Reaction of hexafluorothioacetone dimer with azoles. Practical synthesis of N-(hexafluoro-iso-propyl)azoles

Article abstract of DOI:10.1016/j.jfluchem.2013.07.004

The reaction of azoles with 2,2,4,4-tetrakis-(trifluoromethyl)-1,3- dithietane led to the unexpected formation of N-(hexafluoro-isopropyl)azoles and sulfur, providing access to a group of compounds bearing a (CF ₃)₂CH-group at nitrog

Full text of DOI:10.1016/j.jfluchem.2013.07.004

Journal of Fluorine Chemistry 156 (2013) 262–267
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Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Reaction of hexafluorothioacetone dimer with azoles. Practical
synthesis of N-(hexafluoro-iso-propyl)azoles
a,
b
Viacheslav A. Petrov *, Will Marshall
a
1
DuPont Central Research and Development, Experimental Station, PO Box 80500, Wilmington, DE 19880-0500, United States
DuPont Corporate Center for Analytical Sciences, Experimental Station, PO Box 80500, Wilmington, DE 19880-0500, United States
b
A R T I C L E I N F O
A B S T R A C T
Article history:
The reaction of azoles with 2,2,4,4-tetrakis-(trifluoromethyl)-1,3-dithietane led to the unexpected
Received 26 June 2013
Received in revised form 28 June 2013
Accepted 5 July 2013
formation of N-(hexafluoro-isopropyl)azoles and sulfur, providing access to a group of compounds
bearing a (CF
derivatives of imidazole and triazole were found to undergo alkylation via reaction with 2,2,4,4-tetrakis-
trifluoromethyl)-1,3-dithietane, producing the corresponding derivatives in 54–83% yield.
ß 2013 Elsevier B.V. All rights reserved.
3 2
) CH-group at nitrogen. Imidazole, pyrazole, 1,2,3- and 1,2,4-triazoles and benzo-
Available online 19 July 2013
(
Keywords:
2
,2,4,4-Tetrakis-(trifluoromethyl)-1,3-
dithietane
Reaction with azoles
N-(Hexafluoro-isopropyl)azoles
1
. Introduction
pyrrole [12], and HFTA-dimer with primary amines, leading in this
case to the formation of imines of hexafluoroacetone and sulfur
[13,14].
In this study we report an unusual reaction of azoles with HFTA-
dimer, leading to the selective formation of N-(hexafluoro-
isopropyl)-azoles.
Imidazole, a moderately strong base (imidazole conjugate acid
= 7.0 [1]), has previously been shown to react with the
pK
a
electrophilic double bond of fluoroolefins, such as tetrafluoroethy-
lene, chlorotrifluoroethylene and hexafluoropropene (HFP) to form
the corresponding 1-fluoroalkylazoles [2–4]. Even weakly basic
imidazolium salts were reported to react with hexafluoropropene
to produce the corresponding N-fluoroalkyl imidazolium salts [5].
An intensive study of the reactions of hexafluorothioacetone
2. Results and discussion
A repeat of the literature procedure [2] confirmed that the
reaction of HFP with imidazole (1) in DMF led to formation of the
product mixture 2a, along with a smaller amount of unsaturated
material 2b and 2c (2b trans- and 2c cis-isomer, Eq. (1)).
(HFTA) with a wide range of organic substrates, including cyclic
dienes [6], vinyl ethers, vinyl sulfides [7,8] and styrenes [9], was
recently carried out. These reactions used the readily available
cyclic dimer [10] of hexafluorothioacetone (2,2,4,4-tetrakis-(tri-
fluoromethyl)-1,3-dithietane) and a catalytic amount of CsF. Many
of these reactions can be carried out using a ‘‘one pot’’ procedure:
the HFTA cyclic dimer is first generated by the reaction of HFP with
sulfur, followed by the addition of the corresponding organic
substrate to the reaction mixture.
Despite the fact that HFTA and HFTA-dimer have been known
for over 45 years, the reported examples of reactions with
nitrogen-containing compounds are limited to a few transforma-
tions, including reactions of HFTA with azomethanes [11] and
o
N
25-35 C
DMF
N
+
CF =CFCF
2
3
2a
N
H
HFP
N
CF CFHCF
2
3
1
+
N
(1)
N
CF=CFCF3
2
b- trans-
c, cis-
2
*
Corresponding author. Tel.: +1 302 695 1958.
E-mail address: viacheslav.a.petrov@usa.dupont.com (V.A. Petrov).
