Facile synthesis of α-monofluoromethyl alcohols: Nucleophilic monofluoromethylation of aldehydes using TMSCF(SO2Ph)2

Article abstract of DOI:10.1016/j.jfluchem.2011.10.010

α-Fluoromethyl phenyl sulfone derivatives have been extensively employed in various reactions as versatile fluoromethylating reagents. While nucleophilic monofluoromethylations of aldehydes have been achieved using fluoromethyl phenyl sulfone or fluorobis

Full text of DOI:10.1016/j.jfluchem.2011.10.010

Journal of Fluorine Chemistry 133 (2012) 27–32
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Facile synthesis of
monofluoromethylation of aldehydes using TMSCF(SO2Ph)2
a
-monofluoromethyl alcohols: Nucleophilic
§
1
1
*
G.K. Surya Prakash , Nan Shao , Zhe Zhang , Chuanfa Ni, Fang Wang, Ralf Haiges, George A. Olah
Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, CA, 90089-1661, USA
A R T I C L E I N F O
A B S T R A C T
-Fluoromethyl phenyl sulfone derivatives have been extensively employed in various reactions as
Article history:
a
Received 11 October 2011
Accepted 15 October 2011
Available online 12 November 2011
versatile fluoromethylating reagents. While nucleophilic monofluoromethylations of aldehydes have
been achieved using fluoromethyl phenyl sulfone or fluorobis(sulfonyl)methanes, a facile protocol under
mild reaction conditions remains an ardently sought goal. We now report a feasible synthetic approach
toward
b-monofluorinated alcohols using a-trimethylsilyl-a-fluorobis(phenylsulfonyl)methane
Keywords:
[TMSCF(SO2Ph)2, TFBSM] as a novel monofluoromethylating reagent. Initiated by a catalytic amount
of fluoride, the reagent can be readily added to a variety of aldehydes providing the desired products in
high yields. Computational and kinetic studies have revealed the exceptional lability of the Si–C bond in
TFBSM compared with other fluoromethylsilane counterparts.
Nucleophilic monofluoromethylation
Sulfone
Fluorinated alcohols
Si–C bond strengths
ß 2011 Elsevier B.V. All rights reserved.
1. Introduction
mechanism by utilizing a-trimethylsilyl-a-fluorobis(phenylsulfo-
nyl)methane [TMSCF(SO2Ph)2, TFBSM], which serves as both a
pronucleophile and a Lewis acid [6,7].
Selective incorporation of fluoromethyl moieties into organic
molecules has received increasing attention because of the
immense potential of fluoroorganics in life and materials sciences
2. Results and discussion
[1]. To address this synthetic demand,
a-fluoromethyl phenyl
sulfone derivatives were recently developed as viable fluoro-
methylating reagents [2]. Of particular interest, fluorobis(phenyl-
sulfonyl)methane (FBSM) and its analogues have facilitated many
transformations, which are otherwise difficult to achieve [3]. In
spite of these successful documentations, the nucleophilic addition
of FBSM to aldehydes was previously claimed to be unattainable
because of its reversibility, thereby necessitating the utilization of
2-fluoro-1,3-benzodithiole-1,1,3,3-tetraoxide as the pronucleo-
phile [4]. Hu et al., however, showed that FBSM anion can be added
to aldehydes using LiHMDS as the base [5]. The obtained lithium
carbinolates, stabilized through strong Li–O interactions, were
then in situ quenched with Bronsted acids (for example,
trifluoroacetic acid) to afford the corresponding alcohols (Scheme
1). We therefore surmised that FBSM anion-aldehyde adducts
(carbinolates) can also be captured through a reaction with Lewis
acids. Moreover, a one-pot addition reaction between the FBSM
anion and aldehydes can be achieved under a self-quenching
To examine our proposal, we initially focused on the prepara-
tion of TFBSM using FBSM, which was readily obtained on large
scale according to a method developed in our laboratory [8]. After
an extensive reaction condition screening, the desired reagent was
successfully prepared in 43% yield by treating FBSM sodium salt
with TMSCl in THF (Scheme 2). The compound was found to be
stable and can be stored in a glove box for several months.
