Samarium reagent-promoted formation of benzoins from diarylmethanones and DMF via a carbene rearrangement reaction

Article abstract of DOI:10.1016/j.tet.2004.03.093

Prompted by samarium metal in DMF with TMSCl or iodine as an activator, or by SmI₂/THF system, diarylmethanones react readily with DMF to afford benzoins in moderate to good yields via rearrangement of aryl groups. As for asymmetric diarylmethanones, products resulting from the migration of either aryl group were obtained, where the migration of aryl groups shows certain priority.

Full text of DOI:10.1016/j.tet.2004.03.093

Tetrahedron 60 (2004) 4867–4873
Samarium reagent-promoted formation of benzoins
from diarylmethanones and DMF via a carbene
rearrangement reaction
Yongjun Liu,a Xiaoliang Xua and Yongmin Zhanga,b
,
*
aDepartment of Chemistry, Zhejiang University (Campus Xixi), Hangzhou 310028, People’s Republic of China
bState Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, People’s Republic of China
Received 11 December 2003; revised 26 February 2004; accepted 30 March 2004
Abstract—Prompted by samarium metal in DMF with TMSCl or iodine as an activator, or by SmI2/THF system, diarylmethanones react
readily with DMF to afford benzoins in moderate to good yields via rearrangement of aryl groups. As for asymmetric diarylmethanones,
products resulting from the migration of either aryl group were obtained, where the migration of aryl groups shows certain priority.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
readily forms ketyl, which has considerable stability and
constitutes the important intermediate in cross-coupling
reactions with ketones, aldehydes, imines, aroyl chlorides,
conjugated carbon–carbon double bonds, and so on.1
Since the pioneering studies of Kagan and his co-workers
demonstrated the particular effectiveness of samarium
diiodide (SmI2) as a powerful one-electron transfer
reductant, the utilization of SmI2 in synthetic organic
synthesis has been widely documented.1 Although
samarium diiodide is a very useful reducing reagent, its
application in organic synthesis is, to some extent, limited.
Its storage is difficult due to its sensitivity to air oxidation.
Besides, Sm2þ can only donate one electron in the reaction
and the lack of atom economy seriously restricts its large
scale application. Therefore, the direct use of metallic
samarium as a reducing agent in organic transformations has
attracted the attention of many organic chemists.2 Usually,
reactions promoted directly by samarium metal are carried
out in THF,3 and metallic samarium has to be activated by
other reagents such as iodine, hydrochloric acid, alkyl
halides, TMSCl, etc.1,3,4 so as to ensure that the reactions
proceed smoothly. We recently found that metallic
samarium exhibits some interesting properties in organic
synthesis when N,N-dimethylformamide (DMF) is used as a
solvent instead of THF.5
2. Results and discussion
However, when diphenylmethanone was treated with
samarium metal activated by TMSCl in DMF, surprisingly,
benzoin was obtained in excellent yield (Scheme 1).
Scheme 1.
The unexpected formation of benzoin indicates that the
additional carbonyl group comes from dimethylformamide,
and the dimethylamino group acts as a leaving group in this
reaction. Despite the fact that the carbonyl groups of amides
are unreactive towards many carbon nucleophiles and are
consequently employed as solvents in carbon–carbon bond-
formation reactions,8 DMF is well known for being a good
formylation reagent (Vilsmeier–Haack reaction).9 Besides,
such necleophiles as Grignard reagents,10a organolithium10a,b
and the radical anions10c resulting from the reduction by
sodium in THF can attack the carbonyl group in DMF to
afford the corresponding aldehydes. In the reactions
mentioned above, the formoyl group in DMF was
The diarylmethanone dianion is a known species6 whose
reactions with carbonyl compounds or benzonitrile have
long been observed.7 Reduced by SmI2, diarylmethanone
Keywords: Samarium; DMF; Diarylmethanone; Rearrangement reaction;
Benzoin; Benzil.
*
Corresponding author. Tel.: þ86-571-5178611; fax: þ86-571-8807077;
e-mail address: yminzhang@mail.hz.zj.cn
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.03.093

4868
Y. Liu et al. / Tetrahedron 60 (2004) 4867–4873
Scheme 2.
introduced into the products, with dimethylamino anion
acting as a leaving group.
that bis(p-dimethylaminophenyl)-methanone (1d) did not
undergo the reaction under the same conditions. The amino
group might have some effects on TMSCl and thus bear an
electron-withdrawing character, which made it difficult for
the reaction to occur, as in the case of bis(p-chlorophenyl)-
methanone (1e). As for asymmetric diarylmethanones, two
kinds of benzoins could be obtained, with the carbonyl
groups adjacent to the electron-richer aryl groups being
predominant. This may indicate that the reaction followed a
certain rule in the rearrangement.