Publication # 2013-784.
yield %;
ratio 2a:2b:2c - 86:12:2
1
0022-1139/$ – see front matter ß 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jfluchem.2013.07.004

V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 156 (2013) 262–267
263
When the same reaction was carried out in the presence of
o
2
5-55 C
elemental sulfur and CsF catalyst, the formation of compounds 2a–
c and the cyclic dimer of HFTA (3) was observed, indicating
comparable rates of reaction between imidazole and HFP (leading
[3]
S + HFP
x
DMF, CsF
N
N
(
5)
to products 2a–c) and (CF
3
)
2
CF-anion with sulfur (leading to 3).
o
5
-15 C, 2h
The outcome of this process strongly depended on the order of
addition of reagents. For example, when HFP was allowed to react
with sulfur to generate dimer 3, followed by the addition of the
imidazole, an exothermic reaction occurred, producing a mixture
of imidazole 4 and sulfur (>95% isolated yield) (Eq. (2)).
(
3)
N
+
Sx
N
CH(CF3)2
6
, 57%
CF3
o
S
CF3
3
As long as polar solvents (i.e., DMF, DMSO, CH CN) are used, the
25-55 C
reaction of imidazoles with dimer 3 does not require a catalyst. For
example, the addition of 3 to a solution of 4-phenylimidazole (7) in
CH CN resulted in an exothermic reaction and the fast precipitation
3
of sulfur, giving selective formation of 8 (NMR, Eq. (4)). The structure
of 8 was also confirmed by single crystal X-ray diffraction.
Sx + HFP
F3C
S
DMF, CsF
CF3
3
(
2)
o
1
5-15 C, 2h
C H
C H
6 5
25-35 C, 2h
6
5
o
N
N
N
+
3
+
Sx
+
Sx
(4)
N
H
CH CN
N
3
N
CH(CF3)2
, 54%
CH(CF3)
2
7
8
4
, 63%
The use of a relatively low boiling point solvent, such as
acetonitrile, significantly simplified the isolation of the product.
The isolation protocol included removal of sulfur by filtration,
The structure of 4 was established by single crystal X-ray
diffraction (Fig. 1).
3
followed by removal of CH CN, and crystallization of 8 from
In sharp contrast to liquid 2a [2], compound 4 was a white
crystalline solid (m.p. 63–64 8C, Table 1), with a melting point
slightly lower than the starting imidazole (m.p. 89–91 8C). Despite
its relatively high melting point, imidazole 4 sublimes easily under
reduced pressure.
The reaction from (Eq. (2)) was found to be general. For
example, the reaction of 2-methylimidazole (5) with 3 gave
compound 6 (57% yield), along with one mole of sulfur
hexane.
The reaction of the less basic benzimidazole 9 with 3 in DMF in
the absence of catalyst was significantly slower compared to the
imidazoles. When the reaction was carried out in the presence of
CsF catalyst, it resulted in the high yield formation of product 10
(Eq. (5)).
o
N
N
N
25 C, 12h
(
Eq. (3)).
+ 3
N
H
DMF, CsF;
(5)
-S
x
9
CH(CF
3 2
)
1
0, 83%
Other azoles were also found to undergo a similar alkylation
reaction with 3. The addition of 3 to a mixture of pyrazole (11)
and CsF catalyst led to the rapid formation of sulfur and 1-
(
(
hexafluoroisopropyl)pyrazole (12), isolated in 58% yield
Eq. (6)).
o
2
5-35 C, 2h
+
3
N
N + Sx
CsF, DMF
N
H
N
(
6)
CH(CF3)2
2,58%
1
1
1
The outcome of the reaction
3 with pyrazole strongly
depended on the reaction conditions. For example, the
reaction in the absence of CsF catalyst in dry acetone
solvent did not produce sulfur, but unexpectedly led to the
clean formation of 1:1 adduct 12a, isolated in 68% yield
(
Eq. (7)). Surprisingly, this compound was found to have a
Fig. 1. Structure of compound 4 shown with thermal ellipsoids drawn to the 30%
disulfide linkage, which was not present in the starting
material.
probability level.

2
64
V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 156 (2013) 262–267
2
5oC, 7 d
+
3
N
N
Acetone
N
N
(7)
H
C(CF ) S-SC(CF ) H
3
2
3 2
1
1
1
2a, 68%
The structure of this material was firmly established by single
crystal X-ray diffraction (see Fig. 2).
