Synthesis of trifluoromethylthiolated and trifluoromethylselenolated pyrones

Article abstract of DOI:10.1016/j.tet.2017.05.051

Trifluoromethylthiolation and trifluoromethylselenolation of 3- or 4-iodo(bromo)-2-pyrones with (bpy)CuSCF₃ and [(bpy)CuSeCF₃]₂ provide a convenient method for the synthesis of trifluoromethylthio(seleno)lated 4-alkoxy-, aryloxy-, and benzyloxy-2-pyrones in high yields.

Full text of DOI:10.1016/j.tet.2017.05.051

Accepted Manuscript
Synthesis of trifluoromethylthiolated and trifluoromethylselenolated pyrones
Yunxiao Zhang, Ding-Yah Yang, Zhiqiang Weng
PII:
S0040-4020(17)30538-0
10.1016/j.tet.2017.05.051
TET 28717
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 1 April 2017
Revised Date: 9 May 2017
Accepted Date: 12 May 2017
Please cite this article as: Zhang Y, Yang D-Y, Weng Z, Synthesis of trifluoromethylthiolated and
trifluoromethylselenolated pyrones, Tetrahedron (2017), doi: 10.1016/j.tet.2017.05.051.
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Synthesis of trifluoromethylthiolated and
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Yunxiao Zhang, Ding-Yah Yang,* and Zhiqiang Weng

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Tetrahedron
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Synthesis of trifluoromethylthiolated and trifluoromethylselenolated pyrones
Yunxiao Zhang a, Ding-Yah Yang b,*, and Zhiqiang Weng a,*
a State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University, Fuzhou, 350108, China.
bDepartment of Chemistry, Tunghai University, No. 1727, Sec. 4, Taiwan Boulevard, Xitun District, Taichung City 40704, Taiwan.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Trifluoromethylthiolation and trifluoromethylselenolation of 3- or 4-iodo(bromo)-2-pyrones
with (bpy)CuSCF3 and [(bpy)CuSeCF3]2 provide a convenient method for the synthesis of
trifluoromethylthio(seleno)lated 4-alkoxy-, aryloxy-, and benzyloxy-2-pyrones in high yields.
2009 Elsevier Ltd. All rights reserved
.
Available online
Keywords:
Trifluoromethylthiolation
Trifluoromethylselenolation
Pyrones
Copper
1. Introduction
the SCF3-functionalization of parent substrates play a pivotal
role in this transformation. Examples of the transition-metal-
catalyzed or metal-free trifluoromethylthiolation of organic
halides,25,26,27,28,29 boronic acids,30,31,32 organometallic species,33
C−H bonds,34,35,36,37,38,39,40 alcohols,41,42 and alkynes43,44,45 with
stable nucleophilic or electrophilic trifluoromethylthiolating
reagents have recently been developed.
The synthesis of 2-pyrones and their derivatives has
attracted much attention in the context of the biological
activities of these compounds induced by the hetero-cyclic
moiety.1,2,3,4 These compounds display a wide range of
biological activities such as cytotoxic, antibiotic and antifungal
activity. Among them, compounds containing methyl or
trifluoromethyl-substituted at C-3 position of the 2-pyrone
moiety are privileged (Figure 1), as they are found in a large
number of biologically and pharmaceutically active molecules
that have a broad spectrum of properties. Further, they act as
potential therapeutic agents for treatment of central nervous
system disorders, and some exhibit fungicidal activity.5,6,7,8
Consequently, the development of new practical methods for
the synthesis of methyl- or trifluoromethyl-2-pyrone scaffold is
of considerable interest.9,10,11
Trifluoromethylthiolated heterocycles are attracting
growing interest in pharmaceutical and agricultural related
research due to the unique properties of the trifluoromethylthio
(SCF3) group.12,13,14,15,16 Because of its strong electron-
withdrawing effects (Hammett constant: σm = 0.40 and σp =
0.50) and high lipophilicity (πR = 1.44),17,18,19 the introduction
of SCF3 group can influence the chemical, physical, and
physiological properties of the resulting molecules. This
realization has led to a rapid development of efficient and
Figure 1. Bioactive 2-pyrone derivatives.
Recently, we reported the utilization of novel copper
reagents (bpy)CuSCF3 (1a) and [(bpy)CuSeCF3]2 (1b) for
trifluoromethylthiolation46 and trifluoromethylselenolation.47
These copper reagents reacted with organic halides to provide
the corresponding trifluoromethyl thio or selenoethers in good
to excellent yields.48,49,50,51,52
convenient
trifluoromethylthiolation
methods.20,21,22,23,24
Among these, the use of trifluoromethylthiolating reagents for
−−−−−−−−−−−−−−−−
* Corresponding authors. Tel./fax: +86 59122866121; e-mail
addresses: yang@thu.edu.tw (DYY); zweng@fzu.edu.cn (ZW).
In view of the aforementioned success, we planned to
explore
the
possibility
of
introducing
a

2
Tetrahedron
trifluoromethylthio(seleno) group into a pyrone ring through
3e in high yields (97% and 91%, respectively) after isolation
ACCEPTED MANUSCRIPT
nucleophilic
trifluoromethylthio(seleno)lation
of
the
by column chromatography. Additionally, the reaction of 3-
iodo-4-benzyloxy-2-pyrones 2f-2j with 1a led to the formation
of the expected products 3f-3j in excellent yields (91-99%).
halogenated 2-pyrones with copper reagents 1a and 1b. We
herein disclose our investigation into a synthetic strategy to
trifluoromethylthio (seleno)lated pyrones.
2. Results and Discussion
Table 2
Substrate scope of trifluoromethylthiolation of 3-iodo-2-
In the preliminary studies, we chose 3-iodo-4-isopropoxy-6-
methyl-2H-pyran-2-one (2c) as a model substrate to determine
the reaction conditions (Table 1). The initial attempt was
pyronesa,b
carried
out
using
(bpy)CuSCF3
(1a)
as
the
trifluoromethylthiolating reagent in CH3CN at 100 °C.
Pleasingly, the desired trifluoromethylthiolated pyrones (3c)
was obtained in 79% yield after 16 h (Table 1, Entry 1). A
screening of solvents showed that DMSO, and DMF were
inefficient (Table 1, Entries 2 and 3), whereas diglyme, THF,
and dioxane gave better yields (Table 1, Entries 4-6). Toluene
turned out to be the best solvent for this transformation (Table
1, Entry 7). Decreasing the reaction temperature from 100 °C
to 80 °C led to a lower yield of product 3c (68%; Table 1,
Entry 8). Furthermore, a shorter reaction time (8 h) resulted in
a slight decrease in the yield of 3c (89%; Table 1, Entry 9).