To have some idea about the mechanism of such a reaction,
we carried out an extensive literature survey and were
fortunate to find some clues to this reaction in the electron
spin resonance study of the radicals obtained from
acetophenone and benzaldehyde.11 At high reduction
potentials and by an irreversible electrode process, the
conversion of acetophenone to 1-phenyl-propane-1,2-semi-
dione in DMF was proposed to undergo a carbene
rearrangement.11b
It is worth noting that besides the 40-chlorobenzoin (3h),
benzoin (2a) was also obtained (entry 8). The formation of
2a obviously resulted from a dechlorination process
under the reaction conditions accompanying the rearrange-
ment. As for phenyl p-bromophenyl methanone, the
debromination reaction proceeded to such an extent that
benzoin (2a) was isolated as the only product. Attempt was
also made to investigate whether acetophenone and
benzaldehyde could undergo such a reaction, but the result
was negative.
2.1. Sm/TMSCl-promoted formation of benzoin from
diarylmethanone in DMF
To have an in-depth understanding of the reaction, a series
of diarylketones were subjected to the same conditions and
the desired benzoins were formed smoothly. In some cases,
benzils were also obtained as unexpected byproducts
(Scheme 2).
The results of the reactions are shown in Table 1.
2.2. Sm/I2-promoted formation of benzoin from
diarylmethanone in DMF
The reaction of diarylketones with electron-donating group
attached to the aromatic rings proceeded efficiently. In
contrast, diarylketones with electron-withdrawing group
require a relatively harsh reaction conditions and gave lower
total yields. As can be seen, bis(p-methylphenyl)-
methanone (1b) and0 bis(p-methoxyphenyl)-methanone
(1c) produced 4,4 -dimethylbenzoin and anisoin,
respectively (entries 2 and 3) in good yields, while bis(p-
chlorophenyl)-methanone (1e) failed to afford the corre-
sponding types of products 2 and 3. It was surprising to find
Considering that TMSCl is an acidic activator, we explored
neutral activator iodine in our further investigations. To our
delight, better results were obtained in the presence of I2, as
shown in Table 2.
With iodine as an activator, the reaction proceeded more
easily in milder reaction conditions and produced higher
total yields than that activated by TMSCl, except that
substrate bis-(p-chlorophenyl)-methanone (1e) still failed to
Table 1. Reactions of diarylmethanones with DMF promoted by Sm/TMSCl in DMF
Entry
R1, R2 in substrate 1
Temperature (8C)
Time (h)
Total yield of 2, 3 (%)a
Ratiob of 2/3
Yield of 4 (%)
1
2
3
4
5
6
7
8
9
H, H (1a)
90
80
80
120
120
90
80
120
120
10
6
4
36
12
8
5
24
24
91 (2a)
74 (2b)
53 (2c)
—
0 (4a)
18 (4b)
35 (4c)
—
4-CH3, 4-CH3 (1b)
4-CH3O, 4-CH3O (1c)
4-(CH3)2N, 4-(CH3)2N (1d)
4-Cl, 4-Cl (1e)
4-CH3, H (1f)
4-Ph, H (1g)
—
—
77 (2f, 3f)
47c (2g, 3g)
52d (2a, 3h)
53e (2a)
68/32
19/81
0/100
14 (4f)
16 (4g)
0
4-Cl, H (1h)
4-Br, H (1i)
0
a
Products 2 and 3 were inseparable and the overall yields were given.
The ratio was determined by HPLC and 1H NMR.
A considerable amount of reductive product biphenyl-4-yl-phenyl-methanol was detected.
Dechlorination reaction affording 26% of 2a occurred simultaneously in the formation of the corresponding benzoin.
