Generation of diarylcarbenium ion poolsviaelectrochemical C-H bond dissociation

Article abstract of DOI:10.1246/bcsj.82.594

The "cation pools" of diarylcarbenium ions have been generated by the low-temperature electrochemical oxidation of diphenylmethane derivatives. In addition to diphenylmethanes having various substituents, 9,10-dihydroanthracene, dibenzosuberane, and xanth

Full text of DOI:10.1246/bcsj.82.594

594
Bull. Chem. Soc. Jpn. Vol. 82, No. 5, 594–599 (2009)
© 2009 The Chemical Society of Japan
Generation of Diarylcarbenium Ion Pools via Electrochemical
C-H Bond Dissociation
Masayuki Okajima, Kazuya Soga, Takashi Watanabe, Kimitada Terao,
Toshiki Nokami, Seiji Suga, and Jun-ichi Yoshida*
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University,
Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8510
Received December 22, 2008; E-mail: yoshida@sbchem.kyoto-u.ac.jp
The “cation pools” of diarylcarbenium ions have been generated by the low-temperature electrochemical oxidation
of diphenylmethane derivatives. In addition to diphenylmethanes having various substituents, 9,10-dihydroanthracene,
dibenzosuberane, and xanthenes, which are annulated derivatives of diphenylmethane were also found to serve as a
precursor of cation pools. The generation of the diarylcarbenium ion was confirmed by low-temperature NMR analysis
and cold-spray mass analysis. Reactivity was also investigated by reactions with various carbon nucleophiles such as
allyltrimethylsilane, 1,3,5-trimethylbenzene, and anisole.
Electron transfer (ET) activation1 such as electrochemical
bond caused by the overlap of its · orbital with the SOMO of
the aromatic ring seems to be responsible for the success of this
process. Indeed, the deprotonation rate of an aromatic radical
cation is affected by the structural feature of substrates,
especially the relative orientation of the scissile C-H bond
and the aromatic ³-system.
We have developed a cation pool method that involves
electrochemical oxidative generation and accumulation of
carbocations in the absence of nucleophiles at low temper-
ature.6 The reactions involve the oxidative cleavage of C-H,
although the dissociation of C-Si and C-C bonds are also
effective (Scheme 2). It is important to note that the accumu-
lation of cationic species was confirmed by low-temperature
NMR spectroscopy.
Thus, we envisioned that diarylcarbenium ions would be
generated by the anodic oxidation of diarylmethanes deriva-
tives via benzylic C-H bond dissociation. Some diarylcarbe-
nium ions have received significant research interest from
mechanistic7 and synthetic view points,8 although, to the best
of our knowledge, the generation of diarylcarbenium ions by
electrochemical methods had never been examined.9 Recently,
we reported the generation of diarylcarbenium ion pools via
oxidative C-H bond cleavage of diarylmethanes.6p During the
course of our study, we found that the efficiency of the cation
generation process depends on the structures of diarylmethanes.
In this paper we report the full details of the electrochemical
generation of diarylcarbenium ion pools.
oxidation2,3 has emerged as a valuable method for selective
transformation in organic synthesis. In pioneering work
concerning anodic oxidation of aromatic compounds, Eberson
and Nyberg reported side-chain anodic acetoxylation of
alkylaromatic compounds.4 Several groups including Eberson’s
proposed a mechanism involving two electron transfer pro-
cesses (Scheme 1).5 The one electron oxidation of alkylaro-
matic compounds (1st ET) results in the formation of the
corresponding radical cation, which is highly reactive and
undergoes fast subsequent reactions. The benzylic C-H bond
cleavage (elimination) is typically observed for alkyl-substi-
tuted aromatic compounds having at least one hydrogen atom
in the benzylic position. The thus-generated radicals are more
easily oxidized than the corresponding neutral compounds,
making possible the second electron transfer at the electrode
(2nd ET). The cationic intermediates thus produced are finally
converted to neutral products by nucleophilic attack of an
acetate ion (addition). This reaction mechanism has been well
accepted as an anodic behavior of alkylaromatics.