However, it underwent a swift decomposition (usually within a
few days) to FBSM in the presence of moisture or in CDCl3 solution,
which contains some protic acid impurities. Surprisingly, unlike
TMSCF3 (the Ruppert-Prakash reagent) and [(phenylsulfonyl)di-
fluoromethyl]trimethylsilane (TMSCF2SO2Ph), which are substan-
tially inert toward aqueous HCl solution, instantly hydrolysis of
TFBSM was observed in concentrated aq. HCl (12 M), indicating the
exceptional lability of the Si–CF bond.
With the desired reagent in hand, we initially performed the
reaction between TFBSM and benzaldehyde using tetra-n-buty-
lammonium difluorotriphenylsilicate (TBAT) as an initiator in THF.
As expected, the desired
b-fluoro silyl ether was obtained,
however, in only 22% yield (Table 1, entry 1). In an effort to
enhance the efficacy of the protocol, we further investigated
various reaction parameters, such as initiators, solvents, tempera-
tures, and proportions of substrates. We found that the proportions
of the substrates can significantly impact outcomes of the reaction
§
Dedicated to Professor Wei-Yuan Huang on the occasion of his Ninetieth
Birthday.
* Corresponding author. Tel.: +1 213 7405984; fax: +1 213 7405087.
E-mail address: gprakash@usc.edu (G.K. Surya Prakash).
1
Contributed equally to this work.
0022-1139/$ – see front matter ß 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2011.10.010

28
G.K.S. Prakash et al. / Journal of Fluorine Chemistry 133 (2012) 27–32
Table 2
Monofluoromethylation of aldehydes with TFBSM.
Entry
1
Carbonyl compounds
Product
Yield (%)a
99/81
Scheme 1. Nucleophilic addition of FBSM and TFBSM to aldehydes.
PhCHO
1a
2
93/90
Scheme 2. Preparation of
a-trimethylsilyl-a-fluorobis(phenylsulfonyl)methane
(TFBSM).
3
4
99/86
97/87
(Table 1, entries 1–5 and 6–9). Low yields observed in entries 1–5
can be rationalized as the competitive protonation of FBSM anion
due to the presence of moisture in the reaction system. Employing
an excess amount of TFBSM can, therefore, compensate the
consumption of the pronucleophile. In addition, CsF was found to
be a superior initiator over several other Lewis bases (Table 1,
entries 1–9). Solvent effects were also pronounced (Table 1, entries
9, 11–13), which showed THF as the optimal reaction medium.
While addition sequences of reagents were critical (Table 1, entries
8 and 10), yields did not decrease, when the reaction time was
shortened to 4 h (Table 1, entry 14). In particular, performing the
reaction at room temperature resulted in a decrease in yield to 75%.
With optimized reaction conditions established, we explored
the scope of this protocol (Table 2). The reaction was found to be
applicable to aromatic aldehydes bearing both electron-withdraw-
ing and electron-donating groups, and furnished products in high
yields (entries 1–5, Table 2). While the 2,4,6-trimethoxybenzal-
dehyde 1d underwent the reaction smoothly (entry 4, Table 2), the
5
6
7
96/83
0/0
Table 1
Optimization of the addition reaction of TFBSM with benzaldehyde.
88/80
8
9
64/54
Entry Initiator
Solvent TFBSM/1a/Initiator Temp. ( 8C) Time (h) Yield (%)c
1a
2a
3a
4a
5a
6a
7a
8a
9a
TBAT
THF
THF
1/2/0.05
1/2/0.05
1/2/0.20
1/2/0.20
1/2/0.20
2/1/0.05
2/1/0.20
2/1/0.20
2/1/0.20
2/1/0.20
2/1/0.20
2/1/0.20
0–rt
0–rt
0–rt
0–rt
0–rt
0–rt
0–rt
0–rt
0–rt
0–rt
0–rt
0–rt
0–rt
0
12
12
12
12
12
12
12
12
12
12
12
12
12
4
22
0
TBAFd
Me3N+–OÀ THF
34
38
31
66
71
78
99
0
0/0
KF
THF
THF
THF
CsF
TBAT
Me3N+–OÀ THF
KF
THF
THF
THF
Et2O
DMF
CsF
10
0/0
10b KF
11a CsF
12a CsF
13a CsF
14a CsF
15a CsF
25
0
Toluene 2/1/0.20
54
99
75
THF
THF
2/1/0.30
2/1/0.20
a
19F NMR yields/isolated yields.
rt
4
a
Fluoride source in THF was added to a mixture of TFBSM and 1a in THF.
TFBSM in THF was added to a mixture of KF and 1a in THF.
