Multigram Scale Syntheses of First and Second Generation of Trifluoromethanesulfenamide Reagents

Article abstract of DOI:10.1021/acs.oprd.6b00062

Trifluoromethanesulfenamide reagents constitute a family of very efficient reagents to trifluoromethylthiolate various molecules. Optimized syntheses have been developed to easily obtain, in a reproducible manner, large quantities of these reagents, with good overall yields. Up to 84 g have already been obtained, at a reasonable cost.

Full text of DOI:10.1021/acs.oprd.6b00062

Article
pubs.acs.org/OPRD
Multigram Scale Syntheses of First and Second Generation of
Trifluoromethanesulfenamide Reagents
Quentin Glenadel,† Sebastien Alazet,† Francois Baert,† and Thierry Billard*,†,‡
̧
́
†Institute of Chemistry and Biochemistry (ICBMS − UMR CNRS 5246), Univ Lyon, Universite
́
Lyon 1, CNRS, 43 Bd du 11
novembre 1918, F-69622 Villeurbanne, France
‡CERMEP − In Vivo Imaging, Groupement Hospitalier Est, 59 Bd Pinel, F-69003 Lyon, France
S
* Supporting Information
ABSTRACT: Trifluoromethanesulfenamide reagents constitute a family of very efficient reagents to trifluoromethylthiolate
various molecules. Optimized syntheses have been developed to easily obtain, in a reproducible manner, large quantities of these
reagents, with good overall yields. Up to 84 g have already been obtained, at a reasonable cost.
toxicity of the historical reagent CF3SCl.30 Therefore, some
INTRODUCTION
■
new efficient reagents and methods have emerged these last
years to propose to the chemist community convenient tools to
easily prepare various CF3S molecules.17,31−36 Among all of
these new reagents, trifluoromethanesulfenamides (BB re-
agents, Figure 2), developed in our laboratory, appeared as
very efficient and versatile reagents allowing either electrophilic
or nucleophilic trifluoromethylthiolations.37−41
Since a long time, fluorinated compounds have always known a
particular attention, essentially because of the specific intrinsic
properties of fluorine atom.1−12 With time, this interest has
constantly grown to reach, these last years, its paroxysm with
the development of new original and efficient methods to
synthesize fluorinated compounds.13−18 This availability of new
synthetic strategies has largely contributed to the development
of new fluorinated groups with various specific properties,
finding applications in a large panel of various fields. In
particular, association of fluorinated moieties with heteroatoms
turned out very interesting because of the extraordinary
properties brought by such substituents.16,17,19−21 Among
these new moieties, the trifluoromethylsulfanyl group (CF3S)
has recently emerged. This infatuation is notably justified by its
specific electronic properties (Hammett constants σp = 0.50, σm
= 0.40; Swain−Lupton constants F = 0.36, R = 0.14)22 and its
high lipophilicity (Hansch parameter πR = 1.44).23−25
Furthermore, some CF3S molecules have found pertinent
applications in life sciences (Figure 1).26−29
Figure 2. Trifluoromethanesulfenamide reagents (BB reagents). In
parentheses, the CAS Registry Number is shown.
Such an interest in trifluoromethylthiolated compounds has
required the development of new methods to synthesize these
targeted products, but above all, the design of new
trifluoromethylthiolating reagents to circumvent the high
Consequently, because of the increasing use of these
reagents, large-scale production appeared to be essential.
RESULTS AND DISCUSSION
■
The syntheses of these reagents are based on the specific
rearrangement of the corresponding trifluoromethanesulfina-
midines (1) arising from the reaction of Ruppert−Prakash
reagent with DAST and a primary amine (Scheme 1). In the
case of BB13 and BB23, a postmethylation is then performed.42
Synthesis of BB13H. In this case, the trifluoromethane-
sulfinamidine (1a) obtained after addition of aniline is very
sensitive, and the acidity of the reaction medium is strong
enough to induce, in situ, the rearrangement into BB13H.
