Wittig olefination of trifluoromethyl ketones and allylic carbonates mediated by phosphines

Article abstract of DOI:10.1055/s-0030-1260185

The Wittig olefination of trifluromethyl ketones and allylic carbonates mediated by tributylphosphine was realized to give corresponding trifluoromethyl dienes in good yields with excellent E-selectivities. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0030-1260185

PAPER
3359
Wittig Olefination of Trifluoromethyl Ketones and Allylic Carbonates
Mediated by Phosphines
W
ittig Olefinati
o
on of Trifluo
n
romethyl
K
e
g
tones and Allylic
C
W
arbonates ang, Li-Tao Shen, Song Ye*
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100190, P. R. of China
Fax +86(10)62554449; E-mail: songye@iccas.ac.cn
Received 20 June 2011; revised 15 July 2011
possible competition between annulation and
Abstract: The Wittig olefination of trifluromethyl ketones and al-
olefination15 was also interesting (Scheme 2, equation b).
lylic carbonates mediated by tributylphosphine was realized to give
corresponding trifluoromethyl dienes in good yields with excellent
E-selectivities.
Initially, the model reaction of allylic carbonate 1a and tri-
fluoromethyl ketone 2a with 10 mol% triphenylphosphine
Key words: Wittig, trifluoromethyl ketones, trifluoromethyl ole- as the catalyst was investigated. No annulation product
fins, ylides, allylic carbonate
and only a trace of olefination product 3aa was observed,
along with the recovery of the substrates, for the ‘catalyt-
ic’ reaction. Based on an analysis of the mechanism (see
below), it is clear that phosphine acts as the reagent for the
olefination reaction. Thus, significantly more phosphine
The phosphonium ylide has become established as a clas-
sic reagent for the olefination of carbonyl groups.1 Gener-
ally, phosphonium ylides are generated from the salt of
phosphine and haloalkanes in the presence of base
(Scheme 1, equation a). In 1995, Lu et al. reported their
pioneering phosphine-catalyzed [3+2] annulation of alle-
noates with electron-deficient olefins, involving phospho-
nium zwitterions (1,3-dipole) as the key intermediate
(Scheme 1, equation b).2a The phosphine-catalyzed annu-
lation of allenoate then becomes a powerful tool for the
construction of (hetero)cycles.2 In 2003, the same group
reported the generation of phosphonium allylic ylides
from allylic carbonates and the application of these inter-
mediates in annulation reactions (Scheme 1, equation c).3
In the past decade, allylic carbonates4 were successfully
used as C3 synthons in phosphine-catalyzed [3+2] annula-
tions with olefins5 and imines,6 in [3+4] annulation with
coumalate,7 and in [3+6] annulation8 with tropone. In ad-
dition, allylic carbonates were also used as C1 synthons
for phosphine-catalyzed [4+1] annulation.9 Interestingly,
a phosphine-mediated Wittig olefination reaction of allyl-
ic carbonates and aldehydes was reported recently by He
et al. (Scheme 1, equation d).10
R'CHO
ref. 1
R3P
R
(a)
R3P
R
Hal
R
R'
base
ylide
(1,2-dipole)
γ
α
EWG
X
olefin/imine
ref. 2
R3P
Y
EWG
(b)
PR3
EWG
zwitterion
(1,3-dipole)
OBoc
X
EWG
R
olefin/imine
ref. 3–8
Y
EWG
R3P
(c)
R
PR3
EWG
R
allylic ylide
EWG
R'CHO
ref. 10
(d)
R'
R
EWG = electron-withdrawing group
Scheme 1 Generation of phosphonium ylides and their reactions
CO2Et
O
Recently, we have reported an oxygen-version of the
[3+2] annulation of allenoates with trifluoromethyl ke-
tones, previously developed by Lu et al. (Scheme 2,
equation a).11 The use of trifluoromethyl ketones was the
key to the success of the annulation reaction, compared
with previously reported use of aldehydes.12 Considering
the many applications of fluorinated compounds13 and the
ready availability of the allylic carbonates through
Morita–Baylis–Hillman reaction,14 we were interested in
exploring the phosphine-catalyzed (or mediated) reaction
of allylic carbonates and trifluoromethyl ketones. The
Ph3P
Ar
(a)
+
annulation
ref. 11
EtO2C
CF3
Ar
CF3
O
EtO2C
R
Ar
annulation
CF3
OBoc
O
(b)
O
(not observed)
CO2CH3
Ar
R3P
CO2Et
or
+
R
Ar
CF3
olefination
R
(this work)
CF3
(observed)
SYNTHESIS 2011, No. 20, pp 3359–3363
x
x.
x
x
.
