Enantioselective fluorination of 2-oxindoles by structure-micro-tuned n-fluorobenzenesulfonamides

Article abstract of DOI:10.1002/ejoc.201402072

We describe our attempts to fine-tune the reactivity and selectivity of N-fluorobenzenesulfonamide in fluorination reactions by changing the substituents on its phenyl rings. A series of N-fluorobenzenesulfonamides bearing substituents at the ortho, meta, and para positions were prepared, and were used in the enantioselective fluorination of 2-oxindoles catalysed by chiral palladium complexes. Fluorinating reagents 1b, 1c, 1d, 1e, 1h, 1i, and 1j gave similar results to 1a, while 1f, 1g, and 1n gave worse yields and selectivities. Under mild reaction conditions, a series of 3-fluoro-2-oxindoles were obtained in excellent yields (up to 98%) and enantioselectivities (up to 99% ee) using N-fluoro-4,4′-difluoro-benzenesulfonamide as the fluorination agent. Copyright

Full text of DOI:10.1002/ejoc.201402072

FULL PAPER
DOI: 10.1002/ejoc.201402072
Enantioselective Fluorination of 2-Oxindoles by Structure-Micro-Tuned
N-Fluorobenzenesulfonamides
Fajie Wang,[a] Juli Li,[a] Qingyang Hu,[a] Xianjin Yang,*[a,b] Xin-Yan Wu,*[a] and
Haoming He[c]
Keywords: Homogeneous catalysis / Palladium / Fluorine / Fluorination / Nitrogen heterocycles / Enantioselectivity
We describe our attempts to fine-tune the reactivity and
selectivity of N-fluorobenzenesulfonamide in fluorination re-
actions by changing the substituents on its phenyl rings. A
series of N-fluorobenzenesulfonamides bearing substituents
at the ortho, meta, and para positions were prepared, and
were used in the enantioselective fluorination of 2-oxindoles
catalysed by chiral palladium complexes. Fluorinating rea-
gents 1b, 1c, 1d, 1e, 1h, 1i, and 1j gave similar results to 1a,
while 1f, 1g, and 1n gave worse yields and selectivities. Un-
der mild reaction conditions, a series of 3-fluoro-2-oxindoles
were obtained in excellent yields (up to 98%) and enantio-
selectivities (up to 99% ee) using N-fluoro-4,4Ј-difluoro-
benzenesulfonamide as the fluorination agent.
Introduction
In the last few decades, fluorine-containing compounds
have drawn a lot of interest from synthetic chemists, as a
result of their specific properties in materials and pharma-
ceuticals.[1] The enantioselective electrophilic fluorination
of carbonyl compounds is one of the most efficient strate-
gies for the construction of chiral fluorine-containing com-
pounds. A lot of research has focussed on chiral catalysts,
including metal complexes and bis-cinchona alkaloids.[2]
NFSI (N-fluorobenzenesulfonamide) is the best electro-
philic fluorinating reagent for enantioselective fluorination,
but to date, only a few admirable examples of its use have
been reported.[3] It is possible that structural micro-tuning
of NFSIs would improve the enantioselectivity of some
fluorination reactions.[4] In this paper, we disclose the re-
sults of our research into catalytic enantioselective fluor-
ination using ortho-, meta-, and para-substituted NFSI ana-
logues.
Figure 1. Structure of the chiral catalysts.
Results and Discussion
As part of our plan to increase enantioselectivity by
screening fluorinating reagents and using cheaper catalysts,
(R)-BINAP-palladium(II) complexes Pd-1 and Pd-2 were
chosen as chiral catalysts for this work (Figure 1).[5]
We initially investigated the reaction of 2-oxindole 2a
and NFSI (1a) in the presence of a chiral palladium(II) cat-
alyst in THF at room temperature (Table 1). In THF, Pd
complex Pd-2 (2.5 mol-%) promoted the reaction smoothly,
and gave a better selectivity (88% ee) than did Pd-1 (81%
[a] Key Lab for Advanced Materials & Institute of Fine Chemicals, ee) (Table 1, entries 1 and 2). Ether solvents like THF, di-
East China University of Science and Technology,
ethyl ether, and 1,4-dioxane gave the best results (Table 1,
130 Meilong Road, 200237 Shanghai
entries 2–4); when the fluorination was run in MeOH,
toluene, DMF, or acetonitrile, lower enantioselectivities
were seen (Table 1, entries 5–8).
It is astonishing that diethyl ether led to the highest
enantioselectivity, despite the poor solubility of catalyst Pd-
2 in this solvent (Table 1, entry 3). Inspired by this repro-
ducible result, we wondered whether the amount of catalyst
E-mail: yxj@ecust.edu.cn
http://hyxy.ecust.edu.cn/new/viewProf.php?id=376
[b] Shanghai Institute of Organic Chemistry, Chinese Academy of
Science,
345 Lingling Road, 200032 Shanghai
[c] Wengfu Group Co. Ltd.,
Guizhou 550000, China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201402072.
Eur. J. Org. Chem. 2014, 3607–3613
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F. Wang, J. Li, Q. Hu, X. Yang, X.-Y. Wu, H. He
FULL PAPER
Table 1. Screening of conditions for the fluorination of 2a with 1a; amounts of catalyst Pd-2 ranging from 0.25 to 2.5 mol-%
Boc = tert-butoxycarbonyl.
(Table 1, entries 3, 9–11). Further reducing the amount of
catalyst Pd-2 to 0.1 mol-% led to a slight decrease in the ee
(Table 1, entry 12). Thus, the amount of catalyst could be
reduced tenfold without decreasing the selectivity.[5] The re-
action temperature was then screened, using 0.5 mol-% Pd-
2 in diethyl ether. It turned out that 0 °C was the most suit-
able temperature, and the product was formed in 96% yield
Entry Catalyst (mol-%) Conditions
Yield [%][a] (ee)
with 98% ee (Table 1, entries 11, 13, and 14).
