Preparation of tri- and difluoromethylsilanes via an unusual magnesium metal-mediated reductive tri- and difluoromethylation of chlorosilanes using tri- and difluoromethyl sulfides, sulfoxides, and sulfones

Article abstract of DOI:10.1021/jo030110z

A new and efficient method for the preparation of tri- and difluoromethylsilanes using magnesium metal-mediated reductive tri- and difluoromethylation of chlorosilanes is reported using tri- and difluoromethyl sulfides, sulfoxides, and sulfones. The byproduct of the process is diphenyl disulfide. Since phenyl trifluoromethyl sulfone, sulfoxide, and sulfide are readily prepared from trifluoromethane (CF₃H) and diphenyl disulfide, the method can be considered to be catalytic in diphenyl disulfide for the preparation of (trifluoromethyl)trimethylsilane (TMS-CF₃) from non-ozone-depleting trifluoromethane.

Full text of DOI:10.1021/jo030110z

P r ep a r a tion of Tr i- a n d Diflu or om eth ylsila n es via a n Un u su a l
Ma gn esiu m Meta l-Med ia ted Red u ctive Tr i- a n d
Diflu or om eth yla tion of Ch lor osila n es Usin g Tr i- a n d
Diflu or om eth yl Su lfid es, Su lfoxid es, a n d Su lfon es
G. K. Surya Prakash,* J inbo Hu, and George A. Olah
Donald P. and Katherine B. Loker Hydrocarbon Research Institute and Department of Chemistry,
University of Southern California, Los Angeles, California 90089-1661
gprakash@usc.edu
Received March 31, 2003
A new and efficient method for the preparation of tri- and difluoromethylsilanes using magnesium
metal-mediated reductive tri- and difluoromethylation of chlorosilanes is reported using tri- and
difluoromethyl sulfides, sulfoxides, and sulfones. The byproduct of the process is diphenyl disulfide.
Since phenyl trifluoromethyl sulfone, sulfoxide, and sulfide are readily prepared from trifluo-
romethane (CF H) and diphenyl disulfide, the method can be considered to be catalytic in diphenyl
3
3
disulfide for the preparation of (trifluoromethyl)trimethylsilane (TMS-CF ) from non-ozone-
depleting trifluoromethane.
In tr od u ction
TMS-CF
3
was first prepared by Ruppert et al. in
984, and since then, several other procedures have been
4
1
3
The introduction of the trifluoromethyl (CF ) and the
difluoromethyl (CF
developed by us and others via both chemical and
electrochemical methods during the last two decades.
However, all of these methods have some drawbacks.
2
H) groups into organic molecules has
5
gained increasing attention due to the potential use of
trifluoromethylated and difluoromethylated compounds
in materials science and medicinal and agricultural
First of all, they all use bromotrifluoromethane (CF
3
Br)
I) as a source for the
trifluoromethyl group. Trifluoromethyl halides, particu-
larly CF Br, in general are ozone depleting, and recently
3a
or iodotrifluoromethane (CF
3
1
chemistry. Although there are few approaches to achieve
this goal, fluoride-induced trifluoromethylation or dif-
3
luoromethylation with organosilicon reagents (R
CF , CF H) has been considered a straightforward and
reliable method. (Trifluoromethyl)trimethylsilane (TMS-
CF
), first developed by us2b in 1989 as a nulceophilic
f 3 f
SiR , R
their manufacture and use have been regulated. Second,
these procedures need special apparatus and well-
controlled reaction conditions, and the product yields vary
widely. Finally, none of the reported methods are ame-
nable for the preparation of structurally diverse trifluo-
romethylsilanes. Compared with trifluoromethylation,
little is known about nucleophilic difluoromethylation.
This is mainly due to the lack of general and efficient
methods for the preparation of difluoromethylsilanes.
)
3
2
2
3
trifluoromethylating reagent of choice under mild condi-
tions, is widely used and also works with enolizable
carbonyl compounds. Recently developed nucleophilic
trifluoromethylation methods are inefficient in the case
of enolizable systems.3
2f
6
We now wish to report a new general and efficient
method for the preparation of both trifluoromethylsilanes
and difluoromethylsilanes using unusual magnesium
metal-mediated reductive tri- and difluoromethylation of
various chlorosilanes. Magnesium metal-promoted reac-
tions through an electron-transfer process have attracted
*
Corresponding author. Phone: (213) 740-5984. Fax: (213) 740-
270.
1) (a) Hiyama, T., Eds. Organofluorine Compounds. Chemistry and
6
(
Applications; Springer: New York, 2000. (b) Banks, R. E., Smart, B.