2
0
1
1
Advanced online publication: 24.08.2011
DOI: 10.1055/s-0030-1260185; Art ID: H62511SS
© Georg Thieme Verlag Stuttgart · New York
Scheme 2 Comparison of the reactions of allenoates and allylic car-
bonates with trifluoromethyl ketones

3360
T. Wang et al.
PAPER
was employed to optimize the reaction conditions donating (Ar = 4-Me, 4-MeOC6H4) and electron-with-
(Table 1). It was found that 69% total yield of the olefina- drawing (Ar = 4-ClC6H4) substituents worked well, to
tion products was obtained when two equivalents of triph- furnish the corresponding dienes in good yields (Table 2,
enylphosphine (Ph3P) was used, albeit with poor E/Z- entries 2–4). Ketone 2e, with a meta-methylphenyl group
selectivity (Table 1, entry 1). Solvent screening resulted worked well to give the corresponding diene 3ae in 69%
in varied yields without improvement of E/Z-selectivities yield (Table 2, entry 5). Ketone 2f, with a 2-thienyl group,
(Table 1, entries 2–6). Several phosphines were then test- also worked but with somewhat low yield (Table 2, entry
ed in the reaction (Table 1, entries 7–13). Besides triphe- 6). Several allylic carbonates with a range of aryl groups
nylphosphine, other triarylphosphines with either were also tested (Table 2, entries 7–10). Substrates with
electron-withdrawing (4-F, Cl) or electron-donating (4- both electron-donating (Ar = 4-Me C6H4) and electron-
Me, MeO) groups gave olefination products in similar withdrawing substituents (Ar = 4-ClC6H4) were tolerated
yields and E/Z-selectivity (Table 1, entries 7–10). Better (Table 2, entries 7–8). Both meta- and ortho-substituted
E/Z-selectivity resulted when methyldiphenylphosphine substrates (1d and 1e, R = 3-ClC6H4, 2-ClC6H4) showed
was used (Table 1, entry 11). Finally, trimethylphosphine comparable results to those obtained with para-substitut-
and tri(n-butyl)phosphine were identified as optimal; ap- ed substrates (1c, R = 4-ClC6H4; Table 2, entries 9, 10 vs.
plication of these reagents gave the dienes in good yield 8). The structure of the diene 3aa was unambiguously es-
with excellent E/Z-selectivity (Table 1, entries 12 and 13). tablished by X-ray analysis of its crystal (Figure 1).
In addition, no loss of yield or selectivity was observed
Table 2 Wittig Olefination of Morita–Baylis–Hillman Carbonates
with Trifluoromethylketones
when the amount of phosphine was reduced from 2 to 1.5
equivalents (Table 1, entry 14).
E
CO2Me
OBoc
With the optimized reaction conditions in hand, the reac-
tion scope was then briefly investigated (Table 2). It was
found that both aryltrifluoromethyl ketones with electron-
O
R
n-Bu3P (1.5 equiv)
CO2Me
E
+
Ar
CH2Cl2, reflux
24 h
R
Ar
CF3
(2.0 equiv)
CF3
3
Table 1 Optimization of Reaction Conditions
1
2
E
CO2Me
Entry
1
R
2
Ar
3
Yield
OBoc
O
Ph
(%)a
65
58
69
61
69
58
67
72
66
76
R3P (2.0 equiv)
solvent, reflux
CF3
E
CO2Me
Ph
+
Ph
Ph
1
2
1a
1a
1a
1a
1a
1a
1b
1c
1d
1e
Ph
Ph
Ph
Ph
Ph
Ph
2a
2b
2c
2d
2e
2f
Ph
3aa
3ab
3ac
3ad
3ae
3af
(2.0 equiv)
CF3
(major isomer)
2a
1a
4-MeC6H4
4-MeOC6H4
4-ClC6H4
3-MeC6H4
2-thienyl
Ph
3aa
3
Entry R3P
Solvent
CH2Cl2
dr ratioa
Yield (%)b
4
1
2
Ph3P
Ph3P
Ph3P
Ph3P
Ph3P
Ph3P
1:0.17:0.1
1:0.14:0.21
1:0.13:0.17
1:1.36:0.12
1:1.0:0.44
N.D.c
69
66
66
42
48
0
5
toluene
THF
6
3
7
4-MeC6H4 2a
3ba
3ca
3da
3ea
4
MeCN
EtOAc
MeOH
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
8
4-ClC6H4
3-ClC6H4
2-ClC6H4
2a
2a
2a
Ph
5
9
Ph
6
10
Ph
7
(4-FC6H4)3P
(4-ClC6H4)3P
(4-MeOC6H4)3P
(4-MeC6H4)3P
Ph2PMe
1:0.14:0.26
1:0.14:0.23
1:0.19:0.13
1:0.19:0.13
1:0.10:0.03
1:0:0.04
53
47
52
54
53
49
57
65
a Isolated yield of (E,E)-3 with dr >20:1 in all cases.