19FNMR yields.
b
c
d
A TBAF solution in THF (1M) containing 5 wt% H2O was used.

G.K.S. Prakash et al. / Journal of Fluorine Chemistry 133 (2012) 27–32
29
Scheme 3. Synthesis of 2-fluoro-1-(naphthalen-1-yl)ethanol via reductive
desulfonation of 2e.
addition reaction was completely impeded in the case of 2,4-
dimethyl benzaldehyde (1f), probably due to more effective steric
demand of the methyl groups (entry 6, Table 2). The protocol was
also suitable to
a,b-unsaturated aldehyde (cinnamaldehyde) 1g,
which exclusively gave 1,2-adduct (2g) in 80% yield (entry 7, Table
2). Aliphatic aldehyde 1h was also compatible to the method,
which, however, afforded the corresponding carbinol 2h in a lower
yield (entry 8, Table 2). Similar to the addition reaction to aromatic
aldehydes, the steric encumbrance of aliphatic aldehydes can
considerably affect the outcome of the reaction as well. As
demonstrated, pivalaldehyde (1i) was unable to participate in the
addition reaction (entry 9, Table 2). It is worth noting that the
attempt to add TFBSM to benzophenone was unsuccessful under
similar reaction conditions, indicating the limitation of the present
protocol (entry 10, Table 2). Since the previous study demonstrated
that fluoromethyl phenyl sulfone (PhSO2CH2F) readily underwent
addition reaction with various ketones [9], the low reactivity of the
FBSM anion toward ketones can be probably attributed to steric
effects.
Fig. 1. Crystal structures of various fluoromethyl silane reagents and their
computed structures at the B3LYP/6-311+G(d,p) level.
˚
molecule (bond distances range from 1.848 to 1.862 A) (Fig. 1 and
Table 3) [10]. Crystal structures of [(phenylsulfonyl)difluoro-
methyl]trimethylsilane (TMSCF2SO2Ph, 5) and TFBSM were
obtained herein, which demonstrated even longer Si–CF bonds
˚
˚
of 1.957 A and 1.994 A, respectively (Fig. 1 and Table 3). This result
presumably suggests a gradual decrease in the strengths of Si–CF
bonds from TMSCF3 to TFBSM.
To demonstrate the synthetic utility of the present protocol,
b
-
To achieve a quantitative assessment of Si–CF bond strengths in
these reagents, systematic theoretical calculations on 4, 5, and
TFBSM were carried out at the B3LYP/6-311+G(d,p) level [11]. As
depicted in Fig. 1, optimized geometries of these molecules highly
resemble their structures in the solid state. Consistent with the
tendency observed in crystal structures, the Si–CF bond distance
order of TFBSM > TMSCF2SO2Ph > TMSCF3 is followed (column 2,
Table 3). Wiberg bond indices [12] of Si–CF bonds were computed
to reveal the weakness of the Si–CF bond in TFBSM, which was
shown to be only 77% of the value of the TMS–CH3 bond [13]! A
more accurate evaluation of bond strengths was achieved on the
fluoro silyl ether 2e was subjected to the reductive Mg/acetic acid
desulfonation system. As depicted in Scheme 3, the corresponding
monosulfones (3e) were generated in 74% yield as a mixture of two
diastereomers under the reaction conditions. Further desulfona-
tion of the monosulfones was achieved using Na/Hg/MeOH system
to form
b-monofluorinated alcohol 4e in 48% yield. Importantly,
we noticed that the rate of the desilylation of 2e was slower than
that of its desulfonation in Mg/acetic acid system, thereby
permitting the desulfonation without significant decomposition
of 2e. In comparison, rapid degradation of 2e was found to be
inevitable under Mg/MeOH reductive conditions.
basis of free energy changes (DG) of hypothesized reactions
As aforementioned, the Si–CF bond in TFBSM was found to be
rather labile compared with those in TMSCF3 and PhSO2CF2TMS.