E., Tatlow, J . C., Eds. Organofluorine Chemistry-Principles and
Commercial Applications; Plenum Press: New York, 1994. (c) Welch,
J . T., Eshwarakrishman, S., Eds. Fluorine in Bioorganic Chemistry;
Wiley: New York, 1991. (d) Liebman, J . F., Greenberg, A., Dolbier,
W. R., J r., Eds. Fluorine-Containing Molecules. Structure, Reactivity,
Synthesis, and Applications; VCH: New York, 1988.
(4) Ruppert, I.; Schlich, K.; Volbach, W. Tetrahedron Lett. 1984, 25,
2195.
(
2) (a) Prakash, G. K. S.; Yudin, A. K. Chem. Rev. 1997, 97, 757.
b) Prakash, G. K. S.; Krishnamuti, R.; Olah, G. A. J . Am. Chem. Soc.
989, 111, 393. (c) Yudin, K. Y.; Prakash, G. K. S.; Deffieux, D.,
Bradley, M.; Bau, R.; Olah, G. A. J . Am. Chem. Soc. 1997, 119, 1572.
d) Krishnamurti, R.; Bellew, D. R.; Prakash, G. K. S. J . Org. Chem.
1
3
(5) (a) Pawelke, G. J . Fluorine Chem. 1989, 42, 429. (b) Krishna-
murti, R.; Bellew, D. R.; Prakash, G. K. S. J . Org. Chem. 1991, 56,
984. (c) Aymard, F.; Nedelec, J .-Y.; Perichon J . Tetrahedron Lett. 1994,
35, 8623. (d) Prakash, G. K. S.; Deffieux, D.; Yudin, A. K.; Olah, G. A.
Synlett 1994, 1057. (e) Ramaiah, P.; Krishnamurti, R.; Prakash, G. K.
S. Org. Synth. 1995, 72, 232. (f) Grobe, J .; Hegge, J . Synlett 1995, 641.
(6) Although several different (difluoromethyl)silanes are docu-
mented in the literature, their preparations give low yields or need
(
1
(
991, 56, 984. (e) Broicher, V.; Geffken, D. Tetrahedron Lett. 1989,
0, 5243. (f) Hagiwara, T.; Fuchikami, T. Synlett 1995, 717.
3
(3) (a) Recently, CF I was also reported as a trifluoromethylating
reagent: Ait-Mohand, S.; Takechi, N.; Medebielle, M.; Dolbier, W., J r.
Org. Lett. 2001, 3, 4271. (b) Motherwell, W. B.; Storey, L. Synlett 2002,
2
high-cost precursors such as TMS-CF Cl. See reports: (a) Liu, E. K.
S.; Lagow, R. J . J . Organomet. Chem. 1978, 145, 167. (b) Broicher, V.;
Geffken, D. J . Orgnomet. Chem. 1990, 381, 315. (c) Buerger, H.; Moritz,
P. J . Organomet. Chem. 1992, 427, 293. (d) Fuchikami, T.; Ojima, I.
J . Organomet. Chem. 1981, 212, 145.
6
1
46. (c) Billard, T.; Langlois, B. R.; Blond, G. Eur. J . Org. Chem. 2001,
467. (d) Billard, T.; Bruns, S.; Langlois, B. R. Org. Lett. 2000, 2, 2101.
(e) Russell, J .; Roques, N. Tetrahedron 1998, 54, 13771.
1
0.1021/jo030110z CCC: $25.00 © 2003 American Chemical Society
Published on Web 05/08/2003
J . Org. Chem. 2003, 68, 4457-4463
4457

Prakash et al.
SCHEME 1a
a
X ) F, H; L ) electrophiles such as trimethylsilyl group or magnesium cation, etc.
SCHEME 2
increasing interest recently, including C-F bond cleavage
7
of trifluoromethyl ketones (Scheme 1, eq I), trifluoroac-
8
9
etates, trifluoromethylimines, p-bis(trifluoromethyl) ben-
zene10 and difluoromethyl ketones, O-silylation of ter-
11
1
2
tiary alcohols, cross-coupling of carbonyl compounds
with TMSCl,13 and C-acylation of aromatic R,â-unsatur-
1
4
ated carbonyl compounds. However, the magnesium
metal-mediated reduction of trifluoromethyl and difluo-
romethyl sulfones or sulfoxides still has not been ex-
plored, and we felt that it may exhibit some different,
interesting aspects as related to the well-known reductive
7
,11
C-F bond cleavage of tri- and difluoromethyl ketones.