1
2
3
4
5
6
7
8
Pd-1 (5)
THF, 25 °C, 5 h
THF, 25 °C, 2.5 h
diethyl ether, 25 °C, 4 h
1,4-dioxane, 25 °C, 15 h
CH3OH, 25 °C, 3 h
toluene, 25 °C, 24 h
DMF, 25 °C, 25 h
acetonitrile, 25 °C, 39 h
diethyl ether, 25 °C, 3 h
diethyl ether, 25 °C, 3 h
diethyl ether, 25 °C, 3 h
diethyl ether, 25 °C, 4 h
diethyl ether, 0 °C, 3 h
diethyl ether, –10 °C, 8 h
85 (81)
91 (88)
98 (95)
90 (93)
44 (77)
78 (67)
87 (13)
76 (27)
94 (97)
92 (97)
90 (96)
91 (93)
96 (98)
90 (97)
Next, various substituted N-fluorobenzenesulfonamides
were synthesized as described in Table 2. Symmetrically
substituted NFSIs 1b–1g were synthesized according to
method A (Table 2, entries 1–6), and unsymmetrically sub-
stituted NFSIs 1h–1n were synthesized according to
method B (Table 2, entries 7–13). Generally, the isolated
yields were low or moderate.
Reagents 1b–1n were then screened under the optimized
conditions (Table 3). Our results show that the majority of
NFSIs with substituents in the para position give improved
or similar selectivities, while those with substituents in the
ortho or meta positions give worse selectivities. In more de-
tail, para-F and para-tBu substituents gave positive effects
(Table 3, entries 2 and 3), para-Me and para-Cl gave neutral
effects (Table 3, entries 4 and 5), and para-NO2 gave a
slightly negative effect, probably due to the fact that the
Pd-2 (2.5)
Pd-2 (2.5)
Pd-2 (2.5)
Pd-2 (2.5)
Pd-2 (2.5)
Pd-2 (2.5)
Pd-2 (2.5)
Pd-2 (1.0)
Pd-2 (0.5)
Pd2 (0.25)
Pd-2 (0.1)
Pd-2 (2.5)
Pd-2 (2.5)
9
10
11
12
13
14
[a] Isolated yields.
Pd-2 necessary to determine the enantioselectivity may be
far less than 2.5 mol-%. We ran a series of reactions with
decreased amounts of catalyst to test this hypothesis. Amaz- electron-withdrawing NO2 group destabilizes the N–F bond
ingly, the enantioselectivity remained rather stable for (Table 3, entry 11). The para-Br substituted reagent gave
Table 2. Preparation of NFSIs.
Entry
NFSI 1
Method
Yield [%][a]
1
2
3
4
5
6
7
8
4,4Ј-di-F-NFSI (1b)
4,4Ј-di-tBu-NFSI (1c)
4,4Ј-di-Me-NFSI (1d)
4,4Ј-di-Cl-NFSI (1e)
4,4Ј-di-Br-NFSI (1f)
2,2Ј-di-F-NFSI (1g)
4-F,4Ј-NO2-NFSI (1h)
2,4Ј-di-F-NFSI (1i)
4-F,4Ј-tBu-NFSI (1j)
4-NO2-NFSI (1k)
2-F-NFSI (1l)
A
A
A
A
A
A
B
B
B
B
B
B
B
65
23
34
47
36
65
66
72
60
69
45
57
56
9
10
11
12
13
3-F-NFSI (1m)
2-Me-NFSI (1n)
[a] Isolated yields.
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Enantioselective Fluorination of 2-Oxindoles
very bad results, because it is easy for the bromo substituent ylphenyl)-2-oxindole 2c, which gave 3c with 88% ee and in
on the electron-poor phenyl ring to leave as a Br– anion 92% yield (Table 4, entry 3).
(Table 3, entry 6). The ortho-F, meta-F, and ortho-Me
Table 4. The fluorination of 2-oxindoles 2 with 1b.
NFSIs gave significantly worse yields and selectivities
(Table 3, entries 12, 13, and 14). This could be due to strong
inductive effects or steric effects resulting in an instability
of the N–F bond, the C–F or C–H bonds of the phenyl
group, or even the C–H bonds in the methyl group. These
effects apparently exist even though the two phenyl rings of
the NFSIs are not in the same plane (Figure 2). For exam-
ple, for para-F-containing cases, 1b gave better results than
1h, 1i, and 1j (Table 3, entries 2, 8, 9, and 10); for ortho-F-
containing cases, 1i gave better results than 1g and 1l
(Table 3, entries 7, 9, and 12); for para-NO2-containing
cases, 1h gave better results than 1k (Table 3, entries 8 and
11).
Entry
2-Oxindole 2 (R1/R2)
Time [h]
Yield [%][a] (ee)
1
2
3
4
5
6
7
8
H/H (2a)
2
2
4
18
2
2
7
7
12
3
2
96 (98)
95 (99)
92 (88)
90 (98)
92 (99)
93 (99)
91 (99)
90 (99)
93 (99)
97 (99)
94 (99)
92 (99)
90 (99)
93 (98)
95 (98)
H/4-Me (2b)
H/2-Me (2c)
H/4-F (2d)
F/H (2e)
Me/H (2f)
Table 3. Screening of NFSIs for the fluorination of 2 with 1.
H/β-naphthyl (2g)
MeO/H (2h)
Cl/H (2i)
9
10
11
12
13
14
15
F/4-F (2j)
F/4-Me (2k)
Me/4-F (2l)
Me/4-Me (2m)
MeO/4-F (2n)
MeO/4-Me (2o)
3
2
3
5
Entry
NFSI 1
Time [h]
Yield [%][a] (ee)
1
2
3
4
5
6
7
8
NFSI (1a)
12
3
3
90 (97)
96 (98)
91 (97)
89 (97)
90 (97)
67 (50)
75 (41)
88 (96)
90 (96)
92 (97)
85 (94)
80 (81)
87 (83)
75 (58)
[a] Isolated yields.
