Rhodium(II)-catalyzed addition of 2-diazo(fluoroalkyl)acetoacetates to sulfides: A simple synthesis of stable sulfonium ylides

Article abstract of DOI:10.1016/j.jfluchem.2004.01.012

2-Diazo(fluoroalkyl)acetoacetates 1 reacted readily with many sulfides under mild reaction conditions in the presence of catalytic Rh₂(OAc)₄ affording to the corresponding sulfonium ylides. While thianthrene gave trans-thianthrenium

Full text of DOI:10.1016/j.jfluchem.2004.01.012

Journal of Fluorine Chemistry 125 (2004) 1071–1076
Rhodium(II)-catalyzed addition of 2-diazo(fluoroalkyl)acetoacetates
to sulfides: a simple synthesis of stable sulfonium ylides
Shizheng Zhu*, Shifa Zhu, Yuanxi Liao
Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
354 Fenglin Lu, Shanghai 200032, China
Received 9 October 2003; received in revised form 7 January 2004; accepted 9 January 2004
Available online 15 April 2004
Abstract
2-Diazo(fluoroalkyl)acetoacetates 1 reacted readily with many sulfides under mild reaction conditions in the presence of catalytic Rh2(OAc)4
affording to the corresponding sulfonium ylides. While thianthrene gave trans-thianthrenium 5,10-di(fluoroalkylacetoethoxycarbonyl)methy-
lides (7a and 7b) under the same reaction condition, the structure of 7b trans-thianthrenium 5,10-di(bromodifluoroacetoethoxy-carbonyl)-
methylides was fully confirmed by spectral methods and X-ray single crystal diffraction analysis. All the ylide products obtained are fairly stable
due to the strong electron-withdrawing properties of the fluorine atom.
# 2003 Elsevier B.V. All rights reserved.
Keywords: 2-Diazo(fluoroalkyl)acetoacetate; Sulfide; Rhodium catalysis; Sulfur ylide; X-ray diffraction analysis
1. Introduction
olefins, and in these reactions the 1,3-dipolar cycloaddi–
tion products were formed in excellent yields (Scheme 2)
[5,6].
The generation of sulfur ylides and their chemical trans-
formation have received considerable attention because of
their application in synthesis and their probable involvement
in biochemical processes [1,2]. For example, sulfonium
ylides have been utilized for the synthesis of a number of
b-lactam antibiotics, pyrolizidine alkaloids and other natural
products [3]. The formation of sulfur ylides from diazocar-
bonyl compounds has been developed. It generally involves
the addition of a carbene derived from diazo-carbonyl com-
pound to sulfide. It is known that the sulfur ylides can be
isolated as stable reaction products if two electron-withdraw-
ing groups stabilize the ylide carbon. Porte and co-workers [4]
have reported thiophenium bis(methoxycarbonyl)methylide
from rhodium-catalyzed decomposition of dimethyl diazo-
malonate in thiophene at room temperature. However, other
diazocarbonyl compounds such as ethyl diazoacetoacetate,
diazoactophenone did not form the corresponding thiophe-
nium ylides (Scheme 1).
As a part of our continuing study on the chemical trans-
formation of 2-diazo(fluoroalkyl)acetoacetates, herein we
reported their reactions with sulfides.
2. Results and discussion
Reactions of the 2-diazo(fluoroalkyl)acetoacetates 1 with
sulfides occurred smoothly in the presence of catalytic
amount Rh(II). For example, heating a mixture of 1a and
thioanisole 2a at 110 8C for 2 h afforded to the sulfonium
ylide 3aa in 83% yield, which is a stable colorless solid.
When dimethyl sulfide 2b (bp 38 8C) was used as the
substrate, it reacted with 1a in a sealed tube, and the
corresponding dimethyl sulfonium ylide 3ab was obtained
in 86% yield after reacting in benzene for 2 h. Refluxing of
excess dimethyl sulfide 2b with 1a (2b:1a ¼ 10:1) in toluene
for 4 h gave better yield (90%) of 3ab. The sulfoxonium
ylides 3ac and 3bc were also formed when 1a or 1b were
decomposed by Rh2(OAc)4 in DMSO. Similarly, the corre-
sponding arsonium ylide can be formed through the reaction
of 1 with triphenylarsine. We tried to react the sulfonium or
arsonium ylide with phenyl aldehyde in refluxing toluene for
Recently, we reported the rhodium(II)-catalyzed reactions
of ethyl 2-diazo(fluoro-alkyl)acetoacetates with electron-rich
* Corresponding author. Fax: þ86-21-64166128.