As depicted in Scheme 1, the benzylic C-H bond cleavage
of radical cation is an essential step in the side-chain oxidation
of alkylaromatics. Significant weakening of the benzylic C-H
anodic
oxidation
-e
anodic
oxidation
-e
C H
C H
C
+
-H
1st ET
elimination
2nd ET
anodic
oxidation
-
-
Nu
C OAc
- H
C
-
+
C
Y
C H
Y
C Nu
Y
OAc
Bu4NBF4
CH2Cl2
-78 °C
Y = N, O
"Cation Pool"
addition
Scheme 1.
Scheme 2.
Published on the web May 13, 2009; doi:10.1246/bcsj.82.594

M. Okajima et al.
Table 1.
Bull. Chem. Soc. Jpn. Vol. 82, No. 5 (2009)
595
anodic
oxidation
anodic
oxidation
Bu4NBF4
/CH2Cl2
-78 °C
+
Bu4NBF4
/CH2Cl2
1f (Eox = 1.75 V)
2f
2a-e
H
H
H
1a-e
SiMe3
SiMe3
3a-e
3f 56%
Entry Substrate/Eox Temperature/°C
Product/yield
Scheme 3.
1
2
3
¹78
¹78
¹78
1a Eox = 1.91 V
1b Eox = 1.52 V
temperature (¹48 °C) (Entries 4 and 5). In both cases, yields of
allylated products were moderate at ¹78 °C as shown in
parentheses.
3a 0%
It is still uncertain why simple diphenylmethane (1a) did not
give the corresponding allylated product at all. The introduc-
tion of electron-donating groups on both phenyl groups was
examined because it should cause a decrease in the oxidation
potential. Thus, we examined bis(p-methylphenyl)methane (1f)
as a precursor of the “diarylcarbenium ion pool” as depicted in
Scheme 3. In this case the allylated product 3f was obtained in
56% yield.
3b 0%
1c Eox = 1.44 V
3c 80%
O
O
4
5
¹48
¹48
The introduction of other substituents at para positions of
diarylmethanes was found to be effective for accumulation of
diarylcarbenium ions and the corresponding allylated diaryl-
methanes 3 were obtained in moderate to high yields (Table 2).
It was surprising that not only electron-donating substituents
(1g and 1h), but also electron-withdrawing substituents such as
halogen atoms (1k and 1l) were effective. It is interesting that
the introduction of a methyl group at the para position of one of
the two benzene rings is effective for generation of diaryl-
carbenium ion (1i), although meta substitution is not effective
(1m). On the other hand, the introduction of an acetyl group at
least one of two benzene rings retards generation of diaryl-
carbenium ions (1j and 1n). Successful reaction of diaryl-
methane 1o at higher temperatures indicated that the cleavage
reaction depends upon the bond dissociation energy of the
benzylic C-H bond in the radical cation and that the cleavage
can be thermally promoted. It seems to be reasonable to
consider that the deprotonation of the initially formed radical
cation requires higher temperature because of the charge
delocalization through the extended ³-system. Though the
detailed mechanism has not been clarified yet, the substituent
effect can be explained as follows. The introduction of an
electron-donating group makes the electron transfer easier, but
decreases the rate of deprotonation. On the other hand, the
introduction of an electron-withdrawing group facilitates the
C-H bond cleavage, although the initial electron transfer is less
favorable.
1d Eox = 1.36 V
3d 70%
(38%)a)
3e 71%
(17%)a)
1e Eox = 1.91 V
a) Reactions were performed at ¹78 °C.
