Preparation of (E)-1-aryl-3,3,3-trifluoro-1,2-di(trimethylsilyl)-1-propenes via stereoselective bissilylation of trifluoromethyl aryl acetylenes and electrophilic substitution of its TMS groups

Article abstract of DOI:10.1016/j.tet.2011.03.005

Preparations and reactions of (E)-1-aryl-3,3,3-trifluoro-1,2- di(trimethylsilyl)-1-propenes are described. (E)-1-Aryl-3,3,3-trifluoro-1,2- di(trimethylsilyl)-1-propene was prepared from aryl trifluoromethyl acetylenes via reductive bissilylation by TMSCl/

Full text of DOI:10.1016/j.tet.2011.03.005

Tetrahedron 67 (2011) 3041e3045
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Preparation of (E)-1-aryl-3,3,3-trifluoro-1,2-di(trimethylsilyl)-1-propenes via
stereoselective bissilylation of trifluoromethyl aryl acetylenes and electrophilic
substitution of its TMS groups
*
Toshimasa Katagiri , Hayato Nakanishi, Kenichi Ohno, Takayuki Seiki, Akira Isobe, Keisuke Kataoka,
Kenji Uneyama
Department of Applied Chemistry, Faculty of Engineering, Okayama University, Tsushimanaka 3-1-1, Kita-ku, Okayama 700-8530, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Preparations and reactions of (E)-1-aryl-3,3,3-trifluoro-1,2-di(trimethylsilyl)-1-propenes are described.
(E)-1-Aryl-3,3,3-trifluoro-1,2-di(trimethylsilyl)-1-propene was prepared from aryl trifluoromethyl acet-
ylenes via reductive bissilylation by TMSCl/Mg in good yields. The silyl groups of (E)-3,3,3-trifluoro-1,2-di
(trimethylsilyl)-1-phenyl-1-propene were substituted by electrophiles in both a stepwise and stereo-
selective (and/or stereospecific) manner. This compound could be a building block for preparations of
substituted trifluoropropenes.
Received 20 December 2010
Received in revised form 3 March 2011
Accepted 3 March 2011
Keywords:
Ó 2011 Elsevier Ltd. All rights reserved.
Reductive bissilylation
Trifluoromethylated olefin
Trifluoropropene
Stereoselective anti addition
1. Introduction
Difficulty in the bissilylation of alkynes by the TMSCl/Mg re-
agent could be caused by an intermediary composed of semi-stable
Organosilicone compounds play an important role as carbanion
synthons in the field of synthetic organic chemistry.1 Di-silylated
compounds are of high synthetic value because they work as dia-
nion synthons.2 Disilyl-olefin works as the dianion synthon in the
synthesis of tetra-substituted olefins. Inexpensive and easy prep-
arations of disilyl-olefin are in high demand.
anion radical species, which could be an initiator of radicalic olig-
omerizations to aromatic rings7 and/or polymerizations.8 Thus,
after the first electron transfer, the bissilylation reaction would
need a second one-electron transfer to generate the dianion spe-
cies. However, although magnesium is a powerful reducing agent,9
a dianion species of the 1-phenyl-1-propyne is not easily generated
due to the possible localization of negative charges on the same p-
R1
TMS
TMS
R2
R1
system. Thus, stabilization of the dianion by delocalization of the
negative charge is essential for the preparation of bissilylated ole-
fins via reductive silylation by the TMSCl/Mg reagent. Here, the
strong electron withdrawing effect of the trifluoromethyl group
will stabilize the dianion species of the 1-aryl-3,3,3-trifluoro-1-
propene (Scheme 1).