Therefore, we the conditions of using toluene as solvent with
conventional heating at 100 °C for 16 h were adopted for the
subsequent reactions.
Table 1
Optimization of trifluoromethylthiolation of 3-iodo-4-
isopropoxy-6-methyl-2H-pyran-2-one (2c) a
Entry
Solvent
Temp (°C)
Time (h)
Yield (%)b
a Reaction conditions: 1a (0.75 mmol), 2 (0.50 mmol), toluene (5 mL), 100
°C, 16 h, N2.
1
2
3
4
5
6
7
8
9
CH3CN
DMSO
DMF
100
100
100
100
100
100
100
80
16
16
16
16
16
16
16
16
8
79
trace
14
b Yields shown are of isolated products.
Diglyme
THF
87
The trifluoromethylselenolation of 3-iodo-2-pyrones with
[(bpy)CuSeCF3]2 (1b) was then investigated (Table 3). In most
cases, the trifluoromethylselenolation proceeded smoothly to
produce the desired trifluoromethylthiolated pyrones in
excellent yields under the similar reaction conditions as those
of 1a.
91
Dioxane
Toluene
Toluene
Toluene
85
97
68
Next, we extended the substrate scope of the reaction by
conducting trifluoromethylthio(seleno)lation of 4-iodo-6-
methyl-2H-pyran-2-one (5a) with 1a or 1b under the optimal
conditions, to afford products 6a and 6b in 80% and 98%
yields, respectively (Scheme 1).
100
89
a
Reaction conditions: 1a (0.075 mmol), 2c (0.050 mmol), solvent (1.2
mL), under N2 atmosphere.
The yield was determined by 19F NMR spectroscopy with PhOCF3 as
b
internal standard.
To further investigate the substrate scope of this
trifluoromethylthio(seleno)lation sequence, 4-bromo-2-pyrone
was also explored. However, the trifluoromethylthiolation of
4-bromo-6-methyl-2H-pyran-2-one (5b) with 1a gave the
desired product 6a in low yield (20%) under conditions used
for the corresponding iodo starting material.8 Taking into
account the fact that trifluoromethylthiolation of organic
With the optimized conditions in hand, we investigated the
scope of the transformation. As showed in Table 2, the 3-iodo-
4-alkoxy-2-pyrones 2a-2c were efficiently converted into the
corresponding trifluoromethylthiolated pyrone derivatives, and
the resulting products 3a-3c were isolated in high yield (92-
98%). Similarly, the use of 3-iodo-4-aryloxy-2-pyrones 2d and
2e as electrophile afforded the corresponding products 3d and

3
bromides has previously been carried out successfully in the
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synthesis of α-trifluoromethylthio-α,β-unsaturated carbonyl
compounds with 2 equiv of CsF as an additive,53 we decided to
further optimize the reaction conditions by employing the
same strategy. When the reaction was conducted in the
presence of 2 equiv of CsF at 120 °C, indeed the yield of target
compound 6a was increased to 67%. The process was also
found to be effective between 4-bromo-6-methyl-2H-pyran-
2-one (5b) and 1b
,
leading to the corresponding
trifluoromethylselenolated pyrone 6b in good yield (81%)
(Scheme 2).
Scheme
2.
Trifluoromethylthiolation
and
trifluoromethylselenolation of 6-methyl-3-bromo-2-pyrones
(5b)
Table 3
Substrate scope of trifluoromethylselenolation of 3-iodo-2-
pyronesa,b
To demonstrate the scalability of this procedure, 1.75 g of
4-(4-fluorophenoxy)-3-iodo-6-methyl-2H-pyran-2-one
(2e)
was reacted with 2.5 g of 1a in toluene at 100 °C for 16 h. The
corresponding trifluoromethylthiolated pyrone 3e was isolated
in 1.23 g (77% yield, Scheme 3), indicating that the reaction
can be scaled up without major difficulties.
F
F
O
O
I
SCF3
O
Toluene
100°C, 16 h
(bpy)CuSCF3
+
1a
O
O
O
2e
3e
2.5 g
1.75 g
1.23 g, 77%
Scheme 3. Scalability of the trifluoromethylthiolation of 2e
To demonstrate the synthetic application of this
methodology, ring-opening reaction of trifluoromethylthiolated
pyrone 3e was carried out at r.t., and the desired 7e was
obtained in 25% yield (Scheme 4). Thus, this method provided
a new approach for the synthesis of novel SCF3-substituted
unsaturated carboxylic acids.
a Reaction conditions: 1b (0.375 mmol), 2 (0.50 mmol), toluene (5 mL),
100 °C, 16 h, N2.
b Yields shown are of isolated products.
Scheme 4. Ring-opening reaction of 3e
3. Conclusions
In summary, we have developed an efficient route to
prepare
trifluoromethylthio(seleno)lated
pyrones
by
Scheme
1.
Trifluoromethylthiolation
and
trifluoromethylthio(seleno)lation of 3- or 4-iodo(bromo)-2-
pyrones with (bpy)CuSCF3 (1a) and [(bpy)CuSeCF3]2 (1b).
The reaction afforded good to excellent yields of a variety of
trifluoromethylthio(seleno)lated 4-alkoxy-, aryloxy-, and
trifluoromethylselenolation of 4-iodo-6-methyl-2H-pyran-
2-one (5a)

4
Tetrahedron
ACCEPTED MANUSCRIP
benzyloxy-2-pyrones. Investigations of this methodology to
MHz, CDCl3) δ -42.8 (s, 3F). 13C NMR (101 MHz, CDCl3) δ
T
the synthesis of new trifluoromethylthio(seleno)lated
heterocyclic derivatives are currently in progress in our
laboratory.
174.6 (s), 167.8 (s), 163.0 (s), 129.4 (q, J = 311.2 Hz), 95.8 (s),
87.2 (q, J = 2.0 Hz), 72.5 (s), 22.3 (s), 20.8(s), 10.0(s).
IR (KBr): ν 2982, 2937, 1698, 1633, 1501, 1452, 1385, 1214,
1105, 898, 752, 531 cm-1. GC-MS m/z 268 (M+). HRMS (EI)
m/z: calcd. for C10H11O3F3S: 268.0381; found: 268.0385.
