Palladium-Catalyzed Allylation of Polyfluoroarenes with Allylic Pivalates

Article abstract of DOI:10.1055/s-0036-1590914

An efficient 1,5-cyclooctadiene-PdCl ₂ /dicyclohexyl(2′,4′,6′-triisopropylbiphenyl-2-yl)phosphine (XPhos) catalytic system was developed for C-H allylation of polyfluoroarenes with allylic pivalates. The reactions showed excellent functional-group tolerance, good yields, and high regioselectivities. Mechanistic investigations supported a (π-allyl)palladium complex pathway through a directed oxidative addition of the allylic pivalate to palladium, followed by sequential nucleophilic attack by the polyfluorobenzene and reductive elimination. In a gram-scale reaction, a palladium loading of 0.5 mol% was enough to afford the required product in good yield.

Full text of DOI:10.1055/s-0036-1590914

SYNLETT
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© Georg Thieme Verlag Stuttgart · New York
2017, 28, A–E
letter
A
en
X. Jiang et al.
Letter
Synlett
Palladium-Catalyzed Allylation of Polyfluoroarenes with Allylic
Pivalates
Xinpeng Jianga
Yong Liua
Lei Zhanga
COD-PdCl2 (5 mol%)
R
Fn
+
Fn
R
OPiv
H
XPhos (10 mol%)
Cs2CO3 (1.2 equiv)
Jinkang Chena
Kang Chenga
Chuanming Yu*a,b
18 examples
up to 98% yields
R = alkyl, aryl
Substrates are easier to prepare
low catalyst loading in gram-scale synthesis
n = 2–5
0
0
0
0
0-
0
0
2
1-
3
4
5
0-
7
7
8
a College of Pharmaceutical Sciences, Zhejiang University of
Technology, Hangzhou 310014, P. R. of China
b Collaborative Innovation Center of Yangtze River Delta Region
Green Pharmaceuticals, Zhejiang University of Technology,
Hangzhou 310014, P. R. of China
ycm@zjut.edu.cn
Received: 04.07.2017
Accepted after revision: 03.09.2017
Published online: 19.09.2017
alyzed C–H allylation under mild conditions.11 Neverthe-
less, most of these methods require either substrates con-
taining specific leaving groups that are difficult to install or
relatively high catalyst loadings. Consequently, it would be
highly desirable to develop a method to synthesize allylated
polyfluoroarenes that would overcome these limitations.
We recently developed a series of methods to synthesize
functionalized polyfluoroarenes12 and polyfluorohetero-
cycles.13 In a continuation of this work, we report a simple
palladium-catalyzed allylation reaction with allylic piva-
lates for the synthesis of allyl-substituted polyfluoroben-
zenes (Scheme 1b).
DOI: 10.1055/s-0036-1590914; Art ID: st-2017-w0541-l
Abstract An efficient 1,5-cyclooctadiene–PdCl2/dicyclohexyl(2′,4′,6′-
triisopropylbiphenyl-2-yl)phosphine (XPhos) catalytic system was de-
veloped for C–H allylation of polyfluoroarenes with allylic pivalates. The
reactions showed excellent functional-group tolerance, good yields,
and high regioselectivities. Mechanistic investigations supported a (π-
allyl)palladium complex pathway through a directed oxidative addition
of the allylic pivalate to palladium, followed by sequential nucleophilic
attack by the polyfluorobenzene and reductive elimination. In a gram-
scale reaction, a palladium loading of 0.5 mol% was enough to afford
the required product in good yield.
A. Previous works
Key words polyfluoroarenes, allylation, palladium catalysis, C–H func-
[Pd] or [Cu]
R
tionalization, fluoro compounds
Fn
Fn
+
R
LG
Owing to their unique physicochemical and biological
properties, polyfluoroarenes have been widely used in life
science,1 agrochemicals,2 and materials science.3 Because
the conventional Friedel–Crafts reaction is limited to elec-
tron-rich substrates,4 the development of efficient methods
to functionalize these important structural motifs is there-
fore highly valuable.5 Although the allyl group is syntheti-
cally useful due to its diverse functional-group transforma-
tions through simple treatments,6 few examples have been
reported of direct transition-metal-catalyzed allylations of
electron-deficient polyfluoroarenes (Scheme 1a). As an al-
ternative, stoichiometric amounts of aryl metal reagents
have been used to generate allylic polyfluoroarenes.7 Only a
few groups have reported direct allylations of polyfluoro-
arenes. For instance, Zhang and co-workers reported palla-
dium-catalyzed allylations of polyfluorobenzenes with al-
lylic carbonates8 or allylic halides.9 Similarly, Miura and co-
workers employed allyl phosphates in the presence of a
[Cu(acac)2]/1,10-phenanthroline catalyst system,10 and Xie
and Chang developed a copper/N-heterocyclic carbene cat-
LG = Br/Cl, OCO2R, OP(O)(OEt)2 etc.
