Single-step synthesis of pentaaryl-monohydro[60]fullerenes through fivefold addition of organocopper reagent to C60

Article abstract of DOI:10.1016/S0022-328X(99)00660-9

The reaction of an organocopper reagent (ArMgBr/CuBr·SMe₂) with C₆₀ was optimized for the fivefold addition forming a novel Cp-type ligand precursor 1,4,11,15,30-pentaaryl-2-hydro[60]fullerene (C₆₀Ar₅H, 1), where Ar stands for Ph, 4-CF₃C₆H₄, 4-MeOC₆H₄, 4-ClC₆H₄, 4-BuC₆H₄, 4-PhC₆H₄, and 1-naphthyl groups. Under the optimized conditions, a large quantity (8.90 g) of C₆₀Ph₅H has been synthesized in a single operation.

Full text of DOI:10.1016/S0022-328X(99)00660-9

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 599 (2000) 32–36
Single-step synthesis of pentaaryl-monohydro[60]fullerenes through
fivefold addition of organocopper reagent to C60
Masaya Sawamura *, Hitoshi Iikura, Takayuki Ohama, Ulrich E. Hackler,
Eiichi Nakamura 1
Department of Chemistry, The Uni6ersity of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Received 9 September 1999; received in revised form 12 October 1999
Abstract
The reaction of an organocopper reagent (ArMgBr/CuBr·SMe2) with C60 was optimized for the fivefold addition forming a
novel Cp-type ligand precursor 1,4,11,15,30-pentaaryl-2-hydro[60]fullerene (C60Ar5H, 1), where Ar stands for Ph, 4-CF3C6H4,
4-MeOC6H4, 4-ClC6H4, 4-BuC6H4, 4-PhC6H4, and 1-naphthyl groups. Under the optimized conditions, a large quantity (8.90 g)
of C60Ph5H has been synthesized in a single operation. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Fullerene; Organocopper reagent; Multiple addition; Cyclopentadiene; Cp ligand
as revealed by ab initio MO calculations and electro-
chemical measurements [3]. Upon treatment with a
metal alkoxide (LiOtBu, KOtBu, TlOEt, CuOEt·PEt3),
the cyclopentadiene 1 has been converted into the cor-
responding metal cyclopentadienides MLn(h5-C60Ph5)
(2, MLn=Li, K, Tl, Cu·PEt3) [1a]. These compounds
are the first fullerene–metal complexes involving h5-
fullerene–metal bonding.
In the present paper, we report the full details of the
synthesis of the new ligand molecules C60Ar5H (1a–g)
through the fivefold organocopper addition as applied
for various aryl groups of different electronic and steric
properties. The method optimized for a large-scale
preparation gave 1a of 98% HPLC purity in a quantity
as large as 8.90 g in a single operation.
1. Introduction
The three-dimensional reactive polyene system of
fullerene will serve as a platform for nano-scale molecu-
lar architectures, if multiple-site functionalization is
achieved with high regio- and stereoselectivities. To this
goal, we have developed and reported previously, the
fivefold addition of an organocopper reagent to C60
(Scheme 1 1a) [1]. Thus, an organocopper reagent
which was prepared in situ from PhMgBr and
CuBr·SMe2 adds regioselectively to the [5]radialene par-
tial structure in C60 and gives, after aqueous work up,
1,4,11,15,30-pentaphenyl-2-hydro[60]fullerene (C60Ph5-
H, 1a) [2] in a quantitative yield.
Salient features of this new fullerene derivative reside
not only in its concave crown-like structure created by
the five aromatic rings, but also in the properties as a
cyclopentadiene, which is embedded in the spherical
carbon network of C60. The cyclopentadiene moiety is
electronically connected with the bottom 50 p-electron
polyene system through endohedral homoconjugation
* Corresponding author. Fax: +81-3-3812-8099.
E-mail addresses: sawamura@chem.s.u-tokyo.ac.jp (M. Sawa-
mura), nakamura@chem.s.u-tokyo.ac.jp (E. Nakamura)
1Also corresponding author.