The formation of compound 12a was also observed in other
3
solvents (such as THF, CH CN and DMF), however the reaction was
not as clean, leading to the formation of other by-products (by
NMR).
Disulfide 12a is sensitive to the action of fluoride anion, since
the treatment of this material with CsF in DMF solvent resulted in
fast and clean formation of compounds 12 and 3 (Eq. (8))
.
5oC, 3h
CsF, DMF
C(CF ) SSC(CF ) H
Fig. 2. X-ray structure of 12a shown with thermal ellipsoids drawn to the 30%
2
N
+
3
probability level.
N
N
N
CH(CF3)2
3
2
3 2
(8)
1
2a
12, quant (NMR)
o
N
25 C, 16h
N
+
3
ratio 12 : 3
N
N + Sx
DMF
=
87 : 13
N
H
N
(10)
CH(CF
6, 63%
3 2
)
1
5
The conversion of 12a into 12 can also be carried out in the absence
of the catalyst, if it is kept in polar solvent, such as DMF or DMSO
1
(
ꢀ1 week at ambient temperature).
,2,4-Triazole (13) had lower reactivity towards 3 and the non-
Benzotriazole (1H-benzo[d][1,2,3]triazole, 17) was the least
reactive among the azoles studied, since no reaction between it
and 3 was observed in the absence of catalyst (DMF, 2d, 25 8C). On
the other hand, the reaction in the presence of CsF was rapid and
exothermic, leading to a mixture of two isomeric products, 18a and
1
catalyzed reaction required a longer time (>12 h) at ambient
temperature to selectively give compound 14a, while the
symmetrical isomer (14b) was not detected in the reaction
mixture (NMR). However, when the same reaction was carried
out in the presence of CsF catalyst, it resulted in the formation of a
mixture of isomers 14a and 14b (Eq. (9)).
18b (Eq. (11))
o
N
N
N
2
5-35 C, 2h
o
N
25 C, 16h
N
N + 3
N
+
3
N
H
N
N + S
x
CsF,
DMF;
-Sx
DMF
N
H
N
17
CH(CF3)2
CH(CF
3 2
)
+
18a
13
1
4a, 52%
(11)
N
N
N CH(CF3)2
(
9)
o
18b
N
N
2
5-35 C, 12h
1
3 + 3
14a +
Yield of mixture
18a and 18b - 58%
ratio 18a : 18b - 87 : 13
CsF, DMF
N
-
Sx
CH(CF
4b
3 2
)
1
Although the mechanism of the reaction of azoles with 2,2,4,4-
tetrakis-(trifluoromethyl)-1,3-dithietane (3) is not entirely clear,
some aspects of it can be discussed at this point. The reaction of
azoles with 3 is believed to start with nucleophilic attack of the
nitrogen atom of the azole on the carbon of dimer 3, resulting in the
formation of zwitter-ion A (See Scheme 1 p 5, exemplified by
reaction of pyrazole).
Yield of mixture 62%
Ratio 14a : 14b - 77 : 23
Triazoles 14a and 14b have different physical properties. For
example, isomer 14a has a much lower melting point (m.p. 32–
4 8C), than its symmetrical isomer 14b (95–96 8C). The substantial
difference in boiling points made separation of compounds 14a
and 14b by vacuum distillation possible, and the structures of both
isomers 14a and 14b were established by a single crystal X-ray
diffraction (Fig. 3).
3
Proton transfer from nitrogen to carbon leads to the
formation of compound B. Since this thiol is relatively acidic,
it may undergo deprotonation under the action of a relatively
weak base such as DMF to give anionic intermediate C. It is
believed that C can undergo rearrangement through intramo-
The reaction of isomeric 1,2,3-triazole (15) with 3 carried out in
the absence of the catalyst resulted in the selective formation of
isomer 16 (Eq. (10))
À
lecular attack of the sulfur anion –S on the electron-poor

V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 156 (2013) 262–267
265
Fig. 3. Structures of 14a (left) and 14b (right) shown with thermal ellipsoids drawn to the 30% probability level.
sulfur, resulting in the formation of carbanion D, which
3. Experimental
contains a disulfide link. In the absence of a strong base (such
as fluoride from CsF), anion D rapidly protonates, forming 12a.
However, in the presence of CsF, 12a can be deprotonated and
its anion may undergo fragmentation with extrusion of
hexafluorothioacetone (HFTA), leading to the formation of
final product 12. HFTA under basic conditions rapidly under-
goes a [2+2] cycloaddition to form 3.
