACS Catal. 9 (2018) 1103;
(d) T. Rawner, E. Lutsker, C.A. Kaiser, O. Reiser, ACS Catal. 8 (2018) 3950;
(e) H. Yang, G. Wei, Z. Jiang, ACS Catal. 9 (2019) 9599;
(f) D. Wu, S. Cui, Y. Lin, L. Li, W. Yu, J. Org. Chem. 84 (2019) 10978;
(g) Y. Liu, Z. Chen, Q. Wang, P. Chen, J. Xie, B. Xiong, P. Zhang, K. Tang, J. Org.
Chem. 85 (2020) 2385.
(o) S. Trofymchuk, M.Y. Bugera, A.A. Klipkov, B. Razhyk, S. Semenov, K.
Tarasenko, V.S. Starova, O.A. Zaporozhets, O.Y. Tananaiko, A.N. Alekseenko, Y.
Pustovit, O. Kiriakov, I.I. Gerus, A.A. Tolmachev, P.K. Mykhailiuk, J. Org. Chem.
85 (2020) 3110.
[5] (a) T. Besset, D. Cahard, X. Pannecoucke, J. Org. Chem. 79 (2014) 413;
(b) Q. Lin, X. Xu, F. Qing, J. Org. Chem. 79 (2014) 10434;
(c) S.P. Pitre, C.D. McTiernan, H. Ismaili, J.C. Scaiano, ACS Catal. 4 (2014) 2530;
(d) C. Alonso, E. Martinez de Marigorta, G. Rubiales, F. Palacios, Chem. Rev. 115
(2015) 1847;
(e) J. Moon, Y.K. Moon, D.D. Park, S. Choi, Y. You, E.J. Cho, J. Org. Chem. 84
(2019) 12925.
[6] (a) P. Gao, X. Song, X. Liu, Y. Liang, Chem. Eur. J. 21 (2015) 7648;
(b) L. He, X. Yang, G.C. Tsui, J. Org. Chem. 82 (2017) 6192;
(c) H.S. Han, Y.J. Lee, Y.S. Jung, S.B. Han, Org. Lett. 19 (2017) 1962;
(d) Y. Yamamoto, J. Org. Chem. 83 (2018) 12775;
[13] (a) M. Chen, M. Zhong, J.A. Johnson, Chem. Rev. 116 (2016) 10167;
(b) X. Liu, L. Zhang, Z. Cheng, X. Zhu, Polym. Chem. 7 (2016) 689;
(c) N. Corrigan, S. Shanmugam, J. Xu, C. Boyer, Chem. Soc. Rev. 45 (2016) 6165;
(d) V.K. Singh, C. Yu, S. Badgujar, Y. Kim, Y. Kwon, D. Kim, J. Lee, T. Akhter, G.
Thangavel, L.S. Park, Nature Catal. 1 (2018) 794;
(e) C. Kütahya, P. Wang, S. Li, S. Liu, J. Li, Z. Chen, B. Strehmel, Angew. Chem.
Int. Ed. 59 (2020) 3166.
[14] (a) X. Dai, D. Cheng, B. Guan, W. Mao, X. Xu, X. Li, J. Org. Chem. 79 (2014)
7212;
(b) X. Dai, R. Mao, B. Guan, X. Xu, X. Li, RSC Adv. 5 (2015) 55290;
(c) H. Ye, Q. Ye, D. Cheng, X. Li, X. Xu, Tetrahedron Lett. 59 (2018) 2046;
(e) L. Chen, L. Wu, W. Duan, T. Wang, L. Li, K. Zhang, J. Zhu, Z. Peng, F. Xiong, J.
Org. Chem. 83 (2018) 8607;
4

S. Ren, J. Fu, D. Cheng et al.
Tetrahedron Letters 66 (2021) 152829
(d) H. Ye, H. Zhao, S. Ren, H. Ye, D. Cheng, X. Li, X. Xu, Tetrahedron Lett. 60
(2019) 1302.
[18] (a) K. Iseki, Y. Kuroki, T. Nagai, Y. Kobayashi, J. Fluor. Chem. 69 (1994) 5;
(b) H. Lu, D.J. Burton, Tetrahedron Lett. 36 (1995) 3973.
[15] F. Hong, X. Tang, C. Hu, J. Chem. Soc. Chem. Commun. (1994) 289.
[16] K. Uneyama, T. Katagiri, H. Amii, Acc. Chem. Res. 41 (2008) 817.
[17] Y. Chen, N. Ni, D. Cheng, X. Xu, Tetrahedron Lett. (2020) 152425.
[19] F. Lima, U.K. Sharma, L. Grunenberg, D. Saha, S. Johannsen, J. Sedelmeier, E.V.
Van der Eycken, S.V. Ley, Angew. Chem. Int. Ed. 56 (2017) 15136.
5