4,4Ј-di-F-NFSI (1b)
4,4Ј-di-tBu-NFSI (1c)
4,4Ј-di-Me-NFSI (1d)
4,4Ј-di-Cl-NFSI (1e)
4,4Ј-di-Br-NFSI (1f)
2,2Ј-di-F-NFSI (1g)
4-F,4Ј-NO2-NFSI (1h)
2,4Ј-di-F-NFSI (1i)
4-F,4Ј-tBu-NFSI (1j)
4-NO2-NFSI (1k)
2-F-NFSI (1l)
It is difficult to explain the great influence of the various
substituents on the phenyl group on the enantioselectivity
using the reaction mechanism proposed by Sodeoka[6]
(route 1 in Scheme 1). Based on the literature,[7] an alterna-
tive mechanism involving a PdII–PdIV–PdII cycle is pro-
posed here. As shown in route 2 in Scheme 1, NFSIs add
to the PdII of intermediate B to form PdIV intermediate C,
then reductive elimination gives D. Ligand exchange occurs
between D and starting material 2 to give product 3
[(ArSO2)2NH] and intermediate A, which takes part in an-
other catalytic cycle. In this mechanism, the bisbenzene-
sulfonamide moiety of the NFSIs participates in the
enantioselectivity-determining steps, thus the substituents
on the phenyl group of the NFSIs naturally influence the
enantioselectivity of the reaction.
3
12
24
24
12
6
9
10
11
12
13
14
2
12
15
3
3-F-NFSI (1m)
2-Me-NFSI (1n)
47
[a] Isolated yields.
Conclusions
Structurally fine-tuned NFSIs were synthesized and used
in the fluorination of 2-oxindoles. Substituents on the
phenyl group of the NFSIs influence the reaction dramati-
cally. In this improved fluorination process, the amount of
catalyst Pd-2 may be decreased from 2.5 mol-% to 0.1 mol-
% without loss of enantioselectivity. Fluorinating reagents
Figure 2. The stereostructure of 4-nitro-4Ј-fluoro-NFSI 1h drawn
using Chemdraw 3D.
Based on the above results, 4,4Ј-difluoro-NFSI 1b was 1b, 1c, 1d, 1e, 1h, 1i, and 1j gave similar results to 1a, while
chosen to react with a series of 2-oxindoles 2 to explore the 1f, 1g, and 1n gave worse yields and enantioselectivities.
substrate scope. Satisfactorily, the reaction of 1b with 2a– Using 0.5 mol-% Pd-2 as a catalyst, the reactions of 1b with
2o (0.03 m) in diethyl ether at 0 °C gave 3-fluoro-2-oxindoles substituted oxindoles 2a–2o in diethyl ether at 0 °C gave 3-
3a–3o in Ͼ90% yields and mostly Ͼ98% ee (Table 4). The fluoro-2-oxindoles 3a–3o mostly in Ͼ90% yields and Ͼ98%
only low enantioselectivity was observed for 3-(2-meth- ee.
Eur. J. Org. Chem. 2014, 3607–3613
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F. Wang, J. Li, Q. Hu, X. Yang, X.-Y. Wu, H. He
FULL PAPER
Scheme 1. Proposed fluorination mechanism.
ance of compound 4b. Nitrogen gas was introduced to remove the
residual F2 gas. The insoluble solid was removed by filtration. The
filtrate was concentrated under vacuum and washed with water to
give a yellow solid. Purification by column chromatography (petro-
leum ether/EtOAc, 20:1) gave pure compound 1b (0.920 g, 65%) as
a white solid, m.p. 114.8–116.0 °C. 1H NMR (CDCl3, 400 MHz):
δ = 8.08–8.05 (m, 4 H), 7.33–7.29 (m, 4 H) ppm. 19F NMR (CDCl3,
376 MHz): δ = –36.42 (s, 1 F), –98.36 (s, 2 F) ppm.[8]
Experimental Section
General Methods: Optical rotations were measured with a digital
polarimeter at the wavelength of the sodium D line (589 nm) at
1
20 °C. H, 13C, and 19F NMR spectra were recorded with a 400 or
300 MHz spectrometer. 1H NMR spectra were referenced to
tetramethylsilane (δ = 0.00 ppm), and CDCl3 or CD3CN was used
as solvent. 13C NMR spectra were referenced to solvent carbons (δ
= 77.0 ppm for CDCl3; δ = 1.32, 118.26 ppm for CD3CN). High-
resolution mass spectra (HRMS) were recorded with a Micromass
GCT spectrometer using an Electron Impact (EI) ionization source.
HPLC analysis was carried out with Waters equipment with a 2487
detector using a Daicel Chiralcel OD-H, or Chiralpak AD-H col-
umn. All solvents were purified and dried according to standard
methods before use. NFSI (1a) and compounds 6 were bought from
commercial suppliers.
Benzenesulfonamide Derivative 1c: White solid, m.p. 149.5–
150.3 °C. 1H NMR (CDCl3, 400 MHz): δ = 7.96–7.94 (d, J =
8.8 Hz, 4 H), 7.62–7.60 (d, J = 7.2, 4 H), 1.36 (s, 18 H) ppm. 19F
NMR (CDCl3, 376 MHz): δ = –37.6 (s, 1 F) ppm.[8]
Benzenesulfonamide Derivative 1d: White solid, m.p. 113.1–
113.8 °C. 1H NMR (CDCl3, 400 MHz): δ = 7.90–7.88 (d, J =
8.4 Hz, 4 H), 7.40–7.38 (d, J = 8.4 Hz, 4 H), 2.48 (s, 6 H) ppm. 19
NMR (CDCl3, 376 MHz): δ = –37.629 (s, 1 F) ppm.[8]
F
General Procedure for the Synthesis of Fluorinating Reagents
N,4-Difluoro-N-[(4-fluorophenyl)sulfonyl]benzenesulfonamide (1b).