=
R2
To date, reductive bissilylation of imines,2 ketones,3 and nitriles4
using TMSCl/Mg, an inexpensive silylating reagent has been repor-
ted. Meanwhile, only a few instances of the reductive bissilylation of
alkynes with the reagent have been reported.5 A reaction of methyl
phenyl acetylene by TMSCl/Mg in HMPA resulted in the formation of
only 1% (E)-1-phenyl-1,2-di(trimethylsilyl)-1-propene5 and viscous
black tar. In general, bissilylation of alkynes has been attained by
transition metal-catalyzed syn-addition of disilanes.6
2. Results and discussion
The starting alkynes, 1-aryl-3,3,3-trifluoro-1-propenes (1), were
prepared by a previously reported procedure.10 The optimized
condition for bissilylation of 3,3,3-trifluoro-1-phenyl-1-propene
(1a) to an alkene 2a is shown in Scheme 2.
The optimum conditions for bissilylation by excess amounts of
TMSCl/Mg involved DMF as a solvent at a temperature of 0 ꢀC. The
reaction with reflux of THF resulted only in a recovery of starting
material, but in DMI at 0 ꢀC it resulted in the formation of black tar.
* Corresponding author. Tel.: þ81 86 251 8605; fax: þ81 86 251 8021; e-mail
address: tkata@cc.okayama-u.ac.jp (T. Katagiri).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.03.005

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T. Katagiri et al. / Tetrahedron 67 (2011) 3041e3045
ET
ET
R
R
R = CF3
CF3
1
dianion
anion radical
R = CH3
radicalic
process
TMSCl
CH3
Si
CH3
CH3
polymer
R
CF3
A
TMSCl
TMS
CF3
TMS
2a
Scheme 1. Working hypothesis.
R
consistent with our experimental results; the reaction of the al-
kyne, 1b, with a smaller silylating agent, H(CH3)2SiCl, led to two
stereoisomers (major 2d at 58%; minor 2e at 7% Scheme 3).
The two silyl groups of the compounds 2 were substituted regio-
selectivelyand stereoselectively. The reaction of compound 2a, which
involved two-step reactions with methyl iodide (58%), was followed
by the reaction with PhCHO (43%) to produce the tetra-substituted
olefin 4 (Scheme 4). The stereochemistry of the product was again
confirmed by an X-ray crystallographic analysis of 5, and the product
was found to have maintained its configuration (Scheme 4).
Mg (2 equiv.)
TMSCl (8 equiv.)
/ DMF (0.25 M)
TMS
CF3
R
CF3
0 °C, time
TMS
2a: 2 h, 78% (conv. 100%)
2b: 1 h, 81% (conv. 100%)
2c: 6 h, 43% (conv. 82%)
1a: R = H
1b: R = Cl
1c: R = OMe
Scheme 2. Optimized bissilylation reaction of 1.
Similarly, the reaction of compound 2a with 1.1 equiv amount of
PhCHO gave mono-substituted product 6 in 53% isolate yield, and
that with 2.0 equiv amount of PhCHO gave double substituted
product 7 as a mixture of the diastereomer in 84% yield (Scheme 5).
The regioselectivity of the first step of the TMS substitution
would be due to rather stable nature of the carbanion A in Scheme
In case of DMF solvent, the use of an excess amount (8 equiv) of
TMSCl was needed for a good yield of the bissilylated product 2a.
The reaction with 4 equiv amounts of TMSCl resulted in a 10% lower
yield of 2a. The reaction of substrate 1c, which has an electron-
donating para-substituent on the phenyl group, required a longer
reaction time and resulted in lower yield of the bissilylated olefin
2c. The reactions of 1 with TMSCl/Mg gave rise to stereoisomers
with E-configurations. The E-selective nature of the reaction was
confirmed by a single crystal X-ray diffraction analysis of 2b (Fig. 1).
The high stereoselectivity of the product (2) could be explained
by the structure of the plausible intermediate A (Scheme 1), which
was generated by the first addition of TMSCl to the dianion of the
alkyne. Here, the bulky trimethylsilyl group covers one side of the
sp carbanion center of the intermediate A. Thus, the second tri-
methylsilyl group can only attach to the carbanion center from the
side of the trifluoromethyl group. This plausible mechanism is
1. More stable
p-carbanion would be generated at first. Thus, the
first substitution would be stereoselective reaction caused by the
steric hindrance of the other TMS group. Meanwhile, the second
substitution of the TMS group would be underwent via sp2-carb-
anion type species, thus the reaction would be stereospecific.