This observation intrigued us to explore the nature of Si–CF bonds
in these fluoromethylating reagents. The previously reported
crystal structure of TMSCF3 (4) has showed an elongated Si–CF
between silane reagents and a fluoride anion (Table 3, Eq. (1)). For
all three reagents, the Si–CF bond cleavage was thermodynamically
favorable both in the gas phase and in THF solution. Among these
reagents, the Si–CF bond in TFBSM was found to be particularly
labile (57.1 kcal/mol and 37.8 kcal/mol weaker than 4 and 5 in the
gas phase, respectively). Intriguingly, such a bond strength order
˚
bond (1.944 A) compared with other Si–CH bond in the same
Table 3
Investigation of Si–CF bond strength in various fluoromethyl silane reagents.
a
a,c
GTHF (kcal/mol)
d
R-TMS
Exp./Cal. Si–CFn bond
NBO charge on Si
Wiberg bond
indices (Si–CFn)a,b
D
Ggas (kcal/mol)
D
kdec. (L molÀ1 sÀ1
)
˚
distances (A)
TMSCF(SO2Ph)2
TMSCF2SO2Ph
TMSCF3
1.994/2.010
1.957/1.971
1.943/1.953
–/1.936
+1.618
+1.545
+1.493
+1.497
+1.518
+1.563
0.6457 (77%)
0.7085 (85%)
0.7564 (91%)
0.7895 (95%)
0.8120 (97%)
0.8339 (100%)
À89.4
À51.6
À32.3
À13.0
+0.5
À34.6
À17.3
À8.0
Ins. Dec.
2.6 Â 10À5
1.1 Â 10À5
TMSCF2H
+9.8
–
–
–
TMSCFH2
–/1.913
+23.5
+35.2
TMSCH3
–/1.891
+11.0
a
Computed at the B3LYP/6-311+G(d,p) level.
b
c
Compared with the Wiberg bond index of 0.8339 in tetramethylsilane.
The effect of THF solvent was treated implicitly using the standard PCM method of Gaussian03.
Determined via 19F NMR a 0.1 M solution of the corresponding reagent at 298 K.
d

30
G.K.S. Prakash et al. / Journal of Fluorine Chemistry 133 (2012) 27–32
can also be experimentally supported by methanolysis rates of
these reagents as TFBSM > TMSCF2SO2Ph > TMSCF3 (Eq. (2) and
column 7, Table 1).
in a freezer (À20 8C) for 24–48 h until a large amount of colorless
needles was formed (a small amount of cloudy precipitate may be
formed as well). The solvents were then removed from the tube via
a syringe under Ar. The crystals were rinsed with anhydrous
hexanes (2Â 10 mL), which were also removed via a syringe. The
product was dried under vacuum at room temperature and then
stored in a glove box (997 mg, 43%).
To rationalize the remarkably elongated Si–CF bonds in TFBSM,
we further computed Si–CF bond distances in TMSCF2H, TMSCH2F,
and TMSCH3 at the B3LYP/6-311+G(d,p) level. Clear trends were
observed through a systematic structural variation from TMSCH3
to TFBSM. As shown in Table 3, the increase in bond distances and
the decrease in Wiberg bond indices can be seen from TMSCH3 to
TFBSM, indicating a gradual weakening of the Si–CF bonds. In
particular, by comparing the Si–CF bond distances of
TMSCH2F < TMSCF3 < TFBSM, we can conclude that the excep-
tionally long Si–CF bond distance in TFBSM is unlikely to result
from the removal of the fluorine substituent. Simply, it can be
understood as the prevailing stabilizing effect of the phenylsulfo-
nyl group over fluorine on the carbanions, which leads to more
contribution from ionic resonance structures (comparing the NBO
charges on Si atoms in column 3 in Table 3, and Eq. (3)) [14].
1H NMR (C6D6):
6.67–6.70 (m, 2H), 7.35–7.37 (m, 4H). 19F NMR (C6D6):
1F). 13C NMR (C6D6):
128.4, 128.5, 130.2 (d, J = 1.9 Hz), 133.6. HRMS data were not
obtained due to the extreme lability of the compound. M.p. dec.
139–147 8C.
d
0.70 (d, J = 0.7 Hz, 9H), 6.45–6.48 (m, 4H),
À157.0 (s,
d
d
À0.43 (d, J = 2.4 Hz) 121.0 (d, J = 268.3 Hz),
4.2. Typical procedure for the addition reaction of TFBSM to aldehydes
and benzophenone
To a solution of benzaldehyde (1a, 20.2 mg, 0.19 mmol) and
TFBSM (147 mg, 0.38 mmol, 2 equiv.) in anhydrous THF (0.5 mL)
was quickly added a suspension of CsF (6 mg, 0.04 mmol, 20 mol%)
in anhydrous THF (0.5 mL) under Ar at 0 8C. The progress of the
reaction was monitored via 19F NMR spectroscopy, which showed
the completion of the reaction after stirring for 4 h. The solvent was
evaporated under vacuum. The resulting crude product was
purified via silica gel column chromatography using ethyl acetate
and hexanes as eluent.