E-mail address: zhusz@mail.sioc.ac.cn (S. Zhu).
0022-1139/$ – see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2004.01.012

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S. Zhu et al. / Journal of Fluorine Chemistry 125 (2004) 1071–1076
H3CO
O
COOCH3
r.t.
+
N2
S
S
COOCH3
O
H3CO
Y
Y
r.t.
N2
+
S
Y = Ph, CH3CO ,EtOCO
COOCH3
O
S
H3CO
Scheme 1.
COOEt
CF3
COOEt
O
O
Rh2(OAc)4
ROH
+
RO
CF3
OEt
RO
CF3
O
O
N2
Scheme 2.
24 h, however, the ylide was recovered in almost quantitative
yields (Scheme 3).
increasing the mole ratio of thianthrene to 1 to 1:2.2 giving
nearly 1:1 of 6 and 7 (see Table 1, Entries 12 and 13). Fig. 1
showed the crystal structure of compound 7b.
The molecular structure of 7b and its packing map are
shown in Fig. 1. It is clear that the two methylide groups are
in two sides of the thianthrene plane, the angle between the
plane containing C(7), C(8) and C(10) atoms and thian-
threne plane is 868, they are nearly perpendicular to the
thianthrene plane (see Fig. 1). The two C–C bonds invol-
Under the same reaction conditions, treatment of triphe-
nylphosphine with 1 did not isolate the expected phospho-
nium ylide, but another product hydrazone 4 was formed
almost in quantitative ylide (Scheme 4). The product hydra-
zone 4 should come from the intermediary phosphazine
1
[7,8]. Its H NMR spectrum shows two different chemical
shifts at 11.47 and 8.46 ppm for the two NH protons.
The reaction of thianthrene 5, which has two sulfur
atoms, with 1 gave two products: mono-sulfonium ylide
6 and bis-sulfonium ylide 7, respectively (Scheme 5).
Increasing the molar ratio of thianthrene to 1 to 1:2.2 gave
more bis-sulfonium ylide. For example, equimolar reaction
of thianthrene with 1 formed 90% of 6 and 10% of 7, while
˚
ving the methylide carbon are 1.448 and 1.420 A, consistent
with greater C¼C double bond character in the latter, i.e. in
the bromo difluoro acetyl group. The two carbonyl C¼O
˚
bonds possess lengths of 1.196 and 1.219 A, respectively,
for the ethoxyl carbonyl and the bromodifluoro acetyl
group.
O
O
O
O
Rh2(OAc)4
(1 mol%)
-
XF2C
OEt
+
Y
XF2C
OEt
+
benzene or toluene
N2
1 (a-b)
Y
2 (a-d)
3 (aa-bd)
a: Y=CH3SPh
b: Y=CH3SCH3
c: Me2S(O)
d: AsPh3
a: X=F
b: X=Br
toluene
reflux 24h
no reaction
3
ArCHO
+
Scheme 3.
O
H
O
O
O
Rh2(OAc)4
reflux
moisture
XCF2
OEt
1 a
+
XCF2
OEt
+ Ph3P
Ph3P
N
N
N
N
H
PPh3
4a
Scheme 4.

S. Zhu et al. / Journal of Fluorine Chemistry 125 (2004) 1071–1076
1073
O
O
O
O
XCF2
EtO
OEt
XCF2
OEt
S
S
S
S
S
Rh2(OAc)4
1 (a-b)
+
+
benzene, reflux
S
CF2X
5
O
O
7 (a-b)
6 (a-b)
Scheme 5.
