Reactions of novel mono- and difluoroacetyltrialkylsilanes with sulfur and phosphorus ylides

Article abstract of DOI:10.1016/S0022-1139(02)00188-4

The reactions of difluoroacetyltrialkylsilanes with methylidene triphenylphosphorane and benzylidene triphenylphosphorane are affected by the nature of the silyl substituents giving either the enol silyl ether or normal Wittig product exclusively, or mixture of both. Reactions with Horner-Emmons type ylide gave only the alkene products. Reactions of mono- and difluoroacetyltrialkylsilanes with dimethylsulfoxonium methylide gave the enol silyl ether products exclusively. Conversion of an enol silyl ether to an epoxide was effected with m-CPBA.

Full text of DOI:10.1016/S0022-1139(02)00188-4

Journal of Fluorine Chemistry 117 (2002) 207–211
Reactions of novel mono- and difluoroacetyltrialkylsilanes
with sulfur and phosphorus ylides
Silvana C. Ngo, Woo Jin Chung, Dong Sung Lim,
Seiichiro Higashiya, John T. Welch*
Department of Chemistry, University at Albany, State University of New York, 1400 Washington Ave.,
Albany, NY 12222, USA
Received 6 May 2002; received in revised form 25 July 2002; accepted 26 July 2002
Dedicated to Professor Lev M. Yagupolskii on the occasion of his 80th birthday.
Abstract
The reactions of difluoroacetyltrialkylsilanes with methylidene triphenylphosphorane and benzylidene triphenylphosphorane are affected
by the nature of the silyl substituents giving either the enol silyl ether or normal Wittig product exclusively, or mixture of both. Reactions with
Horner–Emmons type ylide gave only the alkene products. Reactions of mono- and difluoroacetyltrialkylsilanes with dimethylsulfoxonium
methylide gave the enol silyl ether products exclusively. Conversion of an enol silyl ether to an epoxide was effected with m-CPBA.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Fluorinated acetylsilanes; Wittig reaction; Horner–Emmons reaction; Ylides; Dimethylsulfoxonium methylide; Enol silyl ether
1. Introduction
2. Results and discussion
Acylsilanes, known as the synthetic equivalent of alde-
hydes due to the easy removal of the silyl group by treatment
with fluoride ion, have been used as versatile building blocks
for the syntheses of complex organic molecules [1,2].
Furthermore, fluorinated acylsilanes are also useful building
blocks for the formation of fluorinated enol silyl ethers [3,4].
Preparations of difluoroenol silyl ethers from fluorinated
acylsilanes by treatment with organometallic reagents [3,4]
or from non-fluorinated acylsilanes by reaction with trifluor-
omethyltrimethylsilane [5] are reported. However, the pre-
paration of fluorinated acylsilanes [3] or the synthetic utility
of these building blocks [6,7] has still not been fully
explored.
As part of our research on the development of new
fluorinated building blocks, we recently reported the synth-
esis of novel mono- and difluoroacetyltrialkylsilanes [8]. In
this paper, we wish to present the results of our continuing
studies on the synthetic utility of mono- and difluoroacetyl-
trialkylsilanes (1, 2a–c), in particular, by reactions with
sulfur and phosphorus ylides Scheme 1.
Reactions of acylsilanes with sulfur and phosphorus
ylides are profoundly influenced by silyl group migration
forming the silyl enol ethers as one of the products [9–13].
This tendency is even more pronounced in the transforma-
tions of fluorinated acylsilanes, giving the enol silyl ethers as
the major product [10,11]. However, no information on the
influence of the nature of the silyl group on the reaction
pathway is available.
Wittig reaction of difluoroacetyltriethylsilane (1a) with
triphenylphosphonium methylide generated from methyltri-
phenylphosphonium bromide by deprotonation with n-
butyllithium (Scheme 2), produced two fluorinated com-
pounds: the expected alkene (3a) and the enol silyl ether (4a)
(Table 1). However, it is clear that the nature of both the
reactive ylide and silyl group substituents affect the out
come of the reaction.