Method A: A mixture of 4,4Ј-difluoro-bisbenzenesulfonamide (4b;
1.332 g, 4.0 mmol), sodium hydroxide (1.28 g, 32 mmol), and aceto-
nitrile (45 mL) in a 100 mL three-necked flask was stirred for 1.0 h
at room temperature, then it was cooled to –30 to –40 °C. A gas-
eous mixture of F2 in nitrogen (10% v/v) was introduced at a rate
of 150 mL/min to the solution until TLC indicated the disappear-
Benzenesulfonamide Derivative 1e: White crystals, m.p. 142.8–
1
143.9 °C. H NMR (CDCl3, 400 MHz): δ = 7.86 (d, J = 8.8 Hz, 4
H), 7.76 (d, J = 8.8 Hz, 4 H) ppm. 19F NMR (CDCl3, 376 MHz):
δ = –36.46 (s, 1 F) ppm.[8]
Benzenesulfonamide Derivative 1f: White crystals, m.p. 181.8–
1
182.9 °C. H NMR (CDCl3, 400 MHz): δ = 7.85 (d, J = 8.8 Hz, 4
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Enantioselective Fluorination of 2-Oxindoles
H), 7.78 (d, J = 8.8 Hz, 4 H) ppm. 19F NMR (CDCl3, 376 MHz):
δ = –37.10 (s, 1 F) ppm.[8]
J = 23.0 Hz), 35.61, 30.94 ppm. HRMS (EI): calcd. for
C16H17F2NO4S2 389.0567; found 389.0567.
Benzenesulfonamide Derivative 1g: White solid, m.p. 125.7–
Benzenesulfonamide Derivative 1k: A mixture of benzenesulfon-
127.1 °C. IR (KBr): ν = 3107, 1597, 1583, 1477, 1454, 1400, 1385, amide 6a (0.875 g, 5 mmol), sodium hydroxide (0.22 g, 5.5 mmol),
˜
1272, 1239, 1188, 1070, 833.6, 766 cm–1. 1H NMR (CDCl3,
400 MHz): δ = 7.97–8.01 (m, 2 H), 7.76–7.80 (m, 2 H), 7.36–7.39 0.5 h, and then it was cooled to 0 °C. p-nitrobenzene sulfonyl chlor-
(m, 2 H), 7.29–7.33 (m, 2 H) ppm. 19F NMR (CDCl3, 376 MHz):
ide (5c; 1.22 g, 5.5 mmol) was added, and the mixure was stirred
δ = –37.639 (m, 1 F), –103.282 (m, 2 F) ppm. 13C NMR (CDCl3, until TLC indicated the disappearance of compound 6b. The mix-
and MeOH (10 mL) in a 50 mL three-necked flask was stirred for
100 MHz): δ = 160.26 (d, J = 262 Hz), 138.80 (d, J = 9 Hz), 132.63,
124.90 (d, J = 4 Hz), 122.83 (d, J = 12 Hz), 118.07 (d, J = 21 Hz)
ture was filtered, and the insoluble solid was collected to give 1k
(1.24 g, 69%) as white crystals, m.p. 148.5.1–152.6. IR (KBr): ν =
˜
ppm. HRMS (EI): calcd. for C12H8F3NO4S2 350.9847; found 3105, 3070, 3037, 1606, 1538, 1454, 1383, 1347, 1311, 1196, 1175,
350.9849.
860, 738 cm–1. 1H NMR (400 MHz, CDCl3): δ = 8.44 (d, J = 9 Hz,
2 H), 8.23 (d, J = 8.9 Hz, 2 H), 8.01 (d, J = 7.5 Hz, 2 H), 7.80 (t, J
= 7.5 Hz, 1 H), 7.63 (t, J = 7.9 Hz, 2 H) ppm. 19F NMR (367 MHz,
CDCl3): δ = –36.06 (s, 1 F) ppm. 13C NMR (100 MHz, CDCl3): δ =
151.84, 140.04, 136.35, 134.33, 131.35, 129.86, 129.72, 124.59 ppm.
HRMS (EI): calcd. for C12H9FN2O6S2 359.9886; found 359.9886.
N,4-Difluoro-N-[(4-nitrophenyl)sulfonyl]benzenesulfonamide
(1h).
Method B: A mixture of benzenesulfonamide 6b (0.965 g, 5 mmol),
sodium hydroxide (0.22 g, 5.5 mmol), and MeOH (10 mL) in a
50 mL three-necked flask was stirred for 0.5 h, and then it was
cooled to 0 °C. 4-Nitrobenzenesulfonyl chloride (5c; 1.22 g,
5.5 mmol) was added, and the mixture was stirred until TLC indi-
cated the disappearance of compound 6b. The mixture was filtered,
and the insoluble solid was collected to give 1h (1.24 g, 66%) as
Benzenesulfonamide Derivative 1l: A mixture of benzenesulfon-
amide 6a (0.875 g, 5 mmol), sodium hydroxide (0.22 g, 5.5 mmol),
and MeOH (10 mL) in a 50 mL three-necked flask was stirred for
0.5 h, and then it was cooled to 0 °C. 2-Fluorobenzenesulfonyl
white crystals, m.p. 138.7–138.9. IR (KBr): ν = 3110, 3069, 1587,
˜
1535, 1409, 1187, 1080, 845, 789 cm–1. 1H NMR (400 MHz, chloride (5e; 1.07 g, 5.5 mmol) was added, and the mixure was
CDCl3): δ = 8.47 (d, J = 8.8 Hz, 2 H), 8.26 (d, J = 8.8 Hz, 2 H),
8.09–8.07 (m, 2 H), 7.36–7.30 (m, 2 H) ppm. 19F NMR (367 MHz,
CDCl3): δ = –36.19 (s, 1 F), –98.10 (s, 1 F) ppm. 13C NMR
stirred until TLC indicated the disappearance of compound 6a.
The mixture was filtered, and the insoluble solid was collected to
give 1l (0.754 g, 45%) as white crystals, m.p. 100.8–101.6. IR (KBr):
(100 MHz, CDCl3): δ = 167.42 (d, J = 261.6 Hz), 151.90, 139.98, ν = 3107, 1597, 1581, 1478, 1452, 1398, 1272, 1189, 1071, 831, 794,
˜
133.12 (d, J = 10.4 Hz), 131.36, 130.20 (d, J = 3.1 Hz), 124.73,
117.33 (d, 23.1 Hz) ppm. HRMS (EI): calcd. for
C12H8F2N2O6S2 377.9792; found 377.9794.