3. Conclusion
In conclusion, we have successfully synthesized
a-trimethylsi-
lyl- -fluorobis(phenylsulfonyl)methane (TFBSM) as a viable nu-
a
cleophilic monofluoromethylating reagent for aldehydes.
Functioning as both a pronucleophile and a Lewis acid, the reagent
allowed the one-step addition of the FBSM anion toward various
aldehydes via a self-quenching mechanism. Undergoing a reduc-
tive desulfonation reaction, the silyl ether adduct can be further
(2-Fluoro-1-phenyl-2,2-bis(phenylsulfonyl)ethoxy)trimethyl-
silane (2a). 1H NMR (CDCl3):
d 0.10 (s, 9H), 5.92 (d, J = 7.8 Hz, 1H),
7.14–7.27 (m, 5H), 7.35–7.39 (m, 2H), 7.53–7.56 (m, 2H), 7.56–7.60
(m, 1H), 7.64–7.66 (m, 2H), 7.68–7.71(m, 1H), 7.98–8.00 (m, 2H).
converted to
feasible from the corresponding
alcohol. Mechanistic studies revealed the remarkably weak nature
of the Si–CF bond in TFBSM, which facilitated the facile cleavage of
the Si–CF bond.
b
-monofluorinated alcohol, which, however, was not
-bis(phenylsulfonyl)- -fluoro-
b
b
19F NMR (CDCl3):
d
À132.3 (d, J = 7.8 Hz, 1F). 13C NMR (CDCl3):
d
0.2, 73.7 (d, J = 23.1 Hz), 114.4 (d, J = 270.7 Hz), 127.8, 128.3 (d,
J = 2.4 Hz), 128.4, 128.7, 128.8, 131.0 (d, J = 1.6 Hz), 131.4 (d,
J = 1.8 Hz), 134.4, 135.0, 135.6 (d, J = 1.4 Hz), 136.5, 138.2. HRMS:
calcd for C23H24F2NaO5S2Si+ 535.0695 (M+Na+), found: 535.0692.
M.p. 113–115 8C.
4. Experimental
Unless otherwise mentioned, all chemicals were purchased
from commercial sources. THF was freshly distilled over Na before
use. The NMR spectra were recorded on 400 MHz and 500 MHz
superconducting NMR spectrometers, respectively. All the un-
known compounds have been fully characterized by NMR
spectroscopy and high resolution MS analysis, whereas structures
of all known products were confirmed by comparison of their 1H
NMR and 19F NMR spectra with reported data. 1H NMR chemical
(2-Fluoro-1-(4-fluorophenyl)-2,2-bis(phenylsulfonyl)ethoxy)-
d 0.08 (s, 9H), 5.89 (d,
J = 8.2 Hz, 1H), 6.86–6.90 (m, 2H), 7.15–7.18 (m, 2H), 7.38–7.42 (m,
trimethylsilane (2b). 1H NMR (CDCl3):
2H), 7.52–7.56 (m, 2H), 7.56–7.61 (m, 1H), 7.66–7.72 (m, 3H),
7.95–7.97 (m, 2H). 19F NMR (CDCl3):
d
À113.3 (m, 1F), À132.52 (d,
J = 8.1 Hz, 1F). 13C NMR (CDCl3):
d 0.1, 73.3 (d, J = 23.0 Hz), 114.3 (d,
J = 270.4 Hz), 114.7, 114.9, 128.5, 128.8, 130.2 (dd, J = 8.4 Hz,
J = 2.5 Hz), 131.0 (dd, J = 30.0 Hz, J = 1.8 Hz), 131.4 (dd, J = 3.2 Hz,
J = 1.8 Hz), 134.6, 135.0, 136.6, 138.1, 163.0 (d, J = 247.8 Hz).