Scheme 1. Synthesis of pentahaptofullerene–metal complexes through
fivefold organocopper addition.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 9 9 ) 0 0 6 6 0 - 9

M. Sawamura et al. / Journal of Organometallic Chemistry 599 (2000) 32–36
33
Scheme 2. Fivefold addition of organocopper reagent to C60
.
fold addition proceeds smoothly and very cleanly when
the ratio is 1:1. As shown in Table 1, entry 4, the
reaction with 16 equivalents each of PhMgBr and
CuBr·SMe2 led to completion within 40 h and formed
1a quantitatively (\99% by HPLC). The reaction of
330 mg (0.458 mmol) of C60 afforded 496 mg (94%) of
1a as an orange amorphous solid. The reaction is so
clean that the product obtained after aqueous work up,
followed by removal of biphenyl through hexane wash-
ing and drying in vacuo, gave an analytically pure
product.
The reaction conditions thus optimized (method A)
could successfully be applied to the synthesis of various
pentaaryl-monohydro[60]fullerenes (1b–d) bearing aro-
matic groups with different electronic and steric proper-
ties. Results are summarized in Table 2. Substitution at
the para position of PhMgBr with an electron-with-
drawing CF3 group caused significant acceleration of
the reaction (Table 2, entry 1). The reaction was again
very clean, affording the pentaarylation product C60(4-
CF4ꢀC6H4)5H (1b) in a quantitative yield. On the other
hand, the substitution with the electron-donating MeO
2. Results and discussion
In contrast to the monoaddition reactions of the
Grignard and organolithium reagents to C60 [4], an
organocopper reagent prepared in situ from PhMgBr
and CuBr·SMe2 exhibited unusual reactivity, giving a
fivefold addition product C60Ph5H (1a) (Scheme 2). The
efficiency of the fivefold addition and selectivity of the
reaction depend on the amount and ratio of the Grig-
nard reagent and the copper(I) salt. Results of the
HPLC analysis (Buckyprep column (Nacalai Tesque
Co., 4.6×250 mm), 7:3 toluene–i-PrOH, 350 nm de-
tection) of the organocopper reaction are summarized
in Table 1. Reaction of C60 with eight equivalents of
PhMgBr and one equivalent of CuBr·SMe2 (1:8:1 C60–
PhMgBr–CuBr·SMe2) in toluene–THF at room tem-
perature (r.t.) for 10 min formed 1a in 2% HPLC yield
along with a trace of monoadduct C60PhH (B1%) and
several unidentified products (18%), leaving 80% of C60
unreacted (Table 1, entry 1). Standing the reaction
mixture for 1 h resulted in the disappearance of the
peak of 1a and led to the formation of a complex
mixture (data not shown). The selectivity for the five-
fold addition could be improved by increasing the
amount of CuBr·SMe2 rather than that of the Grignard
reagent. As shown in Table 1, entry 2, the reaction with
six equivalents of PhMgBr and three equivalents of
CuBr·SMe2 for 18 h gave 1a in 25% yield with 28% C60
conversion. The product distribution did not change
when the reaction stood at r.t. for a prolonged period.
The conversion of C60 was increased to 97% by using 20
equivalents of PhMgBr and ten equivalents of
CuBr·SMe2, giving 1a in 88% HPLC yield (Table 1,
entry 3). Next, we re-examined the ratio of the Grig-
nard reagent and CuBr·SMe2, and found that the five-
Table 1
Reaction of PhMgBr–CuBr·SMe2 with C60 (optimization of reaction
conditions) a
Run Equivalent to C60
Time b
HPLC intensity
ratio (%)
PhMgBr
CuBr·SMe2
C60
1a
1
2
3
4
8
6
20
16
1
3
10
16
10 min
18 h
144 h
44 h
80
72
3
2
25
88
0
100
a Reaction was carried out in toluene–THF.
b Reaction time at r.t.

34
M. Sawamura et al. / Journal of Organometallic Chemistry 599 (2000) 32–36
Table 2
98% HPLC purity in 95% chemical yield in a single
operation (Table 3, entry 2).
Fivefold organocopper addition to C60 with various aryl Grignard
reagents (method A) a
b
Run ArMgBr
Time (h) HPLC intensity ratio (%)
3. Conclusions
C60
1
The Cp-type ligand precursors 1 that can be used for
the synthesis of pentahaptofullerene–metal complexes 2
were synthesized in one step by the fivefold addition of
the organocopper reagent (1:1 ArMgBr–CuBr·SMe2) to
C60. This synthetic method is versatile and very effi-
cient, providing the compounds with various aryl
groups in high yields and in large quantities. Studies to
extend this method to the synthesis of alkyl, alkenyl,
and alkynyl derivatives are in progress in our
laboratory.