Consequently, the expected reagent is directly obtained after
Received: March 1, 2016
Figure 1. Some bioactive CF3S molecules.
© XXXX American Chemical Society
A
DOI: 10.1021/acs.oprd.6b00062
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Organic Process Research & Development
Article
Scheme 1. Synthetic Scheme of
Table 2. Methylation of BB13H To Provide BB13
Trifluoromethanesulfenamides
BB13H
(g)
methylating reagent BB13 (quantity/
entry
base (g)
(g)
yield)
a
1
2.80
3.00
1.00
NaH (0.70)
NaH (0.75)
MeI (2.71)
MeI (2.96)
MeI (0.81)
2.40 g (80%)
2.74 g (85%)
2
3
i-PrNEt2
(0.74)
4
1.00
i-PrNEt2
(0.74)
TfOMe (0.93)
5
0.50
K2CO3 (0.72)
NaH (3.87)
TfOMe (0.51)
MeI (13.74)
b
6
17.00
16.40 g (90%)
a
b
Without chromatographic purification of BB13H. Use of a
aniline addition. The production of this first reagent has been
scaled up to 17 g without major issues, following the initially
described procedure (Table 1).42 It is noteworthy that no
mechanical stirrer.
mechanical stirring seems to improve the yield. It is important
to notice that BB13H and BB13 are relatively volatile and
require the use of pentane as chromatographic solvent and
evaporation under moderate controlled vacuum (110 mbar, at
25 °C).
Table 1. Multigram Synthesis of BB13H
CF3SiMe3
(g)
DAST
(g)
i-PrNEt2
(g)
aniline
(g)
BB13H (quantity/
yield)
entry
Synthesis of BB23. The second generation of trifluor-
omethanesulfenamides (BB23) is in general more reactive,39
and to this day it constitutes the most used reagent of this
family. Consequently, its production at a large scale, still bigger
than for BB13, was highly expected. The synthesis of this
reagent requires a supplementary step because the intermediate
trifluoromethanesulfinamidine (1b), arising from tosylamide, is
stable and cannot be rearranged during the first step.
Consequently, 1b must be transformed into corresponding
trifluoromethanesulfenamide (BB23H) under acidic conditions,
before the methylation step (Scheme 2).
1
2
3
4
0.28
2.13
0.35
2.66
0.26
1.94
0.19
1.40
4.69
9.31
9.28
0.30 g (79%)
2.58 g (89%)
8.68 g (89%)
15.42 g (80%)
17.00 g (88%)
7.12
8.84
6.49
14.22
14.24
17.73
17.80
12.93
12.95
a
5
a
Use of a mechanical stirrer.
diminution of yields was observed by increasing the starting
material quantity. On the contrary, generally, better yields were
obtained. With the biggest quantity, the amount of final
product slightly decreases with a standard magnetic stirrer
(entry 3), whereas an optimal yield is obtained under
mechanical stirring, certainly due to a more efficient stirring,
and species diffusion, with larger volume.
Scheme 2. Synthesis of Trifluoromethanesulfenamide BB23
It is noteworthy that the low temperature (−20 °C) is
necessary to well control the first step and to observe an
optimal formation of the transient difluoro(trifluoromethyl)-λ4-
sulfanamine without degradation.
Concerning the use of iPrNEt2, a previous study42 has
demonstrated that other tertiary amines (pyridine, 2,6-lutidine,
triethylamine) could be also used, but in general, better results
−
were observed with Hunig’s base. Other sources of “CF ”
̈
3
species have been also screened. In particular, fluoral
hemiaminals,43,44 arising from trifluoroacetaldehyde or fluoro-
form, trifluoroacetamides,45,46 arising from trifluoroacetic acid,
or trifluoromethanesulfinamides,47,48 arising from trifluorome-
thanesulfinate, have been tested without success.