Brook has reported that reactions of aryl silyl ketones with
methylidene triphenylphosphoranes as well as alkyl-substi-
tuted methylene-phosphoranes such as ethylidene and pro-
pylidene triphenylphosphoranes resulted in the formation of
silyl enol ethers, the Brook rearrangement products
(Scheme 3, path a), while the reactions of alkyl silyl ketones
only gave normal Wittig products (path b) [9].
* Corresponding author. Tel.: þ1-518-442-4455; fax: þ1-518-442-3462.
E-mail address: jwelch@uamail.albany.edu (J.T. Welch).
0022-1139/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 0 2 ) 0 0 1 8 8 - 4

208
S.C. Ngo et al. / Journal of Fluorine Chemistry 117 (2002) 207–211
Scheme 3. Formation of enol silyl ether (a) and normal Wittig product (b).
Scheme 1. Mono- and difluoroacetyltrialkylsilanes.
Table 1
The promotion of silyl group migration in the reaction of
Wittig reactions of difluoroacetyltrialkylsilanes
fluoroacetylsilanes is consistent with the premise that sub-
stituents (R3) alpha to the carbonyl of the acylsilane capable
of reducing the buildup of charge density resulting on silyl
migration and will promote the rearrangement. Xu and
coworker reported the formation of only enol silyl ethers
from the Wittig reactions of trifluoroacetyltriphenylsilane
with various alkylidenetriphenylphosphoranes, reasoning
that the electron-withdrawing ability of the CF3 enhances
oxygen attack on silicon over that on phosphorus [11].
Similarly, in our hands, reactions of difluoroacetyl-tert-butyl-
diphenylsilane (1c) yielded only the silyl enol ether (4c).
However, use of a less positive silyl group (as estimated by
PM3 calculations) as in compound (1a) (R2 ¼ Et) resulted in
formation of both the enol silyl ether (4a) and the alkene (3a).
Since alkyl groups increase the electron density at the silicon
center, paths a and b become competitive even on such a
subtle perturbation. Furthermore, when compound (1a) was
allowed to react with a resonance-stabilized ylide such as
triphenylphosphonium benzylide (R4 ¼ Ph), the only pro-
duct isolated was the normal Wittig product, the alkene (3d).
Clearly, the nature of the substituents on the silicon affects
the reaction pathway. Ab initio calculations of intermediate A
(Scheme 3, R1 ¼ H, R2 ¼ H, R3 ¼ CF2H, R4 ¼ H, atomic
charges calculated using B3LYP and a 6-31Gꢀ basis set)
showed an increase in the charge difference between Si and
P when R4 ¼ CO2Me, CN or Ph compared to when R4 ¼ H.
A similar trend is observed when R2 ¼ Et. This suggests the
electrophilicity of phosphorous increases relative to silicon
with the result that olefination is increasingly favored over
Brooke type rearrangement to form the enol ether. It is certain
however that steric encumbrance to the assumption of the
necessary synperiplanar conformation by oxygen and phos-
phorous can also influence the course of the reaction.
Previously, no reports have been made on the influence of
the silyl substituents on the outcome of ylide additions. We
are continuing to explore these phenomena to rationalize
the reactivity of mono- and difluoroacetyltrialkylsilanes with
Wittig reagents, sulfur ylides and diazo compounds.
Entry
1
R3
Time (h)
Yield (%)a
Yield (%)a
1
2
3
a
c
a
H
1
1
3a (21)
3c (0)
3d (75)
4a (25)
4c (63)
4d (0)
H
Phenyl
24
a Isolated yield.
Table 2
Horner–Emmons reactions of difluoroacetyltrialkylsilanes
Product
1
Time (h)
Yield (%)a
5a
5b
5c
a
b
c
1
4
1
61
52
59
a Isolated yield.
Treatment of difluoroacetyltrialkylsilanes with the Hor-
ner–Emmons type reagent [14], triethyl phosphonoacetate,
was also studied (Scheme 4) and results are summarized in
Table 2.