8
9
A possible mechanism for the olefination reaction is de-
picted in Scheme 3. The phosphonium allylic ylide A is
initially generated from the phosphine and allylic carbon-
ate. Addition of the ylide to the trifluoromethyl ketone
gives the adduct B, which collapses to furnish the dienes
and phosphine oxide. The vicinal position of the oxygen
and phosphine in adduct B may then facilitate the forma-
tion of phosphine oxide, which gives dienes as the product
rather than dihydrofuran as for the reaction of allenoate
with ketone.11 The better E-selectivity for the olefination
catalyzed by (n-Bu)3P rather than Ph3P may be due to the
favored formation of trialkylphosphine oxide over tri-
arylphosphine oxide.
10
11
12
13
14
Me3P
(n-Bu)3P
1:0:0.03
(n-Bu)3Pd
1:0:0.03
a Determined by 1H NMR (300 MHz) analysis of the isolated product
with (E,E)-3aa as the major isomer.
b Isolated yield.
c N.D. = not determined.
d 1.5 equivalents were used.
Synthesis 2011, No. 20, 3359–3363 © Thieme Stuttgart · New York

PAPER
Wittig Olefination of Trifluoromethyl Ketones and Allylic Carbonates
3361
tography on silica gel (CH2Cl2–petroleum ether, typically 3:1) to
furnish the corresponding diene 3.
(2E,3E)-Methyl 2-Benzylidene-5,5,5-trifluoro-4-phenylpent-3-
enoate (3aa)
Yield: 76 mg (65%); white solid; mp 92–93 °C; Rf = 0.4 (petroleum
ether–EtOAc, 10:1).
IR (KBr): 1716, 1645, 1494, 1358, 1259, 1167, 953, 898, 765 cm–1.
1H NMR (CDCl3, 300 MHz): d = 7.48 (d, J = 1.5 Hz, 1 H), 7.28–
7.15 (m, 8 H), 7.07–7.05 (m, 2 H), 7.01–7.00 (m, 1 H), 3.31 (s,
3 H).
13C NMR (CDCl3, 75 MHz): d = 166.9, 143.3, 134.62 (q,
J = 29.3 Hz), 134.58, 132.7, 130.2, 129.9, 128.8, 128.75, 128.73,
128.6 (q, J = 6.2 Hz), 128.4, 126.9, 123.6 (q, J = 272 Hz), 52.0.
19F NMR (CDCl3, 376 MHz): d = –64.8.
HRMS (EI): m/z [M]+ calcd for C19H15F3O2: 332.1024; found:
332.1027.
Figure 1 X-ray structure of diene 3aa
(2E,3E)-Methyl 2-Benzylidene-5,5,5-trifluoro-4-p-tolylpent-3-
enoate (3ab)
OBoc
Yield: 70 mg (58%); white solid; mp 76–77 °C; Rf = 0.4 (petroleum
ether–EtOAc, 10:1).
CO2Me
Ph
PR3
EWG
Ph
IR (KBr): 1711, 1591, 1119, 892, 739 cm–1.
