Visible Light-Mediated Photocatalytic Metal-Free Cross-Coupling Reaction of Alkenyl Carboxylic Acids with Diarylphosphine Oxides Leading to β-Ketophosphine Oxides

Article abstract of DOI:10.1021/acs.orglett.8b02639

A new visible light-mediated photocatalytic decarboxylative oxyphosphorylation of cinnamic acids with diarylphosphine oxides is described. This reaction is performed under mild conditions to afford the corresponding β-ketophosphine oxides.

Full text of DOI:10.1021/acs.orglett.8b02639

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Visible Light-Mediated Photocatalytic Metal-Free Cross-Coupling
Reaction of Alkenyl Carboxylic Acids with Diarylphosphine Oxides
Leading to β‑Ketophosphine Oxides
Hai-Feng Qian, Cheng-Kun Li, Zhi-Hao Zhou, Ze-Kun Tao, Adedamola Shoberu, and Jian-Ping Zou*
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry and Chemical Engineering, Soochow University, 199
Renai Street, Suzhou, Jiangsu 215123, China
S
* Supporting Information
ABSTRACT: A new visible light-mediated photocatalytic
decarboxylative oxyphosphorylation of cinnamic acids with
diarylphosphine oxides is described. This reaction is
performed under mild conditions to afford the corresponding
β-ketophosphine oxides.
Scheme 1. Synthesis of β-Ketophosphine Oxides from
Alkenes
β-Ketophosphine oxides are important organophosphorus
compounds that have been widely used as metal extractants1
and potential ligands2 due to their coordination ability. They
have also been employed as intermediates for the preparation
of important heterocycles,3 α,β-unsaturated carbonyl com-
pounds via the Horner−Wadsworth−Emmons (HWE) re-
actions4 as well as in other vital chemical transformations.3a,5
Therefore, the development of methods for their preparation is
still of considerable importance. Traditionally, β-ketophos-
phine oxides can be synthesized by the reactions of α-
haloketones and trialkylphosphites (Arbuzov reaction)6 or via
the acylation of alkylphosphine oxides.7 Recently, a number of
reports have been described based on the transition metal-
catalyzed oxyphosphorylation of alkenes and their derivatives
(Scheme 1a and 1b).8,9 Another recent strategy is phosphor-
ylation of α,β-conjugated alkenes via cleavage of the C = C
double bond (Scheme 1c).10
Visible light-mediated photoredox catalysis has become a
powerful tool in modern synthetic chemistry due to its mild
and energy saving nature, environmental friendliness and
potential application in industry.11 This strategy has been
employed by several groups in recent years to construct
important phosphorylated compounds via C(sp2)−P bond
formation.12 On the other hand, cinnamic acids due to their
stability and accessibility, have been employed as viable
substrates via extrusion of carbon dioxide, to access a variety
of valuable compounds.13 Our goal is to develop a greener
access to β-ketophosphine oxides via the visible light-induced
photocatalytic reaction of cinnamic acids with H-phosphine
oxides. In continuation of our recent efforts on C(sp3)−P
bond formation,8c,14 we report the first example of visible light-
mediated photocatalytic metal-free decarboxylative oxyphos-
phorylation of alkenyl carboxylic acids with diarylphosphine
oxides leading to β-ketophosphine oxides (Scheme 1d).