B. This work
[Pd]
R
Fn
Fn
+
R
OPiv
Scheme 1 Approaches to allylation of electron-deficient arenes
We commenced our study by choosing cinnamyl acetate
[(E)-2a] and pentafluorobenzene (1a) as substrates. Initial-
ly, the reaction of pentafluorobenzene (1a) with cinnamyl
acetate [(E)-2a] was investigated in the presence of
Pd(OAc)2 (5 mol%) and PPh3 (10 mol%) in toluene at 120 ℃.
We were please to observe the formation of coupling prod-
uct 4a in 68% yield (Table 1, entry 1). When the leaving
group was changed to OPiv, the yield of 4a reached 87%
(entry 2). Other transition-metal catalysts, such as Cu(OAC)2
and NiCl2, proved to be ineffective with these substrates
(entries 3 and 4).
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

B
X. Jiang et al.
Letter
Synlett
Table 1 Screening of Substrate Leaving Groups and Transition-Metal
Table 2 Optimization of the Reaction Conditionsa
Catalystsa
Ph
F5
cat. (5 mol%)
Ph
Ph
OR
F5
+
F5
cat. (5 mol%)
PPh3 (10 mol%)
F5
+
Ph
OPiv
4a
5a
ligand (10 mol%)
Cs2CO3 (1.2 equiv)
toluene, 120 °C, 8 h
Cs2CO3 (1.2 equiv)
1a
4a
R = Ac (E)-2a
R = Piv (E)-3a
Ph
1a
(E)-3a
F5
Entry
R
Catalyst
Yieldb (%)
1
2
3
4
Ac
Pd(OAc)2
Pd(OAc)2
NiCl2
68
Entry
Catalyst
Ligand
Yieldb (%)
4a/5ac
Piv
Piv
Piv
87
NRc
trace
1
2
Pd(OAc)2
Pd2(dba)3
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(PPh3)4
Pd(TFA)2
PdCl2
PPh3
87
17
18
trace
64
79
75
89
43
83
68
85
91
98
74
25:1
> 33:1
20:1
–
Cu(OAc)2
–
a Reaction conditions: (E)-2a or (E)-3a (1.0 mmol), 1a (2.0 equiv), Cs2CO3
(1.2 equiv), catalyst (5 mol%), PPh3 (10 mol%), PhMe (3.0 mL), 120 °C, 8 h,
under argon.
3
–
4
bpy
b Yield of the isolated product.
c NR = no reaction.
5
dppf
>33:1
33:1
10:1
>33:1
15:1
20:1
20:1
25:1
15:1
>33:1
>33:1
6
dppp
(R)-BINAP
XPhos
XPhos
XPhos
XPhos
XPhos
XPhos
XPhos
XPhos
7
Encouraged by these results, we chose pentafluoroben-
zene (1a) and allylic pivalate [(E)-3a] for further optimiza-
tion of the reaction conditions (Table 2). In the absence of a
ligand,9 the reaction in the presence of Pd2(dba)3 (dba =
dibenzylideneacetone) or Pd(OAc)2 afforded 4a in 17 and
18% yield, respectively (Table 2, entries 2 and 3). Various li-
gands were then evaluated in the presence of 5 mol% of
Pd(OAc)2. The nitrogen ligand 2,2′-bipyridine gave a trace of
the product (entry 4); consequently, we screened various
phosphine ligands. The bidentate ligands 1,1′-bis(diphenyl-
phosphino)ferrocene (dppf), bis(diphenylphosphino)pro-
pane (dppp), and (R)-BINAP were less effective than PPh3
(entries 5–7), possibly due to hampered formation of the
(π-allyl)palladium pivalate, which is important for the effi-
ciency of the reaction.9 It’s worth noting that (R)-BINAP
produced a small amount of isomer 5a along with required
product 4a (4a/5a = 10:1). Fortunately, the monodentate li-
gand dicyclohexyl(2′,4′,6′-triisopropylbiphenyl-2-yl)phos-
phine (XPhos) gave a higher yield under similar conditions
(entry 8). Further investigation of the palladium catalyst
showed that Pd(PPh3)4 gave a lower yield and selectivity
(entry 9). The Pd(II) catalysts Pd(TFA)2, PdCl2, and
Pd(PPh3)2Cl2 afforded the corresponding products in 83, 68,
and 85% yield, respectively (entries 10–12). When Pd(acac)2
was used, a 91% yield of 4a was obtained with lower regio-
selectivity (4a/5a = 15:1) (entry 13). The best palladium
catalyst was found to be COD–PdCl2, giving 98% of 4a with
high regioselectivity (4a/5a > 33:1) (entry 14). With respect
to the base, K2CO3 gave a lower yield, suggesting that strong
basic conditions are essential for this reaction (entry 15).