4. Experimental
4.2.3 4-Isopropoxy-6-methyl-3-((trifluoromethyl)thio)-2H-
pyran-2-one (3c). Following the general procedure and
workup, 3c was isolated as a white solid in 98% yield (131
4.1 General experimental
1H NMR, 19F NMR and 13C NMR spectra were recorded
1
mg). M.p. 119.3-120.3 °C. Rf (diethyl ether) = 0.64. H NMR
using Bruker AVIII 400 spectrometer. H NMR and 13C NMR
1
(400 MHz, CDCl3) δ 6.11 (s, 1H), 4.87 – 4.62 (m, 1H), 2.34 (s,
3H), 1.43 (d, J = 6.0 Hz, 6H). 19F NMR (376 MHz, CDCl3) δ -
42.9 (s, 3F). 13C NMR (101 MHz, CDCl3) δ 173.6 (s), 167.4
(s), 163.2 (s), 129.8 (q, J = 311.2 Hz), 95.9 (s), 87.7 (q, J = 2.0
Hz), 74.4 (s), 22.0 (s), 20.8 (s). IR (KBr): ν 3098, 2988,
2924, 1702, 1633, 1507, 1453, 1318, 1215, 1094, 935, 765,
534 cm-1. GC-MS m/z 268 (M+). HRMS (EI) m/z: calcd. for
C10H11O3F3S: 268.0381; found: 268.0386.
chemical shifts were reported in parts per million (ppm)
downfield from tetramethylsilane and 19F NMR chemical shifts
were determined relative to CFCl3 as the external standard and
low field is positive. Coupling constants (J) are reported in
Hertz (Hz). The residual solvent peak was used as an internal
reference: 1H NMR (chloroform δ 7.26) and 13C NMR
(chloroform δ 77.0). The following abbreviations were used to
explain the multiplicities: s = singlet, d = doublet, t = triplet, q
= quartet, m = multiplet, br = broad. HRMS were obtained on
Waters GCT-TOF at the Shanghai Institute of Organic
Chemistry. The (bpy)CuSCF3 (1a), [(bpy)CuSeCF3]2 (1b)47,
and 3-iodo-2-pyrones (2)8,54 were prepared according to the
published procedures. Other reagents were received from
commercial sources. Solvents were freshly dried and degassed
according to the purification handbook Purification of
Laboratory Chemicals prior to use. Column chromatography
purifications were performed by flash chromatography using
Merck silica gel 60.
4.2.4
6-Methyl-4-phenoxy-3-((trifluoromethyl)thio)-2H-
pyran-2-one (3d). Following the general procedure and workup,
3d was isolated as a white solid in 97% yield (148 mg). M.p.
1
99.1-99.8 °C. Rf (diethyl ether/n-pentane 1:1) = 0.38. H NMR
(400 MHz, CDCl3) δ 7.48 (t, J = 7.9 Hz, 2H), 7.35 (t, J = 7.4
Hz, 1H), 7.08 (d, J = 8.0 Hz, 2H), 5.70 (s, 1H), 2.22 (s, 3H).
19F NMR (376 MHz, CDCl3) δ -42.6 (s, 3F). 13C NMR (101
MHz, CDCl3) δ 172.5 (s), 167.2 (s), 162.7 (s), 152.7 (s), 130.4
(s), 126.8 (s), 122.2 (q, J = 335.7 Hz), 120.9 (s), 97.1 (s), 89.6
(q, J = 1.6 Hz), 67.9 (s), 25.6 (s), 20.5 (s). IR (KBr): ν 2924,
1725 , 1635, 1514, 1486, 1317, 1225, 1102, 915, 762, 695,
528 cm-1. GC-MS m/z 302 (M+). HRMS (EI) m/z: calcd. for
C13H9O3F3S: 302.0225; found: 302.0218.
4.2
General
procedure
for
trifluoromethylthiolation/trifluoromethylselenolation of 3-
iodo-2-pyrones with (bpy)Cu(SCF3)/[(bpy)Cu(SeCF3)]2
3-Iodo-2-pyrones (2) (0.50 mmol), (bpy)Cu(SCF3) (250 mg,
0.75 mmol, 1.5 equiv) or [(bpy)Cu(SeCF3)]2 (280 mg, 0.375
mmol, 0.75 equiv) and toluene (5 mL) were added to a reaction
tube equipped with a stir bar. The mixture was stirred at 100
°C for 16 hours. After cooled down to room temperature, the
reaction mixture was filtered through a pad of celite. The
filtrate was added water (3×10 mL) at 0 °C. The resulting
mixture was extracted with Et2O (3×15 mL), and the combined
organic layers was washed with water, and then dried over
MgSO4. The solvent was removed by rotary evaporation in an
ice bath and the resulting product was purified by flash
chromatography on silica gel using diethyl ether/n-pentane for
elution.
4.2.5
4-(4-Fluorophenoxy)-6-methyl-3-
((trifluoromethyl)thio)-2H-pyran-2-one (3e). Following the
general procedure and workup, 3e was isolated as a brown
solid in 91% yield (145 mg). M.p. 123.7-124.8 °C. Rf (diethyl
1
ether/n-pentane 1:1) = 0.46. H NMR (400 MHz, CDCl3) δ
7.20 – 7.11 (m, 2H), 7.09 – 7.05 (m, 2H), 5.69 (s, 1H), 2.23 (s,
3H). 19F NMR (376 MHz, CDCl3) δ -42.6 (s, 3F), -114.4 – -
114.5 (m, 1F). 13C NMR (101 MHz, CDCl3) δ 173.6 (s), 168.0
(s), 162.2 (d, J = 53.4 Hz), 159.5 (s), 148.4 (d, J = 3.2 Hz),
129.3 (q, J = 311.3 Hz), 122.6 (s), 122.5 (s), 117.3 (s), 117.1
(s), 97.0 (s), 89.7 (q, J = 2.2 Hz), 20.6 (s). IR (KBr): ν 3099,
2923, 1725, 1636, 1523, 1500, 1319, 1202, 1132, 1103, 994,
847, 752, 540 cm-1. GC-MS m/z 320 (M+). HRMS (EI) m/z:
calcd. for C13H8O3F4S: 320.0130; found: 320.0120.
4.2.1 4-Ethoxy-6-methyl-3-((trifluoromethyl)thio)-2H-
pyran-2-one (3a). Following the general procedure and workup,
3a was isolated as a white solid in 96% yield (122 mg). M.p.
4.2.6 4-(Benzyloxy)-6-methyl-3-((trifluoromethyl)thio)-2H-
pyran-2-one (3f). Following the general procedure and workup,
3f was isolated as a pale yellow solid in 95% yield (150 mg).