Our initial study focused on the reaction of cinnamic acid
(1a) and diphenylphosphine oxide (2a) under 23W white
LED irradiation using Eosin Y as a photocatalyst. To our
delight, the desired product 3a (50%) was obtained in MeCN
after 24 h at 40 °C (Table 1, entry 1). The reaction was further
investigated in other solvents (Table 1, entries 2−7), and we
observed a slightly improved yield (56%) in DMSO (Table 1,
entry 2). In order to adhere to the original goal of developing a
low-cost and greener protocol, we lowered the amount of
Eosin Y to 3 mol % and this led to a further improvement in
the yield of 3a to 67% (Table 1, entry 8). However, a further
reduction in the amount of photocatalyst (to 1 mol %) had a
detrimental effect on the reaction yield (Table 1, entry 9). In
search of a more efficient catalyst, other kinds of organic dyes
were evaluated as photoredox catalysts (Table 1, entries 10−
13). While all tested catalysts furnished product 3a, Rose
Bengal (RB) was most efficient thus affording 3a in 70% yield
Received: August 18, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b02639
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
a
Table 1. Optimization of the Reaction Conditions
Scheme 2. Scope of Alkenyl Carboxylic Acids 1
b
entry
catalyst (mol %)
solvent
MeCN
DMSO
t-BuOH
EtOH
yield (%)
1
2
3
4
Eosin Y (5)
Eosin Y (5)
Eosin Y (5)
Eosin Y (5)
50
56
25
23
5
Eosin Y (5)
DMF
47
6
Eosin Y (5)
DCE
33
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Eosin Y (5)
Eosin Y (3)
Eosin Y (1)
1,4-dioxane
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
trace
67
21
70
62
67
47
59
Rose Bengal (3)
fluorescein (3)
rhodamine B (3)
rhodamine 6G (3)
Rose Bengal (3)
Rose Bengal (3)
−
Rose Bengal (3)
Rose Bengal (3)
Rose Bengal (3)
Rose Bengal (3)
Rose Bengal (3)
Rose Bengal (3)
c
d
trace
e
NR
f
63
45
33
trace
43
65
g
h
i
j
k
a
Reaction conditions: 1a (0.25 mmol), 2a (1 mmol), photocatalyst,
solvent (1.5 mL), and irradiation with a 23 W white LED lamp at 40
b
c
d
°C for 24 h under air. Isolated yield. With 16 W green LED. No
e
f
g
h
light. NR means no reaction. 1a:2a = 1:3. 1a:2a = 1:2. At 30 °C.
At 20 °C. 12 h. 50 °C.
a
Reaction conditions: 1 (0.25 mmol), 2a (1 mmol), Rose Bengal (3
mol %) in DMSO (1.5 mL), and irradiation with a 23 W white LED
lamp at 40 °C for 24 h under air.
i
j
k
(Table 1, entry 10). Furthermore, when the visible light source
was switched to green LED, a lower yield was obtained (Table
1, entry 14). Notably, only a trace amount of 3a was observed
without the LED lamp while there was no reaction in the
absence of a photocatalyst (Table 1, entries 15 and 16). After a
quick screen of other conditions such as the ratio of reactants,
reaction temperature and time (Table 1, entries 17−20), the
reaction conditions in entry 10 were chosen as optimal for the
investigation of substrate scope.
After the optimized reaction conditions were established, a
variety of alkenyl carboxylic acids were subsequently examined.
As shown in Scheme 2, substrates with different electronic and
steric properties all underwent the reaction to deliver the
corresponding difunctionalized products in satisfactory yields.
The presence of either electron-donating or halo groups at
various positions on the aromatic ring had no obvious effect on
the reaction outcome. As a result, good yields of products were
observed in all cases (Scheme 2, 3b−3m). The reaction of the
trifluoromethyl containing substrates resulted in good yields of
the desired products 3n and 3o, product 3p could only be
obtained in 32% yield due to the strong electron-withdrawing
effect of the 4-nitro group. Meanwhile, the 2-naphthyl
containing substrate afforded 70% yield of the corresponding
product 3q. Furthermore, the effect of α- and β-substituents
were investigated. Thus, 3-phenylbut-2-enoic acid, a β-methyl
substrate, was subjected to the reaction, but unfortunately, the
expected product 3r was not detected. Acetophenone was
isolated instead, which might result from cleavage of the CC
double bond. Likewise, no desired product 3s was detected
with 2-methyl-3-phenylacrylic acid, probably due to the steric
hindrance caused by the α-methyl group. No reaction was
observed for aliphatic acrylic acid, probably attributed to the
low reactivity of substrate. The reaction of (furan-2-yl) acrylic
acid resulted in complicated mixtures of products. The desired
product 3u could only be detected in trace amounts by HRMS.
The poor selectivity of the reaction might be attributed to the
high reactivity of the starting material. However, the reaction
with (thiophen-2-yl) acrylic acid gave the desired product 3v in
61% yield. In addition, the reactions of substrates such as
conjugated (hetero)cyclohexenyl carboxylic acids, heteroaryl
carboxylic acids and (E)-3-(pyridin-3-yl)acrylic acid were
carried out. While the first two types of compounds were
inert toward the reaction, (E)-3-(pyridin-3-yl)acrylic acid
produced the desired product 3w in 37% yield (see Supporting
Informtion, Scheme S1).
Next, the reactions of cinnamic acid with a variety of
phosphine oxides were also investigated (Scheme 3). Both
electron-rich and halo- containing diaryl phosphine oxides gave
the expected products in yields ranging from 65 to 72%
(Scheme 3, 4a−4c, 4e, 4f). However, phenyl(p-tolyl)-
phosphine oxide produced a mixture of products 4d and 4d′
(2.5:1). The reason for this outcome remains unknown. Due
to the obvious steric hindrance, the reaction of dinaphthyl
phosphine oxide did not take place. Fortunately, di(thiophen-
2-yl)phosphine oxide was compatible under the present
condition to afford the expected product 4h in 65% yield.