Exclusive debromination product 2a was formed.
b
c
d
e

Y. Liu et al. / Tetrahedron 60 (2004) 4867–4873
Table 2. Reaction of diarylmethanones with DMF promoted by Sm/I2 in DMF
4869
Entry
R1, R2 in substrate 1
Temperature (8C)
Time (h)
Total yield of 2, 3 (%)
Ratio of 2/3
Yield of 4 (%)
1
2
3
4
5
6
7
8
9
H, H (1a)
80
70
50
80
120
70
50
2
1
1
1
5
1
1
5
5
90 (2a)12b
79 (2b)12b
78 (2c)12b
63 (2d)12d
—
82 (2f, 3f)12c
87 (2g, 3g)12e
41 (2h, 3h)12c
58 (2a)
0
4-CH3, 4-CH3 (1b)
4-CH3O, 4-CH3O (1c)
4-(CH3)2N, 4-(CH3)2N (1d)
4-Cl, 4-Cl (1e)
4-CH3, H (1f)
4-Ph, H (1g)
15 (4b)12f
16 (4c)12f
21 (4d)12f
—
68/32
81/19
0/100
11 (4f)12g
9 (4g)12h
13 (4h)12f
0
4-Cl, H (1h)
4-Br, H (1i)
100
100
give encouraging results (entry 5). Bis-(p-dimethylamino-
phenyl)-methanone, to our expectations, underwent the
same kind of reactions under similar conditions and afforded
the corresponding benzoin and benzil in high total yield
(entry 4). The benzoins with the carbonyl groups adjacent to
the electron-richer aryl groups still predominated in the
products when asymmetric diarylmethanones were used as
substrates under the Sm/DMF/I2 conditions. An exception
was that biphenyl-4-yl-phenyl-methanone (1g) produced the
benzoin with the carbonyl group adjacent to the biphenyl
group as the major product (entry 7). However, the
relationship between the reaction chemoselectivity and
activator remains unclear.
of benzoin. This result may indicate that the additional
carbonyl group came from DMF.
Therefore, we made further investigations to find out
whether or not SmI2 can promote the coupling rearrange-
ment reaction of diarylmethanone and DMF in THF. To our
expectations, the reaction occurred smoothly and completed
in a very short time, despite a relatively low total yield and
more byproduct benzil (Scheme 3, Table 3). The chemo-
selectivity of rearrangement reaction is generally similar to
that in the Sm/DMF/I2 system.
2.4. Possible mechanism
2.3. SmI2-promoted formation of benzoin from
diarylmethanone and DMF in THF
The formation of benzils could be explained as a result of
the auto-oxidation of benzoins. The presence of reports
claiming that some metal salts such as copper (I)13a and Ce
(IV)13b could easily catalyze the autoxidation of benzoins
into the corresponding benzils made us deduce that the
presence of samarium salts might have accelerated the
formation of benzils from benzoins during the treatment
process. Further investigations showed that the benzil
We made the attempt and found that without activator
(TMSCl or I2) the reaction could not occur at all, and further
attempts to expand the reaction to other metal such as zinc
failed. We also tried other solvents instead of DMF, such as
THF, DMSO and toluene, but did not detect any formation
Scheme 3.
Table 3. Reaction of diaryl-methanones with DMF promoted by SmI2 in THF
Entry
R1, R2 in substrate 1
Total yield of 2, 3 (%)
Ratio of 2/3
Yield of 4 (%)
1
2
3
4
5
6
7
8
9
H, H (1a)
42 (2a)
29 (2b)
48 (2c)
33 (2d)
0
42 (2f, 3f)
27 (2g, 3g)
0
39 (4a)12f
51 (4b)
36 (4c)
31 (4d)
0
31 (4f)
39 (4g)
0
4-CH3, 4-CH3 (1b)
4-CH3O, 4-CH3O (1c)
4-(CH3)2N, 4-(CH3)2N (1d)
4-Cl, 4-Cl (1e)
4-CH3, H (1f)
4-Ph, H (1g)
71/29
78/22
4-Cl, H (1h)
4-Br, H (1i)
0
0

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Y. Liu et al. / Tetrahedron 60 (2004) 4867–4873
Scheme 4.
could also have been obtained when benzoin was treated
under the same reaction conditions. This validates our
suggestion.
3. Experimental
3.1. General
We made the attempt and found that without activator
(TMSCl or I2) the reaction could not occur at all, and further
attempts to expand the reaction to other metal such as zinc
failed. On the other hand, the fact that without diarylmetha-
none in the reaction system, no obvious reaction between
Sm/activator and DMF was observed shows the reaction
must be initiated by ketyl resulting from diarylmethanone.
Based on our experimental results and the ESR studies on
the relevant radicals,11b a possible mechanism is suggested
(Scheme 4).