707 cm–1. 1H NMR (300 MHz, CDCl3): δ = 8.13–8.05 (m, 2 H),
8.01–7.93 (m, 1 H), 7.84–7.76 (m, 2 H), 7.65 (t, J = 7.8 Hz, 2 H),
7.43–7.30 (m, 2 H) ppm. 19F NMR (282 MHz, CDCl3): δ = –37.13
(d, J = 11.5 Hz, 1 F), –103.35 (d, J = 11.3 Hz, 1 F) ppm. 13C NMR
(75 MHz, CDCl3): δ = 160.18 (d, J = 265.1 Hz), 138.56 (d, J =
8.9 Hz), 136.04, 134.53, 132.48, 129.97, 129.54, 124.82 (d, J =
4.0 Hz), 122.98 (d, J = 12.8 Hz), 118.03 (d, J = 20.8 Hz) ppm.
HRMS (EI): calcd. for C12H9F2NO4S2 332.9941; found 332.9942.
J
=
Benzenesulfonamide Derivative 1i: A mixture of benzenesulfon-
amide 6b (0.965 g, 5 mmol), sodium hydroxide (0.22 g, 5.5 mmol),
and MeOH (10 mL) in a 50 mL three-necked flask was stirred for
0.5 h, and then it was cooled to 0 °C. 2-Fluorobenzenesulfonyl
chloride (5e; 1.07 g, 5.5 mmol) was added, and the mixture was
stirred until TLC indicated the disappearance of compound 6b. The
mixture was filtered, and the insoluble solid was collected to give
Benzenesulfonamide Derivative 1m: A mixture of benzenesulfon-
amide 6a (0.875 g, 5 mmol), sodium hydroxide (0.22 g, 5.5 mmol),
and MeOH (10 mL) in a 50 mL three-necked flask was stirred for
0.5 h, and then it was cooled to 0 °C. 3-Fluorobenzenesulfonyl
1i (1.20 g, 72%) as white crystals, m.p. 107.7–107.8. IR (KBr): ν =
˜
1
3017, 3064, 1586, 1478, 1403, 1194, 1158, 832, 699 cm–1. H NMR
(300 MHz, CDCl3): δ = 8.14–8.09 (m, 2 H), 8.00–7.94 (m, 1 H), chloride 5d (1.07 g, 5.5 mmol) was added, and the mixure was
7.85–7.77 (m, 1 H), 7.42–7.30 (m, 4 H) ppm. 19F NMR (367 MHz,
stirred until TLC indicated the disappearance of compound 6a.
CDCl3): δ = –36.70 (d, J = 11.1 Hz, 1 F), –98.33 (s, 1 F), –103.35 The mixture was filtered, and the insoluble solid was collected to
(d, J = 10.8 Hz, 1 F) ppm. 13C NMR (75 MHz, CDCl3): δ = 167.27
(d, J = 260.8 Hz), 160.18 (d, J = 265.3 Hz), 138.71 (d, J = 9.0 Hz),
give 1m (0.956 g, 57%) as white crystals, m.p. 113.0–113.8. IR
(KBr): ν = 3101, 1594, 1476, 1450, 1403, 1389, 1314, 1231, 1198,
˜
1
133.18 (d, J = 10.3 Hz), 132.45, 130.39 (d, J = 3.2 Hz), 124.88 (d, 1177, 1085, 892, 820, 727 cm–1. H NMR (300 MHz, CDCl3): δ =
J = 4.0 Hz), 122.86 (d, J = 12.7 Hz), 118.07 (d, J = 20.8 Hz), 117.11
(d, J = 23.1 Hz) ppm. HRMS (EI): calcd. for C12H8F3NO4S2
350.9847; found 350.9847.
8.09–8.01 (m, 2 H), 7.89–7.77 (m, 2 H), 7.76–7.70 (m, 1 H), 7.69–
7.58 (m, 3 H), 7.55–7.44 (m, 1 H) ppm. 19F NMR (367 MHz,
CDCl3): δ = –36.72 (s, 1 F), –108.04 (s, 1 F) ppm. 13C NMR
(100 MHz, CDCl3): δ = 162.20 (d, J = 253.6 Hz), 136.28 (d, J =
7.4 Hz), 136.10, 134.46, 131.37 (d, J = 7.7 Hz), 129.84, 129.59,
125.74 (d, J = 3.5 Hz), 123.29 (d, J = 21.1 Hz), 117.09 (d, J =
25.3 Hz) ppm. HRMS (EI): calcd. for C12H9F2NO4S2 332.9941;
found 332.9940.
Benzenesulfonamide Derivative 1j: A mixture of benzenesulfon-
amide 6b (0.965 g, 5 mmol), sodium hydroxide (0.22 g, 5.5 mmol),
and MeOH (10 mL) in a 50 mL three-necked flask was stirred for
0.5 h, and then it was cooled to 0 °C. 4-tert-butylbenzenesulfonyl
chloride (5a; 1.28 g, 5.5 mmol) was added, and the mixture was
stirred until TLC indicated the disappearance of compound 6b. The
mixture was filtered, and the insoluble solid was collected to give
Benzenesulfonamide Derivative 1n: A mixture of benzenesulfon-
amide 6a (0.875 g, 5 mmol), sodium hydroxide (0.22 g, 5.5 mmol),
and MeOH (10 mL) in a 50 mL three-necked flask was stirred for
0.5 h, and then it was cooled to 0 °C. 2-Methylbenzenesulfonyl
1j (1.16 g, 60%) as white crystals, m.p. 97.2–98.7. IR (KBr): ν =
˜
3111, 3970, 2874, 1591, 1491, 1404, 1387, 1198, 1081, 841,
817 cm–1. 1H NMR (300 MHz, CDCl3): δ = 8.15–8.01 (m, 2 H), chloride (5f; 1.05 g, 5.5 mmol) was added, and the mixure was
7.92 (d, J = 8.7 Hz, 2 H), 7.62 (d, J = 8.7 Hz, 2 H), 7.30–7.26 (d,
J = 8.7 Hz, 2 H), 1.38 (s, 9 H) ppm. 19F NMR (367 MHz, CDCl3):
δ = –36.46 (s, 1 F), –98.31 (m, 1 F) ppm. 13C NMR (100 MHz,
CDCl3): δ = 167.09 (d, J = 260.3 Hz), 160.52, 133.04 (d, J =
10.4 Hz), 131.27, 130.50 (d, J = 3.1 Hz), 129.74, 126.61, 116.97 (d,
stirred until TLC indicated the disappearance of compound 6a.