All three difluoroacetyltrialkylsilanes gave only the nor-
mal Horner–Emmons products with no rearrangement pro-
ducts found. Since the carboethoxy group stabilizes the
ylide, these results are in agreement with those obtained
with triphenylphosphonium benzylide (Table 1, entry 3).
The reaction of difluoroacetyltriisopropylsilane (1b)
required longer reaction times than compounds (1a and
1c) as a consequence of steric obstruction of the carbonyl
carbon by the alkyl groups on silicon. Only one vinyl proton
resonance and a single fluorine peak was observed at around
6 ppm in the 1H NMR spectrum and about ꢁ110 ppm in the
19F NMR spectrum, respectively, indicating the high stereo-
selectivity of the reaction although additional experiments
will be required to establish the exact stereochemistry of the
products.
Reactions of mono- and difluoroacetyltrialkylsilanes with
sulfur ylides were also attempted (Scheme 5). Reactions of
Scheme 2. Reactions of difluoroacetyltrialkylsilanes with phosphorus ylides.

S.C. Ngo et al. / Journal of Fluorine Chemistry 117 (2002) 207–211
209
Scheme 4. Reaction of difluoroacetyltrialkylsilanes with a Horner–Emmons reagent.
Scheme 5. Reactions of mono- and difluoroacetyltrialkylsilanes with sulfoxonium ylide.
Table 3
the least bulky derivative, difluoroacetyltriethylsilane (1a),
with dimethylsulfonium methylides, generated by the depro-
tonation of trimethylsulfonium iodide with n-butyllithium,
in various solvents and at different reaction temperatures
produced complex mixtures of fluorinated compounds. On
the other hand, dimethylsulfoxonium methylide generated
from trimethyloxosulfonium iodide and n-butyllithium in
THF at 0 8C formed a single fluorinated product cleanly. It is
well known that dimethylsulfonium methylide is more
reactive with carbonyl groups and less stable than dimethyl-
sulfoxonium methylide [15]. The pronounced reactivity of
this ylide has been suggested to account for the lack of
selectivity in the formation of fluorinated products observed.
Dimethylsulfoxonium methylide reacted with all fluoro-
acylsilanes examined to give the enol silyl ether products
exclusively. Nakajima et al. has reported similar silyl migra-
tion results for the reaction of non-fluorinated acylsilanes
with sulfur ylides [12]. Those authors obtained both the enol
silyl ether products resulting from a cationotropic rearran-
gement (Scheme 6, path a), and b-ketosilanes (path b)
resulting from anionotropic rearrangement. It appears that
the electron-withdrawing fluorines at the a-position (R)
hinder the second type of migration (path b).
Formation of enol silyl ether with mono- and difluoroacetyltrialkylsilanes
and dimethylsulfoxonium methylide
Product
Silyl ketone
Yield (%)a
4a
4b
4c
6b
6c
1a
1b
1c
2b
2c
31
70
84
69
67
a Isolated yield.
a consequence of the low boiling point of the compound.
Unfortunately, the monofluoroacetyltriethylsilane (2a) did
not undergo reaction in a manner that lead to facile isolation
of the product.
In preliminary experiments, reactivity of the product enol
silyl ethers was explored by treatment of the enol silyl ether
(4c) with m-CPBA to form the desired epoxide (7c)
(Scheme 7), a building block with wide potential utility.
Further reactions of the enol silyl ethers are underway.
Preliminary results from the Mukaiyama aldol condensation
with benzaldehyde show that the difluoro derivatives, espe-
cially those with more sterically demanding silyl substitu-
ents, (4b, 4c), are remarkably unreactive under common
reaction conditions. While the monofluoro compounds (6b,
6c) react readily at room temperature, compound (4a)
reacted sluggishly under the same conditions. All three
derivatives furnished a dehydrated aldol product under the
reaction conditions explored to date.