First, scale-up of the synthesis of 1b has been studied (Table
3).
The solubility of tosylamide is a major issue in this multigram
extrapolation. Indeed, if with a small amount, a homogeneous
Synthesis of BB13. Initially, the methylation step had been
performed with NaH and MeI. To try to avoid the
manipulation of large amount of NaH, a few other systems
has been tested (Table 2). Nevertheless, by using a less strong
base, such as iPrNEt2 or K2CO3, no methylation has been
observed, even with stronger methylating agent or by heating
the reaction medium. In the initial published procedure,
BB13H was obtained relatively clean after the first step, and
no further purification was performed before the methylation
step. However, several attempts have shown that not only the
methylation yield was slightly lower but that the final BB13
product was of lesser quality, even after purification.
Consequently, it is recommended to systematically purified
BB13H by chromatography before the methylation step.
Finally, on multigram scale, the methylation works well, and
up to 17 g of final product BB13 could be obtained. Again, a
Table 3. Synthesis of Trifluoromethanesulfinamidine 1b
CF3SiMe3
(g)
DAST
(g)
iPrNEt2
(g)
tosylamide
(g)
1b (quantity/
entry
yield)
1
2
3
4
5
4.90
6.92
6.11
7.85
4.45
6.29
5.90
10.88 g (92%)
15.10 g (91%)
14.87 g (71%)
35.30 g (88%)
28.79 g (72%)
8.76 g (88%)
87.60 g (88%)
83.00 g (83%)
95.00 g (86%)
10.00
10.40
20.00
20.05
8.64
10.77
20.71
20.76
5.18
7.85
16.61
16.65
4.15
15.10
13.13
3.77
a
a
6
5.00
a
a
7
41.52
41.52
45.67
51.79
51.78
56.96
37.74
37.74
41.51
50.00
a
a
8
50.00
a
a
9
55.00
a
Solid addition of tosylamide.
B
DOI: 10.1021/acs.oprd.6b00062
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solution in ethyl acetate is easy to obtain in reasonable volume
(entry 1), with larger quantities tosylamide must be solubilized
in hot solution, to minimize the added volume of solvent, and
this final solution must be kept warm during the dropwise
addition. By the way, this technical issue is source of variability
in the observed yields (entries 2−3 and 4−5). To better control
this critical addition, a solid addition has been envisaged. To
validate this modification, the reaction has been first performed
in small scale (entry 6). The obtained results are in accordance
with the previous “liquid addition” (entry 1). Then, this
strategy has been scaled up to 50 g of starting tosylamide with
good, and reproducible, results (entries 7−8). To this day, this
method has allowed the production of 95 g of 1b in one batch,
with good yields (entry 9). It is noteworthy that, from the
experience acquired from BB13 synthesis, this step has been
systematically performed under mechanical stirring as, also, the
following steps.
In general, NaH, as s base, did not lead to satisfactory yields,
whatever the methylating agent. Even if satisfactory results have
been obtained with NaH/Me2SO4 system on a 6 g scale (entry
4), lower, unsatisfactory yields were systematically obtained at a
larger scale (entries 5−6). If iPrNEt2/MeI system leads to a
disappointing result (entry 7), with the iPrNEt2/TfOMe
system, excellent, and reproducible, results were obtained
whatever the starting quantities (from 7 to 91 g). It is
noteworthy that TfOMe must be added rapidly following the
deprotonation (around 5 min after) because of the relative
instability of deprotonated species.
In a practical point of view, during the synthesis of BB23
reagent, the chromatographic purification of intermediates 1b is
highly recommended to achieve optimal yields. However,
BB23H is only purified by trituration with pentane before to be
engaged in last step.