All 1H NMR spectra were measured in CDCl3 and recorded
on Brucker Avance-400 (400 MHz) spectrometer with TMS
as the internal standard. Chemical shifts are expressed in
ppm and J values are given in Hz. IR spectra were run on a
Bruck vector 22 spectrometer. EI-MS were determined with
a HP5989B mass spectrometer. Melting points are uncor-
rected. All the reactions in this paper were performed under
nitrogen atmosphere. DMF was redistilled and dried over
molecular sieve before use.
3.2. Sm/DMF/TMSCl system promoted rearrangement
reaction of diarylketones with DMF
Due to the strongly electrophilic character of carbene,14
A
undergoes a rearrangement (intramolecular insertion reac-
tion) in which the electron-richer aryl group of the two
preferably migrates to form enol intermediates (B.C),
which in turn tautomerize immediately, and are followed by
protonation to give the corresponding benzoins,
respectively.
General procedure. To a mixture of Sm powder (2 mmol)
and diarylketone (2 mmol) in freshly distilled N,N-
dimethylformamide (DMF, 10 mL) TMSCl (0.2 mL,
freshly distilled) was added at room temperature, with
magnetic stirring under a nitrogen atmosphere. The reaction
mixture was then heated to a certain temperature so as to
ensure that the reaction occurred (as indicated in Table 1).
After the completion of the reaction (monitored by TLC),
dilute hydrochloric acid (2 M, 5 mL) was added and the
resulting mixture was extracted with diethyl ether
(3£20 mL). The combined organic layer was washed with
brine, dried over anhydrous sodium sulfate, and concen-
trated under reduced pressure. The crude products were
purified with flash chromatography (silica/hexanes–ethyl
In conclusion, with TMSCl or iodine as the activator in
DMF or performed in SmI2/THF system, the reaction
between diarylketones and DMF via a rearrangement
process promoted by samarium metal can afford benzoins
and benzils in good overall yields. The complexing of DMF
with samarium ion15 may have played an important role in
enabling the reaction to occur, and studies on the exact
mechanism are currently in progress.

Y. Liu et al. / Tetrahedron 60 (2004) 4867–4873
4871
1
acetate, 9:1 v/v) to afford the corresponding benzoins and/or
benzils.
(2c). White solid; mp 111–113 8C; H NMR (400 MHz,
CDCl3) d 7.90–7.94 (m, 2H), 7.25–7.28 (m, 2H), 6.85–
6.90 (m, 4H), 5.87 (d, 1H, J¼5.2 Hz), 4.60 (d, 1H,
J¼5.2 Hz), 3.84 (s, 3H), 3.78 (s, 3H); 13C NMR d
(CDCl3): 197.3, 164.0, 159.6, 132.4, 131.9, 131.6, 129.0,
114.5, 113.9, 75.3, 55.5, 55.2; IR (KBr) 3465, 3077, 2939,
1667, 1598, 1514, 1469 cm21; mass spectrum, m/z
(relative intensity, %) 272 (0.61, Mþ), 255 (0.88,
Mþ2OH), 137 (100), 135 (86.2), 107 (17.31), 77 (80.38).
Anal. Calcd for C16H16O4: C, 70.58; H, 5.92. Found: C,
70.89; H, 5.88.
3.3. Sm/DMF/I2 system promoted rearrangement
reaction of diarylketones with DMF
General procedure. To a mixture of Sm powder (2 mmol)
and diarylketone (2 mmol) in freshly distilled N,N-
dimethylformamide (DMF, 10 mL) I2 (0.13 g, 0.5 mmol)
was added at room temperature, with magnetic stirring
under a nitrogen atmosphere. The reaction mixture was then
heated to a certain temperature so as to ensure that the
reaction occurred (as indicated in Table 2). After the
completion of the reaction (monitored by TLC), dilute
hydrochloric acid (2 M, 5 mL) was added and the resulting
mixture was extracted with diethyl ether (3£20 mL). The
combined organic layer was washed with brine, dried over
anhydrous sodium sulfate, and concentrated under reduced
pressure. The crude products were purified with flash
chromatography (silica/hexanes–ethyl acetate, 9:1 v/v) to
afford the corresponding benzoins and/or benzils.