1
98.9-99.6 °C. Rf (diethyl ether) = 0.57. H NMR (400 MHz,
CDCl3) δ 6.14 (s, 1H), 4.29 (q, J = 6.9 Hz, 2H), 2.34 (s, 3H),
1.48 (t, J = 6.9 Hz, 3H). 19F NMR (376 MHz, CDCl3) δ -42.8 (s,
3F). 13C NMR (101 MHz, CDCl3) δ 174.4 (s), 167.8 (s), 163.0
(s), 129.4 (q, J = 311.3 Hz), 95.7 (s), 87.2 (q, J = 2.0 Hz), 66.9
1
M.p. 112.5-113.5°C. Rf (diethyl ether) = 0.43. H NMR (400
MHz, CDCl3) δ 7.48 – 7.36 (m, 5H), 6.18 (s, 1H), 5.32 (s, 2H),
2.32 (s, 3H). 19F NMR (376 MHz, CDCl3) δ -42.5 (s, 3F). 13C
NMR (101 MHz, CDCl3) δ 167.8 (s), 162.9 (s), 134.1 (s),
129.4 (q, J = 311.4 Hz), 129.1 (s), 129.0 (s), 128.9 (s), 128.8
(s), 126.9 (s), 126.8 (s), 96.1 (s), 88.0 (q, J = 2.0 Hz), 72.2 (d, J
(s),
20.8
(s),
14.4(s).
IR (KBr): ν 3105, 2923, 2853, 1698, 1636, 1505, 1454, 1323,
1219, 1102, 923, 751, 527 cm-1. GC-MS m/z 254 (M+). HRMS
(EI) m/z: calcd. for C9H9O3F3S: 254.0225; found: 254.0224.
=
1.5 Hz), 20.9 (s). IR (KBr):
ν
3107, 1707, 1630,
1511, 1454, 1327, 1103, 904, 729, 691, 466 cm-1. GC-MS m/z
316 (M+). HRMS (EI) m/z: calcd. for C14H11O3F3S: 316.0381;
found: 316.0387.
4.2.2 6-Methyl-4-propoxy-3-((trifluoromethyl)thio)-2H-
pyran-2-one (3b). Following the general procedure and workup,
3b was isolated as a white solid in 92% yield (120 mg). M.p.
1
4.2.7
6-Methyl-4-((4-methylbenzyl)oxy)-3-
63.2-64.5 °C. Rf (diethyl ether) = 0.66. H NMR (400 MHz,
((trifluoromethyl)thio)-2H-pyran-2-one (3g). Following the
general procedure and workup, 3g was isolated as a pale
yellow solid in 99% yield (160 mg). M.p. 118.6-119.3 °C. Rf
CDCl3) δ 6.14 (s, 1H), 4.16 (t, J = 6.2 Hz, 2H), 2.33 (s, 3H),
1.92 – 1.81 (m, 2H), 1.06 (t, J = 7.3 Hz, 3H). 19F NMR (376

5
1
(diethyl ether) = 0.70. H NMR (400 MHz, CDCl3) δ 7.32 –
4.2.12 6-Methyl-4-propoxy-3-((trifluoromethyl)selanyl)-
ACCEPTED MANUSCRIPT
7.21 (m, 4H), 6.16 (s, 1H), 5.28 (s, 2H), 2.40 (s, 3H), 2.32 (s,
3H). 19F NMR (376 MHz, CDCl3) δ -42.5 (s, 3F). 13C NMR
(101 MHz, CDCl3) δ 174.3 (s), 167.7 (s), 162.9 (s), 138.9 (s),
131.1 (s), 129.7 (s), 129.5 (q, J = 311.4 Hz), 127.1 (s), 96.1
(s), 87.9 (q, J = 2.1 Hz), 72.2 (s), 21.2 (s), 20.9 (s).
IR (KBr): ν 2924, 1700, 1635, 1503, 1324, 1211, 1114, 901,
765, 491 cm-1. GC-MS m/z 330 (M+). HRMS (EI) m/z: calcd.
for C15H13O3F3S: 330.0538; found: 330.0546.
2H-pyran-2-one (4b). Following the general procedure and
workup, 4b was isolated as a white solid in 93% yield (146
mg). M.p. 66.2-67.2 °C. Rf (diethyl ether) = 0.68. H NMR
1
(400 MHz, CDCl3) δ 6.12 (s, 1H), 4.15 (t, J = 6.2 Hz, 2H),
2.34 (s, 3H), 1.91 – 1.80 (dt, 2H), 1.06 (t, J = 7.3 Hz, 3H). 19
F
NMR (376 MHz, CDCl3) δ -35.4 (s, 3F). 13C NMR (101 MHz,
CDCl3) δ 173.3 (s), 167.4 (s), 163.0 (s), 122.2 (q, J = 335.7
Hz), 95.5 (s), 87.2 (q, J = 1.1 Hz), 72.3 (s), 22.3 (s), 20.7 (s),
10.2 (s). IR (KBr): ν 3094, 2974, 1697, 1631, 1510, 1453,
1380, 1324, 1213, 1085, 940, 757, 737, 531 cm-1. GC-MS m/z
316 (M+). HRMS (EI) m/z: calcd. for C10H11O3F374Se:
309.9885; found: 309.9883.
4.2.8
4-((4-Fluorobenzyl)oxy)-6-methyl-3-
((trifluoromethyl)thio)-2H-pyran-2-one (3h). Following the
general procedure and workup, 3h was isolated as a yellow
solid in 91% yield (150 mg). M.p. 131.7-132.3°C. Rf (diethyl
1
ether) = 0.58. H NMR (400 MHz, CDCl3) δ 7.42 – 7.37 (m,
4.2.13 4-Isopropoxy-6-methyl-3-((trifluoromethyl)selanyl)-
2H-pyran-2-one (4c). Following the general procedure and
workup, 4c was isolated as a white solid in 95% yield (148
2H), 7.14 (t, J = 8.0 Hz, 2H), 6.17 (s, 1H), 5.27 (s, 2H), 2.34
(s, 3H). 19F NMR (376 MHz, CDCl3) δ -42.5 (s, 3F), -112.24 –
-112.34 (m, 1F). 13C NMR (101 MHz, CDCl3) δ 174.0 (s),
168.0 (s), 164.2 (s), 162.8 (s), 161.7 (s), 129.4 (q, J = 311.4
Hz), 129.0 (d, J = 8.4 Hz), 116.1 (d, J = 21.8 Hz), 95.9 (s),
88.1 (q, J = 2.1 Hz), 71.5 (s), 20.9 (s). IR (KBr): ν 3073, 2920,
1720, 1628, 1509, 1402, 1327, 1104, 1070, 903, 750, 545 cm-1.
GC-MS m/z 334 (M+). HRMS (EI) m/z: calcd. for
C14H10O3F4S: 334.0287; found: 334.0293.