Unfortunately, other phenylphosphine oxides containing the 2-
B
DOI: 10.1021/acs.orglett.8b02639
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
Scheme 3. Scope of Diphenylphosphine Oxide Derivatives
Scheme 5. Gram Experiment
TLC). After workup, the desired product 3a was obtained in
69% yield (5.017 g).
In order to gain an insight into the reaction mechanism,
some control experiments were carried out as shown in
Scheme 6. Initially, the standard reactions were performed in
Scheme 6. Control Experiments
a
Reaction conditions: 1a (0.25 mmol), 2 (1 mmol), Rose Bengal (3
mol %) in DMSO (1.5 mL), and irradiation with a 23 W white LED
lamp at 40 °C for 24 h under air.
pyridyl, n-butyl, and ethoxy groups could not furnish the
corresponding products probably due to their lower reactivity.
In order to know the generality and limit for this
methodology, the reaction of styrene, cinnamaldehyde, methyl
cinnamate, and an alkynyl carboxylic acid, phenyl propiolic
acid (5) with diphenylphosphine oxide (2a) were also explored
under the same reaction conditions. The results indicate that
the reaction with styrene and phenyl propiolic acid (5) could
all produce 2-(diphenylphosphoryl)-1-phenylethan-1-one (3a)
in 58% and 51% yields, respectively; however, the reaction with
cinnamaldehyde afforded the nucleophilic addition product
6,15 and no reaction was observed for methyl cinnamate
(Scheme 4).
the presence of either TEMPO or BHT. Although, there was
no radical capture in both cases, the suppressed formation of
3a suggests that radical species were involved in the reaction
(Scheme 6a). Delightfully, the participation of phosphoryl
radicals was confirmed via the reaction of cinnamic acid (1a)
and diphenylphosphine oxide (2a) in the presence of N-
methyl-N-phenylmethacrylamide 7. This resulted in only 14%
yield of product 3a along with 34% of phosphoryl radical
mediated cyclization product 8 (Scheme 6b). Furthermore, to
confirm the presence of superoxide anion radical and
diphenylphosphoryl radical, trapping experiments with 5,5-
dimethyl-1-pyrroline N-oxide (DMPO) were performed.
Pleasingly, the EPR experiment detected the presence of the
Scheme 4. Reaction of Styrene, Cinnamaldehyde, Methyl
Cinnamate, and Phenyl Propiolic Acid (5) with Diphenyl
Phosphine Oxide
•−
adduct of DMPO−O2 (see Supporting Information, Figures
•
S1 and S2 and Scheme S2) and DMPO-POPh2 (see
Supporting Information, Figure S3 and Scheme S3).16
On the basis of the results above and studies from
literature,14,16−18 a mechanism is proposed for the visible-
light driven photocatalytic decarboxylative oxyphosphorylation
of cinnamic acids (Scheme 7). Under visible light irradiation,
the RB photocatalyst is induced into its excited state (RB*)
which further interacts with oxygen from air to give the
superoxide anion radical and RB radical cation (RB•+).16c
Then, 2a could interact with RB•+ to give the radical cation A
and ground state RB to complete the photoredox cycle. The
radical cation A could initially undergo loss of proton to afford
the key phosphorus-centered radical B which subsequently
attacks the α-position of cinnamic acid 1 to form intermediate
radical C. Cinnamic acid 1 could not be oxidized by RB* due
In order to demonstrate the scalability of this visible-light
driven photocatalytic reaction, a 5-g scale preparation of β-
ketophosphine oxide 3a was performed as illustrated in
Scheme 5. Cinnamic acid (1a) (3.36 g, 22.7 mmol),
diphenylphosphine oxide (2a) (13.76 g, 68.1 mmol), Rose
Bengal (0.69 g, 0.68 mmol), and DMSO (100 mL) were
placed in a crystallizing dish (diameter 8 cm). The mixture was
stirred at 40 °C for 40 h under irradiation by a 23 W white
LED until the completion of the reaction (monitored by
ox
to its high oxidation potential (E1/2 = +2.01 V vs SCE in
MeCN).18b The resultant intermediate radical C could react
with molecular oxygen to form radical E via peroxo radical
D.18a The abstraction of a proton by the superoxide anion
radical from E would give intermediate F,18b which can further
undergo decarboxylation and electron transfer process to
C
DOI: 10.1021/acs.orglett.8b02639
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 7. Proposed Mechanism for Decarboxylative
Oxyphosphorylation of Cinnamic Acid
REFERENCES
■
(1) (a) Cotton, F. A.; Schunn, R. A. J. Am. Chem. Soc. 1963, 85,
2394. (b) Youinou, M. T. R.; Guerchais, J. E.; Louer, M. E.;
Grandjean, D. Inorg. Chem. 1977, 16, 872. (c) Bottin-Strzalko, T.;
Corset, J.; Froment, F.; Pouet, M. J.; Seyden-Penne, J.; Simonnin, M.