Financial Estimations for Reagent Production. To this
day, we have been able to produce 17 g of BB13H, nearly 17 g
of BB13 and 84 g of BB23 with respective overall yields 88%,
79% and 72%. The production of BB23 in similar amounts is
now an implemented routine in the laboratory. We have tried
to determined the cost of these batches. To perform such
analysis, we have taken in consideration the reagents, the
solvents used for reactions, extractions and purifications, the
silica for chromatography, and the drying agent (MgSO4), and
we have also estimated the acetone volume used for cleaning
(Table 6).
The rearrangement in acidic conditions of 1b has been, next,
optimized (Table 4).
Table 4. Acidic Rearrangement of 1b To Provide BB23H
entry
1b (g)
acid (g)
BB23H (quantity/yield)
1
2
3
4
5
6
25.76
34.60
23.14
80.00
96.40
120.60
CF3CO2H (30.02)
CF3CO2H (40.33)
H2SO4 (23.20)
H2SO4 (79.60)
H2SO4 (95.92)
H2SO4 (120.00)
19.20 g (94%)
24.50 g (89%)
17.73 g (97%)
61.43 g (97%)
74.44 g (97%)
91.00 g (95%)
Table 6. Estimated Costs of BB Reagents
a
BB
(batch)
cleaning
silica
+
“chemical
cost”
a
a
a
a
reagents solvents
acetone
MgSO4
The acidic treatment of 1b led to BB23H with good
reproducible yields at around 30 g scale (entries 1−2).
Nevertheless, to try to reduce costs at larger scale, trifluoro-
acetic acid has been successfully substituted by less expensive
sulfuric acid (entry 3). In a larger scale, excellent yields were
obtained (entries 4−6), with, to this day, a one-batch
production of 91 g of BB23H.
The last step to obtain the expected BB23 reagent is the
methylation of the previous BB23H. Before, to extrapolate to
large quantities, some optimizations have been performed to
determine the best methylating system in this case (Table 5).
BB13H
(7 g)
41 €
51 €
419 €
23 €
60 €
60 €
7 €
5 €
10.90 €/g
b
11.86 $/g
18.90 €/g
20.57 $/g
8.00 €/g
BB13
(7 g)
12 €
15 €
9 €
b
BB23
(63 g)
15 €
b
8.71 $/g
a
b
Negotiated prices with chemical suppliers. Exchange rate on 03/01/
16, 07:46 UTC.
Surprisingly, despite a lower step number, the first generation
of trifluoromethanesulfenamide reagents (BB13H and BB13B)
is more expensive than the second generation (BB23). This is
mainly due to the pentane, used for chromatographic
purifications, which is a more expensive solvent than cyclo-
hexane, used for BB23. Nevertheless, globally the cost per gram
of these reagents stays reasonable.
Table 5. Methylation of BB23H To Provide BB23
BB23H
(g)
methylating
reagent (g)
BB23 (quantity/
yield)
entry
base (g)
1
2
3
4
5
6
7
0.50
0.50
0.50
6.00
9.20
18.60
0.50
NaH (0.08)
NaH (0.08)
BuLi (0.12)
NaH (1.06)
NaH (1.63)
NaH (3.23)
MeI (0.35)
0.29 g (55%)
0.30 g (57%)
0.15 g (29%)
5.00 g (79%)
4.9 g (51%)
TfOMe (0.33)
TfOMe (0.30)
Me2SO4 (3.63)
Me2SO4 (5.56)
Me2SO4 (11.24)
MeI (0.28)
CONCLUSION
■
To conclude, the production of trifluoromethanesulfemanide
reagents has been optimized to be scaled-up on multigram
scale, up to 84 g for the second generation. Nevertheless, this
quantity does not constitute an upper limit, and larger
quantities should be obtained with these optimized conditions,
with good overall yields. Furthermore, the estimated costs are
really reasonable and clearly compatible with low cost
applications of these reagents. These efficient conditions open
the way to easy syntheses of large amounts of these reagents by
any research laboratories for further applications. This should
contribute to the development of chemistry around these
reagents in the future and to popularize their use.