Results and Discussion
We initiated our study by measuring the oxidation potential
of diphenylmethane derivatives. As shown in Table 1, oxida-
tion potentials of diphenylmethane derivatives were lower than
2 V. These values indicated that all these molecules can be
oxidized under conventional preparative electrochemical con-
ditions. The low-temperature anodic oxidation of diphenyl-
methane derivatives was performed under the “cation pool”
condition and thus-generated cations were treated with allyl-
trimethylsilane as a nucleophile (Table 1). Diphenylmethane
(1a) did not give the corresponding allylated product 3a and
a significant amount (54%) of diphenylmethane (1a) was
recovered unchanged (Entry 1). Although the conversion of
diphenylmethane (1a) was slightly increased (73% conversion)
at higher reaction temperature (¹48 °C), the allylated product
3a was not observed. The anodic oxidation of fluorene (1b)
seems to be interesting because fluorenyl cation is anti-
aromatic. Though 1b was consumed completely during the
electrolysis, the allylated product 3b was not obtained after
treatment with allyltrimethylsilane (Entry 2). 9,10-Dihydro-
anthracene (1c) gave the allylated product 3c in 80% yield
at ¹78 °C (Entry 3). Xanthene (1d) and dibenzosuberane
(=10,11-dihydro-5H-dibenzo[a,d]cycloheptene) (1e) gave
allylated products 3d and 3e in reasonable yields at higher
The accumulation of diarylcarbenium ion was confirmed by
low-temperature NMR spectroscopy (Figure 1). For example,
a solution of a pool of 2k, which was generated from 1k
exhibited a signal at 192.6 ppm due the carbenium carbon
Ca. The HMQC spectrum shows a cross peak between this
carbenium carbon Ca and the remaining benzylic hydrogen Ha
(9.90 ppm). The chemical shift of Ca is very close to that
(193.3 ppm) of 2k generated in a super acid media (SO2ClF).10

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Bull. Chem. Soc. Jpn. Vol. 82, No. 5 (2009)
Diarylcarbenium Ion Pools
Table 2.
Ha
Hc
Hd
anodic
oxidation
SiMe3
Ar
Ar
Ar
Ar
ppm
120
Ar
Ar
Bu4NBF4/CH2Cl2
-78 °C, 20 min
2
-78 °C
1
3
Cd
Cb
OMe
MeO
OMe
140
160
180
1g
1h
Cc
Eox = 1.43 V
3g 53%
E
ox = 1.46 V
3h 57%
Ac
F
e F
d
b
a
Ha Hc
Ce
1j
1i
Hd
c
E
ox = 1.94 V
Eox = 1.82 V
3i 60%
3j 0%
Ca
ppm
10.0
9.0
8.0
7.0
Cl
Cl
F
F
Figure 1. HMQC spectrum of diarylcarbenium ion 2k.
NMR measurement was performed at ¹78 °C in CD2Cl2
with CH2Cl2 as an internal standard (1H NMR: 600 MHz,
13C NMR: 150 MHz).
1l
1k
Eox = 2.03 V
3l 44%
Eox = 1.96 V
3k 76%
Ac
Ac
a good nucleophile for diarylcarbenium ions,6p it is difficult to
obtain mono-substituted product 11 selectively (Entry 8). We
observed a significant amount of 2,5-di-substituted product
(40%) even in the reaction with a large excess amount of
thiophene, because mono-substituted thiophene 10 is more
nucleophilic than thiophene itself. Thus, a special mixing
technique like ultra-high speed mixing using a micro mixer
might be necessary for selective preparation of the mono-
substituted product in this case.6h,6m,13
F
F
1m
1n
E
ox = 2.08 V
Eox = 2.12 V
3n 0%
3m 0%
3o 0% (83%)a)
1o
Eox = 1.83 V
Conclusion
a) The reaction was performed at ¹10 °C.
The “cation pool” method was found to be effective for the
generation of diarylcarbenium ions, although the efficiency
depends on the nature of the starting diarylmethanes. The
present method serves as a powerful method for the con-
struction of organic compounds having diarylmethane struc-
tures, and it is hoped that various substituted diarylmethanes
will be synthesized using the present method.
We also observed the peaks assigned to the ortho and meta
carbons (Cc and Cd), which split into two separate peaks,
indicating a high rotation barrier for each p-fluorophenyl group
because of the effective overlap of the ³-system with the
carbenium ion center as Olah and Watkins reported.11 CSI-MS
analysis12 (spray temperature: ¹20 °C) also supported the
formation of 2k (m/z = 203).