HRMS: calcd for C23H24F2NaO5S2Si+ 535.0695 (M+Na+), found:
535.0692. M.p. 130–132 8C.
shifts (
0.0 ppm or to the signal of a residual solvent in CDCl3
7.26 ppm). 13C NMR chemical shifts were determined relative to
internal tetramethylsilane at
0.0 ppm or to the 13C signal of CDCl3
at
77.16 ppm. 19F NMR chemical shifts were determined relative
to internal CFCl3 at 0.0 ppm.
d) were determined relative to internal tetramethylsilane at
d
(d
d
(2-Fluoro-1-(4-nitrophenyl)-2,2-bis(phenylsulfonyl)ethoxy)tri-
d
methylsilane (2c). 1H NMR (CDCl3):
d
0.09 (s, 9H), 6.00 (d, J = 7.0 Hz,
d
1H), 7.40–7.44 (m, 4H), 7.54–7.58 (m, 2H), 7.63–7.67 (m, 1H), 7.70–
7.74 (m, 3H), 7.94–7.96 (m, 2H), 8.07–8.10 (m, 2H). 19FNMR (CDCl3):
d
4.1. Typical procedure for the preparation of
fluorobis(phenylsulfonyl)methane (TFBSM)
a
-trimethylsilyl-
a-
À132.5 (d, J = 7.0 Hz, 1F). 13C NMR (CDCl3):
d 0.1, 73.2 (d, J = 22.7 Hz),
113.8 (d, J = 270.3 Hz), 122.8, 128.6, 129.0, 129.3 (d, J = 2.7 Hz), 131.1
(d, J = 1.6 Hz), 131.2 (d, J = 1.8 Hz), 135.0, 135.3, 136.1, 137.6, 143.1 (d,
J = 2.1 Hz), 148.1. HRMS: calcd for C23H25FNO7S2Si+ 538.0820 (M+H+),
found: 538.0827. M.p. 126–127 8C.
To a suspension of NaH (216 mg, 9 mmol) in THF (11 mL) was
slowly added a solution of FBSM (1.88 g, 6 mmol) in THF (11 mL) at
0 8C. The reaction mixture was stirred at the same temperature for
30 min, and TMSCl (1.52 mL, 12 mmol, freshly distilled) was added
dropwise to the reaction mixture. The reaction mixture was further
stirred for 1 h and transferred into a 25 mL syringe through a
needle. The suspension was then passed through a 25 mm GD/X
(2-Fluoro-2,2-bis(phenylsulfonyl)-1-(2,4,6-trimethoxypheny-
l)ethoxy)trimethylsilane (2d). 1H NMR (CDCl3):
d 0.00 (s, 9H), 3.47
(br s, 3H), 3.89 (s, 3H), 4.04 (br s, 3H), 5.75 (br s, 1H), 6.17(br s, 1H),
6.77 (d, J = 27.5 Hz, 1H), 7.39–7.44 (m, 2H), 7.59–7.67 (m, 5H),
7.76–7.80 (m, 1H), 8.15–8.17 (m, 2H). 19F NMR (CDCl3):
d
À143.8
Whatman syringe filter (0.45
m
m GMF, heated in an oven at 90 8C
(d, J = 27.5 Hz, 1F). 13C NMR (CDCl3):
d 0.1, 54.9, 55.3, 56.3, 64.4 (d,
for 1 h before use) into a Schlenk tube under Ar. Anhydrous
hexanes (20 mL) was carefully added onto the top of the solution.
Agitation of the THF layer should be avoided, so that a two-layer
system can be formed. The Schlenk tube was subsequently stored
J = 16.8 Hz), 89.9, 91.0, 106.4, 118.2 (d, J = 291.3 Hz), 128.0, 128.5,
130.0 (d, J = 1.8 Hz), 130.9 (d, J = 1.4 Hz), 133.8, 134.2, 137.9, 139.1,
+
162.4. HRMS: calcd for C23H24FNO8S2 511.0891 (MÀTMS+H+),
found: 511.0886. M.p. (dec.) 142–143 8C.

G.K.S. Prakash et al. / Journal of Fluorine Chemistry 133 (2012) 27–32
31
(2-Fluoro-1-(naphthalen-1-yl)-2,2-bis(phenylsulfonyl)ethox-
y)trimethylsilane (2e). 1H NMR (CDCl3):
0.11 (s, 9H), 6.80 (br s,
1H), 7.21–7.25 (m, 1H), 7.33–7.37 (m, 3H), 7.41–7.47 (m, 4H),
7.51–7.59 (m, 1H), 7.67–7.79 (m, 5H), 7.92–7.96 (m, 3H). 19F NMR
amalgam (10 wt% Na in Hg, net sodium content 90 mg,
3.72 mmol). The reaction mixture was stirred at À20 to 0 8C for
7 h. The liquid phase was decanted, and the solid residue was
washed with Et2O. The solid was then treated with elemental
sulfur powder. The solvents were removed under vacuum, and
25 mL brine was added before extraction with Et2O (20 Â 3 mL).