1
mg). M.p. 125.7-127.0 °C. Rf (diethyl ether) = 0.68. H NMR
(400 MHz, CDCl3) δ 6.09 (s, 1H), 4.80 – 4.69 (m, 1H), 2.33 (s,
3H), 1.41 (d, J = 6.0 Hz, 6H). 19F NMR (376 MHz, CDCl3) δ -
35.4 (s, 3F). 13C NMR (101 MHz, CDCl3) δ 172.4 (s), 167.0
(s), 163.1 (s), 122.2 (q, J = 335.6 Hz), 95.8 (s), 87.7 (q, J = 1.2
Hz), 74.2 (s), 22.1 (s), 20.7 (s). IR (KBr): ν 3097, 2988, 1696,
1631, 1507, 1453, 1316, 1214, 1120, 1089, 897, 757, 737, 532
cm-1. GC-MS m/z 315 (M+). HRMS (EI) m/z: calcd. for
C10H11O3F374Se: 309.9885; found: 309.9877.
4.2.9
6-Methyl-4-((4-(trifluoromethyl)benzyl)oxy)-3-
((trifluoromethyl)thio)-2H-pyran-2-one (3i). Following the
general procedure and workup, 3i was isolated as a pale yellow
solid in 99% yield (190 mg). M.p. 158.4-158.9 °C. Rf (diethyl
4.2.14 6-Methyl-4-phenoxy-3-((trifluoromethyl)selanyl)-2H-
pyran-2-one (4d). Following the general procedure and workup,
4d was isolated as a pale yellow solid in 94% yield (158 mg).
M.p. 101.8-102.8 °C. Rf (diethyl ether/n-pentane 1:1) = 0.48.
1H NMR (400 MHz, CDCl3) δ 7.52 – 7.45 (m, 2H), 7.39 – 7.32
(m, 1H), 7.09 (d, J = 7.9 Hz, 2H), 5.68 (s, 1H), 2.23 (s, 3H).
19F NMR (376 MHz, CDCl3) δ -35.2 (s, 3F). 13C NMR (101
MHz, CDCl3) δ 172.5 (s), 167.3 (s), 162.8 (s), 152.8 (s), 130.5
(s), 126.9 (s), 122.2 (q, J = 335.7 Hz), 120.9 s), 97.1 (s), 89.6
(q, J = 1.6 Hz), 20.6 (s). IR (KBr): ν 3100, 2919, 1720, 1639,
1522, 1486, 1382, 1313, 1212, 1087, 991, 754, 687, 531 cm-1.
GC-MS m/z 349 (M+). HRMS (EI) m/z: calcd. for
C13H9O3F374Se: 343.9729; found: 343.9735.
1
ether) = 0.54. H NMR (400 MHz, CDCl3) δ 7.72 (d, J = 8.1
Hz, 2H), 7.55 (d, J = 8.1 Hz, 2H), 6.16 (s, 1H), 5.37 (s, 2H),
2.35 (s, 3H). 19F NMR (376 MHz, CDCl3) δ -42.4 (s, 3F), -62.8
(s, 3F). 13C NMR (101 MHz, CDCl3) δ 173.8 (s), 168.3 (s),
162.6 (s), 138.0 (q, J = 1.3 Hz), 131.0 (q, J = 32.7 Hz), 127.0
(s), 126.0 (q, J = 3.8 Hz), 123.8 (q, J = 272.3 Hz), 95.8 (s),
88.4 (q, J = 2.0 Hz), 71.1 (s), 30.3 (s), 21.0 (s). IR(KBr): ν
3105, 2925, 1716, 1629, 1513, 1322, 1153, 1106, 1064, 1005,
900, 823, 753, 592 cm-1. GC-MS m/z 384 (M+). HRMS (EI)
m/z: calcd. for C15H10O3F6S: 384.0255; found: 384.0256.
4.2.10
4-((3-Methoxybenzyl)oxy)-6-methyl-3-
((trifluoromethyl)thio)-2H-pyran-2-one (3j). Following the
general procedure and workup, 3j was isolated as a pale yellow
solid in 98% yield (167 mg). M.p. 96.3-96.9 °C. Rf (diethyl
4.2.15
4-(4-Fluorophenoxy)-6-methyl-3-
((trifluoromethyl)selanyl)-2H-pyran-2-one (4e). Following the
general procedure and workup, 4e was isolated as a pale
yellow solid in 96% yield (176 mg). M.p. 123.0-124.2 °C. Rf
(diethyl ether/n-pentane 1:1) = 0.40. 1H NMR (400 MHz,
CDCl3) δ 7.20 – 7.11 (m, 2H), 7.09 – 7.04 (m, 2H), 5.67 (s,
1H), 2.24 (s, 3H). 19F NMR (376 MHz, CDCl3) δ -35.2 (s, 3F),
-114.6 – -114.7 (m, 1F). 13C NMR (101 MHz, CDCl3) δ 172.4
(s), 167.6 (s), 162.3 (d, J = 64.2 Hz), 159.5 (s), 148.6 (d, J =
3.0 Hz), 122.6 (s), 122.5 (s), 122.2 (q, J = 335.6 Hz), 117.3 (s),
117.1 (s), 96.8 (s), 89.6 (q, J = 1.4 Hz), 20.6 (s). IR (KBr): ν
3097, 1719, 1636, 1521, 1499, 1444, 1381, 1312, 1201, 1130,
1086, 992, 846, 738, 537, 485 cm-1. GC-MS m/z 367 (M+).
HRMS (EI) m/z: calcd. for C13H8O3F474Se: 361.9634; found:
361.9640.
1
ether) = 0.64. H NMR (400 MHz, CDCl3) δ 7.41 – 7.31 (m,
1H), 7.06 – 6.78 (m, 3H), 6.15 (s, 1H), 5.30 (s, 2H), 3.83 (s,
3H), 2.32 (s, 3H). 19F NMR (376 MHz, CDCl3) δ -42.5 (s, 3F).
13C NMR (101 MHz, CDCl3) δ 174.2 (s), 167.9 (s), 162.9 (s),
160.1 (s), 135.7 (s), 130.1 (s), 127.8 (q, J = 390.6), 118.7 (s),
114.6 (s), 111.9 (s), 96.1 (s), 88.1 (q, J = 2.0 Hz), 71.9 (s), 55.3
(s),
20.9
(s).
IR (KBr):
ν
3105,
2926, 2839,1699, 1634, 1504, 1449, 1321, 1272, 1108, 785,
753, 696 cm-1. GC-MS m/z 346 (M+). HRMS (EI) m/z: calcd.
for C15H13O4F3S: 346.0487; found: 346.0499.
4.2.11 4-Ethoxy-6-methyl-3-((trifluoromethyl)selanyl)-2H-
pyran-2-one (4a). Following the general procedure and workup,
4a was isolated as a white solid in 95% yield (143 mg). M.p.