Experimental
General. 1H and 13C NMR spectra were recorded on Varian
MERCURY plus-400 (1H 400 MHz, 13C 100 MHz) and JEOL
ECA-600P (1H 600 MHz, 13C 150 MHz) instruments. EI mass
spectra were recorded on a JMS-SX102A spectrometer. FAB mass
spectra were recorded on a JMS-HX110A spectrometer. CSI mass
spectra were recorded on a JMS-T100CSK spectrometer. Starting
materials 1g,14 1h,15 1i,15 1j,15 1m,15 and 1o16 were prepared
according to reported procedures. Unless otherwise noted, all
materials were obtained from commercial suppliers and used
without further purification. Dichloromethane was washed with
water, distilled from P2O5, redistilled from dried K2CO3 to remove
a trace amount of acid, and stored over molecular sieves 4A.
Unless otherwise noted, all oxidation potential were measured as
follows. Rotating-disk electrode voltammetry was carried out
using BAS 100B and Nikko Keisoku RRDE-1 rotating disk
electrodes with a Nikko Keisoku SC-5 controller. Measurements
In order to demonstrate the synthetic utility of diarylcarbe-
nium ion pools, reactions with various nucleophiles have been
examined. As shown in Table 3, the diarylcarbenium ion 2k
reacted with a ketene silyl acetal (Entry 1). The reaction with
various organometallic reagents such as Grignard reagents
and alkyllithiums were unsuccessful, but the reaction with
diethylzinc gave the adduct 5 in moderate yield (Entry 2). On
the other hand, Friedel-Crafts type reactions gave the corre-
sponding products in moderate to high yields (Entries 3-7). It
is noteworthy that 1,3-dimethoxybenzene gave the mono-
substituted compound 9 as a single regioisomer, probably
because both methoxy groups work as strong ortho-para
directors (Entry 6). The reaction with anisole also proceeded
regioselectively to give the para-substituted product 10 in
moderate yield (Entry 7). Although thiophene was found to be

M. Okajima et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 5 (2009)
597
Table 3.
were carried out in 0.1 M LiClO4/CH3CN using a glassy carbon
disk working electrode, a platinum wire counter electrode, and an
SCE reference electrode with sweep rate of 10 mV s¹1 at 5000 rpm.
Spectral Analysis of Electrochemically Generated Diaryl-
carbenium Ion. NMR Analysis of Diarylcarbenium Ion 2k:
The anodic oxidation was carried out in an H-type divided cell (4G
glass filter) equipped with a carbon felt anode (Nippon Carbon
JF-20-P7, ca. 160 mg, dried at 250 °C/1 mmHg for 2.5 h before
use) and a platinum plate cathode (10 mm © 10 mm). In the
anodic chamber were placed 1k (21.7 mg, 0.106 mmol) and 0.3 M
Bu4NBF4 in CH2Cl2/CD2Cl2 (10:1) (4.0 mL). In the cathodic
chamber were placed trifluoromethanesulfonic acid (38.2 mg,
0.254 mmol) and 0.3 M Bu4NBF4 in CH2Cl2/CD2Cl2 (10:1)
F
F
anodic
F
F
oxidation
Bu4NBF4/CH2Cl2
1k
2k
-78 °C
Nucleophile
(5.0 equiv)
F
F
-78 °C, 20 min
Nu
Entry
1
Nucleophile
Product (yields)
F
F
F
OSiMe3
OMe
(4.0 mL). The constant current electrolysis (5.0 mA) was carried
¹1
out at ¹78 °C with magnetic stirring. After 2.5 F mol
of
OMe
electricity was consumed, the reaction mixture of the anodic
chamber was transferred to a 5 mm º NMR tube with a septum cap
under Ar atmosphere at ¹78 °C. The NMR measurement was
carried out at ¹80 °C. Chemical shifts are reported using the
methylene signal of CH2Cl2 at ¤ 53.49 (13C NMR) as an internal
standard. The huge signal coming from CH2Cl2 is reduced by usual
pulse techniques: 13C NMR (150 MHz, CH2Cl2/CD2Cl2 (10:1)): ¤
119.3 (d, J = 21.0 Hz), 120.6 (d, J = 22.5 Hz), 132.3, 144.2 (d,
J = 15.0 Hz), 151.1 (d, J = 13.5 Hz), 174.2 (d, J = 283.5 Hz),
192.6. Selected peaks for 1H NMR (600 MHz, CH2Cl2/CD2Cl2
(10:1)): ¤ 7.59 (dm, J = 60.3 Hz, 4H), 8.62 (d, J = 28.7 Hz, 4H),
9.90 (s, 1H).