1
2
3
4-CF3C6H4MgBr 18
4-MeOC6H4MgBr 72
(1-Naph)MgBr 72
0
3
0
100 (1b)
87 (1c)
91 (1d)
a Reaction was carried out in toluene–THF. Ratio=1:1 ArMgBr–
CuBr·SMe2.
b Reaction time at r.t.
group retarded the reaction. In this case, the reaction
stopped at 97% conversion of C60 and gave C60(4-
MeOC6H4)H (1c) in 87% HPLC yield along with small
amounts of unidentified side products (10%). The reac-
tion of an organocopper reagent from (1-naph-
thyl)magnesium bromide, which is sterically more
demanding than that from PhMgBr, led to completion
within 72 h to give the fivefold addition product C60(1-
Naph)5H (1d) of 91% HPLC purity.
4. Experimental
4.1. Synthesis of C60Ph5H (1a)
4.1.1. Method A
By using 1,2-dichlorobenzene as solvent instead of
toluene, the concentration of substrates could be in-
creased about three times, and hence the reaction time
of the fivefold addition was dramatically reduced
(method B). With 15 equivalents each of the Grignard
reagent and CuBr·SMe2, the reaction was completed
within 2 h in all cases examined, which include
the reactions with PhMgBr, 4-CF3C6H4MgBr, 4-
ClC6H4MgBr, 4-MeOC6H4MgBr, 4-BuC6H4MgBr, 4-
PhC6H4MgBr. Results of the preparative experiments
are summarized in Table 3. The low yield observed for
C60(4-BuC6H4)5H (1e) (Table 3, entry 6) is due to the
loss during the hexane precipitation/washing of the
product because of the high solubility of 1e in hexane.
The use of 1,2-dichlorobenzene is also beneficial for a
large-scale preparation. Under essentially the same con-
ditions, we could obtain 8.90 g of C60Ph5H (1a) with
A solution of 330 mg (0.458 mmol) of C60 in 150 ml
of toluene was cooled to −78°C. The solution was
transferred through a cannula over 15 min to a magnet-
ically stirred mixture of an organocopper reagent pre-
pared from PhMgBr (0.94 M in THF, 7.81 ml, 7.33
mmol) and CuBr·SMe2 (1.51 g, 7.35 mmol) in 7.8 ml of
THF at −78°C. The resulting dark green suspension
was gradually warmed to −20°C over 3 h. At this
point, the purple color of the supernatant disappeared
completely (quenching an aliquot of the colorless super-
natant with NH4Cl solution resulted in complete recov-
ery of C60, suggesting that the solid materials are
C60ꢀcopper complexes). The mixture was then allowed
to warm to 25°C. While stirring was continued at this
temperature, the progress of the reaction was moni-
tored by HPLC. After 2 h stirring at r.t., the color of
the solid became bright wine red, the supernatant being
Table 3
Fivefold organocopper addition to C60 with various aryl Grignard reagents (method B) a
Run
ArMgBr (equivalent to C60
)
C60 (g)
Time b (h)
Yield of 1 c (%)
Purity of 1 d (%)
1
2
3
4
5
6
7
PhMgBr (15)
PhMgBr (25)
1.00
6.07
0.20
0.10
0.20
0.20
0.20
2
24
2
2
2
99.5 (1a)
95 (1a)
99 (1b)
99 (1c)
99.6 (1d)
41 (1e)
\99
98
\99
96
95
95
4-CF3C6H4MgBr (12) e
4-MeOC6H4MgBr (16)
4-ClC6H4MgBr (15)
4-BuC6H4MgBr (15)
4-PhC6H4MgBr (15)
2
2
99.8 (1f)
\99
a Reaction was carried out in 1,2-dichlorobenzene–THF. Ratio=1:1 ArMgBr–CuBr·SMe2, unless otherwise noted.
b Reaction time at r.t.
c Isolated yield of 1 with a purity indicated in the next column.
d Intensity ratio (350 nm) in the HPLC analysis of the isolated product.
e Ratio=1:12:15 C60–ArMgBr–CuBr·SMe2.