O
O
Rh2(OAc)4
XCF2
OR
S
AsPh3
or
R1
R2
N2
2
X=F, Br
1
O
O
O
O
XCF2
OR
or
XCF2
OR
AsPh3
N2
S
Rh=CR'R"
R1
R2
X=F, Br
45-90%
3
Scheme 6.
It was worth noting that the intermolecular halogen
bonding and hydrogen bonding co-existing in this com-
pound.
The reaction was proceeding according to the below
catalytic cycle. The dizaocompound first was decomposed
by Rh2(OAc)4 to form the rhodium carbenoid. Then the
corresponding sulfonium or arsonium ylide was formed in
the presence of sulfide or triphenyl arsine (Scheme 6).
In contrast to the corresponding acetoacetate derivatives,
which can still process further chemical transformation [9],
all the ylide products obtained are fairly stable even in the
refluxing xylene due to the strong electron-withdrawing pro-
perty of the fluorine atom. In our previous work we found
that the sulfonium bis(perfluoroalkylsulfonyl)methides,
which were prepared from the reaction of methyl sulfide
with phenyliodonium bis(perfluoroalkylsulfonyl)methides,
Table 1
Reaction results of 2-diazo(fluoroalkyl)acetoacetate 1 with 2 and 5a
Entry
Reactants 1, 2 or 5
Mole ratio 2 or 5:1
Condition
Sol
Products yield
Yieldb (%)
mp (8C)
T (8C)
t (h)
1
2
1a, 2a
1a, 2b
1a, 2bc
1a, 2b
1a, 2c
1a, 2d
1a, 2d
1b, 2a
1b, 2b
1b, 2c
1b, 2d
1a, 5
1.1
5
Toluene
Toluene
Benzene
Benzene
110
110
80
2
3aa
3ab
3ab
3ab
3ac
3ad
3ad
3ba
3bb
3bc
3bd
6a
83
90
86
52
80
51
72
71
45
65
54
90
10
47
44
48
16
53–55
139–141
3
3
5
0.5
4
4
10
–
80
d
d
5
–
110
110
80
2
75–77
127–129
127–129
Oil
6
1.1
1.5
1.1
10
Toluene
Benzene
Toluene
Toluene
2
7
3
8
110
110
110
110
80
2
9
2
129–131
72–74
d
d
–
10
11
12
–
2
1.1
1
Toluene
Benzene
2
156–158
136–138
227–229
3
7a
6a
13
14
1a, 5
1b, 5
2.2
1.2
Toluene
Toluene
110
110
3
3
7a
6b
160–162
198–200
7b
a Reaction carried out in the presence of 1 mol% Rh2(OAc)4.
b Isolated yield based on diazo compounds 1.
c Reaction carried out in a sealed tube.
d DMSO used as solvent (8 ml).

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S. Zhu et al. / Journal of Fluorine Chemistry 125 (2004) 1071–1076
these ylides to 140 8C for several hours, none forms the
products expected from the Stevens rearrangement.
3. Conclusion
In conclusion, stable fluorine-containing sulfur ylides and
arsonium ylides can be readily prepared through the decom-
position of 2-diazo(fluoroalkyl)acetoacetates in the presence
of rhodium catalyst. The further chemical transformation of
these ylides is under investigating.
4. Experimental
Melting points were measured in Temp-Melt apparatus
1
and were uncorrected. H, 13C and 19F NMR spectra were
recorded in CDCl3 on Bruker AM-300 instruments with
Me4Si and CFCl3 (with upfield negative) as the internal and
external standards, respectively. IR spectra were obtained
with a Nicolet AV-360 spectrophotometer. Lower resolution
mass spectrum or high resolution mass spectra (HRMS)
were obtained on a Finnigan MAT-8430 instrument using the
electron impact ionization technique (70 eV), respectively.
Elemental analyses were performed by this Institute. All
reactions as well as column chromatography were moni-
tored routinely with the aid of TLC or 19F NMR spectro-
scopy. 1a–1b were prepared according to the procedures
reported [5].