3. Conclusion
In conclusion, we prepared disilyl olefins (2) from the corre-
sponding alkynes (1). The reaction with TMSCl/Mg was found to be
highly stereoselective; it only resulted in the E-stereoisomer. The
two silyl groups of 2 were substituted by electrophiles in both
a regioselective and stereoselective (and/or stereospecific) manner.
Further utilizations of the reductive silylation agent (TMSCl/Mg) are
currently under investigation.
4. Experimental section
4.1. General
Reagents and solvents were purchased from TCI, WAKO, and
Aldrich. IR spectra were measured on a Hitachi Model 270e30 In-
frared Spectrophotometer. Elemental analyses were performed on
a PerkineElmer series II CHNS/O Analyzer 2400. GC/MS analyses
were carried out on a Shimadzu GCMS-QP5050A. Melting points
Fig. 1. ORTEP illustration of the bissilylated compound 2b (CCDC 787293).

T. Katagiri et al. / Tetrahedron 67 (2011) 3041e3045
3043
Cl
Cl
Mg (2 equiv.)
HMe2SiCl (8 equiv.)
/ DMF (0.25 M)
SiHMe2
CF3
Cl
CF3
0 °C, 1 h,
+
conv. 94%
Me2HSi
CF3
Me2HSi
SiHMe2
1b
2d
2e
(58%)
(7%)
Scheme 3. Bissilylation by H(CH3)2SiCl.
Scheme 4. Regio- and stereo-selective substitutions of TMS groups (CCDC 786885).
Scheme 5. Stepwise substitutions of TMS groups.
were recorded by a Yanako MP-S3 melting point measurement
apparatus. 1H (300 MHz), 19F (282 MHz), and 13C (75 MHz) NMR
spectra were recorded on a Varian MERCURY 300 instrument and
stirred for 2 h, the reaction mixture was quenched with 10% HCl aq
and extracted with Et2O (5 mL) three times. The organic layer was
dried over MgSO4 and concentrated in vacuo. The residue was
purified by silica gel column chromatography eluted with hexane.
The 19F NMR estimated the yield of the crude product 2a to be 84%.
Further distillation of the crude product (100 ꢀC/0.5 mmHg) pro-
vided 2a as a colorless oil (0.497 g, 78% yield).
the chemical shifts are reported in
7.26 ppm for 1H NMR in CDCl3), C6F6
CDCl3), and CDCl3
77 ppm for 13C NMR in CDCl3). Coupling
d
(ppm) values relative to CDCl3
(d
(d
0 ppm for 19F NMR in
(d
constants are reported in hertz (Hz).
4.2.1. (E)-3,3,3-Trifluoro-1-phenyl-1,2-ditrimethylsilyl-1-propene
(2a, Scheme 2). Isolate yield (78%), colorless oil; 1H NMR (300 MHz,
4.2. Reductive bissilylation of alkynes (1) to disilylalkenes (2)
CDCl3):
2H), 7.17e7.30 (m, 3H) ppm; 19F NMR (282 MHz, CDCl3):
ppm; 13C NMR (75 MHz, CDCl3):
0.7 (q, J¼4 Hz), 1.0 (s), 126.6 (d,
d
ꢁ0.19 (q, J¼1 Hz, 9H), 0.02 (q, J¼2 Hz, 9H), 6.83e6.87 (m,
TMSCl (16 mmol, 2 mL) and alkyne 1a (2 mmol, 0.34 g) were
added to a suspension of magnesium powder (4 mmol, 0.097 g) in
dry DMF (8 mL) at 0 ꢀC under an argon atmosphere. After being
d
108.7 (s)
d

3044
T. Katagiri et al. / Tetrahedron 67 (2011) 3041e3045
J¼3 Hz), 127.0 (q, J¼275 Hz), 127.3 (q, J¼6 Hz), 128.0 (s), 143.7 (q,
J¼27 Hz),144.1 (s),169.6 (q, J¼7 Hz) ppm; MS m/z (rel Int.)¼209 (6),
132 (100), 73 (68); IR (neat): 1690 cmꢁ1. Anal. Calcd for C15H23F3Si2:
C, 56.92; H, 7.32; N, 0.00. Found: C, 56.91; H, 7.42; N, 0.00.