In the trifluoromethyl and difluoromethyl sulfones or
sulfoxides, due to the strong electron-withdrawing effect
3 2
of CF and CF H groups, the bond between the pseudoha-
fission. With these considerations in mind, we have
embarked on the study of magnesium-mediated reductive
trifluoromethylation and difluromethylation of various
chlorosilanes and have found a long sought after simple,
efficient method for the preparation of diverse trifluo-
romethylsilanes and difluoromethylsilanes.
lide and the sulfur atom is sufficiently polarized by the
pseudohalide group bearing substantial negative charge.
Thus, when the electrons are transferred from magne-
sium metal to the sulfones and sulfoxides, reductive
-
cleavage of the C-S bond to generate anionic CF
3
or
-
CF
2
H species was anticipated over the C-F bond fission
Scheme 1, eqs II and III). Moreover, the phenyl trifluo-
(
Resu lts a n d Discu ssion
romethyl sulfone 1a or the sulfoxide 1b can also be
conveniently prepared from non-ozone depleting precur-
Reaction of sulfone 1a with 3 equiv of maganesium
metal and the chlorotriethylsilane in DMF solution at
sors such as trifluoromethane (CF
(
1
3
H) or trifluoroacetate
Scheme 2, I), and the difluoromethyl phenyl sulfone
i can be obtained using known methods (Scheme 2, II).16
17
1
5
0
°C gave exclusively (trifluoromethyl)triethylsilane, the
19
only product detected by F NMR. After workup and
purification, (trifluoromethyl)triethylsilane 3d was iso-
lated in 95% yield. Diphenyl disulfide (PhSSPh) was also
Furthermore, with these sulfones and sufoxides, the bond
between sulfur and aromatic carbon is also hard to
cleave, resulting in the expected regioselective bond
3
collected as a byproduct. TMS-CF was also prepared
1
9
similarly in quantitative conversions as identified by
NMR.
F
(
7) Amii, H.; Kobaiyashi, T.; Hatamoto, Y.; Uneyama, K. Chem.
Commun. 1999, 1323.
(
(
8) Amii, H.; Kobaiyashi, T.; Uneyama, K. Synthesis 2000, 2001.
9) Mae, M.; Amii, H.; Uneyama, K. Tetrahedron Lett. 2000, 41,
(15) Trifluoromethyl phenyl sulfide, sulfoxide, and sulphone are all
commercially available. A number of reports on their preparation have
appeared in the literature. For recent reports, see: (a) Russell, J .;
Roques, N. Tetrahedron 1998, 54, 13771. (b) Gerard, F.; J ean-Mannel,
M.; Laurent, S.-J . Eur. Pat. Appl. 1996, EP 733614, 13 pp. (c) Chen,
Q.-Y.; Duan, J .-X. Chem. Commun. 1993, 918. (d) Yang, J .-J .; Kirch-
meier, R. L.; Shreeve, J . M. J . Org. Chem. 1998, 63, 2656.
(16) (a) Hine, J .; Porter, J . J . Am. Chem. Soc. 1960, 82, 6178. (b)
Hine, J .; Porter, J . J . Am. Chem. Soc. 1957, 79, 5493. (c) Stahly, G. P.
J . Fluorine Chem. 1989, 43, 53.
7
2
1
893.
(10) Amii, H.; Hatomoto, Y.; Seo, M.; Uneyama, K. J . Org. Chem.
001, 66, 7216.
(
11) Prakash, G. K. S.; Hu, J .; Olah, G. A. J . Fluorine Chem. 2001,
12, 357-362.
12) Nishigachi, I.; Kita, Y.; Watanabe, M.; Ishino, Y.; Ohno, T.;
Maekawa, H. Synlett 2000, 1025.
13) Ishino, Y.; Maekawa, H.; Takenchi, H.; Sukata, K.; Nishiguchi,
I. Chem. Lett. 1995, 829.
14) Ohno, T.; Sakai, M.; Ishino, Y.; Shibata, T.; Maekawa, H.;
Nishiguchi, I. Org. Lett. 2001, 3, 3439.
(
(
(
(17) Commercial magnesium turnings were used without special
pretreatment.
4
458 J . Org. Chem., Vol. 68, No. 11, 2003

Preparation of Tri- and Difluoromethylsilanes
0
TABLE 1. P r ep a r a tion of Tr iflu or om eth ylsila n es a n d Diflu or om eth ylsila n es th r ou gh Mg -Med ia ted Red u ctive
Clea va ge of C-S Bon d s
a
Reaction temperature control is crucial due to the exothermic nature of the reaction. Larger-scale reactions normally need lower
temperatures. Reaction time may vary according to the different reaction scales. c Yields were determined by F NMR, and data in
b
19
parentheses are isolated yields.