4.1. A typical procedure for the catalytic formation of
sulfur ylides from the decomposition of diazocompounds
Under a nitrogen atmosphere, a solution of diazocom-
pound 1 (0.5 mmol) in 2 ml toluene was added to a 5 ml
flask containing Rh2(OAc)4 (2 mg, 1 mol%) with sulfide
(0.55 mmol) and toluene (2 ml) over 2 h by the means of a
syringe pump. After addition, the reaction mixture was
stirred at reflux temperature until disappearance under mon-
itoring by TLC (ca. 3 h). The solvent was removed in vacuo
and the residue was purified on silica gel using ethyl acetate/
hexane (v=v ¼ 1 : 5) to afford the corresponding sulfur
ylides. Preparation of arsonium ylides is similar as the above
procedure.
4.2. Ethyl 2-(methylphenylsulfuranylidene)-3-oxo-
4,4,4-trifluoro-butanoate (3aa)
Fig. 1. (a) The molecular structure of compound 7b. (b) Packing map of
compound 7b.
Colorless solid, mp: 53–55 8C. IR (KBr) cmꢀ1: 3024,
2996, 1705, 1590, 1386, 1270, 1045. H NMR (CDCl3) d
7.72–7.28 (5H, m, Ar), 4.20 (2H, q, J ¼ 7:2 Hz), 1.28 (3H, t,
J ¼ 7:2 Hz), 3.35 (3H, s). 19F NMR d ꢀ71.66 (s). MS: m/z
(%) 307 (Mþ þ 1, 10), 306 (Mþ, 59), 291 (2), 261 (2), 237
(98), 233 (11), 209 (100), 124 (46). Analytically calculated
for C13H13O3SF3: C, 50.98; H, 4.25. Found: C, 50.81;
H, 4.25.
1
are readily oxidized to the sulfoxonium ylides at room
temperature in the air [10].
ꢀ
þ
ꢀ
þ
hv
air
ðRfSO2Þ2C ¼ 1Ph!ðRfSO2Þ2C ꢀ SR2!ðRfSO2Þ2C ꢀ SðOÞR2
r:t:
R2S
However, the sulfonium ylides and arsonium ylide 3 have
not been oxidized in the air for two months. Upon heating

S. Zhu et al. / Journal of Fluorine Chemistry 125 (2004) 1071–1076
1075
4.3. Ethyl 4-bromo-4,4-difluoro-2-
(methylphenylsulfanylidene)-3-oxo-butanoate (3ba)
4.8. Ethyl 3-oxo-4,4,4-trifluoro-2-(triphenyl-l5-
arsanylidene)-butanoate (3ad)
Pale yellow oil. IR (neat) cmꢀ1: 2986, 2935, 1736,
1686, 1449, 1371, 1144. H NMR (CDCl3) d 7.61–7.58
Colorless solid, mp: 127–129 8C. IR (KBr) cmꢀ1: 3058,
2985, 1687, 1576, 1411, 1267, 1065. H NMR (CDCl3) d
1
1
(2H, m, Ar), 7.46–7.44 (3H, m, Ar), 4.11 (2H, q,
J ¼ 7:2 Hz), 3.27 (3H, s), 1.19 (3H, t, J ¼ 7:2 Hz). 19F
NMR d ꢀ55.02 (s). MS: m/z (%) 368 (Mþ þ 2, 6), 366
(Mþ, 6), 321 (4), 237 (100), 209 (28), 84 (79). HRMS
calculated for C13H13O3SF2Br [Mþ]: 365.97368. Found:
365.97436.
7.62-7.26 (15H, m, Ar), 3.84 (2H, q, J ¼ 7:2 Hz), 0.794 (3H,
t, J ¼ 7:2 Hz). 19F NMR d ꢀ70.878 (s). MS: m/z (%) 488
(Mþ,15), 443 (12), 419 (100), 391 (14), 347 (14), 306 (6),
227 (20), 152 (22). Analytically calculated for
C24H20O3F3As: C, 59.02; H, 4.10. Found: C, 59.01; H, 4.02.