Results of the reactions of various mono- and difluoroa-
cetyltrialkylsilanes with dimethylsulfoxonium methylide
are summarized in Table 3. The enol silyl ethers (4a–c,
6b, 6c) were formed in good yields. The rearrangement was
seemingly insensitive to both the steric demand of trialkyl-
silanes and the number of fluorine substituents on the
a-carbon. The low isolated yield of compound (4a) can be
3. Experimental
All reactions were carried out under a dry argon atmo-
sphere with oven-dried glasswares. Reagents were pur-
chased from commercial sources and used without further
purification. The mono- and difluoroacetyltrialkylsilanes
were prepared following reported procedures [8]. Solvents
were purified by standard methods and freshly distilled
under argon from either calcium hydride (CH2Cl2), or
sodium/benzophenone ketyl (THF and Et2O). 1H
Scheme 6. Cationotopic (a) and anionotopic (b) rearrangements.

210
S.C. Ngo et al. / Journal of Fluorine Chemistry 117 (2002) 207–211
Scheme 7. Epoxidation of (4c).
(300 MHz), 13C (75 MHz), and 19F (282 MHz) NMR spec-
tra were measured on a Varian Gemini-300 NMR spectro-
meter. 1H and 13C chemical shifts are reported relative to the
residual signals of the CDCl3 solvents, taken as d 7.24 for 1H
and 77.00 for 13C. 19F chemical shifts are referenced to
CFCl3 as external standard.
The organic layer was dried over anhydrous MgSO4, filtered,
and concentrated. Purification by silica gel column chroma-
tography afforded the pure products.
3.2.1. (1-Difluoromethylvinyloxy)triethylsilane (4a)
Yield: 31%, clear oil. 1H NMR: d 5.81 (t, JHF ¼ 55:2 Hz,
1H), 4.64 (d, J ¼ 2:2 Hz, 1H), 4.46 (dd, J ¼ 3:8, 1.8 Hz, 1H),
0.98(t,J ¼ 8:0 Hz,9H),0.72(q,J ¼ 8:0 Hz,6H).13CNMR:d
150.7 (t, 2JCF ¼ 22:7 Hz), 111.7 (t, 1JCF ¼ 240 Hz), 94.2 (t,
3JCF ¼ 5:9 Hz),6.3,4.7.19FNMR:dꢁ122.1(d,J ¼ 55:2 Hz).
3.1. General procedure for the Wittig reaction
To a solution of alkyltriphenylphosphonium bromide
(1.5 mmol) in 5 ml of Et2O at 0 8C was added n-butyllithium
(1.5 mmol, 0.6 ml of 2.5 M solution in hexanes). The result-
ing solution was stirred for 30 min and a solution of the
difluoroacetyltrialkylsilane (1) (1 mmol) mixed with 5 ml of
Et2O was added. The mixture was stirred for a certain time
(Table 2), quenched with water and then extracted with
Et2O. The organic layer was dried over anhydrous MgSO4,
filtered, and concentrated. Purification by silica gel column
chromatography afforded the pure products.
3.2.2. (1-Difluoromethylvinyloxy)triisopropylsilane (4b)
Yield: 70%, clear oil. 1H NMR: d 5.83 (t, JHF ¼ 55:2 Hz,
1H), 4.63 (d, J ¼ 2:2 Hz, 1H), 4.45 (dd, J ¼ 3:9, 1.8 Hz,
1H), 1.27–1.17 (m, 3H), 1.09 (d, J ¼ 6:7 Hz, 18H). 13C
NMR: d 150.9 (t, 2JCF ¼ 22:8 Hz), 111.8 (t, 1JCF ¼ 240 Hz),
3
93.3 (t, JCF ¼ 5:8 Hz), 17.7, 12.5. 19F NMR: d ꢁ121.9 (d,
J ¼ 55:1 Hz).