1
13
19
H, C and F NMR spectra were recorded on a Bruker DRX-
500 (499.87 MHz) instrument using CFCl or TMS as internal
standards in CDCl as a lock solvent. GC and GC/MS analyses were
3
3
carried out on an HP-6890 instrument, using an HP FFAP capillary
column and either TCD (GC) or mass-selective (GS/MS) detectors,
3
respectively. Dry DMF (99.8%, water, 100 ppm), CH CN, DMSO, and
Table 1
Reaction conditions, yields, and MS data for new materials.
a
Entry No.
1
Compound No.
Method/solvent
A
Temp./time (8C/h)
Yield (%)
49
m.p. (BP) [8C (8C/mm Hg)]
MS (m/z)
+
+
4
Exothermic
58–59
M
6 4 6 2
(218, C H F N )
25–35 (4)
B (DMF or DMSO)
C
25 (12)
63
57
64–65
82–83
+
+
2
6
Exothermic
M
7 6 6 2
(232,C H F N )
5
–15 (4)
+
+
+
+
3
4
8
B (DMF)
A
25–35 (6)
25 (12)
54
83
91–92
M
M
(294, C12
H
H
8
F
F
6
N
N
2
)
)
10
101–101.5
(268, C10
6
6
2
b
+
+
2
5
12
B
C
(DMF)
Exothermic
30
58
9 (46.5–47.5/50)
M
(218, C
6
H
F
4 6
N
)
2
5–35 (2)
Exothermic
–15 (2)
5
+
6
7
12a
14a
B (acetone)
25 (7 days)
25 (16)
68
52
27.5–78 (hex.)
6 3 6 2
217 (C H F N )
b
+
+
+
B
(DMF)
33–34 (54–56/20)
M
(219, C
5
H
3
F
6
N
3
)
)
(
72–76/40)
c
C
C
Exothermic (5–15, 2)
Exothermic
62
c
d
+
8
9
14b
29
95–96
M
(219, C
5
H
3
F
6
N
3
5–15 (2)
b
+
+
+
+
16
B
(DMF)
25 (16)
63
47–48 (68–70/17)
73–75
M
(219, C
(269, C
5
H
H
3
F
6
6
N
3
)
)
d,e,f,g
1
0
18a
A
A
25 (12)
58
M
6
5
F
N
3
d
18b
25
a
b
c
d
e
f
Method A – DMF, CsF cat.; method B – solvent, no cat.; method C – S
x
/HFP/DMF, CsF.
Twofold excess of HFTA dimer.
Mixture of two isomers, ratio 77:23.
Calculated yield.
Mixture of two isomers, ratio 87:13.
Isolated by crystallization from hexane, purity 99% (NMR).
Isolated by crystallization from hexane, purity 98% (NMR).
g

2
66
V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 156 (2013) 262–267
Scheme 1. Mechanism of the reaction of pyrazole (11) and 3.
all starting azoles were obtained from commercial sources and
used without further purification. CsF (Aldrich) was dried at 100–
paper have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication nos. CCDC #930075–
930079. Copies of the data can be obtained, free of charge, on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
+44 1223 336033 or e-mail: deposit@ccdc.cam.ac.uk).
1
20 8C under dynamic vacuum for 4–8 h and was stored and
handled inside a glove box. Compound 1 was prepared according to
a modified procedure using CsF as a catalyst [7]. Due to the high
ratio of sulfur to fluorine, elemental analyses were not attempted
for new materials, and the purity of all isolated compounds was
established by GC and NMR spectroscopy to be at least 96%.
Compounds 2a–c were identified by comparison of NMR data with
data reported in Ref. [2].
3.1.1. Method A
To a mixture of 0.2 g of dry CsF, 30 mL of dry DMF and 0.02 mol
of the corresponding azole, compound 3 (0.01–0.012 mol) was
added slowly at 25–30 8C (exothermic) over 30 min period. The
addition was accompanied by formation of a yellow precipitate
(sulfur). After addition of 3 was complete, the reaction mixture was
agitated at ambient temperature for an additional 3 h, filtered,
filter cake was washed by DCM and dried to give (0.015–
0.019 mol) of pure sulfur. The DMF layer was diluted with water,
extracted with 100 mL hexane, washed with water (300 mL), dried
3.1. Crystallography
X-ray data for 4, 8, 12a, 14a and 14b were collected at À100 8C
using a Bruker 1K CCD system equipped with a sealed tube
molybdenum source and a graphite monochromator. The struc-
tures were solved and refined using the Shelxtl [15] software
4
over MgSO and the solvent was removed under reduced pressure
2
package, refinement by full-matrix least squares on F , scattering
(100–50 mm Hg, temp. <20 8C). Crude product was purified either
by sublimation or crystallization from hexane. Reaction conditions
and NMR data are given in Tables 1 and 2.