The reaction works equally well for diverse types of
chlorosilanes with tri- and difluoromethyl sulfones or
sulfoxides (see Table 1). In the case of phenyl trifluoro-
methyl sulfide 1c (entry c), the reaction was sluggish,
indicating that the fluoroalkyl carbon-sulfur bond is not
efficient in accepting the electron from the Mg metal. This
was also confirmed by the fact that for the sulfide 1k ,
the Barbier product 3k (entry k) was produced in high
yield without the C-S bond cleavage. In the case of
bromodifluoromethyl phenyl sulfone 1l (entry l), 1,2-bis-
likelihood of path B was supported by the experimental
result that, under similar reaction conditions using Mg
and TMSCl in DMF, both sulfone 1m (PhSO
2 2 3
CF SiMe )
and disulfone 1n (PhSO CF SPh) readily produce
2
2 2
O
compound 3l in good yields (Scheme 4).
It should also be mentioned that the use of several
reducing metals such as zinc, aluminum, indium, sodium,
and lithium was explored to replace magnesium as the
reducing agent, among which only zinc worked but only
with a low yield of products (∼30%). Other reducing or
electron-donating reagents such as samarium iodide
(
trimethylsilyl)-1,1,2,2-tetrafluoroethane 3l was gener-
ated as the major product. This indicates that a Barbier-
type coupling intermediate [PhS(O) CF CF S(O) Ph] 4 is
2
(SmI ) and tetrakis(dimethylamono)ethylene were also
2
2
2
2
investigated to no avail. Attempts to improve the reactiv-
ity of phenyl trifluoromethyl sulfide 1c via electrochem-
istry using magnesium or zinc rod as the sacrificial anode
and platinum as the cathode in DMF were also unsuc-
cessful. DMF is not the only solvent required for this
reaction. Other solvents such as THF can also be used,
although it needs prolonged reaction times. This indicates
presumably formed, which is subsequently transformed
into 3l via a similar reductive fluoroalkylation process
(see Scheme 3, path A).
It is also possible that an alternative Barbier-type
coupled intermediate 1m is formed, which can generate
the trimethylsilyldifluoromethyl radical species 7 that
homocouples to produce 3l (Scheme 3, path B). The
-
15a
there is no need to invoke CF
3
/DMF adduct
as the
J . Org. Chem, Vol. 68, No. 11, 2003 4459

Prakash et al.
SCHEME 3
SCHEME 4
SCHEME 5
-
â-elimination of the fluoride (F ) from the in situ-
-
intermediate for these reactions. On the other hand,
methyl phenyl sulfone in the presence of magnesium and
TMSCl under similar conditions did not produce any
tetramethylsilane.
generated anionic species (CF CH2 ) from 1o via a smilar
3
mechanism as described above (Scheme 6). Scheme 6 also
shows that in the case of 2,2,2-trifluoroethyl phenyl
sulfone, sulfoxide, and sulfide, the order of reactivity is
sulfone > sufoxide > sulfide.
Concerning the mechanism, we propose that a single
electron transfer from magnesium metal to sulfones or
sulfoxides facilitates a reductive cleavage of the C-S
bond to form anionic tri- and difluoromethyl species and
a sulfur-containg radical species (see Scheme 5). This
mechanism provides a working model for this novel type
of trifluoromethylation and difluoromethylation. The
isolation of PhSSPh as a byproduct further confirms the
possibility of the sulfur radical species. This mechanism
is also supported by the fact that, when we used 2,2,2-
It should also be mentioned that methyl trifluorometh-
yl sulfone (CH
al and TMSCl in DMF to produce TMS-CF
3
SO
2
CF
3
) also reacts with magnesium met-
in moder-
3
ate yields (∼40% over a period of 20 h at room temper-
ature). However, the reaction appears to be sluggish. This
indicates that the aromatic ring conjugation in 1a is im-
portant to facilitate the initial electron transfer process.
The reductive fluoroalkylation chemistry was also
attempted with other electrophiles such as aldehydes,
ketones, allyl bromide, benzyl chloride, or tributyltin
chloride with no success. Even tributyltin hydride and
allyltrimethylsilane showed no reactivity. The reason for
such a behavior is not clear.
2 2 3
trifluoroethyl phenyl sulfone [PhS(O) CH CF ] 1o as the
reactant with Mg and TMSCl under similar reaction
conditions, 1,1-difluoroethene was produced readily. Ob-
viously, 1,1-difluoroethene was obtained through the
4
460 J . Org. Chem., Vol. 68, No. 11, 2003

Preparation of Tri- and Difluoromethylsilanes
SCHEME 6
SCHEME 7
of (trifluoromethyl)silanes and (difluoromethyl)silanes via
a magnesium metal-mediated reductive S-C bond cleav-
age process of trifluoromethyl and difluoromethyl sul-
fones, sulfoxides, and sulfides. The method can be
considered to be catalytic with respect to the diphenyl
disulfide since the starting phenyl trifluoromethyl sul-
fones, sulfoxides, and sulfides are themselves readily
2
8
prepared using non-ozone-depleting trifluoromethane
and diphenyl disulfide.