4 66%
O
F
Et2Zn
2
3
5 37%
F
F
N
6 80%a)
N
Typical Procedure for the Generation of a Diarylcarbenium
F
F
F
Ion Pool and Reactions with a Nucleophile.
The anodic
oxidation was carried out in an H-type divided cell (4G glass filter)
equipped with a carbon felt anode (Nippon Carbon JF-20-P7, ca.
160 mg, dried at 250 °C/1 mmHg for 2.5 h before use) and a
platinum plate cathode (10 mm © 10 mm). In the anodic chamber
were placed a solution of dihydroanthracene (1c) (72.1 mg, 0.400
mmol) and 0.3 M Bu4NBF4/CH2Cl2 (8.0 mL). In the cathodic
chamber were placed trifluoromethanesulfonic acid (90 µL) and
0.3 M Bu4NBF4/CH2Cl2 (8.0 mL). The constant current electroly-
sis (10.0 mA) was carried out at ¹78 °C with magnetic stirring
4
5
7 70%
F
MeO
OMe
MeO
OMe
OMe
¹1
8 70%
until 2.5 F mol of electricity was consumed. Then allyltrimeth-
OMe
OMe
ylsilane (133.2 mg, 1.17 mmol) was added to the anodic chamber
at ¹78 °C and the mixture was stirred for 30 min. The resulting
mixture was treated with triethylamine (0.5 mL) at ¹78 °C. After
stirring at room temperature for 10 min, the solvent was removed
under reduced pressure and the residue was quickly filtered
through a short column (2 © 3 cm) of silica gel to remove
Bu4NBF4 by using Et2O as an eluent. Removal of the solvent of
the combined filtrate under reduced pressure and purification of the
crude product by flash chromatography gave 9-(2-propenyl)-9,10-
dihydroanthracene (3c).17
MeO
MeO
F
MeO
MeO
OMe
6
7
9 83%
F
F
F
9-(2-Propenyl)-9,10-dihydroanthracene (3c):
80% yield
from dihydroanthracene (1c) and allyltrimethylsilane. 1H NMR
(400 MHz, CDCl3): ¤ 2.42 (dt, J = 1.2, 7.2 Hz) and 2.55 (dt, J =
0.67, 7.0 Hz) (total 2H), 3.88-4.18 (m, 3H), 4.86-5.08 (m, 2H),
5.68-5.98 (m, 1H), 7.16-7.32 (m, 8H). 13C NMR (100 MHz,
CDCl3): ¤ 35.3, 36.2, 42.2, 46.7, 46.8, 47.7, 116.5, 125.8, 125.90,
125.93, 127.2, 127.6, 127.9, 128.8, 135.9, 136.0, 136.5, 136.8,
138.8, 139.6. HRMS (EI) m/z calcd for C17H15 (M+ ¹ H):
219.1174, found 219.1173.
10 46%
F
S
8
S
9-(2-Propenyl)xanthene (3d): 70% yield from xanthene (1d)
and allyltrimethylsilane at ¹48 °C. 1H NMR (400 MHz, CDCl3): ¤
2.50 (t, J = 6.8 Hz, 2H), 4.79-4.95 (m, 2H), 5.59-5.70 (m, 1H),
7.04-7.09 (m, 4H), 7.19-7.26 (m, 4H); 13C NMR (100 MHz,
11 47%
F
a) NMR yields (1,1¤,2,2¤-tetrachloroethane as an internal
standard).