4.3.2. (Z)-3-Trifluoromethyl-1-hydroxy-1,3-diphenyl-2-butene
Scheme 4). To a suspension of TBAT (0.05 mmol, 0.027 g) in dry
THF (1.5 mL) were added PhCHO (1 mmol, 0.117 g) and
(4,
3
(0.46 mmol, 0.118 g) at room temperature under an argon atmo-
sphere. After the mixture was stirred for 12 h at 50 ꢀC, to the re-
action mixture was added TBAF (0.5 mL, 1 M THF solution).
Reaction mixture was stirred for more 3 h at 50 ꢀC. The reaction
mixture was quenched with NaHCO3 aq (3 mL) and extracted with
Et2O (2 mL) three times. The organic layer was dried over MgSO4
and concentrated in vacuo. The residue was purified by silica gel
column chromatography (hexane/EtOAc¼20:1). After removal of
the solvent, distillation (80 ꢀC/0.5 mmHg,) provided colorless oil of
4.2.2. (E)-1-(4-Chlorophenyl)-3,3,3-trifluoro-1,2-ditrimethylsilyl-1-
propene (2b, Scheme 2). Isolate yield (81%), colorless block; mp
53.0e54.0 ꢀC; 1H NMR (300 MHz, CDCl3):
d
ꢁ0.16 (d, J¼1 Hz, 9H),
0.02 (d, J¼1 Hz, 9H), 6.81 (d, J¼8 Hz, 2H), 7.27 (d, J¼8 Hz, 2H) ppm;
19F NMR (282 MHz, CDCl3): 108.6 (s) ppm; 13C NMR (75 MHz,
CDCl3);
d
d
0.4 (q, J¼4 Hz), 0.9 (br),127.0 (q, J¼275 Hz),128.0 (s),128.5
(s), 132.4 (s), 142.3 (s), 144.4 (q, J¼27 Hz),168.2 (q, J¼7 Hz) ppm; MS
m/z (rel Int.)¼258 (tr), 243 (6), 166 (58), 73 (100); IR (KBr):
1490 cmꢁ1. Anal. Calcd for C15H22ClF3Si2: C, 51.33; H, 6.32; N, 0.00.
Found: C, 51.23; H, 6.55; N, 0.07.
4 (0.198 mmol, 43% yield). 1H NMR (300 MHz, CDCl3):
J¼6 Hz, 1H), 2.32 (q, J¼2 Hz, 3H), 5.46 (br d, J¼6 Hz, 1H), 7.2e7.4 (m,
10H). 19F NMR (282 MHz, CDCl3): 107.3 (s, 3F) ppm; 13C NMR
(50 MHz, CDCl3):
22.9 (d, J¼2 Hz), 71.9 (d, J¼2 Hz), 124.7 (q,
d 2.19 (br d,
d
Crystallographic data for 2b (CCDC 787293): C15H22ClF3Si2,
d
M¼350.96, triclinic, space group Pꢁ1, a¼9.295(3), b¼9.319(5),
J¼279 Hz), 124.9 (s), 126.7 (s), 127.1 (s), 128.0 (s), 128.2 (s), 128.7 (s),
ꢀ
c¼11.820(7) A,
a
¼95.09(2),
b
¼108.339(7),
g
¼99.11(3)ꢀ, V¼949.0
134.9 (s), 141.3 (d, J¼7 Hz), 149.6 (q, J¼4 Hz); IR (neat): 3500 cmꢁ1
;
3
ꢁ3
l
ꢀ
(8) A , Z¼2, Dc¼1.228 g cm
,
(Mo K
a
)¼0.7107 nm, 7208 re-
GC/MS m/z (rel Int.)¼293 (2), 292 (12), 205 (25), 105 (100), 77 (59).