4.9. Ethyl 4-bromo-4,4-difluoro-3-oxo-2-(triphenyl-l5-
arsanylidene)-butanoate (3bd)
4.4. Ethyl 2-(dimethylsulfuranylidene)-3-oxo-4,
4,4-trifluoro-butanoate (3ab)
Yellow solid, mp: 156–158 8C. IR (KBr) cmꢀ1: 3091,
Colorless solid, mp:139–141 8C. IR (KBr) cmꢀ1: 2994,
1695, 1592, 1404, 1385, 1268, 1157, 1069. 1H NMR
(CDCl3) d 4.12 (2H, q, J ¼ 7:2 Hz), 2.92 (6H, s), 1.23
(3H, t, J ¼ 7:2 Hz). 19F NMR d ꢀ71.53 (s). MS: m/z (%)
244 (Mþ, 41), 229 (10), 199 (47), 175 (100), 69 (18), 62 (40).
Analytically calculated for C8H11O3F3S: C, 39.34; H, 4.51.
Found: C, 39.24; H, 4.76.
2986, 1682, 1572, 1439, 1241, 1142, 1069. 1H NMR
(CDCl3)
d 7.64-7.28 (15H, m, Ar), 3.83 (2H, q,
J ¼ 7:2 Hz), 0.786 (3H, t, J ¼ 7:2 Hz). 19F NMRd
ꢀ54.67 (s). MS: m/z (%) 550 (Mþ þ 2, 2), 548 (Mþ, 41),
505 (2), 419 (10), 306 (47), 227 (100), 152 (18), 77 (40).
Analytically calculated for C24H20O3F2BrAs: C, 52.55; H,
3.65. Found: C, 52.53; H, 3.72.
4.5. Ethyl 4-bromo-4,4-difluoro-2-
(dimethylsulfuranylidene)-3-oxo-butyrate (3bb)
4.10. Ethyl 3-oxo-2-(5l4-thianthren-5-ylidene)-4,
4,4-trifluoro-butanoate (6a)
Colorless solid, mp:129–131 8C. IR (KBr) cmꢀ1: 2987,
1689, 1586, 1376,1243, 1145, 1069. H NMR (CDCl3) d
4.22 (2H, q, J ¼ 7:2 Hz), 2.92 (6H, s), 1.33 (3H, t,
J ¼ 7:2 Hz). 19F NMR d ꢀ55.24 (s). MS: m/z (%)
306 (Mþ þ 2, 8), 304 (Mþ, 8), 175 (100), 149 (20),
147 (21), 131 (18), 62 (18). Analytically calculated
for C8H11O2F2SBr: C, 31.58; H, 3.62. Found: C, 31.40;
H, 3.68.
Colorless solid, mp: 136–138 8C. IR (KBr) cmꢀ1: 1553,
1439, 1250, 1101, 1025, 762. 1H NMR (CDCl3) d 7.74-7.40
(8H, m, Ar), 4.00 (2H, q, J ¼ 7:2 Hz), 0.99 (3H, t,
J ¼ 7:2 Hz). 19F NMR d ꢀ71.87 (s). MS: m/z (%) 398
(Mþ, 7), 353 (3), 301 (20), 216 (100), 184 (62), 77 (1),
69 (4). Analytically calculated for C18H13O3S2F3: C, 54.27;
H, 3.27. Found: C, 54.25; H, 3.19.
1
4.11. Ethyl 4-bromo-4,4-difluoro-3-oxo-2-(5l4-thianthren-
5-ylidene)-butanoate (7a)
4.6. Ethyl 2-(dimethyloxosulfuranylidene)-3-oxo-4,
4,4-trifluoro-butanoate (3ac)
Colorless solid, mp: 159–161 8C. IR (KBr) cmꢀ1: 2977,
Colorless solid, mp: 75–77 8C. IR (KBr) cmꢀ1: 3060,
2985, 1666, 1604, 1378, 1301, 1185, 1079. 1H NMR
(CDCl3) d 4.23 (2H, q, J ¼ 7:2 Hz), 3.70 (6H, s), 1.31
(3H, t, J ¼ 7:2 Hz). 19F NMR d ꢀ72.18 (s). MS: m/z (%)
260 (Mþ, 41), 215 (2), 191 (100), 165 (12). Analytically
calculated for C8H11O4F3S: C, 36.92; H, 4.23. Found: C,
36.90; H, 3.94.