Exp er im en ta l Section
(
Tr iflu or om eth yl)tr im eth ylsila n e (3a ). Into a 250 mL
dry Schlenk flask under an argon atmosphere were added 1.14
g of Mg turnings (47.5 mmol) and 11.8 g TMSCl (109 mmol)
in 50 mL of DMF at 0 °C. After the mixture was stirred for 2
min, 4.62 g (23.8 mmol) of 1b in 5 mL of DMF was added
slowly via a syringe. The reaction mixture was stirred at room
temperature at 0 °C for 30 min and then at room temperature
for another 1.5 h until all the starting material was trans-
formed into product 3a (monitored by 19F NMR). All the low-
It is well-known that the phenyl trifluoromethyl sul-
fone 1a and sulfoxide 1b can be readily prepared from
1
8
trifluoromethane (manufactured from methane ) and
diphenyl disulfide.19 Since in our fluoroalkylation process,
diphenyl disulfide is produced as a reductive byproduct,
the presently developed method provides a novel and
useful catalytic pathway (in diphenyl disulfide) for the
production of (trifluoromethyl)silanes from trifluorometh-
ane and chlorosilanes (see Scheme 7).
(
20) Li, X.; J iang X.; Gong, Y.; Pan, H. HuaXue XueBao 1985, 43,
60.
(21) Burton, D. J .; Weimers, D. M. J . Fluorine Chem. 1981, 18, 573.
22) (a) Hine, J .; Ghirardelli, R. G. J . Org. Chem. 1958, 23, 1550.
b) Nakai, T. et al. J . Fluorine Chem. 1977, 9, 89. (c) Long, Z.-Y.; Chen,
Q.-Y. J . Fluorine Chem. 1998, 91, 95.
23) Fuchigami, T.; Yamamoto, K.; Nakagawa, Y. J . Org. Chem.
991, 56, 137.
2
(
(
(
Con clu sion
1
(
24) Stahly, G. P. J . Fluorine Chem. 1989, 43, 53.
In conclusion, we have developed a versatile and new
non-Freon-based method for the preparation of a number
(25) Yamamoto, T.; Watanabe, H. J pn. Kokai Tokkyo Koho 2001,
J P 2001039942.
(26) Stahly, G. P.; Bell, D. R. J . Org. Chem. 1989, 54, 2873.
(
27) Sukharev, V.; Zubkov, V. U.S. Patent 6365528, 2002.
(
(
18) Webster, J . L.; Lerou, J . J . U.S. Patent 5,446,218, 1995.
19) PhS(O)CF and PhS(O) CF can be obtained by oxidation of
, which can be produced from CF H and PhSSPh. See ref 15.
3
(28) Production and use of trifluoromethane (CF H) is not currently
banned. However, it is known that this compound may have relatively
high potential to cause greenhouse warming.
3
2
3
PhSCF
3
3
J . Org. Chem, Vol. 68, No. 11, 2003 4461

Prakash et al.
boiling fractions were collected under vacuum into a trap
cooled in liquid nitrogen), warmed to room temperature, and
-40 °C was slowly added 3 g (10.6 mmol) of tris(timethylsilyl)-
silyl chloride in 10 mL of DMF. The reaction mixture was then
stirred at -40 °C for 1 h and between -40 and - 20 °C for
(
then washed with ice-water (50 mL x 3). After quick drying
over activated molecular sieves, the organic mixture was
fractionally distilled using a 30 cm long column to give 2.73 g
1
9
another 2 h, until all the 1a was consumed (monitored by
F
NMR). The reaction mixture was washed with ice-water,
followed by extraction with pentane (20 mL x 4). The pentane
phase was washed with cold 98% sulfuric acid (10 mL x 3) to
remove most of the siloxane and silanol and washed with cold
2
d
1
(
81% yield) product 3a , bp 53-55 °C (lit. 55-55.5 °C). H
13
NMR (360 MHz, CDCl
3
): δ 0.25 (s, 9H, CH
3
). C NMR (90
); 131.7 (q, J C-F ) 321.8 Hz, CF ).
): δ -67.2.
Similarly, compound 1a was used to prepare 3a in 82%
1
MHz, CDCl
3
): δ -5.3 (s, CH
F NMR (338 MHz, CDCl
3
3
1
9
3
aqueous NaHCO
cated neutral pH. After drying over MgSO
3
solution three times until pH paper indi-
and solvent
4
removal, the crude product was further purified by silica gel
chromatography (pentane as the eluent) to give 0.93 g (62%
isolated yield. Compound 1c also could be used to prepare 3a ,
but the reaction was found to be sluggish.