P. J. Org. Chem. 1980, 45, 1270. (d) McCabe, D. J.; Duesler, E. N.;
Paine, R. T. Inorg. Chem. 1985, 24, 4626. (e) Mitchell, L. A.; Holliday,
B. J. ACS Macro Lett. 2016, 5, 1100.
(2) (a) McManus, H. A.; Guiry, P. J. Chem. Rev. 2004, 104, 4151.
(b) Birkholz, M. N.; Freixa, Z.; van Leeuwen, P. W. Chem. Soc. Rev.
2009, 38, 1099.
́
́
(3) (a) Gonzalez-Calderon, D.; Fuentes-Benítes, A.; Díaz-Torres, E.;
́
́
́
Gonzalez-Gonzalez, C. A.; Gonzalez-Romero, C. Eur. J. Org. Chem.
2016, 2016, 668. (b) Khalladi, K.; Touil, S. Phosphorus, Sulfur Silicon
Relat. Elem. 2013, 188, 711. (c) Reeves, J. T.; Song, J. J.; Tan, Z.; Lee,
H.; Yee, N. K.; Senanayake, C. H. Org. Lett. 2007, 9, 1875.
(4) (a) Boutagy, J.; Thomas, R. Chem. Rev. 1974, 74, 87. (b) Horner,
L.; Hoffmann, H.; Wippel, H. G. Chem. Ber. 1958, 91, 61. (c) Horner,
L.; Hoffmann, H.; Wippel, H. G.; Klahre, G. Chem. Ber. 1959, 92,
2499. (d) Wadsworth, W. S. J. Org. React. 1977, 25, 73. (e) Clayden,
J.; Warren, S. Angew. Chem., Int. Ed. Engl. 1996, 35, 241. (f) Boesen,
T.; Fox, D. J.; Galloway, W.; Pedersen, D. S.; Tyzack, C. R.; Warren,
S. Org. Biomol. Chem. 2005, 3, 630. (g) Murai, M.; Nakamura, M.;
Takai, K. Org. Lett. 2014, 16, 5784.
(5) (a) Maryanoff, B. E.; Reitz, A. B. Chem. Rev. 1989, 89, 863.
(b) Hutton, G.; Jolliff, T.; Mitchell, H.; Warren, S. Tetrahedron Lett.
1995, 36, 7905. (c) Palacios, F.; Aparicio, D.; Vicario, J. Eur. J. Org.
Chem. 2002, 2002, 4131. (d) Fox, D. J.; Pedersen, D. S.; Warren, S.
Chem. Commun. 2004, 22, 2598. (e) Fox, D. J.; Parris, S.; Pedersen, D.
S.; Tyzack, C. R.; Warren, S. Org. Biomol. Chem. 2006, 4, 3108.
(f) Jelaiel, N.; Said, N.; Touil, S.; Efrit, M. L. Phosphorus, Sulfur Silicon
Relat. Elem. 2010, 185, 2382. (g) Khalladi, K.; Touil, S. Phosphorus,
Sulfur Silicon Relat. Elem. 2013, 188, 711. (h) de los Santos, J. M.;
Ignacio, R.; Es Sbai, Z.; Aparicio, D.; Palacios, F. J. Org. Chem. 2014,
79, 7607. (i) Son, S. M.; Lee, H. K. J. Org. Chem. 2014, 79, 2666.
(j) Bisceglia, J. A.; Orelli, L. R. Curr. Org. Chem. 2015, 19, 744.
(k) Chen, H.; Zheng, Q.; Dong, W.; Peng, Z.; An, D. Synth. Commun.