1701, 1621, 1444, 1240, 1062. H NMR (CDCl3) d 7.68-
1
7.46 (8H, m, Ar), 4.20 (2H, q, J ¼ 7:2 Hz), 1.19 (3H, t,
J ¼ 7:2 Hz). 19F NMR d ꢀ55.63 (s). 13C NMR (CDCl3) d
14.26, 60.76, 114.40 (t, JCF ¼ 314:5 Hz), 125.62, 127.37,
128.80, 129.61, 130.24, 131.10, 164.01, 174.67, 206,80.
MS: m/z (%) 460 (Mþ þ 2, 1), 458 (Mþ, 1), 379 (18),
329 (35), 301 (7), 216 (100), 184 (47), 152 (5), 77 (1).
Analytically calculated for C18H13O3S2F2Br: C, 46.96; H,
2.82. Found: C, 46.98; H, 2.79.
4.7. Ethyl 4-bromo-4,4-difluoro-2-
(dimethyloxosulfuranylidene)-3-oxo-butanoate (3bc)
4.12. Trans-thianthrenium 5,10-di
(trifluoroacetoethoxycarbonyl)methylides (6b)
Yellow solid, mp: 72–74 8C. IR (KBr) cmꢀ1: 3021, 2964,
1698, 1604, 1472, 1373, 1343, 1250, 1196. 1H NMR
(CDCl3) d 4.23 (2H, q, J ¼ 7:2 Hz), 3.69(6H, s), 1.32
(3H, t, J ¼ 7:2 Hz). 19F NMR d ꢀ56.21 (s). MS: m/z (%)
322 (Mþ þ 2, 3), 320 (Mþ, 3), 277 (8), 275 (8), 191 (100),
165 (15), 119 (49). Analytically calculated for
C8H11O3F2SBr: C, 30.00; H, 3.43. Found: C, 30.00; H, 3.49.
Colorless solid, mp: 227–229 8C. IR (KBr) cmꢀ1: 3079,
2986, 1664, 1605,1581, 1379, 1288, 1211, 1063. H NMR
(CDCl3) d 7.88–7.70 (8H, m, Ar), 4.30 (4H, q, J ¼ 7:2 Hz),
1.34 (6H, t, J ¼ 7:2 Hz) . 19F NMR d ꢀ72.07 (s). MS: m/z
(%) 580 (Mþ, 11), 561 (3), 535 (12), 398 (4), 216 (100), 184
1

1076
S. Zhu et al. / Journal of Fluorine Chemistry 125 (2004) 1071–1076
(74), 69 (4). Analytically calculated for C24H18O6F6S2: C,
49.66; H, 3.06. Found: C, 49.66; H, 3.18.
were 0.0620 and 0.175, respectively. All calculations were
performed using the SHELX-97 program.
4.13. Trans-thianthrenium 5,10-
di(bromodifluoroacetoethoxycarbonyl)methylides (7b)
Acknowledgements
Colorless solid, mp: 198–200 8C. IR (KBr) cmꢀ1: 3079,
2985, 1665, 1587, 1466, 1371, 1278. H NMR (CDCl3)
The authors thank the National Natural Science Founda-
tion of China (NNSFC) (Nos. 20372077 and 20032010).
1
d 7.91–7.88 (4H, m, Ar), 7.73–7.70 (4H, m, Ar), 4.31
(4H, q, J ¼ 7:2 Hz), 1.37 (6H, t, J ¼ 7:2 Hz). 19F NMR d
ꢀ56.12 (s). 13C NMR (CDCl3) d 14.38, 61.26, 113.90
(t, JCF ¼ 314:6 Hz), 128.72, 128.81, 132.92, 164.05,
174.20, 203.72. MS: m/z (%) 702 (Mþ þ 2, 1), 700
(Mþ, 1), 216 (100), 184 (23). Analytically calculated for
C24H18O4F4S2Br2: C, 41.14; H, 2.57. Found: C, 41.11;
H, 2.57.
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˚
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