1H NMR (CDCl3, 300 MHz): d = 7.48 (d, J = 1.2 Hz, 1 H), 7.34–
7.28 (m, 5 H), 7.01–6.95 (m, 5 H), 3.32 (s, 3 H), 2.21 (s, 3 H).
– CO2
PR3
allylic ylide A
– t-BuOH
O
13C NMR (CDCl3, 75 MHz): d = 167.1, 143.1, 138.8, 134.70 (q,
J = 29.2 Hz), 134.67, 130.2, 129.9, 129.8, 128.7, 128.6, 128.2 (q,
J = 6.2 Hz), 127.8, 127.1, 123.6 (q, J = 272 Hz), 52.0, 21.3.
19F NMR (CDCl3, 376 MHz): d = –64.8.
HRMS (EI): m/z [M]+ calcd for C20H17F3O2: 346.1181; found:
346.1185.
Ar
CF3
CO2Me
CO2Me
Ar
EtO2C
R
Ph
Ar
F3C
Ph
b
a
Ar
CF3
(not observed)
– PR3
PR3
– R3P=O
O
O
CF3
b
a
diene 3
adduct B
(2E,3E)-Methyl 2-Benzylidene-5,5,5-trifluoro-4-(4-methoxy-
phenyl)pent-3-enoate (3ac)
Scheme 3 Proposed reaction mechanism
Yield: 85 mg (69%); white solid; mp 88–89 °C; Rf = 0.3 (petroleum
ether–EtOAc, 10:1).
IR (KBr): 1718, 1607, 1514, 1254, 1169, 1114 cm–1.
1H NMR (CDCl3, 300 MHz): d = 7.49 (d, J = 1.5 Hz, 1 H), 7.35–
7.29 (m, 5 H), 7.03–6.95 (m, 3 H), 6.74–6.69 (m, 2 H), 3.69 (s,
3 H), 3.37 (s, 3 H).
13C NMR (CDCl3, 75 MHz): d = 167.2, 159.9, 143.0, 134.7, 134.4
(q, J = 29.2 Hz), 132.9 (q, J = 2.1 Hz), 130.2, 130.1, 129.9, 128.8,
127.9 (q, J = 6.2 Hz), 127.2, 123.7 (q, J = 272 Hz), 113.8, 55.3,
52.1.
In conclusion, the trialkylphosphine-mediated Wittig ole-
fination of trifluoromethyl ketones gives the correspond-
ing trifluoromethyl dienes in good yields with good E-
selectivities. The formation of olefins is different to the re-
ported formation of dihydrofuran for the phosphine-cata-
lyzed annulation of allenoates and ketones.
Unless otherwise indicated, all starting materials were obtained
from commercial suppliers and used as received. The allylic car-
bonates were prepared according to literature methods.3,5–8 Anhy-
drous THF and toluene were distilled from sodium and
benzophenone. Anhydrous CH2Cl2 was distilled from CaH2. Anhy-
drous EtOAc and MeCN were dried over molecular sieves. All re-
actions utilizing air- or moisture-sensitive reagents were performed
in oven-dried glassware with magnetic stirring under a nitrogen at-
mosphere. Column chromatography was performed with silica gel
200–300 mesh.
19F NMR (CDCl3, 376 MHz): d = –64.9.
HRMS (EI): m/z [M]+ calcd for C20H17F3O3: 362.1130; found:
362.1134.
(2E,3E)-Methyl 2-Benzylidene-4-(4-chlorophenyl)-5,5,5-tri-
fluoropent-3-enoate (3ad)
Yield: 76 mg (61%); white solid; mp 53–54 °C; Rf = 0.5 (petroleum
ether–EtOAc, 10:1).
IR (KBr): 1722, 1636, 1492, 1286, 1172, 764 cm–1.
Wittig Olefination of Allylic Carbonates with Trifluorometh-
ylketones; Typical Procedure
To a stirred solution of allylic carbonate 1 (0.25 mmol) and trifluo-
romethylketone 2 (0.5 mmol) in CH2Cl2 (5 mL), was added tribu-
tylphosphine (0.375 mmol). The solution was stirred at reflux
temperature for 24 h. The reaction mixture was concentrated under
reduced pressure, and the residue was purified by column chroma-
1H NMR (CDCl3, 300 MHz): d = 7.52 (d, J = 1.5 Hz, 1 H), 7.32–
7.28 (m, 5 H), 7.17–7.12 (m, 2 H), 7.03–7.02 (m, 1 H), 6.96–6.93
(m, 2 H), 3.43 (s, 3 H).