3.2.3. (1-Difluoromethylvinyloxy)-tert-butyldiphenylsilane
(4c)
3.1.1. (1-Difluoromethylvinyl)triethylsilane (3a)
1
Yield: 21%, clear oil. H NMR: d 6.09 (m, 1H), 6.05 (t,
Yield: 84%, white solid, mp 56–58 8C. 1H NMR: d 7.74–
7.29 (m, 10H), 5.91 (t, JHF ¼ 54:9 Hz, 1H), 4.48 (d,
J ¼ 2:4 Hz, 1H), 4.04 (dd, J ¼ 3:8, 1.6 Hz, 1H), 1.05 (s,
JHF ¼ 58:1 Hz, 1H), 5.69 (d, J ¼ 1:9 Hz, 1H), 0.93 (t,
J ¼ 8:0 Hz, 9H), 0.68 (q, J ¼ 8:0 Hz, 6H). 13C NMR: d
132.7 (t, 2JCF ¼ 14:9 Hz), 119.6 (t, 1JCF ¼ 236 Hz), 7.0, 2.9.
19F NMR: d ꢁ107.3 (dd, J ¼ 58:0, 3.1 Hz).
2
9H). 13C NMR: d 149.9 (t, JCF ¼ 22:5 Hz), 135.4, 131.6,
1
3
130.1, 127.8, 111.9 (t, JCF ¼ 240 Hz), 95.8 (t, JCF
¼
5:7 Hz), 26.3, 19.4. 19F NMR: d ꢁ122.1 (d, J ¼ 55:1 Hz).
3.1.2. (1-Difluoromethyl-2-phenylvinyl)triethylsilane (3d)
Yield: 75%, clear oil. 1H NMR: d 7.59 (t, J ¼ 3:5 Hz, 1H,
one isomer), 7.37–7.17 (m, 5H), 7.11 (s, 1H the other isomer),
6.38 (t, JHF ¼ 57:7 Hz, 1H the other isomer), 6.15 (t,
JHF ¼ 58:1 Hz, 1H one isomer), 0.83 (t, J ¼ 8:0 Hz, 9H),
3.2.4. (1-Fluoromethylvinyloxy)triisopropylsilane (6b)
Yield: 69%, clear oil. 1H NMR: d 4.63 (d, JHF ¼ 48:2 Hz,
2H), 4.38 (bs, 1H), 4.31 (t, J ¼ 1:7 Hz, 1H), 1.27–1.17 (m,
3H), 1.09 (d, J ¼ 6:4 Hz, 18H). 13C NMR: d 153.9 (d,
3
1
0.51 (q, J ¼ 8:0 Hz, 6H). 13C NMR:
d
148.8 (t,
2JCF ¼ 17:5 Hz), 91.5 (d, JCF ¼ 6:6 Hz), 82.6 (d, JCF
¼
2JCF ¼ 15:5 Hz, one isomer), 147.0 (t, JCF ¼ 14:9 Hz, the
172 Hz), 17.8, 12.6. 19F NMR: d ꢁ218.7 (t, J ¼ 47:1 Hz).
2
1
other isomer), 128.4, 128.3, 128.0, 127.9, 120.8 (t, JCF
¼
1
238 Hz one isomer), 116.7 (t, JCF ¼ 231 Hz the other iso-
mer), 7.2, 3.8. 19F NMR: d ꢁ104.1 (d, J ¼ 57:8 Hz, 2F, the
other isomer), ꢁ104.3 (dd, J ¼ 58:0, 3.1 Hz, 2F, one isomer).
3.2.5. (1-Fluoromethylvinyloxy)-tert-butyldiphenylsilane
(6c)
1
Yield: 67%, white low melting solid. H NMR: d 7.84–
7.74 (m, 4 H), 7.51–7.39 (m, 10H), 4.77 (d, JHF ¼ 47:3 Hz,
3.2. General procedure for the preparation of enol silyl
ethers (4, 6a–c)
2H), 4.36 (bs, 1H), 4.08 (t, J ¼ 1:4 Hz, 1H), 1.11 (s, 9H). 13
C
2
NMR: d 153.1 (d, JCF ¼ 17:2 Hz), 135.5, 132.3, 130.0,
3
1
127.7, 94.5 (d, JCF ¼ 6:7 Hz), 82.9 (d, JCF ¼ 171 Hz),
26.4, 19.3. 19F NMR: d ꢁ218.3 (t, J ¼ 47:4 Hz).