M. Sawamura et al. / Journal of Organometallic Chemistry 599 (2000) 32–36
35
red in color. The reaction was completed in 2 days and
was quenched with NH4Cl solution. The mixture was
separated into two phases, and the aqueous phase was
extracted with toluene three times. The combined or-
ganic phase was washed with brine, dried by passing
through a pad of Na2SO4, and evaporated. The remain-
ing powder was washed with hexane (×4) to remove
biphenyl (100% of theory, 776 mg), and dried in vacuo
to afford 496 mg (94%) of C60Ph5H: 99% purity on
of C60 and a stirring bar. The flask was purged with
nitrogen. To this flask 420 ml of 1,2-dichlorobenzene
was added and stirred. The resulting deep purple solu-
tion was degassed in vacuo.
In a 2 l three-neck round-bottom flask equipped with
a three-way stop cock, a septum rubber and a stop cock,
was placed 42.9 g (208.6 mmol) of CuBr·SMe2 and a
stirring bar. At r.t., 240 ml of THF was added to
CuBr·SMe2. The mixture was cooled to −78°C and
treated with 214 ml (207.6 mmol) of a 0.97 M solution
of PhMgBr in THF. The resulting yellow suspension
was stirred at −78°C for 20 min. Then the solution of
C60 in 1,2-dichlorobenzene was transferred through a
cannula over a period of 25 min. After stirring at
−78°C for 15 min, the cooling bath was replaced with
a water bath (26°C). While stirring was continued at r.t.,
the progress of reaction was monitored by HPLC. The
HPLC analysis indicated that the consumption of C60
was stopped within 24 h at 98% conversion. At r.t., 800
ml of NH4Cl (sat. aq.) was added to the mixture and
stirred for several minutes. The mixture was extracted
three times with toluene. The combined extracts were
dried over Na2SO4, and passed through a short column
of silica gel. The column was washed with toluene.
Toluene and other volatile materials were removed by a
rotary evaporator to leave a red 1,2-dichlorobenzene
solution containing 1a and biphenyl. Most of 1,2-
dichlorobenzene was removed under vacuum to leave
orange amorphous solid. The solid was washed several
times with hexane to give 8.90 g (95%) of C60Ph5H (1a).
The HPLC analysis showed 98% intensity for 1a and 2%
for C60. The 1H-NMR spectrum indicated the content of
1,2-dichlorobenzene is less than 1%.
1
HPLC analysis; H-NMR (400 MHz, CDCl3) [2] l 7.79
(m, 4H), 7.59 (m, 4H), 7.42–7.14 (m, 17H), 5.30 (s, 1H);
13C-NMR (100 MHz, CDCl3–CS2) [2] l 155.59 (2C),
151.81 (2C), 151.66 (2C), 150.82 (2C), 148.36 (2C),
148.32 (2C), 148.26 (2C), 147.98 (2C), 147.84 (2C),
147.63 (2C+1C), 147.34 (2C), 147.19 (2C), 146.76 (2C),
146.67 (2C), 146.48 (1C), 145.68 (2C), 145.36 (2C),
145.18 (2C), 144.89 (2C+1C), 144.09 (2C), 144.02 (2C),
143.94 (4C), 143.86 (2C), 143.80 (2C), 143.23 (2C),
142.89 (2C), 138.95 (2C), 138.80 (2C), 128.58 (4C),
128.51 (2C), 128.25 (4C), 127.79 (4C), 127.59 (4C),
127.41 (2C), 127.29 (2C), 127.14 (2C), 126.86 (1C), 62.76
(2C), 60.44 (2C), 58.44 (1C), 58.34 (1C); UV–vis (1.9×
10−5 M in CH2Cl2) 258 (m 95 000), 273 (m 92 000), 350
(m 26 000), 390 (m 13 000), 442 (m 4900), 470 (m 4200) nm
(M−1 cm−1); FAB MS m/z 1106 [M+], 720 [C60]; Anal.
Calc. for C90H26·(C6H5CH3)0.5: C, 97.38; H, 2.62.
Found: C, 7.04; H 2.87%. The 13C-NMR data agree
almost exactly with those in Ref. [2] (measured in CS2,
CDCl3 for lock signal) except in a region around 144
ppm, where, in our own measurement (in CDCl3–CS2
mixture), there appears to be a substantial shift of the
signal at 143.77 ppm ([2]) causing coincidence with the
signal at 143.94 ppm.