598
Bull. Chem. Soc. Jpn. Vol. 82, No. 5 (2009)
Diarylcarbenium Ion Pools
CDCl3): ¤ 39.4, 45.3, 116.2, 117.5, 122.9, 124.6, 127.4, 128.6,
134.4, 152.0. HRMS (CI) calcd for C16H15O (MH+) 223.1123,
found 223.1122.
J = 7.5 Hz), 136.3, 136.6, 137.3, 138.0 (d, J = 3.2 Hz), 161.2 (d,
J = 243.2 Hz). HRMS (EI) m/z calcd for C22H20F2: 322.1533,
found 322.1534.
5-(2-Propenyl)-10,11-dihydro-5H-dibenzo[a,d]cycloheptene
(3e): 71% yield from dibenzosuberane (1e) and allyltrimethyl-
silane. The reaction was performed at ¹48 °C. 1H NMR (400 MHz,
CDCl3): ¤ 2.85 (t, J = 7.4 Hz, 2H), 3.02-3.11 (m, 2H), 3.28-3.36
(m, 2H), 4.10 (t, J = 8.0 Hz, 1H), 4.90-5.00 (m, 2H), 5.62-5.75
(m, 1H), 7.08-7.16 (m, 8H). 13C NMR (100 MHz, CDCl3): ¤ 33.3,
41.5, 52.7, 115.8, 125.8, 126.2, 126.3, 129.3, 130.1, 136.9, 139.2,
141.1. HRMS (CI) m/z calcd for C18H19 (MH+): 235.1487, found
235.1487.
2-Bis(4-fluorophenyl)methyl-1,3,5-trimethoxybenzene (8):6p
1
70% yield from 1k and 1,3,5-trimethoxybenzene. H NMR (400
MHz, CDCl3): ¤ 3.59 (s, 6H), 3.80 (s, 3H), 5.96 (s, 1H), 6.14 (s,
2H), 6.87-6.92 (m, 4H), 7.09-7.13 (m, 4H).
4-Bis(4-fluorophenyl)methyl-1,3-dimethoxybenzene
(9):
83% yield from 1k and 1,3-dimethoxybenzene. 1H NMR (400
MHz, CDCl3): ¤ 3.69 (s, 3H), 3.79 (s, 3H), 5.75 (s, 1H), 6.39 (dd,
J = 8.4, 2.4 Hz, 1H), 6.46 (d, J = 2.4 Hz, 1H), 6.66 (d, J = 8.4 Hz,
1H), 6.92-7.02 (m, 8H). 13C NMR (100 MHz, CDCl3): ¤ 47.7,
55.3, 55.5, 98.7, 103.8, 114.9 (d, J = 21.0 Hz), 124.8, 130.4, 130.6
(d, J = 7.5 Hz), 139.7 (d, J = 3.2 Hz), 157.8, 159.6, 161.2 (d,
J = 242.8 Hz). HRMS (EI) m/z calcd for C21H18O2F2: 340.1275,
found 340.1273.
4,4-Bis(4-methylphenyl)-1-butene (3f):6p 56% yield from 1f
1
and allyltrimethylsilane. H NMR (400 MHz, CDCl3): ¤ 2.27 (s,
6H), 2.73-2.78 (m, 2H), 3.90 (t, J = 8.0 Hz, 1H), 4.87-4.92 (m,
1H), 4.95-5.01 (m, 1H), 5.61-5.72 (m, 1H), 6.70-7.07 (m, 8H).