4.2.16 4-(Benzyloxy)-6-methyl-3-((trifluoromethyl)selanyl)-
2H-pyran-2-one (4f). Following the general procedure and
workup, 4f was isolated as a white solid in 91% yield (165
1
97.8-99.3 °C. Rf (diethyl ether) = 0.60. H NMR (400 MHz,
CDCl3) δ 6.11 (s, 1H), 4.27 (q, J = 7.0 Hz, 2H), 2.34 (s, 3H),
1.47 (t, J = 7.0 Hz, 3H). 19F NMR (376 MHz, CDCl3) δ -35.4
(s, 3F). 13C NMR (101 MHz, CDCl3) δ 173.0 (s), 167.3 (s),
162.9 (s), 122.2 (q, J = 335.7 Hz), 95.4 (s), 87.4 (q, J = 1.4
Hz), 66.6 (s), 20.7 (s), 14.4 (s). IR (KBr): ν 3103, 2992, 2924,
1696, 1635, 1503, 1452, 1391, 1319, 1088, 910, 757, 734, 524
cm-1. GC-MS m/z 301 (M+). HRMS (EI) m/z: calcd. for
C9H9O3F374Se: 295.9729; found: 295.9735.
1
mg). M.p. 107.7-108.6 °C. Rf (diethyl ether) = 0.45. H NMR
(400 MHz, CDCl3) δ 7.49 – 7.33 (m, 5H), 6.18 (s, 1H), 5.31 (s,
2H), 2.31 (s, 3H). 19F NMR (376 MHz, CDCl3) δ -35.1 (s, 3F).
13C NMR (101 MHz, CDCl3) δ 173.2 (s), 167.6 (s), 162.9 (s),
134.3 (s), 128.9 (s), 128.8 (s), 126.9 (s), 122.3 (q, J = 335.8
Hz), 95.9 (s), 87.8 (d, J = 1.2 Hz), 72.1 (s), 20.7 (s). IR (KBr):
ν 3106, 1702, 1630, 1515, 1455, 1381, 1322, 1088, 1053, 999,

6
Tetrahedron
ACCEPTED MANUSCRIPT
729, 691, 466 cm-1. GC-MS m/z 363 (M+). HRMS (EI) m/z:
CDCl3) δ -38.7 (s, 3F). 13C NMR (101 MHz, CDCl3) δ 162.6
calcd. for C14H11O3F374Se: 357.9885; found: 357.9876.
(s), 160.1 (s), 146.4 (q, J = 2.0 Hz), 128.1 (q, J = 309.9 Hz),
112.6 (q, J = 1.9 Hz), 103.7 (q, J = 1.8 Hz), 20.0 (s). IR (KBr):
ν 3102, 2921, 1725, 1625, 1538, 1180, 1109, 739, 529 cm-1.
GC-MS m/z 210 (M+). HRMS (EI) m/z: calcd. for C7H5O2F3S:
209.9962; Found: 209.9965.
4.2.17 6-Methyl-4-((4-methylbenzyl)oxy)-3-
((trifluoromethyl)selanyl)-2H-pyran-2-one (4g). Following the
general procedure and workup, 4g was isolated as a pale
yellow solid in 96% yield (181 mg). M.p. 115.8-116.1 °C. Rf
(diethyl ether) = 0.73. 1H NMR (400 MHz, CDCl3) δ 7.28 (d, J
= 8.1 Hz, 2H), 7.23 (d, J = 8.0 Hz, 2H), 6.17 (s, 1H), 5.26 (s,
2H), 2.38 (s, 3H), 2.31 (s, 3H). 19F NMR (376 MHz, CDCl3) δ
-35.2 (s, 3F). 13C NMR (101 MHz, CDCl3) δ 173.2 (s), 167.5
(s), 162.9 (s), 138.9 (s), 131.2 (s), 129.6 (s), 127.1 (s), 122.3
(q, J = 335.9 Hz), 95.9 (s), 87.9 (q, J = 1.4 Hz), 72.2 (s), 21.2
(s), 20.8 (s). IR (KBr): ν 2922, 1709, 1635, 1511, 1444, 1378,
1318, 1209, 1090, 1002, 892, 810, 733, 493 cm-1. GC-MS m/z
377 (M+). HRMS (EI) m/z: calcd. for C15H13O3F474Se:
372.0042; found: 372.0058.
4.2.22 6-Methyl-4-((trifluoromethyl)selanyl)-2H-pyran-2-
one (6b). Following the general procedure and workup, 6b was
isolated as a pale yellow oil in 98% yield (125 mg). Rf (diethyl
1
ether/n-pentane 1:1) = 0.63. H NMR (400 MHz, CDCl3) δ
6.44 (s, 1H), 6.14 (s, 1H), 2.27 (s, 3H). 19F NMR (376 MHz,
CDCl3) δ -32.2 (s, 3F). 13C NMR (101 MHz, CDCl3) δ 162.2
(s), 160.0 (s), 144.7 (q, J = 1.5 Hz), 121.9 (q, J = 333.1 Hz),
115.5 (q, J = 1.8 Hz), 105.9 (q, J = 1.6 Hz), 19.9 (s). IR (KBr):
ν 3103, 2923, 1725, 1620, 1535, 1149, 1098, 737, 526 cm-1.
GC-MS m/z 257 (M+). HRMS (EI) m/z: calcd. for
C7H5O2F374Se: 251.9466; Found: 251.9470.
4.2.18
4-((4-Fluorobenzyl)oxy)-6-methyl-3-
((trifluoromethyl)selanyl)-2H-pyran-2-one (4h). Following the
general procedure and workup, 4h was isolated as a white solid
in 93% yield (177 mg). M.p. 120.0-120.9 °C. Rf (diethyl ether)
Procedure
for
Ring-opening reaction of
4-(4-
Fluorophenoxy)-6-methyl-3-((trifluoromethyl)thio)-2H-
pyran-2-one (3e)
1
= 0.56. H NMR (400 MHz, CDCl3) δ 7.45 – 7.35 (m, 2H),
A suspension of 3e (200 mg, 0.625 mmol) in NaOH
aqueous solution (2M, 40 mL) was stirred at 60 °C for 16 h.
Upon cooling, the reaction mixture was filtered. The filterate
was added dropwise of HCl aqueous solution (2M) to pH 4-5
at 0 °C. The mixture was extracted with EtOAc (3 × 20 mL),
and the combined organic layers were dried over MgSO4,
filtered, and concentrated under reduced pressure. The residues
were purified by flash chromatography on silica gel using ethyl
acetate/n-pentane (1:20) for elution.