To a solution of trimethylsulfoxonium iodide (1.5 mmol,
0.33 g) in 5 ml of THF at 0 8C was added n-butyllithium
(1.5 mmol, 0.6 ml of a 2.5 M solution in hexanes). The
resulting solution was stirred for 30 min and a solution of
(1) or (2) (1 mmol) mixed with 5 ml of THF was added.
After stirring for a further 30 min at 0 8C, the reaction was
quenched with water and then extracted with diethyl ether.
3.3. General procedure for the Horner–Emmons
reactions with difluoroacetyltrialkylsilanes
To a solution of triethyl phosphonoacetate (1.5 mmol,
0.34 g) in 5 ml of an Et2O at 0 8C was added n-butyllithium

S.C. Ngo et al. / Journal of Fluorine Chemistry 117 (2002) 207–211
211
(1.5 mmol, 0.6 ml of 2.5 M solution in hexanes). After
stirring for 1 h, a solution of the difluoroacetyltrialkylsilane
(1) (1 mmol) mixed with 5 ml of Et2O was added. The
reaction mixture was stirred for a certain time (Table 3)
at 0 8C and then quenched with water and extracted with
Et2O. The organic layer was dried over anhydrous MgSO4,
filtered, and concentrated. Purification by silica gel column
chromatography afforded the pure products.
Yield: 92%, clear oil. 1H NMR: d 7.75–7.63 (m, 4H), 7.47–
7.33 (m, 6H), 5.71 (t, JHF ¼ 55:3 Hz, 1H), 2.68 (d,
J ¼ 3:6 Hz, 1H), 2.66–2.62 (m, 1H), 1.06 (s, 9H). 13C
NMR: d 135.5, 135.4, 132.4, 130.3, 130.2, 127.8, 127.8,
1
2
112.2 (t, JCF ¼ 245 Hz), 78.8 (t, JCF ¼ 30:6 Hz), 49.7,
26.5, 19.2. 19F NMR: d ꢁ130.2 (dd, J ¼ 57:2, 7.8 Hz).
Acknowledgements
3.3.1. 4,4-Difluoro-3-triethylsilanyl-2-butenoic acid
ethyl ester (5a)
Financial support of this work by National Institutes of
Health Grant no. AI40972 is gratefully acknowledged.
Yield: 61%, light yellow oil. 1H NMR: d 7.30 (t,
JHF ¼ 57:7 Hz, 1H), 6.19 (s, 1H), 4.18 (q, J ¼ 7:2 Hz, 2H),
1.28 (t, J ¼ 7:2 Hz, 3H), 0.93 (t, J ¼ 8:0 Hz, 9H), 0.73 (q,
J ¼ 8:0 Hz,6H).13CNMR:d163.9,152.9(t,2JCF ¼32:2 Hz),
References
3
1
134.3 (t, JCF ¼ 13:1 Hz), 113.4 (t, JCF ¼ 232 Hz), 60.9,
14.0, 7.0, 33.1. 19F NMR: d ꢁ110.1 (d, J ¼ 57:7 Hz).
[1] A. Capperucci, A. Degl’Innocenti, Recent Res. Dev. Org. Chem. 3
(1999) 385–406.
[2] P.C.B. Page, S.S. Klair, S. Rosenthal, Chem. Soc. Rev. 19 (1990)
147–195.
3.3.2. 4,4-Difluoro-3-triisopropylsilanyl-2-butenoic acid
ethyl ester (5b)
[3] F. Jin, B. Jiang, Y. Xu, Tetrahedron Lett. 33 (1992) 1221–1224.
[4] F. Jin, Y. Xu, W. Huang, J. Chem. Soc., Perkin Trans. 1 (1993) 795–
799.
Yield: 59%, clear oil. 1H NMR: d 7.30 (t, JHF ¼ 57:3 Hz,
1H), 6.26 (s, 1H), 4.19 (q, J ¼ 7:1 Hz, 2H), 1.33–1.23 (t,
J ¼ 7:1 Hz, 3H and m, 3H), 1.07 (d, J ¼ 7:3 Hz, 18H). 13
C
[5] O. Lefebvre, T. Brigaud, C. Portella, Tetrahedron 54 (1998) 5939–
5948.