1
yield) of solid product 3h that sublimes at 50 °C/10 Torr. H
(
Tr iflu or om eth yl)tr ieth ylsila n e (3d ). Into a flame-dried
1
3
NMR (500 MHz, CDCl
CDCl ): δ 0.5 (s, CH
NMR (470 MHz, CDCl
3
): δ 0.26 (s, 27 H). C NMR (125 MHz,
Schlenk flask containing 1.03 g (43 mmol) of magnesium
turnings and 30 mL of DMF under argon was added 3.0 g (14
mmol) of trifluoromethyl phenyl sulfone 1a at 0 °C. After the
mixture was stirred for 5 min, 6.45 g (43 mmol) of triethylsilyl
chloride was added dropwise via syringe. The color of the
reaction mixture slowly turned yellow. The progress of the
1
1
9
3
3
); 136.8 (q, J C-F )328.0 Hz, CF
3
).
F
2
9
3
): δ -41.4. Si NMR (99 MHz,
2
3
CDCl
3
): δ -66.8 (q, J Si-F ) 27.5 Hz, 1 Si); -12.5 (q, J Si-F )
+
+
4
.6 Hz, 3Si). GC-MS (m/z): 316 (M ), 247 [(Me
3
Si)
3
Si ], 69
+
(CF
3
). High-resolution GC-MS (EI): m/z calcd for C10H F -
27 3
+
1
9
Si
4
(M ) 316.1142, found 316.1110.
Diflu or om eth yl)tr im eth ylsila n e (3i). Into a mixture of
.8 g (200 mmol) of Mg turnings, 28.93 g (266 mmol) of TMSCl,
reaction was monitored by F periodically. After 1 h, the
mixture was slowly warmed to room temperature over a 20
min period and the reaction mixture was washed with 50 mL
of ice-water. After the excess Mg was removed, the solution
was extracted with pentane (30 mL x 3). The pentane phase
was washed carefully with cold 98% sulfuric acid (30 mL x 4)
to remove most of the siloxane and silanol. Subsequently, the
organic phase was washed with cold water (30 mL x 2),
(
4
and 100 mL of DMF at 0 °C was added 12.80 g (66.7 mmol) of
difluoromethyl phenyl sulfone (1i) in 10 mL of DMF slowly.
1
9
The reaction mixture was stirred at 0 °C for 90 min until
F
NMR showed that all the 1i was consumed. All of the low-
boiling species was separated out by bulb to bulb distillation,
followed by washing with ice-water (30 mL x 3) and drying
over molecular sieves. Fractional distillation (using a 30 cm
long distillation column) afforded 4.96 g of product, bp 52 °C
saturated aqueous NaHCO
20 mL x 2) and dried over anhydrous magnesium sulfate. The
3
solution (30 mL x 2), and water
(
solvent was removed under vacuum (∼100 Torr), and the
2
c
1
(
9
lit. 50 °C), yield 76%. H NMR (360 MHz, CDCl
3
): δ 0.15 (s,
resulting crude product also contained PhSSPh as a byproduct
2
13
H); 5.82 (t, J H-F ) 46.5 Hz, 1H). 1 C NMR (90 MHz, CDCl ):
3
(characterized by both GC-MS and NMR). The crude product
3
19
δ -5.4 (t, J C-F ) 2.8 Hz); 123.9 (t, J C-F ) 254.7 Hz). F NMR
was carefully purified by small-scale fractional distillation to
2
(
338 MHz, CDCl
3
): δ -140.1 (d, J F-H ) 46.8 Hz).
give 2.48 g (95% yield) of (trifluoromethyl)triethylsilane 3d ,
2
6
bp ) 56∼58 °C/60 Torr (lit. 52∼54 °C/10 Torr). GC-MS
(Diflu or om eth yl)tr ieth ylsila n e (3j). Into a mixture of 5
1
showed that its purity was higher than 96%. H NMR (500
g (26 mmol) of difluoromethyl phenyl sulfone (1i), 1.9 g of Mg
turnings (78 mmol), and 150 mL of DMF at -40 °C was slowly
added 11.8 g (78 mmol) of chlorotriethylsilane. The reaction
mixture was then stirred at temperatures between -40 and
3
3
MHz, CDCl
7
3
): δ 0.79 (q, J H-H ) 7.9 Hz, 6H); 1.04 (t, J H-H
)
1
3
.9 Hz, 9H). C NMR (125 MHz, CDCl
3
): δ 0.79 (s, CH
2
); 6.37
1
19
(s, CH
3
3
); 132.19 (q, J C-F ) 323.5 Hz, CF ). F NMR (470 MHz,
2
9
2
19
CDCl
3
): -61.30. Si NMR (99 MHz, CDCl
3
): δ 7.74 (q, J Si-F
10 °C over a 4 h period until F NMR indicated that all the
+
)
32.0 Hz). GC-MS (m/z): 184 (M ), 155 (M - Et), 115(Et
3
-
1i was consumed. Similar workup as above and fractional
+
27
Si ).