13C NMR (CDCl3, 75 MHz): d = 166.7, 143.8, 134.9, 134.5, 133.5
(q, J = 29.6 Hz), 131.1, 130.2, 130.12, 130.09, 129.2 (q,
J = 6.2 Hz), 128.8, 128.7, 126.3, 123.3 (q, J = 272 Hz), 52.2.
19F NMR (CDCl3, 376 MHz): d = –65.0.
Synthesis 2011, No. 20, 3359–3363 © Thieme Stuttgart · New York

3362
T. Wang et al.
PAPER
HRMS (EI): m/z [M]+ calcd for C19H14ClF3O2: 366.0634; found:
HRMS (EI): m/z [M]+ calcd for C19H14ClF3O2: 366.0634; found:
366.0638.
366.0637.
(2E,3E)-Methyl 2-Benzylidene-5,5,5-trifluoro-4-m-tolylpent-3-
enoate (3ae)
(2E,3E)-Methyl 2-(3-Chlorobenzylidene)-5,5,5-trifluoro-4-
phenylpent-3-enoate (3da)
Yield: 84 mg (69%); colorless oil; Rf = 0.4 (petroleum ether–
Yield: 84 mg (66%); white solid; mp 74–75 °C; Rf = 0.4 (petroleum
EtOAc, 10:1).
ether–EtOAc, 10:1).
IR (KBr): 1719, 1636, 1260, 1119, 693 cm–1.
IR (KBr): 1723, 1434, 1288, 1172, 1120, 786 cm–1.
1H NMR (CDCl3, 300 MHz): d = 7.47 (d, J = 1.5 Hz, 1 H), 7.30 (m,
5 H), 7.07 (t, J = 7.5 Hz, 1 H), 7.01–6.98 (m, 2 H), 6.88–6.81 (m,
2 H), 3.34 (s, 3 H), 2.17 (s, 3 H).
13C NMR (CDCl3, 75 MHz): d = 167.0, 143.2, 138.0, 134.69 (q,
J = 29.2 Hz), 134.68, 132.6, 130.2, 129.8, 129.6, 129.2, 128.8,
128.6, 128.4 (q, J = 6.2 Hz), 127.1, 125.9, 123.6 (q, J = 272 Hz),
52.0, 21.5.
1H NMR (CDCl3, 300 MHz): d = 7.38 (s, 1 H), 7.24–7.23 (m, 1 H),
7.20–7.11 (m, 6 H), 7.00–6.96 (m, 3 H), 3.40 (s, 3 H).
13C NMR (CDCl3, 75 MHz): d = 166.6, 141.5, 136.3, 135.2 (q,
J = 29.5 Hz), 134.7, 132.3, 129.9, 129.8, 129.7, 128.7, 128.4, 128.3,
128.2, 127.94 (q, J = 6.3 Hz), 127.93, 123.4 (q, J = 272 Hz), 52.2.
19F NMR (CDCl3, 376 MHz): d = –65.0.
HRMS (EI): m/z [M]+ calcd for C19H14ClF3O2: 366.0634; found:
366.0637.
19F NMR (CDCl3, 376 MHz): d = –64.8.
HRMS (EI): m/z [M]+ calcd for C20H17F3O2: 346.1181; found:
346.1184.
(2E,3E)-Methyl 2-(2-Chlorobenzylidene)-5,5,5-trifluoro-4-
phenylpent-3-enoate (3ea)
(2E,3Z)-Methyl 2-Benzylidene-5,5,5-trifluoro-4-(thiophen-2-
yl)pent-3-enoate (3af)
Yield: 95 mg (76%); colorless oil; Rf = 0.4 (petroleum ether–
EtOAc, 10:1).
Yield: 69 mg (58%); white solid; mp 70–71 °C; Rf = 0.4 (petroleum
ether–EtOAc, 10:1).
IR (KBr): 1716, 1596, 1433, 1286, 1257, 1172, 1121, 765 cm–1.