The mixture was filtered, and the insoluble solid was collected to
give 1n (0.926 g, 56%) as white crystals, m.p. 116.1–116.9. IR
(KBr): ν = 3098, 3064, 1583, 1455, 1397, 1376, 1312, 1192, 1182,
˜
1
795, 760, 726 cm–1. H NMR (300 MHz, CDCl3): δ = 8.12 (d, J =
Eur. J. Org. Chem. 2014, 3607–3613
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3611

F. Wang, J. Li, Q. Hu, X. Yang, X.-Y. Wu, H. He
FULL PAPER
7.7 Hz, 2 H), 7.99 (d, J = 8.0 Hz, 1 H), 7.83 (t, J = 7.5 Hz, 1 H),
7.70–7.61 (m, 3 H), 7.44–7.37 (m, 2 H), 2.77 (s, 3 H) ppm. 19F
NMR (367 MHz, CDCl3): δ = –37.49 (s, 1 F) ppm. 13C NMR
(100 MHz, CDCl3): δ = 140.74, 135.90 (d, J = 2.9 Hz), 134.77,
133.36, 133.24, 131.95, 130.06, 129.46, 126.68, 99.99, 20.63 ppm.
HRMS (EI): calcd. for C13H12FNO4S2 329.0192; found 329.0193.
99:1, 0.3 mL/min, 254 nm): tR (minor) = 22.8 min, tR (major) =
25.9 min.
N-tert-Butoxycarbonyl-3-fluoro-3-naphthyl-2-oxindole (3g):[9]
A
colourless oil (55 mg, 91%). ee: 99%. [α]2D0 = +100.5 (c = 0.34,
1
CHCl3). H NMR (CDCl3, 400 MHz): δ = 8.06 (d, J = 8.3 Hz, 1
H), 7.91–7.77 (m, 3 H), 7.73 (s, 1 H), 7.59–7.45 (m, 4 H), 7.42 (d,
J = 7.6 Hz, 1 H), 7.30 (t, J = 7.5 Hz, 1 H), 1.61 (s, 9 H) ppm.
19F NMR (CDCl3, 376 MHz): δ = –145.22 (s, 1 F) ppm. HPLC
(Chiralpak AD-H, hexane/iPrOH = 95:5, 0.5 mL/min, 254 nm): tR
(minor) = 13.0 min, tR (major) = 14.7 min.
General Procedure for the Catalytic Enantioselective Fluorination of
2-Oxindole
N-tert-Butoxycarbonyl-3-fluoro-3-phenyl-2-oxindole (3a):[5] A mix-
ture of 2a (50 mg, 0.16 mmol), Pd-2 (1 mg, 0.5 mol-%), and diethyl
ether (5 mL) in a 10 mL reaction tube was stirred at 0 °C for 0.5 h.
Then 1b (85.2 mg, 0.24 mmol) was added portionwise, and the mix-
ture was stirred until TLC indicated that starting material 2a had
disappeared. The solvent was removed under reduced pressure, and
the residue was purified by column chromatography to give 3a
N-tert-Butoxycarbonyl-3-fluoro-3-phenyl-5-methoxy-2-oxindole
(3h):[5] A colourless oil (51 mg 90%). ee: 99%. [α]2D0 = +116.4 (c =
1
0.19, CHCl3). H NMR (CDCl3, 400 MHz): δ = 7.93 (dd, J = 0.9,
9.0 Hz, 1 H), 7.44–7.32 (m, 5 H), 7.06–7.00 (m, 1 H), 6.90 (t, J =
2.3 Hz, 1 H), 3.79 (s, 3 H), 1.61 (s, 9 H) ppm. 19F NMR (CDCl3,
376 MHz): δ = –146.18 (s, 1 F) ppm. HPLC (Chiralpak AD-H,
(50 mg, 96%) as a white solid. ee: 98%. [α]2D0 = +58.1 (c = 0.21,
1
CHCl3). H NMR (CDCl3, 400 MHz): δ = 8.01 (d, J = 8.4 Hz, 1 hexane/iPrOH = 99:1, 0.5 mL/min, 254 nm): tR (minor) = 23.8 min,
H), 7.53–7.51 (m, 1 H), 7.40–7.29 (m, 6 H), 7.27 (d, J = 6.0 Hz, 1 tR (major) = 25.7 min.
H), 1.62 (s, 9 H) ppm. 19F NMR (CDCl3, 376 MHz): δ = –145.37
N-tert-Butoxycarbonyl-3-fluoro-3-phenyl-5-chloro-2-oxindole (3i):[9]
(s, 1 F) ppm. HPLC (Chiralcel OD-H, hexane/iPrOH = 99:1,
A colourless oil (54 mg, 93%). ee: 99%. [α]2D0 = +56.1 (c = 0.32,
0.3 mL/min, 254 nm): tR (minor) = 27.8 min, tR (major) =
CHCl3). 1H NMR (CD3CN, 400 MHz): δ = 8.32 (dd, J = 8.8,
30.9 min.