3.4.4. 1,2-Bis-(4-dimethylamino-phenyl)-2-hydroxy-
ethanone (2d). White solid; mp 153–156 8C; 1H NMR
(400 MHz, CDCl3) d 7.85–7.88 (m, 2H), 7.20–7.22 (m,
2H), 6.66–6.68 (m, 4H), 5.80 (d, 1H, J¼6.0 Hz), 4.68 (d,
1H, J¼6.0 Hz), 2.92 (s, 6H), 3.03 (s, 6H); 13C NMR d
(CDCl3): 196.6, 154.2, 153.6, 132.2, 131.5, 128.6, 110.8,
110.6, 74.9, 40.1, 39.9; IR (KBr) 3420, 2916, 1681, 1595,
1546, 1483 cm21; mass spectrum, m/z (relative intensity, %)
298 (0.24, Mþ), 150 (2.16), 148 (100), 120 (5.51). Anal.
Calcd for C18H22N2O2: C, 72.46; H, 7.43; N, 9.39. Found:
C, 72.54; H, 7.50; N, 9.45.
3.4. SmI2/THF system promoted rearrangement
reaction of diarylketones with DMF
3.4.5. 2-Hydroxy-2-phenyl-1-p-tolyl-ethanone (2f). The
title compound was obtained as a mixture with 3f; white
solid; H NMR (400 MHz, CDCl3) d 7.83–7.85 (m, 2H),
7.14–7.35 (m, 7H), 5.94 (d, 1H, J¼6.0 Hz), 4.61 (d, 1H,
J¼6.0 Hz), 2.38 (s, 3H); IR (KBr) 3441, 3059, 2945, 1675,
1607, 1510, 1491, 1452, 1390 cm21; mass spectrum, m/z
(relative intensity, %) 227 (0.28, Mþþ1), 226 (0.72, Mþ),
209 (2.59, Mþ2OH), 119 (100), 107 (10.37), 91 (55.09), 77
(57.75). Anal. Calcd for C15H14O2: C, 79.62; H, 6.24.
Found: C, 79.48; H, 6.28.
General procedure. To a solution of SmI2 (3 mmol) in THF
(20 mL), diarylketone (1 mmol) was added at room
temperature under a nitrogen atmosphere. The deep blue
color of the solution turned red immediately, and DMF
(0.5 mL) was added. The color of resultant solution
vanished immediately, which indicated that the reaction
had completed. After being stirred for 5–10 min, dilute
hydrochloric acid (2 M, 5 mL) was added and the resulting
mixture was extracted with diethyl ether (3£20 mL). The
combined organic layer was washed with brine, dried over
anhydrous sodium sulfate, and concentrated under reduced
pressure. The crude products were purified with flash
chromatography (silica/hexanes–ethyl acetate, 9:1 v/v) to
afford the corresponding benzoins and/or benzils.
1
3.4.6. 2-Hydroxy-1-phenyl-2-p-tolyl-ethanone (3f). The
title compound was obtained as a mixture with 2f; white
1
solid; H NMR (400 MHz, CDCl3) d 7.93–7.95 (m, 2H),
7.15–7.37 (m, 7H), 5.94 (d, 1H, J¼6.0 Hz), 4.52 (d, 1H,
J¼6.0 Hz), 2.31 (s, 3H); IR (KBr) 3441, 3059, 2945, 1675,
1607, 1510, 1491, 1452, 1390 cm21; mass spectrum, m/z
(relative intensity, %) 227 (0.28, Mþþ1), 226 (0.72, Mþ),
209 (2.59, Mþ2OH), 121 (82.30), 105 (24.30), 91 (55.09),
77 (57.75). Anal. Calcd for C15H14O2: C, 79.62; H, 6.24.
Found: C, 79.48; H, 6.28.
3.4.1. 2-Hydroxy-1,2-diphenyl-ethanone (2a). White
solid, mp 134–136 8C; 1H NMR (400 MHz, CDCl3) d
7.92–7.95 (m, 2H), 7.52–7.54 (m, 1H), 7.40–7.44 (m, 2H),
7.28–7.36 (m, 5H), 5.97 (d, 1H, J¼6.0 Hz), 4.56 (d, 1H,
J¼6.0 Hz); IR (KBr) 3417, 3060, 2933, 1680, 1596, 1491,
1450 cm21; mass spectrum, m/z (relative intensity, %) 213
(1.16, Mþþ1), 212 (0.43, Mþ), 195 (13.95, Mþ2OH), 107
(61.01), 105 (100), 77 (89.62). Anal. Calcd for C14H12O2: C,
79.23; H, 5.70. Found: C, 79.48; H, 5.74.