4,4-Bis(4-methoxyphenyl)-1-butene (3g):6p 53% yield from
4-Bis(4-fluorophenyl)methyl-1-methoxybenzene (10): 46%
yield from 1k and anisole. 1H NMR (400 MHz, CDCl3): ¤ 3.79 (s,
3H), 5.46 (s, 1H), 6.83-6.87 (m, 2H), 6.95-7.02 (m, 6H), 7.03-
7.08 (m, 4H). 13C NMR (100 MHz, CDCl3): ¤ 54.4, 55.2, 113.8,
115.1 (d, J = 21.0 Hz), 130.1, 130.6 (d, J = 8.0 Hz), 135.7, 139.8
(d, J = 3.2 Hz), 158.1, 161.4 (d, J = 243.2 Hz). HRMS (EI) m/z
calcd for C20H16OF2: 310.1169, found 310.1176.
1
1g and allyltrimethylsilane. H NMR (400 MHz, CDCl3): ¤ 2.74
(dd, J = 7.6, 7.6 Hz, 2H), 3.75 (s, 6H), 3.91 (t, J = 7.6 Hz, 1H),
4.91-4.94 (m, 1H), 4.98-5.03 (m, 1H), 5.65-5.75 (m, 1H), 6.80 (d,
J = 8.0 Hz, 4H), 7.11 (d, J = 8.0 Hz, 4H).
4-(4-Methoxyphenyl)-4-(4-methylphenyl)-1-butene
(3h):6p
1
57% yield from 1h and allyltrimethylsilane. H NMR (400 MHz,
CDCl3): ¤ 2.29 (s, 3H), 2.74-2.78 (m, 2H), 3.75 (s, 3H), 3.92 (t,
J = 8.0 Hz, 1H), 4.91-4.95 (m, 1H), 4.98-5.04 (m, 1H), 5.65-5.75
(m, 1H), 6.78-6.82 (m, 2H), 7.05-7.14 (m, 6H).
2-Bis(4-fluorophenyl)methylthiophene (11): 47% NMR yield
1
from 1k and thiophene. H NMR (400 MHz, CDCl3): ¤ 5.67 (s,
1H), 6.67 (ddd, J = 3.6, 1.5, 1.2 Hz, 1H), 6.95 (dd, J = 5.2, 3.6 Hz,
1H), 6.98-7.04 (m, 4H), 7.14-7.19 (m, 4H), 7.23 (dd, J = 5.2,
1.2 Hz, 1H). 13C NMR (100 MHz, CDCl3): ¤ 50.5, 115.3 (d, J =
21.4 Hz), 124.8, 126.4, 126.7, 130.2 (d, J = 7.9 Hz), 139.3 (d,
J = 3.1 Hz), 147.5, 161.7 (d, J = 244.0 Hz). HRMS (EI) m/z calcd
for C17H12SF2: 286.0629, found 286.0632.
4-(4-Methylphenyl)-4-phenyl-1-butene (3i):6p
60% yield
1
from 1i and allyltrimethylsilane. H NMR (400 MHz, CDCl3): ¤
2.27 (s, 3H), 2.75-2.79 (m, 2H), 3.94 (t, J = 7.6 Hz, 1H), 4.88-
4.91 (m, 1H), 4.96-5.00 (m, 1H), 5.61-5.72 (m, 1H), 7.01-7.11
(m, 5H), 7.15-7.22 (m, 4H).
4,4-Bis(4-fluorophenyl)-1-butene (3k):6p 76% yield from 1k
and allyltrimethylsilane. 1H NMR (400 MHz, CDCl3): ¤ 2.74-2.79
(m, 2H), 3.99 (t, J = 7.8 Hz, 1H), 4.95-5.05 (m, 2H), 5.63-5.73
(m, 1H), 6.94-7.00 (m, 4H), 7.13-7.18 (m, 4H).
This work was partially supported by a Grant-in-Aid for
Scientific Research. The authors thank Dr. Keiko Kuwata of
Kyoto University for MS analyses.
4,4-Bis(4-chlorophenyl)-1-butene (3l):6p 44% yield from 1l
and allyltrimethylsilane. 1H NMR (400 MHz, CDCl3): ¤ 2.70-2.74
(m, 2H), 3.92 (t, J = 7.6 Hz, 1H), 4.90-5.00 (m, 2H), 5.56-5.66
(m, 1H), 7.04-7.07 (m, 4H), 7.16-7.20 (m, 4H).
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