4.1.2. Method B (1 g scale)
4.2. Synthesis of C60(4-CF3C6H4)5H (1b)
At −78°C, 21 ml of 1.0 M solution of PhMgBr in
THF (21.0 mmol) was added to a suspension of 4.30 g
(20.9 mmol) of CuBr·SMe2 in 50 ml of THF. The
mixture was stirred for 5 min. A solution of 1.00 g (1.40
mmol) of C60 in 100 ml of 1,2-Cl2C6H4 was added over
5 min. After completion of the addition, the mixture was
warmed to 25°C with a water bath and was stirred for
2 h. The reaction was quenched by adding 2 ml NH4Cl
(aq.). After dilution with 100 ml of toluene, the mixture
was dried over Na2SO4, and filtered through a pad of
silica gel. Volatile materials were removed under re-
duced pressure on a rotary evaporator, and then most of
1,2-Cl2ꢀC6H4 was removed under vacuum to leave a
thick solution of 1a in 1,2-Cl2ꢀC6H4. Upon addition of
hexane, an amorphous orange solid was precipitated.
The precipitates were collected by suction, washed sev-
eral times with hexane, and dried in vacuo to give 1.53
g (99.5% yield, \99% HPLC purity) of 1a.
Prepared from a 1.07 M solution of 4-CF3C6H4MgBr
in THF by both methods A and B: 1H-NMR (400 MHz,
CDCl3) l 7.87–7.85 (m, 5H), 7.62–7.60 (m, 10H),
7.44–7.42 (m, 5H), 5.19 (s, 1H); 13C-NMR (100 MHz,
CDCl3–CS2) l 154.69, 151.70, 150.64, 149.69, 149.11,
148.57, 148.53, 148.32, 148.04 (overlapping two signals),
147.90, 147.87, 147.77, 147.40, 146.72, 146.63, 146.44,
146.20, 146.11, 144.70, 144.60 (overlapping two signals),
144.30, 144.27, 144.13, 144.08, 144.03, 143.97, 143.41,
142.64, 142.37, 142.18, 125.7–125.5 (m, overlapping two
quartet, 6C), 125.39 (q, JCꢀF=3.72 Hz, 4C), 62.55,
60.09, 58.14, 57.97. Six quartet signals corresponding to
CF3 and CF3ꢀC carbons were not detected because of
their low intensities; APCI MS (LC MS, 7:3 toluene–i-
PrOH) 1446 [M+].
4.3. Synthesis of C60(4-MeOC6H4)5H (1c)
4.1.3. Method B (6 g scale)
Prepared from
a
0.92
M
solution of 4-
In a 1 l two-neck flask was placed 6.07 g (8.43 mmol)
MeOC6H4MgBr in THF by both methods A and B:

36
M. Sawamura et al. / Journal of Organometallic Chemistry 599 (2000) 32–36
1H-NMR (400 MHz, CDCl3) l 7.57 (d, J=8.79 Hz,
4H), 7.36 (d, J=8.79 Hz, 4H), 7.15 (d, J=8.79 Hz,
4H), 6.78 (d, J=8.79 Hz, 2H), 6.62 (d, J=8.79 Hz,
4H), 6.57 (d, J=8.79 Hz, 2H); 13C-NMR measurement
was unsuccessful because of the low solubility of 1c in
common NMR solvents.
4.6. Synthesis of C60(4-BuC6H4)5H (1f)
Prepared from a 1.28 M solution of 4-BuC6H4MgBr
1
in THF by method B: H-NMR (270 MHz, CDCl3) l
7.65 (d, J=8.1 Hz, 4H), 7.47 (d, J=7.8 Hz, 4H), 7.30
(d, J=8.4 Hz, 2H), 7.11 (d, J=7.8 Hz, 4H), 6.97 (d,
J=8.1 Hz, 4H), 6.90 (d, J=8.4 Hz, 2H), 5.22 (s, 1H),
2.8–2.5 (m, 10H), 1.8–1.4 (m, 10H), 1.4–1.2 (m, 10H),
1.0–0.8 (m, 15H); 13C-NMR (100 MHz, CDCl3) l
156.11, 152.41, 152.28, 151.70, 148.49, 148.45, 148.44,
148.16, 148.02, 147.85, 147.51, 146.98, 146.88, 146.68,
146.13, 145.86, 145.62, 145.33, 144.41, 144.14, 144.04,
143.92, 143.84, 143.74, 143.01, 142.92, 142.04, 141.78,
141.55, 137.06, 137.01, 128.91, 128.77, 128.58, 128.53,
128.10, 127.95, 127.86, 127.56, 63.03, 60.81, 58.77,
58.68, 35.28, 35.22, 35.19, 33.61, 33.50, 22.39, 22.24,
22.18, 21.56, 14.13, 14.11, 14.05.