3.4.7. 1-Biphenyl-4-yl-2-hydroxy-2-phenyl-ethanone
(2g). The title compound was obtained as a mixture with
1
3g; white solid; H NMR (400 MHz, CDCl3) d 8.01–8.03
(m, 2H), 7.29–7.65 (m, 12H), 6.00 (d, 1H, J¼6.0 Hz), 4.60
(d, 1H, J¼6.0 Hz); IR (KBr) 3422, 3031, 1678, 1603, 1560,
1487, 1450, 1407 cm21; mass spectrum, m/z (relative
intensity, %) 181 (38.10), 153 (19.85), 107 (6.91), 77
(100). Anal. Calcd for C20H16O2: C, 83.31; H, 5.59. Found:
C, 83.10; H, 5.56.
3.4.2. 2-Hydroxy-1,2-di-p-tolyl-ethanone (2b). White
1
solid, mp 86–88 8C; H NMR (400 MHz, CDCl3) d 7.83–
7.85 (m, 2H), 7.19–7.24 (m, 4H), 7.13–7.15 (m, 2H), 5.91
(d, 1H, J¼6.0 Hz), 4.55 (d, 2H, J¼6.0 Hz), 2.37 (s, 3H),
2.31 (s, 3H); 13C NMR d (CDCl3): 198.6, 144.9, 138.3,
136.4, 131.0, 129.8, 129.4, 129.3, 127.7, 75.8, 21.7, 21.2; IR
(KBr) 3473, 3038, 2921, 1676, 1607, 1513 cm21; mass
spectrum, m/z (relative intensity, %) 241 (0.36, Mþþ1), 240
(1.20, Mþ), 223 (1.79, Mþ2OH), 121 (85.90), 119 (95.45,
Mþ), 91 (100). Anal. Calcd for C16H16O2: C, 79.97; H, 6.71.
Found: C, 79.68; H, 6.73.
3.4.8. 2-Biphenyl-4-yl-2-hydroxy-1-phenyl-ethanone
(3g). The title compound was obtained as a mixture with
1
2g; white solid; H NMR (400 MHz, CDCl3) d 7.97–8.00
(m, 2H), 7.29–7.65 (m, 12H), 6.02 (d, 1H, J¼6.0 Hz), 4.59
(d, 1H, J¼6.0 Hz); IR (KBr) 3422, 3031, 1678, 1603, 1560,
1487, 1450, 1407 cm21; mass spectrum, m/z (relative
intensity, %) 183 (32.29), 153 (19.85), 105 (28.57), 77
3.4.3. 2-Hydroxy-1,2-bis-(4-methoxyphenyl)-ethanone

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Y. Liu et al. / Tetrahedron 60 (2004) 4867–4873
(100). Anal. Calcd for C20H16O2: C, 83.31; H, 5.59. Found:
C, 83.10; H, 5.56.
(400 MHz, CDCl3) d 8.02–8.09 (m, 4H), 7.75–7.77 (m,
2H), 7.65–7.70 (m, 3H), 7.49–7.57 (m, 5H); 13C NMR d
(CDCl3): 194.6, 194.2, 147.6, 139.5, 134.9, 133.0, 131.7,
130.5, 130.0, 129.1, 128.7, 127.7, 127.4, 127.3; IR (KBr)
3062, 1673, 1594, 1580, 1485, 1449 cm21; mass spectrum,
m/z (relative intensity, %) 287 (0.16, Mþþ1), 286 (0.51,
Mþ), 181 (100), 153 (22.18), 105 (22.77), 77 (33.18). Anal.
Calcd for C20H14O2: C, 83.90; H, 4.93. Found: C, 83.75; H,
4.97.
3.4.9. 2-(4-Chloro-phenyl)-2-hydroxy-1-phenyl-etha-
none (3h). White solid; mp 113–115 8C; 1H NMR
(400 MHz, CDCl3) d 7.90–7.92 (m, 2H), 7.54–7.57 (m,
1H), 7.28–7.46 (m, 6H), 5.96 (d, 2H, J¼6.0 Hz), 4.56 (d,
1H, J¼6.0 Hz); IR (KBr) 3417, 3027, 1679, 1618, 1596,
1450 cm21; mass spectrum, m/z (relative intensity, %) 248
(0.07, Mþþ2), 246 (0.20, Mþ), 229 (0.55, Mþ2OH), 141
(13.71), 105 (100), 77 (76.76). Anal. Calcd for C14H11ClO2:
C, 68.16; H, 4.50. Found: C, 68.28; H, 4.47.