1H NMR (CDCl3, 300 MHz): d = 7.65 (d, J = 1.5 Hz, 1 H), 7.38–
7.30 (m, 5 H), 7.24 (dd, J = 5.1, 1.2 Hz, 1 H), 7.00–6.96 (m, 2 H),
6.89 (dd, J = 8.1, 3.6 Hz, 1 H), 3.44 (s, 3 H).
13C NMR (CDCl3, 75 MHz): d = 166.7, 144.3, 134.5, 133.2, 130.9,
130.2, 129.1, 128.9, 128.7, 128.3 (q, J = 6.1 Hz), 127.9, 127.2,
126.6, 123.1 (q, J = 272 Hz), 52.2.
IR (KBr): 1715, 1594, 1435, 1250, 1171, 1119 cm–1.
1H NMR (CDCl3, 300 MHz): d = 7.62 (s, 1 H), 7.30–7.11 (m, 7 H),
6.92–6.90 (m, 3 H), 3.44 (s, 3 H).
13C NMR (CDCl3, 75 MHz): d = 166.7, 139.9, 134.82 (q,
J = 29.4 Hz), 134.81, 133.0, 132.3, 130.8, 130.7, 129.9, 128.9,
128.8, 128.6, 128.4, 127.8 (q, J = 6.2 Hz), 126.6, 123.4 (q,
J = 272 Hz), 52.3.
19F NMR (CDCl3, 376 MHz): d = –65.0.
HRMS (EI): m/z [M]+ calcd for C19H14ClF3O2: 366.0634; found:
19F NMR (CDCl3, 376 MHz): d = –65.6.
HRMS (EI): m/z [M]+ calcd for C17H13F3O2S: 338.0588; found:
366.0638.
338.0592.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.
(2E,3E)-Methyl 5,5,5-Trifluoro-2-(4-methylbenzylidene)-4-
phenylpent-3-enoate (3ba)
Yield: 81 mg (67%); white solid; mp 121–122 °C; Rf = 0.4 (petro-
leum ether–EtOAc, 10:1).
IR (KBr): 1711, 1603, 1261, 1162, 1106, 811, 739 cm–1.
Primary Data for this article are available online at http://
www.thieme-connect.com/ejournals/toc/synthesis and can be cited
using the following DOI: 10.4125/pd0015th
1H NMR (CDCl3, 300 MHz): d = 7.48 (s, 1 H), 7.26–7.11 (m, 9 H),
7.00 (s, 1 H), 3.29 (s, 3 H), 2.30 (s, 3 H).
Acknowledgment
13C NMR (CDCl3, 75 MHz): d = 167.1, 143.5, 140.5, 134.4 (q,
J = 29.5 Hz), 132.9, 131.9, 130.4, 129.6, 128.9 (q, J = 6. 2 Hz),
128.85, 128.79, 128.4, 125.9, 123.7 (q, J = 272 Hz), 51.9, 21.6.
19F NMR (CDCl3, 376 MHz): d = –64.8.
Financial support from the National Natural Science Foundation of
China (20932008), the Ministry of Science and Technology of
China (2011CB808600) and the Chinese Academy of Sciences is
gratefully acknowledged.
HRMS (EI): m/z [M]+ calcd for C20H17F3O2: 346.1181; found:
346.1184.
References
(2E,3E)-Methyl 2-(4-Chlorobenzylidene)-5,5,5-trifluoro-4-
phenylpent-3-enoate (3ca)
Yield: 90 mg (72%); white solid; mp 118–119 °C; Rf = 0.4 (petro-
leum ether–EtOAc, 10:1).
IR (KBr): 2962, 1711, 1489, 1437, 1257, 1164, 823, 766 cm–1.
1H NMR (CDCl3, 300 MHz): d = 7.41 (s, 1 H), 7.28–7.14 (m, 7 H),
7.04–7.01 (m, 2 H), 6.96–6.95 (m, 1 H), 3.36 (s, 3 H).
13C NMR (CDCl3, 75 MHz): d = 166.7, 141.8, 135.9, 135.1 (q,
J = 29.5 Hz), 133.0, 132.5, 131.3, 129.1, 128.9, 128.7, 128.4, 128.1
(q, J = 6.2 Hz), 127.4, 123.5 (q, J = 272 Hz), 52.1.
19F NMR (CDCl3, 376 MHz): d = –64.8.
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