Next, the scope of the substituted allylic pivalates was
examined under the optimal reaction conditions
(Scheme 2). Generally, substrates bearing an electron-do-
nating group afforded the required products 4a–e in good
yields (81–98%), whereas pivalates substituted with elec-
8
9
10
11
12
13
14
15d
Pd(PPh3)2Cl2
Pd(acac)2
COD–PdCl2
COD–PdCl2
a Reagents and conditions: (E)-3a (1.0 mmol), 1a (2.0 equiv), Cs2CO3 (1.2
equiv), catalyst (5 mol%), ligand (10 mol%), PhMe (3.0 mL), 120 °C, 8 h, un-
der argon.
b Yield of the isolated product.
c Determined by 1H NMR and 19F NMR spectroscopy.
d The base was replaced with K2CO3 (1.2 equiv).
tron-withdrawing groups gave lower yields (68–83%)
(Scheme 2; 4f and 4g). Interestingly, when (E)-3-(4-chloro-
phenyl)allyl pivalate was used, the three-component cou-
pling product 4h was obtained in good yield (76%) due to a
sequential C(sp2)–Cl bond activation. Sterically hindered
and less-reactive aliphatic allylic pivalates gave products 4i
and 4j in 71% and 60% yield, respectively. Furthermore, het-
erocyclic-substituted allylic pivalates also give products 4j
and 4k in 58 and 63% yield, respectively.
To further extend the scope of this method, various
fluoroarenes 1 containing two to four fluorine atoms were
tested. In general, the yields increased with increasing
number of fluorine atoms (Scheme 3). Substrates contain-
ing four fluorine atoms gave products 6a–d in 73–84% yield,
regardless of the electronic properties of the substituent
groups. Furthermore, those substrates possessing more
than one reaction site afforded the corresponding monoal-
lylated products 6c and 6d in good yields. For 1,3,5-trifluo-
robenzene, a moderate yield of 6e was obtained under the
standard conditions. We also detected trace amounts (<2%)
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

C
X. Jiang et al.
Letter
Synlett
R
F5
COD-PdCl2 (5 mol%)
4
5
F5
+
R
OPiv
XPhos(10 mol%)
Cs2CO3 (1.2 equiv)
toluene,120 °C
R
F5
1a
(E)-3
F
F
OMe
F
F
F
F
F
F
F
F
F
MeO
F
F
F
F
4a, 98%
4b, 84%
4c, 87%
F
F
F
F
F
F
F
F
F
F
F
Me
F
N
F
F3C
F
F
4d, 82%
4e, 81%
4f, 68%
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
R = 4-ClC6H4, 76%a
4g, 83%
(4i + 5i), 71%
4i/5i = 10:3
4h
F
F
F
F
F
F
F
O
F
N
F
F
F
F
F
F
(4j + 5j), 58%
4j/5j = 4:1
4k, 63%
(4l + 5l), 60%
4l/5l = 9:1
Scheme 2 Reaction of 1a with various allylic pivalates (E)-3. Reaction conditions: (E)-3 (1 mmol), 1a (2 equiv), COD–PdCl2 (5 mol%), XPhos (10 mol%),
Cs2CO3 (1.2 equiv), toluene (3 mL) 120 °C, 8 h, under argon. 4/5 > 20:1, unless otherwise specified. a Reaction conditions: (E)-3 (1 mmol), 1a (4 equiv),
Cs2CO3 (2.4 equiv), COD–PdCl2 (10 mol%), XPhos (20 mol%), toluene (4 mL), 120 °C, 8 h, under argon.