10.10 g (52%)
0.09 g (16%)
i-PrNEt2
(0.27)
8
7.00
10.93
19.20
74.00
91.00
i-PrNEt2
TfOMe (4.66)
TfOMe (6.94)
TfOMe (12.78)
TfOMe (47.00)
TfOMe (57.80)
7.01 g (95%)
10.50 g (91%)
18.10 g (90%)
69.70 g (90%)
84.22 g (88%)
(3.67)
9
i-PrNEt2
(5.73)
10
11
12
i-PrNEt2
(10.06)
i-PrNEt2
(38.78)
i-PrNEt2
(47.69)
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DOI: 10.1021/acs.oprd.6b00062
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after the end of the addition, TMSCF3 (45.67 g, 1.0 equiv) was
added dropwise keeping the temperature between −20 °C and
−10 °C. After the end of the addition, the reaction mixture was
stirred at −20 °C for 1 h, and solid tosylamide (55.0 g, 1.0
equiv) was added, via a funnel, under nitrogen gas counter-flow.
The suspension was stirred at −20 °C for 1 h and then allowed
to warm to room temperature. After 15 hours, the conversion
of tosylamide was checked by TLC (cyclohexane/ethyl acetate:
7:3). The reaction mixture was washed with water and brine.
The organic layer was dried over MgSO4, filtered, and
concentrated to dryness. The crude residue was finally purified
by flash chromatography (cyclohexane/ethyl acetate: 80/20 to
75/25) to afford 1b (95.0 g, 86%, brown liquid).
EXPERIMENTAL SECTION
■
Synthesis of N-[(Trifluoromethyl)sulfanyl]aniline
(BB13H). A dry 500 mL, three-necked, round-bottomed flask
equipped with a thermometer and a mechanical stirrer was
charged with diisopropylethylamine (12.95 g, 1.0 equiv) and
anhydrous dichloromethane (200 mL) under nitrogen. The
resulting mixture was cooled to −20 °C, and DAST (17.80 g,
1.1 equiv) was added dropwise keeping the temperature
between −20 °C and −10 °C. Ten minutes after the end of the
addition, TMSCF3 (14.24 g, 1.0 equiv) was added dropwise
keeping the temperature between −20 °C and −10 °C. After
the end of the addition, the reaction mixture was stirred at −20
°C for 1 h. Aniline (9.28 g, 1.0 equiv) was added keeping the
temperature between −20 °C and −10 °C, and then the
reaction mixture was allowed to warm to room temperature.
After 15 hours, the conversion of aniline was checked by TLC
(pentane/acetone: 98:2). The reaction mixture was washed
with water. Layers were separated, and the aqueous layer was
extracted with dichloromethane. The combined organic layers
were washed with saturated aqueous ammonium chloride,
water, and brine, dried over MgSO4, filtered, and concentrated
to dryness. The crude residue was finally purified by flash
chromatography (pentane/acetone: 100/0 to 98/2) to afford
BB13H (17 g, 88%, colorless liquid).
1H NMR (400 MHz, CDCl3) δ = 7.74 (m, 2H), 7.23 (d, J =
7.8 Hz, 2H), 3.33 (dq, J = 14.4, 7.2 Hz, 2H), 3.22 (dq, J = 14.4,
7.2 Hz, 2H), 2.36 (s, 3H), 1.12 (t, J = 7.2 Hz, 6H). 13C NMR
(101 MHz, CDCl3) δ = 142.6, 140.5, 129.4, 126.2, 123.2 (q,
3J(C,F) = 328 Hz), 42.5 (br), 21.5, 13.3. 19F NMR (376 MHz,
CDCl3) δ = −68.72 (s, 3F).