3.4.16. 1-(4-Chloro-phenyl)-2-phenyl-ethane-1,2-dione
(4h). Yellow crystal (CCl4); mp 73–74 8C; 1H NMR
(400 MHz, CDCl3) d 8.04–8.16 (m, 4H), 7.52–7.60 (m,
5H); IR (KBr) 3023, 1679, 1139, 1609, 1596, 1450 cm21
;
mass spectrum, m/z (relative intensity, %) 246 (0.18,
Mþþ2), 244 (0.55, Mþ), 139 (13.65), 105 (100), 77
(66.67). Anal. Calcd for C14H9ClO2: C, 68.72; H, 3.71.
Found: C, 68.58; H, 3.77.
3.4.10. 1,2-Di-phenyl-ethane-1,2-dione (4a). Yellow crys-
1
tal (CCl4); mp 95–97 8C; H NMR (400 MHz, CDCl3) d
7.97–7.99 (4H, m), 7.64–7.69 (2H, m), 7.50–7.53 (4H, m);
IR (KBr): 3064, 1660, 1594, 1450, 1211, 719, 643 cm21
;
mass spectrum, m/z (relative intensity, %) 210 (1.77, Mþ),
105 (100), 77 (45.51). Anal. Calcd for C14H10O2: C, 79.99;
H, 4.79. Found: C, 80.10; H, 4.80.
Acknowledgements
3.4.11. 1,2-Di-p-tolyl-ethane-1,2-dione (4b). Yellow crys-
tal (CCl4); mp 101–103 8C; 1H NMR (400 MHz, CDCl3) d
7.87–7.89 (m, 4H), 7.31–7.33 (m, 4H), 2.45 (s, 6H); 13C
NMR d (CDCl3): 194.5, 146.1, 130.7, 130.0, 129.7, 21.9; IR
We are grateful to the National Natural Science Foundation
of China (Project No. 20072033) and Specialized Research
Fund for the Doctoral Program of Higher Education of
China.
(KBr) 3063, 2919, 1662, 1605, 1573, 1447, 1410 cm21
;
mass spectrum, m/z (relative intensity, %) 239 (0.37,
Mþþ1), 238 (1.84, Mþ), 119 (100), 91 (40.17). Anal.
Calcd for C16H14O2: C, 80.65; H, 5.92. Found: C, 80.48; H,
5.90.
References and notes
3.4.12. 1,2-Bis-(4-methoxyphenyl)-ethane-1,2-dione (4c).
Yellow crystal (CCl4); mp 132–134 8C; 1H NMR
(400 MHz, CDCl3) d 7.96–7.98 (m, 4H), 6.98–7.00 (m,
4H), 3.91 (s, 6H); 13C NMR d (CDCl3): 193.5, 164.9, 132.4,
126.3, 114.3, 55.6; IR (KBr) 3026, 2959, 1656, 1600, 1573,
1510, 1458 cm21; mass spectrum, m/z (relative intensity, %)
271 (0.16, Mþþ1), 270 (0.87, Mþ), 135 (100), 107 (13.77).
Anal. Calcd for C16H14O4: C, 71.10; H, 5.22. Found: C,
71.48; H, 5.30.
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(m, 4H), 3.09 (s, 12H); 13C NMR d (CDCl3): 194.0, 169.1,
121.6, 121.1, 112.8, 40.5; IR (KBr) 2916, 1644, 1595, 1546,
1483 cm21; mass spectrum, m/z (relative intensity, %) 297
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crystal (CCl4); mp 30–31 8C; 1H NMR (400 MHz, CDCl3)
d 7.97–8.00 (m, 2H), 7.87–7.90 (m, 2H), 7.64–7.67 (m,
1H), 7.50–7.54 (m, 2H), 7.30–7.34 (m, 2H), 2.45 (s, 3H);
IR (KBr) 3062, 2924, 1672, 1605, 1581, 1450 cm21; mass
spectrum, m/z (relative intensity, %) 225 (0.23, Mþþ1), 224
(0.95, Mþ), 119 (100), 105 (38.86), 91 (45.30), 77 (31.63).
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80.38; H, 5.38.
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Yellow crystal (CCl4); mp 103–105 8C; 1H NMR

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