The combined ether phase was dried over MgSO4, and the ether
was removed to afford the crude product. The crude product was
further purified via silica gel column chromatography using ethyl
acetate and hexanes as eluent. Compound 4e was obtained as
d
(CDCl3):
d
À132.0 (br s, 1F) (Two rotamers were observed in 19F
NMR spectrum. The major rotamer appeared as a broad singlet,
whereas the minor one, partially overlapped with the major
isomer, was shown to be a doublet at À132.1 ppm). 13C NMR
(CDCl3):
d 0.2, 69.9 (br s), 115.7 (d, J = 274.1 Hz), 123.3, 124.8,
125.5, 126.4, 128.0, 128.5, 128.7, 128.8, 129.7, 131.0, 131.2, 131.5,
131.7, 133.3, 134.4, 135.0, 136.1, 138.6. HRMS: calcd for
white solid (57 mg, 48%). 1H NMR (CDCl3):
d 2.84–2.98 (m, 1H),
C
27H27FNaO5S2Si+ 565.0945 (M+Na+), found: 565.0945. M.p.
4.54 (ddd, J = 48.7, 9.8, 8.4 Hz, 1H), 4.71 (ddd, J = 48.6, 9.8, 2.8 Hz,
1H), 5.82 (ddt, J = 14.3, 8.4, 2.8 Hz, 1H), 7.76–7.72 (m, 4H), 7.83 (d,
J = 8.2 Hz, 1H), 7.92–7.87 (m, 1H), 8.04 (d, J = 8.2 Hz, 1H). 13C NMR
154–155 8C.
(E)-((1-Fluoro-4-phenyl-1,1-bis(phenylsulfonyl)but-3-en-2-
yl)oxy)trimethylsilane (2g). 1H NMR (CDCl3):
0.00 (s, 9H), 5.37
d
(CDCl3):
d 70.0 (d, J = 20.0 Hz), 87.0 (d, J = 174.8 Hz), 122.5, 124.3
(dd, J = 7.9 Hz, J = 4.9 Hz, 1H), 6.58–6.67 (m, 2H), 7.30–7.38 (m, 1H),
7.38–7.45 (m, 2H), 7.48–7.50 (m, 2H), 7.52–7.58 (m, 2H), 7.59–7.67
(m, 2H), 7.68–7.74 (m, 1H), 7.74–7.82 (m, 1H), 7.93–7.96 (m, 1H),
(d, J = 1.3 Hz), 125.6, 125.9, 126.6, 129.0, 129.2, 130.5, 133.7 (d,
J = 8.7 Hz), 133.8. 19F NMR (CDCl3):
d
À221.3 (ddt, J = 48.6, 14.3,
4.9 Hz). HRMS: calcd for C12H11OF+ 190.0794 (M+), found:
8.13–8.16 (m, 2H). 19F NMR (CDCl3):
13C NMR (CDCl3):
d
À136.87 (d, J = 7.9 Hz, 1F).
190.0793. M.p. 96–99 8C.
d
0.1, 73.7 (d, J = 21.0 Hz), 114.1 (d, J = 269.5 Hz),
123.7 (d, J = 4.4 Hz), 127.2, 128.4, 128.5, 128.6, 128.7, 131.3 (d,
J = 1.5 Hz), 131.8 (d, J = 1.5 Hz), 134.8, 134.9 (d, J = 1.5 Hz), 135.1,
136.2, 137.0, 137.9. HRMS: calcd for C25H27FNaO5S2Si+ 541.0945
(M+Na+), found: 541.0955. M.p. 135–136 8C.
Acknowledgement
Financial support for our work by the Loker Hydrocarbon
Research Institute is greatly acknowledged.
((1-Fluoro-4-phenyl-1,1-bis(phenylsulfonyl)butan-2-yl)oxy)-
trimethylsilane (2h). 1H NMR (CDCl3):
d 0.00 (s, 9H), 2.57–2.72 (m,
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32
G.K.S. Prakash et al. / Journal of Fluorine Chemistry 133 (2012) 27–32
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