2016, 46, 1438. (l) Nagatani, K.; Minami, A.; Tezuka, H.; Hoshino,
Y.; Nakada, M. Org. Lett. 2017, 19, 810.
afford product 3 (path a).18c Alternatively, F can interact with
RB•+ via a single electron transfer process to give H and
subsequent decarboxylation would afford 3 (path b).18b
In summary, a new visible-light-mediated photocatalytic
strategy for the decarboxylative oxyphosphorylation of
cinnamic acids with diarylphosphine oxides under air has
been developed. This metal-free procedure requires neither
oxidant nor additive and is applicable to wide range of
substrates including aryl propiolic acids. Notably, the reaction
could be carried out on a 5 g scale. This reaction represents a
mild and efficient method of preparation of β-ketophosphine
oxides.
(6) (a) Michaelis, A.; Kaehne, R. Ber. Dtsch. Chem. Ges. 1898, 31,
1048. (b) Arbusow, B. A. Pure Appl. Chem. 1964, 9, 307.
(c) Bhattacharya, A. K.; Thyagarajan, G. Chem. Rev. 1981, 81, 415.
(7) (a) Torr, R. S.; Warren, S. J. Chem. Soc. Pak. 1979, 1, 15.
(b) Narkunan, K.; Nagarajan, M. J. Org. Chem. 1994, 59, 6386.
(c) Rodrigues, A.; Vinhato, E.; Rittner, R.; Olivato, P. R. Synthesis
2003, 2003, 1248. (d) Fox, D. J.; Pedersen, D. S.; Warren, S. Org.
Biomol. Chem. 2006, 4, 3102. (e) Maloney, K. M.; Chung, J. Y. J. Org.
Chem. 2009, 74, 7574.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b02639.
■
S
Experimental details and spectral data for compounds 3,
4, 6, and 8 (PDF)
(8) (a) Wei, W.; Ji, J. X. Angew. Chem., Int. Ed. 2011, 50, 9097.
AUTHOR INFORMATION
́
(b) Gutierrez, V.; Mascaro, E.; Alonso, F.; Moglie, Y.; Radivoy, G.
■
RSC Adv. 2015, 5, 65739. (c) Zhang, G. Y.; Li, C. K.; Li, D. P.; Zeng,
R. S.; Shoberu, A.; Zou, J. P. Tetrahedron 2016, 72, 2972. (d) Gu, J.;
Cai, C. Org. Biomol. Chem. 2017, 15, 4226.
Corresponding Author
*(J.-P.Z.) E-mail: jpzou@suda.edu.cn.
ORCID
(9) (a) Zhou, M.; Zhou, Y.; Song, Q. Chem. - Eur. J. 2015, 21,
10654. (b) Zhou, Y.; Zhou, M.; Chen, M.; Su, J.; Du, J.; Song, Q. RSC
Adv. 2015, 5, 103977. (c) Tang, L.; Wen, L.; Sun, T.; Zhang, D.;
Yang, Z.; Feng, C.; Wang, Z. Asian J. Org. Chem. 2017, 6, 1683.
(d) Liang, W.; Zhang, Z.; Yi, D.; Fu, Q.; Chen, S.; Yang, L.; Du, F.; Ji,
J.; Wei, W. Chin. J. Chem. 2017, 35, 1378. (e) Chen, X.; Chen, X.; Li,
X.; Qu, C.; Qu, L.; Bi, W.; Sun, K.; Zhao, Y. Tetrahedron 2017, 73,
2439. (f) Tang, P.; Zhang, C.; Chen, E.; Chen, B.; Chen, W.; Yu, Y.
Tetrahedron Lett. 2017, 58, 2157.
(10) (a) Zhou, Y.; Rao, C.; Mai, S.; Song, Q. J. Org. Chem. 2016, 81,
2027. (b) Zhou, P.; Hu, B.; Li, L.; Rao, K.; Yang, J.; Yu, F. J. Org.
Chem. 2017, 82, 13268.
(11) For selective reviews on the photocatalyzed reactions, see:
(a) Skubi, K. L.; Blum, T. R.; Yoon, T. P. Chem. Rev. 2016, 116,
10035. (b) Ravelli, D.; Protti, S.; Fagnoni, M. Chem. Rev. 2016, 116,
Jian-Ping Zou: 0000-0002-8092-9527
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
J.-P.Z. appreciates the generous financial support by National
Natural Science Foundation of China (No. 21172163,
21472133), the Priority Academic Program Development of
Jiangsu Higher Education Institutions (PAPD), Key Labo-
ratory of Organic Synthesis of Jiangsu Province (KJS1749) &
State, and the Local Joint Engineering Laboratory for Novel
Functional Polymeric Materials.