2
NMR: d 163.8, 151.6 (t, JCF ¼ 31:9 Hz), 135.8 (t,
[6] F. Jin, Y. Xu, W. Huang, J. Chem. Soc., Chem. Commun. (1993)
814–816.
1
3JCF ¼ 13:4 Hz), 113.3 (t, JCF ¼ 234 Hz), 61.0, 18.5,
14.1, 11.5. 19F NMR: d ꢁ109.0 (d, J ¼ 57:5 Hz).
[7] B.F. Bonini, M. Comes-Franchini, M. Fochi, G. Mazzanti, C. Nanni,
A. Ricci, Tetrahedron Lett. 39 (1998) 6737–6740.
[8] S. Higashiya, D.S. Lim, S.C. Ngo, P.J. Toscano, J.T. Welch,
Synthesis of mono- and difluoroacetyltrialkylsilanes and the
corresponding silyl enol ethers: novel and versatile synthons, in:
Abstracts of Papers, 222nd National Meeting of the American
Chemical Society, Chicago, IL; American Chemical Society,
Washington, DC, 2001; ORGN 41.
3.3.3. 4,4-Difluoro-3-(tert-butyldiphenylsilanyl)-2-
butenoic ethyl ester (5c)
1
Yield: 52%, light yellow oil. H NMR: d 7.54–7.16 (m,
11H), 6.33 (s, 1H), 4.18 (q, J ¼ 7:2 Hz, 2H), 1.26 (t,
J ¼ 7:2 Hz, 3H), 1.19 (s, 9H). 13C NMR: d 164.1, 150.6
(t, 2JCF ¼ 31:4 Hz), 139.5 (t, 3JCF ¼ 12:3 Hz), 136.2, 133.1,
[9] A.G. Brook, S.A. Fieldhouse, J. Organometal Chem. 10 (1967) 235–
246.
1
129.6, 127.8, 113.2 (t, JCF ¼ 235 Hz), 61.1, 28.8, 18.8,
[10] J.P. Begue, D. Mesureur, J. Fluorine Chem. 39 (1988) 271–282.
[11] F. Jin, Y. Xu, J. Fluorine Chem. 62 (1993) 207–210.
[12] T. Nakajima, M. Segi, F. Sugimoto, R. Hioki, S. Yokota, K.
Miyashita, Tetrahedron 49 (1993) 8343–8358.
14.0. 19F NMR: d ꢁ106.7 (d, J ¼ 56:8 Hz).
3.4. (2-Difluoromethyl-oxiranyloxy)-tert-
butyldiphenylsilane (7c)
[13] J.A. Soderquist, C.L. Anderson, Tetrahedron Lett. 29 (1988) 2425–
2428.
[14] W.S. Wadsworth Jr., Synthetic applications of phosphonyl-stabilized
anions, in: W.G. Dauben, J.E. Baldwin, A.S. Kend, G.A. Boswell, Jr.,
J.A. Marshall, R.F. Heck, J. Meinwald, R.H. Hirschmann, B.M. Trost
(Eds.), Organic Reactions, vol. 25, Wiley, New York, 1977, pp. 73–253.
[15] (a) E.J. Corey, M. Chaykovsky, J. Am. Chem. Soc. 87 (1965) 1353–
1364;
To a solution of m-CPBA (77%, 1.5 mmol, 0.34 g) in
CH2Cl2 (2 ml) at 0 8C was added a solution of (4c)
(0.5 mmol, 0.17 g) in 5 ml CH2Cl2. The mixture was stirred
at 0 8C for 1 h, allowed to warm to RT and stirred for an
additional 36 h. The reaction was quenched with saturated
NaHCO3, then extracted with CH2Cl2. The organic layer
was dried over MgSO4, filtered and concentrated. Purifica-
tion by silica gel chromatography afforded the pure product.
(b) B.M Trost, L.S. Melvin, Jr., Sulfur Ylides, Academic Press, New
York, 1975;
(c) E. Block, Reactions of Organosulfur Compounds, Academic
Press, New York, 1978.