Synthesis of 4-Methyl-N-[(trifluoromethyl)sulfanyl]-
benzene-1-sulfonamide (BB23H). A 2-L, four-necked,
round-bottomed flask equipped with a thermometer and a
mechanical stirrer was charged with 1b (120.6 g, 1.0 equiv) and
dichloromethane (700 mL). The resulting mixture was cooled
to 0 °C, and sulfuric acid 95% (120 g, 3.3 equiv) was added
dropwise keeping the temperature between 0 and 10 °C. After
the end of the addition, the reaction mixture was allowed to
warm to room temperature. After 2 h, the conversion of 1b was
checked by TLC (cyclohexane/ethyl acetate: 8:2). The reaction
mixture was washed with water. Layers were separated, and the
aqueous layer was twice extracted with dichloromethane. The
combined organic layers were washed with brine, dried over
MgSO4, filtered, and concentrated to dryness. The crude
residue was finally triturated with pentane for 2 h, and the
resulting suspension was filtered and rinsed with pentane to
afford BB23H (91.0 g, 95%, off white solid).
1H NMR (400 MHz, CDCl3) δ = 7.32 (m, 2H), 7.11 (m,
2H), 7.02 (m, 1H), 5.08 (br, 1H). 13C NMR (101 MHz,
3
CDCl3) δ = 145.2, 129.5 (q, J(C,F) = 317 Hz), 129.4, 122.0,
115.2. 19F NMR (376 MHz, CDCl3) δ = −52.89 (s, 3F).
Synthesis of N-Methyl-N-[(trifluoromethyl)sulfanyl]-
aniline (BB13). A dry 500 mL, three-necked, round-bottomed
flask equipped a thermometer and a mechanical stirrer was
charged with sodium hydride (60% dispersion in mineral oil)
(3.87 g, 1.1 equiv) and anhydrous DMF (200 mL) under
nitrogen. The suspension was cooled to −20 °C a solution of
BB13H (17 g, 1.0 equiv) in anhydrous DMF (100 mL) was
added dropwise keeping the temperature between −20 °C and
−10 °C. Ten minutes after the end of the addition,
iodomethane (13.74 g, 1.1 equiv) was added dropwise keeping
the temperature between −20 °C and −10 °C. The suspension
was stirred at −20 °C for 30 min and then allowed to warm to
room temperature. After 4 h, the conversion of BB13H was
checked by TLC (pentane 100%). The reaction mixture was
partitioned between pentane and water, and the aqueous layer
was extracted with pentane. The combined organic layers were
washed with water and brine, dried over MgSO4, filtered, and
concentrated to dryness. The crude residue was finally purified
by flash chromatography (pentane 100%) to afford BB13
(16.40 g, 90%, colorless liquid).
1H NMR (400 MHz, CDCl3) δ = 7.80 (m, 2H), 7.34 (d, J =
8.0 Hz, 2H), 6.73 (s, 1H), 2.44 (s, 3H). 13C NMR (101 MHz,
3
CDCl3) δ = 145.3, 135.1, 130.0, 128.1 (q, J(C,F) = 315 Hz),
127.9, 21.8. 19F NMR (376 MHz, CDCl3) δ = −51.41 (s, 3F).
Synthesis of N-4-Dimethyl-N-[(trifluoromethyl)-
sulfanyl]benzene-1-sulfonamide (BB23). A dry 2-L,
three-necked, round-bottomed flask equipped with a ther-
mometer and a mechanical stirrer was charged with BB23H
(91.0 g, 1.0 equiv) and anhydrous dichloromethane (700 mL)
under nitrogen. The resulting mixture was cooled to 0 °C, and
diisopropylethylamine (47.69 g, 1.1 equiv) was added dropwise
keeping the temperature between 0 and 5 °C. Five minutes
after the end of the addition, MeOTf (57.80 g 1.05 equiv) was
added dropwise keeping the temperature between 0 and 5 °C.