COD-PdCl2 (5 mol%)
ArF
OPiv
XPhos (10 mol%)
Cs2CO3 (1.2 equiv)
Fluoroarene
1
+
MeO
MeO
(E)-3b
6
toluene, 120 °C
F
F
F
F
F
F
F
F
MeO
F
OMe
MeO
F
CF3
MeO
F
F
6a, 81%
6b, 82%
6ca, 84%
F
F
F
F
F
MeO
F
MeO
F
F
MeO
F
6da, 73%
6ea, 56%
6f, 45%
Scheme 3 Cross-coupling reaction of fluoroarenes 1 with allylic pivalates (E)-3b. Reaction conditions: (E)-3b (1 mmol), 1 (2 equiv), Cs2CO3 (1.2 equiv),
COD–PdCl2 (5 mol%), XPhos (10 mol%), PhMe (3 mL), 120 ℃, 8 h, under argon.
a Minor bisallylic products were also detected by 19F NMR spectroscopy (see Supporting Information).
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

D
X. Jiang et al.
Letter
Synlett
of the corresponding bisallylic products for substrates con-
taining four fluorine atoms. Note that 1,3-difluorobenzene,
an unsuitable substrate in previous studies,8,10 provided the
corresponding product 6f in moderate yield, whereas
monofluorobenzenes such as 3-fluorobenzonitrile did not
react owing to the low acidity of the C–H bond to be acti-
vated.
With these results in hand, we conducted a gram-scale
experiment with pivalate 3a and pentafluorobenzene (1a)
under the standard conditions (Scheme 4). Because 5 mol%
of the palladium catalyst would be expensive if the reaction
were scaled up, we reduced the amount of COD–PdCl2 to 0.5
mol%, and the reaction was complete within eight hours,
giving the required product 4a in 80% yield.
with no (Z)-allylated or branched isomers observed. The
high stereo- and regioselectivity indicated that (π-allyl)pal-
ladium intermediates are formed in the catalytic reaction.
On the basis of the above experiment and reports on ki-
netic isotope effect studies,8,9 the reaction does not involve
a concerted metalation/deprotonation process. A plausible
reaction mechanism is therefore proposed in Scheme 6. Ini-
tially, Pd0 is generated from COD–PdCl2 and XPhos. Then,
the (π-allyl)palladium complex I is formed by oxidative ad-
dition of the allylic pivalate to the Pd0 species. Subsequent-
ly, the base-deprotonated polyfluoroaromatic undergoes
nucleophilic attack by the (π-allyl)palladium complex I to
form a (polyfluoroaryl)(allyl)palladium complex III. Finally,
reductive elimination leads to the expected allylated com-
pound, with regeneration of the Pd0 species.
In summary, we have developed a highly efficient COD–
PdCl2/XPhos-catalyzed allylation of polyfluorobenzenes to
synthesize a series of allylfluorobenzenes by means of a C–H
bond-functionalization reaction.14 The new method has ex-
cellent functional-group tolerance, competitive yields, and
excellent selectivity. Last, but not least, the high reactivity
of new catalyst system permits the use of a catalyst loading
of as little as 0.5 mol%, making such allylation reactions in-
dustrially attractive. Further investigations and applications
of this strategy are underway in our laboratory.
COD-PdCl2 (0.5 mol%)
Ph
F5
F5
Ph
OPiv
+
XPhos (1 mol%)
Cs2CO3 (1.2 equiv)
(E)-3a
1.09 g, 5 mmol
1a
2 equiv
4a
1.14 g, 80%
Scheme 4 Gram-scale experiment
To investigate the mechanism, we examined the reac-
tion of the (Z)-allylic pivalate (Z)-3a with pentafluoroben-
zene (1a) under the standard conditions (Scheme 5). The
linear (E)-allylated product 4a was obtained in 87% yield
Funding Information
F
This work was supported by the National Natural Science Foundation
F
F
F
standard
OPiv conditions
of China (NSFC) (grants numbers 21676252 and 21506191).