factors from Int. Tab. Vol. C Tables 4.2.6.8 and 6.1.1.4. Crystallo-
graphic data (excluding structure factors) for the structures in this

V.A. Petrov, W. Marshall / Journal of Fluorine Chemistry 156 (2013) 262–267
267
Table 2
NMR data for new materials.
1
a
19
a
13
a,b
Entry. No.
Comp.
H NMR
(
d
, ppm, J, Hz)
F NMR
d, ppm, J, Hz)
C NMR
(d, ppm, J, Hz)
(
1
2
3
4
6
8
5.17 (1H, sept., 6.5), 7.06 (1H, s), 7.13 (1H, s), 7.58 (1H, s)
2.48 (3H, s), 5.80 (1H, sept., 6.3), 7.05 (1H, s), 7.10 (1H, s)
5.08 (1H, sept., 6.5), 7.23 (1H, s),7.29 (3H, m), 7.59 (1H, s),
À70.16
59.29 (sept., 33), 118.84, 121.20 (q, 286), 130.59, 138.04
À69.94 (d, 6.3)
À69.95 (d, 6.5)
59.70 (sept., 32.0), 113.96, 120.64 (q, 286),
125.16, 127.86, 128.75, 132.62, 138.25, 143.94
57.78 (br.), 108.71 (br.), 121.03 (q, 286), 121.46,
7.71 (1H, s), 7.73 (1H, s)
4
5
10
5.44 (1H, br. s), 7.42 (3H, m), 7.92 (1H, s), 8.19 (1H, s)
À69.41 (br. s)
123.88, 124.88, 140.60 (br.)
12
5.50 (1H, sept., 7.1), 6.39 (1H, t, 2.3), 7.60 (2H, m)
À70.20 (d, 7.1)
À66.06 (d, 7.2),
À66.55 (s)
1
2a
4.81 (1H, sept., 7.2), 6.54 (1H, m), 7.68 (1H, m), 7.84 (1H, m)
57.90 (sept., 30.3), 78.60 (sept., 29.5), 109.34,
121.46 (q, 286.0), 122.09 (q, 280.0), 132.08
(sept., 2.9), 141.92
6
7
8
9
14a
14b
16
5.54 (1H, d, 6.5), 802 (1H, s), 8.30 (1H, s)
5.58 (1H, d, 6.5), 8.30 (2H, s)
À69.88 (d, 6.5)
À70.05 (d, 6.5)
À71.01 (d, 6.4)
À67.75 (d, 7.1)
62.09 (sept., 33.4), 120.21 (q, 282.7), 143.82, 152.78
c
57.23 (sept., 33.4), 120.54 (q, 283), 142.41
6.02 (1H, sept., 6.4), 7.87 (1H, s), 7.88 (1H, s)
6.15 (sept., 7.1), 7.42 (1H, m), 7.58 (2H, m), 8.09 (1H, d)
61.84 (sept., 34.0), 120.21 (qq, 282.0, 2.3), 123.75, 135.03
61.37 (sept., 35.0), 110.10, 120.90
18a
(qq, 284.0, 2.5), 125.12, 129.52
d
1
0
18b
6.05 (1H, sept. 6.2), 7.49 (2H, m), 7.93 (2H, m)
À68.60 (d, 6.2)
a
b
c
In CDCl
3
solvent, unless stated otherwise.
H} C spectrum.
In acetone-d
13
{
6
.
d
Characterized in mixture with 18b.
3
.1.2. Method B
purity ꢀ95–98%, with DMF being the major impurity (2–3%).
Analytically pure samples were prepared by recrystallization of
small sample from hexane. Reaction conditions and NMR data are
given in Tables 1 and 2.