After the end of the addition, the reaction mixture was stirred at
0 °C for 30 min, and the conversion of BB23H was checked by
TLC (cyclohexane/ethyl acetate: 8:2). The reaction mixture
was washed with water and brine. The organic layer was dried
over MgSO4, filtered, and concentrated to dryness. The crude
residue was finally purified by flash chromatography (cyclo-
hexane/ethyl acetate: 99:1 to 96:4) to afford BB23 (84.22 g,
88%, light yellow solid).
1H NMR (400 MHz, CDCl3) δ = 7.31 (m, 2H), 7.24 (m,
2H), 6.97 (tt, J = 7.4, 1.2 Hz, 1H), 3.50 (d, J = 0.9 Hz, 3H). 13C
3
NMR (101 MHz, CDCl3) δ = 148.8, 130.5 (q, J(C,F) = 321
Hz), 129.1, 121.3, 116.1, 46.3. 19F NMR (376 MHz, CDCl3) δ
= −50.35 (s, 3F).
Synthesis of (E)-N,N-Diethyl-1,1,1-trifluoro-N-(4-meth-
ylbenzenesulfonyl) methanesulfinimidamide (1b). A dry
2-L, four-necked, round-bottomed flask equipped with a
thermometer and a mechanical stirrer was charged with
diisopropylethylamine (41.51 g, 1.0 equiv), anhydrous dichloro-
methane (650 mL) and anhydrous ethyl acetate (320 mL)
under nitrogen. The resulting mixture was cooled to −20 °C,
and DAST (56.96 g, 1.1 equiv) was added dropwise keeping
the temperature between −20 °C and −10 °C. Ten minutes
1H NMR (400 MHz, CDCl3) δ = 7.75 (m, 2H), 7.35 (m,
2H), 3.31 (s, 3H), 2.44 (s, 3H). 13C NMR (101 MHz, CDCl3)
3
δ = 145.1, 134.3, 130.1, 129.0 (q, J(C,F) = 316 Hz), 127.9,
43.8, 21.7. 19F NMR (376 MHz, CDCl3) δ = −50.34 (s, 3F).
D
DOI: 10.1021/acs.oprd.6b00062
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Article
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.oprd.6b00062.
■
S
1H, 13C, and 19F NMR spectra (PDF)
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2415.
AUTHOR INFORMATION
Corresponding Author
*E-mail address: Thierry.billard@univ-lyon1.fr.
Author Contributions
■
Q.G. and S.A. contributed equally.
(34) Lin, J.-H.; Ji, Y.-L.; Xiao, J.-C. Curr. Org. Chem. 2015, 19, 1541.
(35) Zhang, K.; Xu, X.; Qing, F. Youji Huaxue 2015, 35, 556.
(36) Zheng, H.; Huang, Y.; Weng, Z. Tetrahedron Lett. 2016, 57,
1397.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(37) Billard, T. In Encyclopedia of Reagents for Organic Synthesis
■
[Online]; John Wiley
047084289X.rn01828.
& Sons Ltd., 2015, 10.1002/
We thank the CNRS and the French Ministry of Research for
their financial support. We also thank the French Fluorine
Network for its support.
(38) Billard, T. In Encyclopedia of Reagents for Organic Synthesis
[Online]; John Wiley
047084289X.rn01763.
& Sons Ltd., 2014, 10.1002/
ABBREVIATIONS
■
(39) Glenadel, Q.; Alazet, S.; Billard, T. J. Fluorine Chem. 2015, 179,
89.
(40) Glenadel, Q.; Alazet, S.; Tlili, A.; Billard, T. Chem. - Eur. J. 2015,
21, 14694.
DAST, (diethylamino)sulfur trifluoride; Tf, trifluoromethane-
sulfinyl; TLC, thin layer chromatography; TMS, trimethylsilyl
(41) Glenadel, Q.; Bordy, M.; Alazet, S.; Tlili, A.; Billard, T. Asian J.
Org. Chem. 2016, 5, 428.
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DOI: 10.1021/acs.oprd.6b00062
Org. Process Res. Dev. XXXX, XXX, XXX−XXX