N
oaitn
a
l
N
a
utarl
Secince
F
o
u
n
d
oaitn
of
C
h
n
i
a
2(
1
6
7
6
2
5
2)
2(
1
5
0
6
1
9
1)
F5
+
F
Supporting Information
4a, 87%
(4a/5a > 33:1)
1a
(Z)-3a
Supporting information for this article is available online at
Scheme 5 Cross-coupling of pentafluorobenzene (1a) with (Z)-3-phe-
nylallyl pivalate [(Z)-3a]
https://doi.org/10.1055/s-0036-1590914.
S
u
p
p
ortiInfogrmoaitn
S
u
p
p
o
nrtogI
f
rmoaitn
Pd(II)
PivO
R
PdLn(0)
R
Fn
R
PdII
OPiv
L
I
base
Fn
Fn
R
H
PdII
Arf
L
II
III
Scheme 6 A possible mechanism for the direct palladium-catalyzed allylation of polyfluoroarenes with allylic pivalates. Arf = polyfluoroaryl.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

E
X. Jiang et al.
Letter
Synlett
References and Notes
(7) (a) Kiyotsuka, Y.; Acharya, H. P.; Katayama, Y.; Hyodo, T.;
Kobayashi, Y. Org. Lett. 2008, 10, 1719. (b) Vinogradov, A. S.;
Krasnov, V. I.; Platonov, V. E. Russ. J. Org. Chem. 2008, 44, 95.
(c) Pigge, F. C. Synthesis 2010, 1745.
(8) Fan, S.; Chen, F.; Zhang, X. Angew. Chem. Int. Ed. 2011, 50, 5918.
(9) Yu, Y.-B.; Fan, S.; Zhang, X. Chem. Eur. J. 2012, 18, 14643.
(10) Yao, T.; Hirano, K.; Satoh, T.; Miura, M. Angew. Chem. Int. Ed.
2011, 50, 2990.
(11) Xie, W.; Chang, S. Angew. Chem. Int. Ed. 2016, 55, 1876.
(12) (a) Yang, G.; Yu, Z.; Jiang, X.; Yu, C. Tetrahedron Lett. 2015, 56,
4689. (b) Yang, G.; Jiang, X.; Liu, Y.; Li, N.; Yin, G.; Yu, C. Asian
J. Org. Chem. 2016, 5, 882. (c) Yang, G.-H.; Liu, M.; Li, N.; Wu,
R.; Chen, X.; Pan, L.-L.; Gao, S.; Huang, X.; Wang, C.; Yu, C.-M.
Eur. J. Org. Chem. 2015, 616.
(1) (a) Purser, S.; Moore, P. R.; Swallow, S.; Gouverneur, V. Chem.
Soc. Rev. 2008, 37, 320. (b) Müller, K.; Faeh, C.; Diederich, F.
Science 2007, 317, 1881. (c) Wang, J.; Sánchez-Roselló, M.;
Aceña, J. L.; del Pozo, C.; Sorochinsky, A. E.; Fustero, S.;
Soloshonok, V. A.; Liu, H. Chem. Rev. 2014, 114, 2432. (d) Jiang,
T.; Zhou, Y.; Chen, Z.; Sun, P.; Zhu, J.; Zhang, Q.; Wang, Z.; Shao,
Q.; Jiang, X.; Li, B.; Chen, K.; Jiang, H.; Wang, H.; Zhu, W.; Shen, J.
ACS Med. Chem. Lett. 2015, 6, 602. (e) Schwehm, C.; Li, J.; Song,
H.; Hu, X.; Kellam, B.; Stocks, M. J. ACS Med. Chem. Lett. 2015, 6,
324. (f) Hansen, K. B.; Hsiao, Y.; Xu, F.; Rivera, N.; Clausen, A.;
Kubryk, M.; Krska, S.; Rosner, T.; Simmons, B.; Balsells, J.;
Ikemoto, N.; Sun, Y.; Spindler, F.; Malan, C.; Grabowski, E. J. J.;
Armstrong, J. D. III. J. Am. Chem. Soc. 2009, 131, 8798.