To a solution of the corresponding azole (0.02–0.04 mol) in 10–
2
0
3
3
0 mL dry solvent (DMF, DMSO or CH CN), compound 3 (0.01–
.0252 mol) was added slowly at 25–30 8C (exothermic) over a
0 min period. The addition was accompanied by the formation of
a yellow precipitate (sulfur). After addition of 3, the reaction
3.2. Preparation of 12a
mixture was agitated at ambient temperature for an additional 3–
1
6 h and filtered (in case of reactions producing sulfur). When
A mixture of 0.4 g (0.059 mol) pyrazole and 2.5 g (0.07 mol) 3 in
15 mL of dry acetone was kept at 25 8C for 7 days. The solvent was
removed under reduced pressure to give 2.4 g of crude 12a (purity
95%, NMR). Recrystallization form hexane gave 1.7 g (68%) of pure
12a, m.p. 27.5–28 8C. Reaction conditions and NMR data are given
in Tables 1 and 2.
CH CN was used as solvent, it was removed under reduced
3
pressure (100–50 mm Hg, temp. <25 8C) and the crude product
was purified either by vacuum distillation, sublimation, or
crystallization from hexane. In the case of high boiling point
solvents (DMF, DMSO), the reaction mixture was diluted with
water, extracted with hexane (100 mL 2Â), washed with water
(
300 mL 2Â), dried over MgSO
4
and the solvent was removed
Acknowledgements
under reduced pressure (100–50 mm Hg, temp. <25 8C). Reaction
conditions and NMR data are given in Tables 1 and 2.
Authors are grateful to Dr. C. Junk for helpful discussions and
suggestions, Karin Karel for help with manuscript and Timothy
Bentz for technical support.
3.1.3. Method C
To a mixture of 0.2–0.5 g dry CsF, 100 mL of dry DMF and 0.1–
.2 mol of sublimed sulfur, hexafluoropropene (HFP) gas was
added at the rate which allowed one to maintain an internal
0
References
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1] T. Eicher, S. Hauptmann, The Chemistry of Heterocycles, Wiley-VCH, Weinheim,
(after addition of 0.12–0.22 mol of HFP), the reaction mixture was
2
003p. 166.
cooled down to 10 8C (appearance of second layer was observed at
this point) and the solution of the corresponding azole in DMF
[2] V.G. Poludnenko, O.B. Didinskaya, A.F. Pozharskii, Khimiya Geterotsiklicheskikh
Soedinenii (1984) 524–528.
[3] V.V. Rudyuk, D.V. Fedyuk, L.M. Yagupolskii, J. Fluorine Chem. 125 (2004)
(
0.1–0.2 mol in 30–50 mL of DMF) was added slowly to the
reaction mixture at 10–15 8C. The reaction mixture was agitated at
5–25 8C for 2–16 h and filtered to remove precipitated sulfur. The
filter cake was washed with DCM. Typical recovery of sulfur was
5–99%. The reaction mixture was diluted with water (500 mL)
and extracted with DCM (50–100 mL). The extract was washed
and the volume of the
1465–1471.
[4] K. Kirk, in: V. Petrov (Ed.), Fluorinated Heterocyclic Compounds, John Willey &
Sons, Hoboken, NJ, 2009, pp. 91–158.
1
[
5] D.S. Kim, D. Natalia, D.Q. Nguyen, D.J. Suh, H. Kim, H.S. Kim, H. Lee, Synlett (2009)
101–2104.
6] V. Petrov, W. Marshall, J. Fluorine Chem. 128 (2007) 729–735.
2
9
[
[7] V.A. Petrov, W. Marshall, J. Fluorine Chem. 131 (2010) 1144–1155.
[
[
8] V. Petrov, W. Marshall, J. Fluorine Chem. 143 (2012) 320–325.
9] V.A. Petrov, W. Marshall, J. Fluorine Chem. 132 (2011) 783–791.
with water (300 mL 2Â), dried over MgSO
4
solvent was reduced by 2/3 (100–50 mm Hg, temp. <25 8C).
Precipitated solids were filtered and washed with 20–30 mL of cold
hexane. The volume of mother liquor was reduced by 2/3 once
again and the solids were filtered and washed with hexane.
Combined solid product was air-dried. Crude product had a typical
[
10] D.C. England, J. Org. Chem. 46 (1981) 153–157.
[11] W.J. Middleton, W.H. Sharkey, J. Org. Chem. (1965) 1384–1390.
12] W.J. Middleton, J. Org. Chem. 30 (1965) 1390–1394.
13] N. Ishikawa, T. Kitazume, Bull. Chem. Soc. Jpn. 46 (1973) 3260–3263.
14] N. Ishikawa, T. Kitazume, Chem. Lett. (1972) 169–170.
[
[
[
[15] G. Sheldrick, SHELXTL Software Suite, v. 6.0, Bruker-AXS Corp., Madison WI, 1996.