distillation gave 2.2 g of product 3j, bp 71 °C/56 Torr, yield
1
3
5
6
1
1
-
3
5
1%. H NMR (500 MHz, CDCl
3
): δ 0.72 (q, J H-H ) 8.0 Hz,
H-F ) 46.0 Hz,
); 6.7 (s, CH );
(
Tr iflu or om eth yl)t-bu tyld im eth ylsila n e (3f). Into a dry
3
H-H ) 8.0 Hz, 9H); 5.95 (t, 2
H); 1.02 (t,
J
J
2
5
50 mL Schlenk flask under an argon atmosphere were added
.14 g of Mg turnings (214 mmol) and 32.3 g (214 mmol) of
H). 13C NMR (125 MHz, CDCl
): δ 0.6 (s, CH
3
2
3
1
19
24.3 (t, J C-F ) 254.8 Hz). F NMR (470 MHz, CDCl
3
): δ
tert-butyldimethylsilyl chloride in 150 mL of DMF at -30 °C.
Subsequently, 15.0 g (71.4 mmol) of 1a in 10 mL of DMF was
added slowly via a syringe. The reaction mixture was stirred
at room temperature at -30 °C for 1 h and then at room
temperature for another 2 h until all the starting material was
2
29
137.6 (d, J F-H ) 45.8 Hz). Si NMR (99 MHz, CDCl
3
): δ
2
+
+
.3 (t, J Si-F ) 24.8 Hz). GC-MS (m/z): 166 (M ); 115 (Et
3
Si );
+
1 (CF
2
H ).
1,2-Bis(t r im et h ylsilyl)-1,1,2,2-t et r a flu or oet h a n e (3l).
1
9
consumed ( F NMR showed that the conversion of 3f was
5%). The reaction mixture was washed with ice-water,
Into a mixture of 0.42 g (17.5 mmol) of Mg turnings, 1.92 g
(17.7 mmol) of TMSCl, and 10 mL of DMF was added 1.60 g
(5.9 mmol) of bromodifluoromethyl phenyl sulfone 1l. The
reaction mixture was stirred at 0 °C for 30 min and then at
room temperature for another 30 min until 19F NMR showed
that all the 1l was consumed (the yield of 3l was 76% and
7
followed by extraction with pentane (30 mL x 4). The combined
pentane phase was further washed carefully with cold 98%
sulfuric acid (20 mL x 4) to remove most of the siloxane and
silanol. Then, the pentane phase was washed with cold
aqueous NaHCO
3
solution three times until pH paper indi-
byproduct TMSCF
2
TMS, 18% by 19F NMR analysis). The
cated neutral pH. The pentane phase was dried over MgSO
and the solvent evaporated to give a crude product that was
fractionally distilled to give 7.46 g of colorless liquid (95 °C/
4
reaction mixture was washed with ice-water followed by
extraction with pentane (10 mL x 4). The pentane phase was
washed with cold 98% sulfuric acid (10 mL x 3) to remove most
of the siloxane and silanol. Then, the pentane solution was
4
10 Torr), which turned to a transparent crystalline solid at
1
room temperature (mp 52∼54 °C, sublimes), yield 57%.
H
washed with cold aqueous NaHCO
3
solution three times until
1
3
NMR (500 MHz, CDCl
3
): δ 0.20 (s, 6H); 0.99 (s, 9H). C NMR
pH paper indicated a neutral pH. After drying over MgSO
4
1
(125 MHz, CDCl
3
): δ -8.8; 16.0; 26.0; 132.0 (q, J C-F ) 323.8
and solvent removal, the crude product was further purified
by fractional distillation and then recrystallization at -20 °C
to give 0.40 g of crystalline product 3l, mp 40∼42 °C, yield
1
9
29
Hz, CF
MHz, CDCl
3
). F NMR (470 MHz, CDCl
3
): δ -61.8. Si NMR (99
2
3
): δ 8.4 (q, J Si-F ) 32.8 Hz). GC-MS (m/z): 184
+
+
t
+
+
1
13
(
5
M ), 127 (M - Bu), 115 (M - CF
3
), 99 (M - CF
3
- CH
3
),
55%. H NMR (500 MHz, CDCl
3
): δ 0.24 (s, 18H). C NMR
3
+
1
7 (tBu ). High-resolution GC-MS (EI): m/z calcd for C
7
H
15
F
3
-
(125 MHz, CDCl
3
): δ -4.0 (m, CH
); 126.6 (tt, J C-F ) 265.0
+
2
19
Si (M ) 184.0895, found 184.0943.