4.4. Synthesis of C60(1-naphthyl)5H (1d)
Prepared from a 0.70 M solution of 1-naphthylmag-
1
nesium bromide in THF by method A: H-NMR (400
MHz, CDCl3) l 9.57 (d, J=8.30 Hz, 2H), 9.19 (d,
J=8.78 Hz, 2H), 8.68 (d, J=8.30 Hz, 1H), 8.35 (d,
J=7.33 Hz, 2H), 8.28 (d, J=6.84 Hz, 2H), 7.90 (d,
J=7.82 Hz, 2H), 7.76 (d, J=7.81 Hz, 2H), 7.66–7.19
(m, 17H), 7.09 (m, 2H), 6.96 (m, 1H), 6.63 (m, 1H),
5.98 (s, 1H), 5.16 (m, 1H); 13C-NMR (100 MHz,
CDCl3–CS2) l 157.80, 154.52, 153.86, 153.45, 149.16,
148.96, 148.83, 148.77, 148.57, 148.55, 148.41, 148.16,
147.97, 147.66, 147.60, 147.57, 146.32, 145.98, 145.83,
145.75, 145.00, 144.49 (overlapping, two peaks), 143.62,
143.44, 143.39, 142.03, 138.67, 135.15, 134.70, 134.56,
133.72, 133.32, 132.47, 132.31, 130.53, 130.27, 129.81,
129.68, 129.62, 129.60, 129.50, 129.18, 128.76, 128.57,
126.51, 126.49, 126.33, 126.25, 125.92, 125.63, 125.19
(overlapping, two peaks), 125.07, 124.97, 124.68,
124.53, 124.00, 63.79, 62.93, 60.04, 59.96.
4.7. Synthesis of C60(4-PhC6H4)5H (1g)
Prepared from a 1.25 M solution of 4-PhC6H4MgBr
1
in THF by method B: H-NMR (400 MHz, CDCl3) l
7.91 (d, J=8.4 Hz, 4H), 7.75 (d, J=8.4 Hz, 4H),
7.7–7.3 (m, 37H), 5.45 (s, 1H); 13C-NMR measurement
was unsuccessful because of low solubility of 1g in
CDCl3.
References
4.5. Synthesis of C60(4-ClC6H4)5H (1e)
[1] (a) M. Sawamura, H. Iikura, E. Nakamura, J. Am. Chem. Soc.
118 (1996) 12850. (b) M. Sawamura, H. Iikura, A. Hirai, E.
Nakamura, J. Am. Chem. Soc. 120 (1998) 8285.
[2] A.G. Avent, P.R. Birkett, J.D. Crane, A.D. Darwish, G.J. Lang-
ley, H.W. Kroto, R. Taylor, D.R.M. Walton, J. Chem. Soc.
Chem. Commun. (1994) 1463.
[3] H. Iikura, S. Mori, M. Sawamura, E. Nakamura, J. Org. Chem.
62 (1997) 7912.
[4] (a) A. Hirsch, T. Gro¨sser, A. Skiebe, A. Soi, Chem. Ber. 126
(1993) 1061. (b) H. Nagashima, H. Terasaki, E. Kimura, K.
Nakajima, K. Itoh, J. Org. Chem. 59 (1994) 1246.
Prepared from a 1.25 M Et2O solution of 4-
ClC6H4MgBr by method B: 1H-NMR (400 MHz,
CDCl3) l 7.70 (d, J=8.4 Hz, 4H), 7.50 (d, J=8.4 Hz,
4H), 7.36 (d, J=8.4 Hz, 4H), 7.27 (d, J=8.4 Hz, 2H),
7.22 (d, J=8.4 Hz, 4H), 7.18 (d, J=8.4 Hz, 2H), 5.20
(s, 1H); 13C-NMR measurement was unsuccessful be-
cause of low solubility of 1e in CDCl3.
.