7.12 (t, J = 8.6 Hz, 2H), 6.15 (s, 1H), 5.26 (s, 2H), 2.33 (s,
3H). 19F NMR (376 MHz, CDCl3) δ -35.1 (s, 3F), -112.3 – -
112.6 (m, 1F). 13C NMR (101 MHz, CDCl3) δ 172.9 (s), 167.7
(s), 164.1 (s), 162.8 (s), 161.6 (s), 129.9 (d, J = 3.3 Hz), 129.0
(d, J = 8.4 Hz), 122.2 (q, J = 335.7 Hz), 116.1 (s), 115.9 (s),
95.7 (s), 88.0 (q, J = 1.5 Hz), 71.4 (s), 20.8 (s). IR (KBr): ν
3106, 1702, 1630, 1515, 1455, 1381, 1322, 1088, 1000, 890,
729, 691, 574, 466 cm-1. GC-MS m/z 381 (M+). HRMS (EI)
m/z: calcd. for C14H10O3F474Se: 375.9786; found: 375.9791.
3-(4-fluorophenoxy)-5-oxo-2-((trifluoromethyl)thio)hex-2-
enoic acid (7e). Obtained as a yellow solid in 25% yield (40
mg, 0.12 mmol) with isomers. Rf (EtOAc/n-pentane 1:10) =
4.2.19
6-Methyl-4-((4-(trifluoromethyl)benzyl)oxy)-3-
((trifluoromethyl)selanyl)-2H-pyran-2-one (4i). Following the
general procedure and workup, 4i was isolated as a white solid
in 89% yield (190 mg). M.p. 167.8-168.3 °C. Rf (diethyl ether)
= 0.42. 1H NMR (400 MHz, CDCl3) δ 7.71 (d, J = 8.2 Hz, 2H),
7.55 (d, J = 8.2 Hz, 2H), 6.14 (s, 1H), 5.36 (s, 2H), 2.35 (s,
3H). 19F NMR (376 MHz, CDCl3) δ -35.0 (s, 3F), -62.7 (s, 3F).
13C NMR (101 MHz, CDCl3) δ 172.6 (s), 167.9 (s), 162.6 (s),
138.2 (q, J = 1.2 Hz), 131.0 (q, J = 32.7 Hz), 127.0 (s), 125.9
(q, J = 3.8 Hz), 123.8 (q, J = 272.2 Hz), 95.5 (s), 88.3 (q, J =
1.5 Hz), 71.0 (s), 20.8 (s). IR (KBr): ν 3103,
2923, 1709, 1629, 1514, 1381, 1319, 1223, 1055, 1000, 824,
755, 737, 526 cm-1. GC-MS m/z 431 (M+). HRMS (EI) m/z:
calcd. for C15H10O3F674Se: 425.9759; found: 425.9750.
1
0.41. M.p. 60.7-61.9 °C. H NMR (400 MHz, CDCl3) δ 8.94
(s, 1H), 7.18 – 7.08 (m, 2H), 7.04 – 6.97 (m, 2H), 3.73 (s, 2H),
2.44 (s, 3H). 19F NMR (376 MHz, CDCl3) δ -42.36 (s), -43.20
(s), -43.93 (s), -115.68 – -115.79 (m), -116.02 – -116.13 (m).
13C NMR (101 MHz, CDCl3) δ 178.9 (s), 171.5 (s), 161.7 (s),
159.2 (s), 148.8 (d, J = 2.9 Hz), 130.0 (q, J = 308.1 Hz), 129.4
(q, J = 312.1 Hz), 122.4 (d, J = 8.6 Hz), 121.8 (d, J = 8.6 Hz),
116.9 (d, J = 23.2 Hz), 116.8 (d, J = 23.8 Hz), 30.9 (s), 19.4 (s).
IR (KBr):
ν
3300,
2500, 2991, 1668, 1552, 1497, 1421, 1375, 1257, 1182, 1103,
842, 771, 752, 735, 523, 486 cm-1. HRMS (EI) m/z: calcd. for
C11H7O3F4S (M+-COCH3+H): 296.0130; found: 296.0136.
4.2.20
4-((3-Methoxybenzyl)oxy)-6-methyl-3-
((trifluoromethyl)selanyl)-2H-pyran-2-one (4j). Following the
general procedure and workup, 4j was isolated as a pale yellow
solid in 98% yield (190 mg). M.p. 100.1-101.4 °C. Rf (diethyl
Acknowledgments
Financial support from National Natural Science
Foundation of China (21372044), and Fuzhou University
(022494) is gratefully acknowledged.
1
ether) = 0.64. H NMR (400 MHz, CDCl3) δ 7.41 – 7.25 (m,
1H), 6.99 – 6.86 (m, 3H), 6.14 (s, 1H), 5.29 (s, 2H), 3.83 (s,
3H), 2.31 (s, 3H). 19F NMR (376 MHz, CDCl3) δ -35.1 (s, 3F).
13C NMR (101 MHz, CDCl3) δ 173.1 (s), 167.6 (s), 162.9 (s),
160.1 (s), 135.9 (s), 130.0 (s), 122.3 (q, J = 335.8 Hz), 118.8
(s), 114.5 (s), 112.0 (s), 95.8 (s), 87.9 (q, J = 1.3 Hz), 71.8 (s),
55.3 (s), 20.8 (s). IR (KBr): ν 2938, 2845, 1712, 1634, 1584,
1520, 1318, 1220, 1090, 1049, 1005, 892, 781, 753, 556 cm-1.
GC-MS m/z 393 (M+). HRMS (EI) m/z: calcd. for
C15H13O4F374Se: 387.9991 ; found: 388.0002.
Supplementary Material
Supplementary data associated with this article can be
found, in the online version.
References and notes
1.
2.
Dickinson, J. M. Natural Product Reports 1993, 10, 71.
McGlacken, G. P.; Fairlamb, I. J. S. Natural Product
Reports 2005, 22, 369.
Fairlamb, I. J. S.; Marrison, L. R.; Dickinson, J. M.; Lu, F.-
J.; Schmidt, J. P. Bioorg. Med. Chem. 2004, 12, 4285.
Goel, A.; Ram, V. J. Tetrahedron 2009, 65, 7865.
4.2.21 6-Methyl-4-((trifluoromethyl)thio)-2H-pyran-2-one
(6a). Following the general procedure and workup, 6a was
isolated as a pale yellow oil in 80% yield (84 mg). Rf (diethyl
3.
4.
1
ether/n-pentane 1:1) = 0.64. H NMR (400 MHz, CDCl3) δ
6.32 (s, 1H), 6.04 (s, 1H), 2.28 (s, 3H). 19F NMR (376 MHz,

7
5.
6.
Pedras, M. S. C.; Erosa-López, C. C.; Quail, J. W.; Taylor, J.