Anal. Calcd for C17H125F3O: C, 69.85; H, 5.17; N, 0.00. Found: C,
70.09; H, 5.20; N, 0.04.
flections measured, 3949 unique, final R¼0.1095 using 2444 re-
flections with I>2.0(I), R(all data)¼0.1815, T¼296 K.
4.2.3. (E)-3,3,3-Trifluoro-1-(4-methoxyphenyl)-1,2-ditrimethylsilyl-
1-propene (2c, Scheme 2). Isolate yield (43%), colorless oil; 1H NMR
4.3.3. (E)-1,3-Diphenyl-2-(trifluoromethyl)-2-butenyl benzoate (5,
Scheme 4). Pyridine (0.7 mmol, 0.060 mL) and BzCl (0.8 mmol,
0.090 mL) were added to a solution of 4 (0.0734 g, 0.25 mmol) in
dry dichloroethane (2.0 mL) at 0 ꢀC under an argon atmosphere.
After the mixture was stirred for 7 h, water was added. The solution
was extracted with Et2O (2 mL) three times. The organic layer was
washed with brine, dried over MgSO4, and concentrated in vacuo.
The residue was purified by silica gel column chromatography
(hexane/EtOAc¼10:1). Removal of the solvent provided colorless
plates of 5 (0.0907 g, 0.229 mmol, 91% yield).
(300 MHz, CDCl3):
d
ꢁ0.17 (q, J¼1 Hz, 9H), 0.03 (q, J¼1 Hz, 9H), 3.81
(s, 3H), 6.76 (d, J¼9 Hz, 2H), 6.82 (d, J¼9 Hz, 2H) ppm; 19F NMR
(282 MHz, CDCl3):
d d 0.5 (q,
108.8 (s); 13C NMR (75 MHz, CDCl3):
J¼4 Hz), 0.9 (q, J¼1 Hz), 55.1 (s), 113.1 (s), 126.8 (q, J¼275 Hz), 128.3
(s), 136.2 (s), 144.0 (q, J¼27 Hz), 158.4 (s), 169.4 (q, J¼7 Hz) ppm; MS
m/z (rel Int.)¼346 (tr), 239 (41), 162 (85), 73 (100); IR (neat): 1610,
1510 cmꢁ1. Anal. Calcd for C16H25OF3Si2: C, 55.46; H, 7.27; N, 0.00.
Found: C, 55.48; H, 7.29; N, 0.03.
Mp¼127.0e128.0 ꢀC, 1H NMR (300 MHz, CDCl3): 2.35 (q,
J¼28 Hz, 3H), 6.80 (br, 1H), 7.26e7.50 (m, 12H), 7.60 (t, J¼8 Hz, 1H),
4.2.4. (E)-3,3,3-Trifluoro-1-(4-chlorophenyl)-1,2-di(dimethylsilyl)-1-
propene (2d, Scheme 3). With compound 2e as a small impurity. 1H
8.12 (d, J¼7 Hz, 2H) ppm; 19F NMR (282 MHz, CDCl3):
d 107.3 (s)
NMR (300 MHz, CDCl3):
d
0.07 (d q, J¼4, 1 Hz, 6H), 0.10 (q d, J¼4,
ppm; IR (KBr): 1730 cmꢁ1; GC/MS m/z (rel Int.)¼274 (29), 259 (8),
205 (50), 177 (9), 105 (100), 77 (35). Anal. Calcd for C24H19F3O2: C,
72.72; H, 4.83. Found: C, 72.73; H, 4.74.