1.0 Hz, 1 H), 7.92 (dt, J = 8.8, 2.1 Hz, 1 H), 7.85–7.74 (m, 4 H),
N-tert-Butoxycarbonyl-3-fluoro-3-(4-methylphenyl)-2-oxindole (3b):[4]
7.73–7.69 (m, 2 H), 1.94 (s, 9 H) ppm. 19F NMR (CD3CN,
A colourless oil (52 mg, 95%). ee: 99%. [α]2D0 = +46.7 (c = 0.21,
376 MHz): δ = –148.74 (s, 1 F) ppm. 13C NMR (101 MHz,
1
CHCl3). H NMR (CDCl3, 400 MHz): δ = 8.00 (d, J = 8.3 Hz, 1 CD3CN): δ = 169.59 (d, J = 24.3 Hz), 148.42, 139.85 (d, J =
H), 7.53–7.46 (m, 1 H), 7.40–7.35 (m, 1 H), 7.29–7.24 (m, 3 H),
7.20–7.18 (m, 2 H), 2.35 (s, 3 H), 1.60 (s, 9 H) ppm. 19F NMR
(CDCl3, 376 MHz): δ = –144.53 (s, 1 F) ppm. HPLC (Chiralcel
OD-H, hexane/iPrOH = 99:1, 0.5 mL/min, 254 nm): tR (minor) =
11.6 min, tR (major) = 14.1 min.
5.3 Hz), 135.22 (d, J = 27.3 Hz), 131.96 (d, J = 3.0 Hz), 130.27 (d,
J = 3.3 Hz), 129.84 (d, J = 1.6 Hz), 128.84, 127.25 (d, J = 18.2 Hz),
125.87, 125.74 (d, J = 6.2 Hz), 117.44, 92.55 (d, J = 188.1 Hz, 10
H), 85.09, 27.19 ppm. HPLC (Chiralcel OD-H, hexane/iPrOH =
98:2, 0.3 mL/min, 254 nm): tR (minor) = 18.3 min, tR (major) =
22.0 min.
N-tert-Butoxycarbonyl-3-fluoro-3-(2-methylphenyl)-2-oxindole (3c):[9]
A colourless oil (50 mg, 92%). ee: 88%. [α]2D0 = +32.4 (c = 0.22,
N-tert-Butoxycarbonyl-3-fluoro-3-(4-fluorophenyl)-5-fluoro-2-ox-
1
CHCl3). H NMR (CDCl3, 400 MHz): δ = 7.97 (d, J = 8.2 Hz, 1 indole (3j):[9] A colourless oil (56 mg, 97%). ee: 99%. [α]2D0 = +77.8
H), 7.59–7.57 (m, 1 H), 7.45–7.49 (m, 1 H), 7.32–7.26 (m, 2 H),
7.22–7.09 (m, 3 H), 2.01 (s, 3 H), 1.64 (s, 9 H) ppm. 19F NMR
(CDCl3, 376 MHz): δ = –143.15 (s, 1 F) ppm. HPLC (Chiralcel
OD-H, hexane/iPrOH = 99:1, 0.3 mL/min, 254 nm): tR (minor) =
21.6 min, tR (major) = 23.1 min.
(c = 0.31, CHCl3). 1H NMR (CDCl3, 400 MHz): δ = 8.05 (dd, J =
9.0, 4.2 Hz, 1 H), 7.37 (dd, J = 8.7, 5.2 Hz, 2 H), 7.30–7.19 (m, 1
H), 7.16–7.07 (m, 3 H), 1.63 (s, 9 H) ppm. 19F NMR (CDCl3,
376 MHz): δ = –111.02 (d, J = 3.4 Hz, 1 F), –115.70 (d, J = 1.9 Hz,
1 F), –144.1 (s, 1 F) ppm. HPLC (Chiralpak AD-H, hexane/iPrOH
= 98:2, 0.5 mL/min, 254 nm): tR (major) = 11.9 min, tR (minor) =
13.4 min.
N-tert-Butoxycarbonyl-3-fluoro-3-(4-fluorophenyl)-5–2-oxindole
(3d):[4] A colourless oil (50 mg, 90%). ee: 98%. [α]2D0 = +40.1 (c =
0.25, CHCl3). 1H NMR (CDCl3, 400 MHz): δ = 8.01 (d, J = N-tert-Butoxycarbonyl-3-fluoro-3-(4-methylphenyl)-5-fluoro-2-ox-
8.3 Hz, 1 H), 7.56–7.49 (m, 1 H), 7.40–7.33 (m, 3 H), 7.29 (t, J =
7.5 Hz, 1 H), 7.07 (t, J = 8.4 Hz, 2 H), 1.62 (s, 9 H) ppm. 19F NMR
(CDCl3, 376 MHz): δ = –111.54 (d, J = 3.2 Hz, 1 F), –142.95 (d, J
= 3.7 Hz, 1 F) ppm. HPLC (Chiralcel OD-H, iPrOH/hexane =
99:1, 0.5 mL/min, 254 nm): tR (minor) = 12.0 min, tR (major) =
15.1 min.
indole (3k):[4] A colourless oil (54 mg, 94%). ee: 99%. [α]2D0 = +35.5
(c = 0.21, CHCl3). 1H NMR (CDCl3, 400 MHz): δ = 8.04 (dd, J =
9.0, 4.3 Hz, 1 H), 7.31–7.20 (m, 5 H), 7.12 (d, J = 7.1 Hz, 1 H),
2.39 (s, 3 H), 1.63 (s, 9 H) ppm. 19F NMR (CDCl3, 376 MHz): δ
= –116.06 (d, J = 1.2 Hz, 1 F), –145.62 (d, J = 1.7 Hz, 1 F) ppm.
HPLC (Chiralpak AD-H, hexane/iPrOH = 99:1, 0.5 mL/min, 254
nm): tR (major) = 12.6 min, tR (minor) = 14.7 min.
N-tert-Butoxycarbonyl-3-fluoro-3-phenyl-5-fluoro-2-oxindole (3e):[4]
A colourless oil (51 mg, 92%). ee: 99%. [α]2D0 = +75.0 (c = 0.21,
N-tert-Butoxycarbonyl-3-fluoro-3-(4-fluorophenyl)-5-methyl-2-ox-
1
CHCl3). H NMR (CDCl3, 400 MHz): δ = 8.02 (ddd, J = 9.0, 4.4,
indole (3l):[4] A colourless oil (53 mg, 92%). ee: 99%. [α]2D0 = +83.5
1
1.0 Hz, 1 H), 7.45–7.30 (m, 5 H), 7.25–7.16 (m, 1 H), 7.12–7.04 (m, (c = 0.20, CHCl3). H NMR (CDCl3, 400 MHz): δ = 7.87 (d, J =
1 H), 1.61 (s, 9 H) ppm. 19F NMR (CDCl3, 376 MHz): δ = –115.93
8.4 Hz, 1 H), 7.40–7.29 (m, 3 H), 7.16 (s, 1 H), 7.07 (t, J = 8.6 Hz, 2
(d, J = 2.7 Hz, 1 F), –146.47 (d, J = 2.3 Hz, 1 F) ppm. HPLC H), 2.37 (s, 3 H), 1.61 (s, 9 H) ppm. 19F NMR (CDCl3, 376 MHz): δ
(Chiralcel OD-H, hexane/iPrOH = 99:1, 0.5 mL/min, 254 nm): tR
(minor) = 12.4 min, tR (major) = 15.4 min.