(2) Jia, X.; Wang, J.; Ding, X.; Yang, J.; Li, N.; Zhao, N.; Huang, Z. J. Org.
Chem. 2015, 80, 10874.
(3) (a) Meyer, E. A.; Castellano, R. K.; Diederich, F. Angew. Chem. Int.
Ed. 2003, 42, 1210. (b) Murphy, A. R.; Fréchet, J. M. J. Chem. Rev.
2007, 107, 1066. (c) Babudri, F.; Farinola, G. M.; Naso, F.; Ragni,
R. Chem. Commun. 2007, 1003.
(4) (a) Roberts, R. M.; Khalaf, A. A. Friedel–Crafts Alkylation Chemis-
try: A Century of Discovery; Marcel Dekker: New York, 1984.
(b) Kodomari, M.; Nawa, S.; Miyoshi, T. J. Chem. Soc., Chem.
Commun. 1995, 1895. (c) Hayashi, R.; Cook, G. R. Org. Lett. 2007,
9, 1311.
(5) (a) Weaver, J.; Senaweera, S. Tetrahedron 2014, 70, 7413.
(b) Ahrens, T.; Kohlmann, J.; Ahrens, M.; Braun, T. Chem. Rev.
2015, 115, 931. (c) Amii, H.; Uneyama, K. Chem. Rev. 2009, 109,
2119. (d) Lafrance, M.; Rowley, C. N.; Woo, T. K.; Fagnou, K. J. Am.
Chem. Soc. 2006, 128, 8754. (e) He, M.; Soulé, J.-F.; Doucet, H.
ChemCatChem 2014, 6, 1824. (f) Fang, X.; Huang, Y.; Chen, X.;
Lin, X.; Bai, Z.; Huang, K.-W.; Yuan, Y.; Weng, Z. J. Fluorine Chem.
2013, 151, 50. (g) Sun, L.; Rong, M.; Kong, D.; Bai, Z.; Yuan, Y.;
Weng, Z. J. Fluorine Chem. 2013, 150, 117.
(13) Yu, C.; Hu, G.; Zhang, C.; Wu, R.; Ye, H.; Yang, G.; Shi, X. J. Fluo-
rine Chem. 2013, 153, 33.
(14) 1,2,3,4,5-Pentafluoro-6-[(2E)-3-phenylprop-2-en-1-yl]ben-
zene (4a); Typical Procedure
COD–PdCl2 (5 mol%), XPhos (10 mol%), Cs2CO3 (1.2 mmol, 1.2
equiv), and toluene (3 mL) were added sequentially to a Schlenk
tube containing allylic pivalate (E)-3a (1.0 mmol, 1.0 equiv) and
pentafluorobenzene (1a; 2.0 mmol, 2.0 equiv) under argon, and
the mixture was stirred at 120 ℃ (oil bath) for 8 h until the reac-
tion was complete (TLC). The mixture was then diluted with
EtOAc (40 mL), washed with brine (3 × 20 mL), and dried (Na2SO4).
After filtration and evaporation of the solvent, the residue was
purified by chromatography (silica gel, hexane) to give a white
solid; yield: 279 mg (98%); mp 62–64 °C.
1H NMR (600 MHz, CDCl3): δ = 7.33–7.25 (m, 4 H), 7.24–7.20 (m, 1
H), 6.47 (d, J = 15.7 Hz, 1 H), 6.21 (dt, J = 15.7, 6.7 Hz, 1 H), 3.59 (dd,
J = 6.7, 1.3 Hz, 2 H). 13C NMR (151 MHz, CDCl3): δ = 145.00 (dm, J =
246.4 Hz), 139.87 (dm, J = 252.4 Hz), 137.52 (dm, J = 250.4 Hz),
136.57, 132.44, 128.55, 127.64, 126.19, 124.24, 113.23 (t, J = 19.1
Hz), 25.60. 19F NMR (565 MHz, CDCl3): δ = –143.90 (dd, J = 22.3,
8.4 Hz, 2 F), –157.23 (t, J = 22.3 Hz, 1 F), –162.48 (td, J = 22.3, 8.4
Hz, 2 F). MS (EI): m/z = 284 [M]+.
(6) For a recent review, see: Cristina Silva Costa, D. Arab. J. Chem.
2017, DOI: 10.1016/j.arabjc.2017.07.017.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E