Hz; J C-F ) 45.9 Hz). F NMR (470 MHz, CDCl
3
): δ -122.3.
CF SPh
2 2
(1n ) or PhSO CF TMS (1m ) as the starting material (see
Tr is(tr im eth ylsilyl)tr iflu or om eth ylsila n e (3h ). The pro-
cedure was similar to the above examples. Into 2 g (83 mmol)
of Mg turnings and 1 g (4.76 mmol) of 1a in 20 mL of DMF at
Compound 3l was also prepared by using PhSO
2
2 2
O
Scheme 4).
4
462 J . Org. Chem., Vol. 68, No. 11, 2003

Preparation of Tri- and Difluoromethylsilanes
P h en yl (Tr im eth ylsilyl)d iflu or om eth yl Su lfid e (3k ).
Into a mixture of 0.22 g (9.2 mmol) of Mg turnings, 1.99 g (18.3
mmol) of TMSCl, and 20 mL of DMF at room temperature was
added 1.1 g (4.6 mmol) of bromodifluoromethyl phenyl sulfide
mmol) was oxidized with mCPBA (9.0 mmol) in 20 mL of CH
Cl
overnight. After filtration, the filtrate was washed with Na
SO solution (10 mL x 3), NaHCO
2
-
-
2
initially at 0 °C, followed by stirring at room temperature
2
3
3
solution (10 mL x 2), and
1
1
k . The reaction was stirred at room temperature for another
h. Excess TMSCl was removed under vacuum (∼10 mmHg).
water sequentially. After drying over MgSO4 and solvent
removal, the crude product was distilled to afford 1.2 g (51%
yield) of product 1m as a colorless liquid, bp 112∼114 °C/1
The residue was washed with ice-water and then extracted
with dichloromethane (20 mL x 3). The organic phase was
further washed with brine and water successively and dried
1
Torr. H NMR (500 MHz, CDCl ): δ 0.44 (s, 9H); 7.61 (t, 2H);
3
7.74 (t, 1H); 7.95 (d, 2H). 19F NMR (470 MHz, CDCl ): δ
3
over MgSO
4
. After solvent removal, the crude product was
-112.9. HRMS (DCI/NH ): m/z calcd for C H F NO SSi (M
3
10 18
2
2
further purified by silica gel chromatography (pentane as
eluent) to give 905 mg (85% yield) of product 3k as a colorless
+
+
NH
4
) 282.0795, found 282.0787.
1
liquid, bp 86∼87 °C/4 Torr. H NMR (500 MHz, CDCl
3
): δ 0.25
1
3
Ack n ow led gm en t. Support of our work in part by
Loker Hydrocarbon Research Institute is gratefully
acknowledged.
(s, 9H); 7.37 (m, 3H); 7.59 (d, 2H). C NMR (125 MHz,
3
CDCl
3
): δ -4.2; 126.3 (t, J C-F ) 4.1 Hz); 128.8; 129.3; 134.0
1
19
(
-
t, J C-F ) 300.1 Hz); 136.2. F NMR (470 MHz, CDCl
3
): δ
2
9
2
88.1 (s). Si NMR (99 MHz, CDCl ): 7.7 (t, J Si-F ) 31.28
3
Hz). IR (neat): 3064; 2965; 2904; 1884; 1585; 1475; 1441; 1414;
Su p p or tin g In for m a tion Ava ila ble: General experimen-
1
6
307; 1255; 1076; 1025; 962; 884; 850; 825; 744; 703; 690; 631;
1
13
19
29
tal paragraph; H, C, F, and Si NMR spectra of compounds
f, 3h , 3i, and 3l; and high-resolution mass spectra of
-
1
+
+
3
07; 496 cm . GC-MS (m/z): 232 (M ), 109 (PhS ), 73 (Me -
3
+
+
Si ). HRMS (DEI): m/z calcd for C10
found 232.0545.
14 2
H F SSi (M ) 232.0553,
compounds 3f, 3h , 3l, and 1m . This material is available free
of charge via the Internet at http://pubs.acs.org.
P h en yl (Tr im eth ylsilyl)d iflu or om eth yl Su lfon e (1m ).
Phenyl (trimethylsilyl)difluoromethyl sulfide (3k ) (2.0 g, 8.6
J O030110Z
J . Org. Chem, Vol. 68, No. 11, 2003 4463