= –111.73 (d, J = 3.4 Hz, 1 F), –143.18 (d, J = 3.4 Hz, 1 F) ppm.
HPLC (Chiralcel OD-H, hexane/iPrOH = 299:1, 0.5 mL/min, 254
nm): tR (minor) = 32.2 min, tR (major) = 40.2 min.
N-tert-Butoxycarbonyl-3-fluoro-3-phenyl-5-methyl-2-oxindole (3f):[4]
A colourless oil (51 mg, 93%). ee: 99%. [α]2D0 = +116.0 (c = 0.21,
N-tert-Butoxycarbonyl-3-fluoro-3-(4-methylphenyl)-5-methyl-2-ox-
1
CHCl3). H NMR (CDCl3, 400 MHz): δ = 7.87 (d, J = 8.4 Hz, 1 indole (3m):[9] A colourless oil (51 mg, 90%). ee: 99%. [α]2D0 = +77.1
H), 7.42–7.33 (m, 5 H), 7.30 (d, J = 8.4 Hz, 1 H), 7.17 (s, 1 H),
2.36 (s, 3 H), 1.61 (s, 9 H) ppm. 19F NMR (CDCl3, 376 MHz): δ
= –145.63 (s, 1 F) ppm. HPLC (Chiralcel OD-H, hexane/iPrOH =
(c = 0.22, CHCl3). 1H NMR (CD3CN, 400 MHz): δ = 7.86 (d, J =
8.4 Hz, 1 H), 7.39 (d, J = 8.4 Hz, 1 H), 7.28–7.22 (m, 5 H), 2.37
(s, 3 H), 2.36 (s, 3 H), 1.61 (s, 9 H) ppm. 19F NMR (CD3CN,
3612
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2014, 3607–3613

Enantioselective Fluorination of 2-Oxindoles
4207; Angew. Chem. 2005, 117, 4276–4279; b) S. Lectard, Y.
Hamashima, M. Sodeoka, Adv. Synth. Catal. 2010, 352, 2708–
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376 MHz): δ = –141.90 (s, 1 F) ppm. HPLC (Chiralcel OD-H, hex-
ane/iPrOH = 98:2, 0.3 mL/min, 254 nm): tR (minor) = 17.0 min, tR
(major) = 19.6 min.
N-tert-Butoxycarbonyl-3-fluoro-3-(4-fluorophenyl)-5-methoxy-2-ox-
indole (3n):[9] A colourless oil (56 mg, 93%). ee: 98%. [α]2D0 = +66.4
(c = 0.23, CHCl3). 1H NMR (CDCl3, 400 MHz): δ = 7.93 (dd, J =
9.0, 0.9 Hz, 1 H), 7.38–7.34 (m, 2 H), 7.10–7.02 (m, 3 H), 6.90 (t, J
= 2.3 Hz, 1 H), 3.80 (s, 3 H), 1.61 (s, 9 H) ppm. 19F NMR (CDCl3,
376 MHz): δ = –111.55 (d, J = 3.4 Hz, 1 F), –143.84 (d, J = 3.7 Hz,
1 F) ppm. HPLC (Chiralcel OD-H, hexane/iPrOH = 99:1, 0.5 mL/
min, 254 nm): tR (minor) = 15.3 min, tR (major) = 19.6 min.
[3] a) T. Ishimaru, N. Shibata, T. Horikawa, N. Yasuda, S. Naka-
mura, T. Toru, M. Shiro, Angew. Chem. Int. Ed. 2008, 47, 4157–
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V. G. Shubin, Russ. J. Org. Chem. 2009, 45, 1468–1473; e) T.
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515–526.
N-tert-Butoxycarbonyl-3-fluoro-3-(4-methylphenyl)-5-methoxy-2-
oxindole (3o):[9] A colourless oil (56mg, 95%). ee: 98%. [α]2D0
=
+57.1 (c = 0.21, CHCl3). 1H NMR (CDCl3, 400 MHz): δ = 7.95
(d, J = 9.0 Hz, 1 H), 7.31–7.18 (m, 4 H), 7.08–7.02 (m, 1 H), 6.93
(t, J = 2.1 Hz, 1 H), 3.82 (s, 3 H), 2.38 (s, 3 H), 1.63 (s, 9 H) ppm.
19F NMR (CDCl3, 376 MHz): δ = –145.33 (s, 1 F) ppm. HPLC
(Chiralcel OD-H, hexane/iPrOH = 98:2, 0.3 mL/min, 254 nm): tR
(minor) = 22.0 min, tR (major) = 24.6 min.
Supporting Information (see footnote on the first page of this arti-
1
cle): H, 13C and 19F NMR spectra. HPLC spectra.
[4] Y. Zhang, X. J. Yang, T. Xie, G. L. Chen, W. H. Zhu, Tetrahe-
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chiya, K. Moriya, T. Goto, M. Sodeoka, Tetrahedron 2006, 62,
7168–7179; b) Y. Hamashima, D. Hotta, M. Sodeoka, J. Am.
Chem. Soc. 2002, 124, 11240–11241.
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Acknowledgment
The authors are grateful to the Chinese National Natural Science
Foundation (NSFC) (grant number 21372077) for financial sup-
port.
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Received: February 13, 2014
Published Online: April 24, 2014
Eur. J. Org. Chem. 2014, 3607–3613
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3613