D
DOI: 10.1021/acs.orglett.8b02639
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
9850. (c) Shaw, M. H.; Twilton, J.; MacMillan, D. W. C. J. Org. Chem.
2016, 81, 6898. (d) Luo, J.; Zhang, J. ACS Catal. 2016, 6, 873.
(12) (a) He, Y.; Wu, H.; Toste, F. D. Chem. Sci. 2015, 6, 1194.
(b) Xuan, J.; Zeng, T.-T.; Chen, J.-R.; Lu, L.-Q.; Xiao, W.-J. Chem. -
Eur. J. 2015, 21, 4962. (c) Li, C.-X.; Tu, D.-S.; Yao, R.; Yan, H.; Lu,
C.-S. Org. Lett. 2016, 18, 4928. (d) Shaikh, R. S.; Dusel, S. J. S.;
̈
̈
Konig, B. ACS Catal. 2016, 6, 8410. (e) Peng, P.; Peng, L.; Wang, G.;
Wang, F.; Luo, Y.; Lei, A. Org. Chem. Front. 2016, 3, 749. (f) Quint,
V.; Morlet-Savary, F.; Lohier, J. F.; Lalevee, J.; Gaumont, A. C.;
Lakhdar, S. J. Am. Chem. Soc. 2016, 138, 7436. (g) Luo, K.; Chen, Y.
Z.; Yang, W. C.; Zhu, J.; Wu, L. Org. Lett. 2016, 18, 452. (h) Liu, D.;
Chen, J.-Q.; Wang, X.-Z.; Xu, P.-F. Adv. Synth. Catal. 2017, 359, 2773.
(13) For selective examples for C−C and C−P(S) bond formation
through decarboxylation, see: (a) Hu, J.; Zhao, N.; Yang, B.; Wang,
G.; Guo, L.-N.; Liang, Y.-M.; Yang, S.-D. Chem. - Eur. J. 2011, 17,
5516. (b) Xu, Y.; Tang, X.; Hu, W.; Jiang, H.; et al. Green Chem. 2014,
16, 3720. (c) Wang, C.; Rakshit, S.; Glorius, F. J. Am. Chem. Soc.
2010, 132, 14006. (d) Singh, R.; Allam, B. K.; Singh, N.; Kumari, K.;
Singh, S. K.; Singh, K. N. Org. Lett. 2015, 17, 2656. (e) Ji, J.; Liu, P.;
Sun, P. Chem. Commun. 2015, 51, 7546.
(14) (a) Li, J. A.; Zhang, P. Z.; Liu, K.; Shoberu, A.; Zou, J. P.;
Zhang, W. Org. Lett. 2017, 19, 4704. (b) Zhang, P. Z.; Zhang, L.; Li, J.
A.; Shoberu, A.; Zou, J. P.; Zhang, W. Org. Lett. 2017, 19, 5537.
(15) Gusarova, N. K.; Ivanova, N. I.; Volkov, P. A.; Khrapova, K. O.;
Larina, L. I.; Smirnov, V. I.; Borodina, T. N.; Trofimov, B. A. Synthesis
2015, 47, 1611.
(16) (a) Ke, J.; Tang, Y. L.; Yi, H.; Li, Y. L.; Cheng, Y. D.; Liu, C.;
Lei, A. W. Angew. Chem. 2015, 127, 6704. (b) Huang, W.; Ma, B. C.;
Lu, H.; Li, R.; Wang, L.; Landfester, K.; Zhang, K. A. I. ACS Catal.
2017, 7, 5438. (c) Schilling, W.; Riemer, D.; Zhang, Y.; Hatami, N.;
Das, S. ACS Catal. 2018, 8, 5425.
(17) Schweitzer, C.; Schmidt, R. Chem. Rev. 2003, 103, 1685.
(18) (a) Ji, P. Y.; Liu, Y.-F.; Xu, J. W.; Luo, W. P.; Liu, Q.; Guo, C.
C. J. Org. Chem. 2017, 82, 2965. (b) Zhang, J. J.; Yang, J. C.; Guo, L.
N.; Duan, X. H. Chem. - Eur. J. 2017, 23, 10259. (c) Wang, C.; Lei, Y.
J.; Guo, M. Z.; Shang, Q. Y.; Liu, H.; Xu, Z. Q.; Wang, R. Org. Lett.
2017, 19, 6412.
E
DOI: 10.1021/acs.orglett.8b02639
Org. Lett. XXXX, XXX, XXX−XXX