45. Zhu, S.-Q.; Xu, X.-H.; Qing, F.-L. Eur. J. Org. Chem.
2014, 4453.
ACCEPTED MANUSCRIPT
L. Bioorg. Med. Chem. Lett. 1999, 9, 3291.
Hochlowski, J. E.; Faulkner, D. J. Tetrahedron Lett. 1983,
24, 1917.
Bereznak, J. F.; Walker, M. P. WO2000008026A2, 2000.
Clarke, S. L.; McGlacken, G. P. Tetrahedron 2015, 71,
2906.
46. Weng, Z.; He, W.; Chen, C.; Lee, R.; Tan, D.; Lai, Z.; Kong,
D.; Yuan, Y.; Huang, K.-W. Angew. Chem. Int. Ed. 2013,
52, 1548.
47. Chen, C.; Ouyang, L.; Lin, Q.; Liu, Y.; Hou, C.; Yuan, Y.;
Weng, Z. Chem.-Eur. J. 2014, 20, 657.
7.
8.
9.
Zhu, X.-F.; Schaffner, A.-P.; Li, R. C.; Kwon, O. Org. Lett.
2005, 7, 2977.
48. Lin, Q.; Chen, L.; Huang, Y.; Rong, M.; Yuan, Y.; Weng, Z.
Org. Biomol. Chem. 2014, 12, 5500.
10. Luo, T.; Dai, M.; Zheng, S.-L.; Schreiber, S. L. Org. Lett.
2011, 13, 2834.
49. Tan, J.; Zhang, G.; Ou, Y.; Yuan, Y.; Weng, Z. Chin. J.
Chem. 2013, 31, 921.
11. Dombray, T.; Blanc, A.; Weibel, J.-M.; Pale, P. Org. Lett.
2010, 12, 5362.
50. Huang, Y.; Ding, J.; Wu, C.; Zheng, H.; Weng, Z. J. Org.
Chem. 2015, 80, 2912.
12. Boiko, V. N. Beilstein J. Org. Chem. 2010, 6, 880.
13. Tlili, A.; Billard, T. Angew. Chem. Int. Ed. 2013, 52, 6818.
14. Toulgoat, F.; Alazet, S.; Billard, T. Eur. J. Org. Chem. 2014,
2415.
15. Xiang, H.; Yang, C. Org. Lett. 2014, 16, 5686.
16. Li, M.; Petersen, J. L.; Hoover, J. M. Org. Lett. 2017, 19,
638.
51. Zhang, M.; Weng, Z. Adv. Synth. Catal. 2016, 358, 386.
52. Luo, B.; Zhang, Y.; You, Y.; Weng, Z. Org. Biomol. Chem.
2016, 14, 8615.
53. Zhu, P.; He, X.; Chen, X.; You, Y.; Yuan, Y.; Weng, Z.
Tetrahedron 2014, 70, 672.
54. Nolan, M.-T.; Pardo, L. M.; Prendergast, A. M.;
McGlacken, G. P. J. Org. Chem. 2015, 80, 10904.
17. Leo, A.; Hansch, C.; Elkins, D. Chem. Rev. 1971, 71, 525.
18. Yagupol'skii, L. M.; Ilchenko, A. Y.; Kondratenko, N. V.
Russ. Chem. Rev. 1974, 43, 32.
19. Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165.
20. Xu, X.-H.; Matsuzaki, K.; Shibata, N. Chem. Rev. 2015,
115, 731.
21. Ni, C.; Hu, M.; Hu, J. Chem. Rev. 2015, 115, 765.
22. Chu, L.; Qing, F.-L. Acc. Chem. Res. 2014, 47, 1513.
23. Shao, X.; Xu, C.; Lu, L.; Shen, Q. Acc. Chem. Res. 2015, 48,
1227.
24. Zheng, H.; Huang, Y.; Weng, Z. Tetrahedron Lett. 2016, 57,
1397.
25. Teverovskiy, G.; Surry, D. S.; Buchwald, S. L. Angew.
Chem. Int. Ed. 2011, 50, 7312.
26. Zhang, C.-P.; Vicic, D. A. J. Am. Chem. Soc. 2012, 134,
183.
27. Rueping, M.; Tolstoluzhsky, N.; Nikolaienko, P. Chem.-Eur.
J. 2013, 19, 14043.
28. Xu, J.; Mu, X.; Chen, P.; Ye, J.; Liu, G. Org. Lett. 2014, 16,
3942.
29. Yin, G.; Kalvet, I.; Schoenebeck, F. Angew. Chem. Int. Ed.
2015, 54, 6809.
30. Zhang, C.-P.; Vicic, D. A. Chem. Asian J. 2012, 7, 1756.
31. Shao, X.; Wang, X.; Yang, T.; Lu, L.; Shen, Q. Angew.
Chem. Int. Ed. 2013, 52, 3457.
32. Shao, X.; Liu, T.; Lu, L.; Shen, Q. Org. Lett. 2014, 16, 4738.
33. Baert, F.; Colomb, J.; Billard, T. Angew. Chem. Int. Ed.
2012, 51, 10382.
34. Tran, L. D.; Popov, I.; Daugulis, O. J. Am. Chem. Soc. 2012,
134, 18237.
35. Yang, Y.-D.; Azuma, A.; Tokunaga, E.; Yamasaki, M.;
Shiro, M.; Shibata, N. J. Am. Chem. Soc. 2013, 135, 8782.
36. Chen, C.; Xu, X.-H.; Yang, B.; Qing, F.-L. Org. Lett. 2014,
16, 3372.
37. Xu, C.; Shen, Q. Org. Lett. 2014, 16, 2046.
38. Guo, S.; Zhang, X.; Tang, P. Angew. Chem. Int. Ed. 2015,
54, 4065.
39. Wu, H.; Xiao, Z.; Wu, J.; Guo, Y.; Xiao, J.-C.; Liu, C.;
Chen, Q.-Y. Angew. Chem. Int. Ed. 2015, 54, 4070.
40. Mukherjee, S.; Maji, B.; Tlahuext-Aca, A.; Glorius, F. J.
Am. Chem. Soc. 2016, 138, 16200.
41. Nikolaienko, P.; Pluta, R.; Rueping, M. Chem.-Eur. J. 2014,
20, 9867.
42. Liu, J.-B.; Chen, C.; Chu, L.; Chen, Z.-H.; Xu, X.-H.; Qing,
F.-L. Angew. Chem. Int. Ed. 2015, 54, 897.
43. Alazet, S.; Zimmer, L.; Billard, T. Angew. Chem. Int. Ed.
2013, 52, 10814.
44. Pluta, R.; Nikolaienko, P.; Rueping, M. Angew. Chem. Int.
Ed. 2014, 53, 1650.