1 Hz, 6H), 3.56 (septet q, J¼4, 2 Hz, 1H), 4.28 (q septet, J¼7, 4 Hz,
1H), 6.85 (d, J¼4 Hz, 2H), 7.30 (d, J¼4 Hz, 2H) ppm; 19F NMR
(282 MHz, CDCl3):
(3), 187 (5), 166 (15), 128 (23), 77 (100).
d
108.0 (d, J¼7 Hz) ppm; MS m/z (rel Int.)¼213
Crystallographic data for 5 (CCDC 786885): C24H19F3O2,
M¼396.40, monoclinic, space group P21/c, a¼9.8246(15), b¼11.2322
ꢀ
(14), c¼18.5397(17) A,
a¼90.000,
b
¼95.003(5),
g
¼90.000ꢀ,
3
ꢁ3
ꢀ
4.2.5. (Z)-3,3,3-Trifluoro-1-(4-chlorophenyl)-1,2-di(dimethylsilyl)-1-
propene (2e, Scheme 3). Obtained as a mixture with 2d. 1H NMR
V¼2038.1(4) A , Z¼4, Dc¼1.292 g cm
,
l
(Mo K
a
)¼0.7107 nm,
12,673 reflections measured, 4654 unique, final R¼0.0674, using
(300 MHz, CDCl3):
d
0.07 (d, J¼4 Hz, 6H), 0.36 (q d, J¼4, 1 Hz, 6H),
3799 reflections with I>2.0.(I), R(all data)¼0.0920, T¼296.1 K.
4.50 (septet, J¼4 Hz, 1H), 4.57 (septet q, J¼4, 1 Hz, 1H), 6.81 (d,
J¼9 Hz, 2H), 7.26 (d, J¼9 Hz, 2H) ppm; 19F NMR (282 MHz, CDCl3):
4.3.4. (E)-1-Hydroxy-4,4,4-trifluoro-1,2-diphenyl-3-(trimethylsilyl)-
2-butene (6, Scheme 5). Compound 2a (1 mmol, 0.315 g) was added
to a suspension of TBAT (0.05 mmol, 0.027 g) and PhCHO (1.1 mmol,
0.116 g) in dry THF (0.33 mL) at 0 ꢀC under an argon atmosphere
after the mixture was stirred for 24 h at 0 ꢀC. Then, 1.1 equiv
amount of HCl aq (1 M, 1.1 mL) was added and stirred for more 5 h.
The reaction mixture was added by satd NaHCO3 aq and extracted
by ether three times. The organic layer was washed by satd NaCl aq
twice and dried over anhydrous MgSO4. Further purification by
silica gel column chromatography, followed by distillation (90 ꢀC/
7 mmHg) gave the product as a colorless oil in 53% yield.
d
110.4 (s) ppm; MS m/z (rel Int.)¼213 (2), 197 (5), 166 (16), 128 (20),
77 (100).
4.3. Stepwise substitutions of TMS groups of disilyl alkene 2a
4.3.1. (Z)-1,1,1-Trifluoro-3-phenyl-2-trimethylsilyl-2-butene (3, Scheme
4). Methyl iodide (5 mmol, 0.62 mL) and 2a (0.48 mmol, 0.151 g)
were added to a suspension of TBAT (0.75 mmol, 0.404 g) in dry THF
(1.5 mL) at room temperature under an argon atmosphere. After the
mixture was stirred for 24 h at 40 ꢀC, an internal standard (
a,a,a-
trifluorotoluene) was added into the reaction mixture at room
temperature. The 19F NMR yield of compound 3 was 62%. And, isolate
yield was 58%.
1H NMR (300 MHz, CDCl3):
d 7.1e7.3 (m, 8H), 7.0 (m, 1H), 6.23
(d, J¼7 Hz, 1H), 6.14(d, J¼8 Hz, 1H), 1.94 (d, J¼7 Hz, 1H), ꢁ0.19(d,
J¼1 Hz, 9H) ppm; 19F NMR (282 MHz, CDCl3):
d 113.2 (s, 3F) ppm;
1H NMR (300 MHz, CDCl3):
d
ꢁ0.16 (s, 9H), 2.28 (q, J¼3 Hz, 3H),
7.1e7.2 (m, 2H), 7.3e7.4 (m, 3H) ppm; 19F NMR (CDCl3, 300 MHz):
109.5 (s); 13C NMR (CDCl3, 75 MHz):
13C NMR (50 MHz, CDCl3):
d 0.5 (s), 72.6 (q), 126.0 (s), 126.3 (q,
J¼276 Hz), 127.0 (s), 127.3 (s), 127.9 (s), 128.2 (s), 129.7 (s), 130.7
(s), 131.8 (q, J¼26 Hz), 136.5 (s), 139.9 (s), 162.6 (q, J¼5 Hz), 227.5
(s) ppm; IR (neat): 3480 cmꢁ1; GC/MS m/z (rel Int.)¼244 (18), 229
(36), 191 (18), 151 (58), 107 (100), 77 (60), 73 (42). Anal. Calcd for
C19H21F3OSi; C, 65.12; H, 6.04; N, 0.00. Found: C, 65.02; H, 6.26; N,
0.04.
d
d
0.6 (d, J¼2 Hz), 25.8 (d,
J¼2 Hz), 126.9 (q, J¼276 Hz), 127.7 (s), 128.1 (s), 128.2 (s), 144.8 (s),
161.1 (q, J¼6 Hz) ppm; GC/MS m/z (rel Int.)¼243 (23), 147 (100), 127
(69), 77 (34); IR (neat): 1600 cmꢁ1. Anal. Calcd for C13H17F3Si: C,
60.44; H, 6.63. Found: C, 60.55; H, 6.52.

T. Katagiri et al. / Tetrahedron 67 (2011) 3041e3045
3045
4.3.5. (Z)-1,2,4-Triphenyl-3-(trifluoromethyl)-2-butene-1,4-diol (7,
References and notes
Scheme 5). Similar to the preparation of compound 6, 2 equiv
amount of PhCHO was allowed to react with 2a. 19F NMR yield was
found 84% as the mixture of a pair of diastereomers (major/
minor¼6:4). The product was obtained as a white powder, and was
purified by recrystallization from hexane/ether (ca. 5%) for ele-
mental analysis.
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Mp¼216e217 ꢀC, 1H NMR (300 MHz, CDCl3):
d 7.2e7.4 (m, 15H),
6.26 (s, minor 1H), 6.24 (s, major 1H), 5.31 (s, minor 1H), 5.29 (s,
major 1H), 2.22 (br, major 1H) 2.19 (br, minor 1H), 2.14 (s, major
1H), 2.12 (s, minor 1H) ppm; 19F NMR (282 MHz, CDCl3):
d
111.1 (s
overlap, 3F) ppm; 13C NMR (75 MHz, CDCl3):
d 71.3 (s), 71.4 (s),
125.4 (q, J¼276 Hz), 125.7 (s), 126.9 (s), 127.4 (s), 127.9 (s), 128.2 (s),
128.6 (s), 128.8 (s) 129.9 (br), 130.9 (s), 131.2 (q J¼25 Hz), 136.0 (s),
142.1 (s), 143.0 (s), 153.4 (br) ppm; IR (KBr): 3300 cmꢁ1; GC/MS m/z
(rel Int.)¼366 (7), 278 (9), 260 (32), 191 (44), 107 (100), 105 (78), 79
(69), 77 (61). Anal. Calcd for C26H25F3O2Si; C, 71.85; H, 4.98. Found:
C, 71.71; H, 4.94.
Acknowledgements
7. Hilt, G.; Hengst, C.; Hess, W. Eur. J. Org. Chem. 2008, 2293.
8. Vyakaranam, K.; Barbour, J. B.; Michl, J. J. Am. Chem. Soc. 2006, 128, 5610.
9. Amii, H.; Uneyama, K. Chem. Rev. 2009, 109, 2119.
10. Konno, T.; Chae, J.; Kanda, M.; Nagai, G.; Tamura, K.; Ishihara, T.; Yamanaka, H.
Tetrahedron 2003, 59, 7571.
The authors express our gratitude to the SC-NMR Laboratory of
Okayama University for NMR analysis and the VBL Laboratory for
X-ray crystallographic analysis.