FeCl3-catalyzed condensation of 2-naphthol and aldehydes under solvent-free reaction conditions: An efficient and green alternative for the synthesis of 14-aryl(Alkyl)-14-H-dibenzo[a, j]xanthenes

Article abstract of DOI:10.1002/cjoc.201190022

An iron-catalyzed condensation of 2-naphthol with aldehydes has been described. In the presence of a catalytic amount of iron(III) chloride (5 mol%), the condensation reaction of 2-naphthol and aldehydes underwent smoothly to generate the corresponding pr

Full text of DOI:10.1002/cjoc.201190022

FULL PAPER
FeCl3-Catalyzed Condensation of 2-Naphthol and Aldehydes
under Solvent-Free Reaction Conditions: An Efficient and
Green Alternative for the Synthesis of
14-Aryl(Alkyl)-14-H-dibenzo[a, j]xanthenes
Wang, Boa(王波)
LI, Pinhua*,a(李品华)
Wang, Lei*,a,b(王磊)
Zhang, Yichenga(张义成)
a Department of Chemistry, Huaibei Normal University, Huaibei, Anhui 235000, China
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, Shanghai 200032, China
An iron-catalyzed condensation of 2-naphthol with aldehydes has been described. In the presence of a catalytic
amount of iron(III) chloride (5 mol%), the condensation reaction of 2-naphthol and aldehydes underwent smoothly
to generate the corresponding products in good to excellent yields under base-, acid-, ligand-, additive-, and sol-
vent-free reaction conditions.
Keywords 2-naphthol, aldehydes, iron(III) chloride, solvent-free, benzoxanthenes
Introduction
tions due to their toxicity and prohibitive price. Iron is
one of the most abundant, and consequently one of the
most inexpensive and environmentally friendly metals
on the earth. Iron salts as effective, alternative and
promising transition-metal catalysts have received much
attention because of their unique properties.12 Over the
past few years, iron-catalyzed oxidation,13 hydrogena-
tion,14 hydrosilylation,15 rearrangement,16 Michael addi-
tion,17 and Mannich reaction18 have been intensively
investigated. Recently, iron-catalyzed C— S,19 C— N,20
C— O21 and C— C bond formation reactions (such as
Sonogashira, Heck, Negishi, Kumada and Suzuki reac-
tions) have been developed.22 However, it is still desir-
able to expand the application scope of iron salts in or-
ganic transformations due to their unique properties and
significant advantages for both the academic and the
industrial community. Recently, our group has reported
the wide use of iron as an efficient catalyst in organic
synthesis.23 As a result of our ongoing interest in
iron-catalyzed organic reactions, we wish to report the
preparation of benzoxanthenes by the FeCl3-catalyzed
(5 mol%) condensation reaction of 2-naphthol with al-
dehydes under base-, acid-, ligand-, additive-, and sol-
vent-free reaction conditions (Scheme 1).
Xanthenes and benzoxanthenes are important sub-
structures found in numerous natural sources.1 They
possess various biological activities and pharmacologi-
cal properties such as anti-bacterial,2 anti-inflamma-
tory,3 and antiviral properties.4 These compounds have
received an extensive attention because some of them
have also been used as leuco-dyes in laser technology,5
as pH-sensitive fluorescent materials for the visualiza-
tion of biomolecular assemblies,6 and antagonists of the
paralyzing action of zoxazalamine.7 Therefore, the syn-
thesis of 14-aryl- and 14-alkyl-14-H-dibenzo[a,j]xan-
thenes has attracted considerable and continuing interest
in organic synthesis and pharmaceutical science. The
recommended synthetic routes, including the reaction of
aryloxymagnesium halides with triethylorthoformate,8
cyclization of polycyclic aryltriflate esters9 and cyclo-
condensation between 2-hydroxy aromatic aldehydes
and 2-tetralone10 have been reported. In addition, other
reactions through the condensation of 2-naphthol with
aldehydes in the presence of an effective catalyst have
been developed.11 Nevertheless, these methods have
several disadvantages, such as toxic organic solvent,
excess of catalysts, and poor yields. Hence, simpler,
more convenient and efficient approaches for the
preparation of benzoxanthenes are still highly desirable.
In contrast, the catalysts derived from heavy or rare
metals have several drawbacks for large-scale applica-
Results and discussion
As a model reaction of this protocol, the reaction of
*
E-mail: leiwang@chnu.edu.cn; Tel.: 0086-0561-3802069; Fax: 0086-561-03090518
Received January 15, 2010; revised June 20, 2010; accepted July 10, 2010.
Project supported by the National Natural Science Foundation of China (No. 20972057), and the Key Project of Science and Technology of the Min-
istry of Education of China (No. ZD2007005-1).
Chin. J. Chem. 2010, 28, 2463— 2468
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Wang et al.
Table 1 Optimization of the reaction conditionsa
FULL PAPER
Scheme 1
2-naphthol with benzaldehyde was chosen as model
substrates for the optimization of the reaction conditions.
The results are summarized in Table 1. It can be seen
from Table 1, this reaction was strongly influenced by
solvents. No desired product was isolated when the re-
action was carried out in DMF, or CH3CN (Table 1,
Entries 8 and 9). Meanwhile, only trace amount of the
products were obtained when the reaction was carried
out in THF, or NMP (Table 1, Entries 6 and 7). When
the reaction was performed in 1,2-dibromoethane,
1,2-dichloroethane, CHCl3, toluene and 1,4-dioxane in
the presence of a catalytic amount of FeCl3 (10 mol%),
56%, 45%, 42%, 16%, and 10% yields of the corre-
sponding products were obtained, respectively (Table 1,
Entries 1— 5). To our delight, 91% of product was iso-
lated when the reaction was carried out in the absence of
any solvent at 100 ℃ for 10 h (Table 1, Entry 10).
Among a variety of catalyst species tested, FeCl3 was
found to be the most effective one (Table 1, Entries
10— 14), which is better than FeBr3, and much better
than FeCl2, FeBr2, and ZnCl2 (Table 1, Entries 11— 14).
With respect to the catalyst loading, when 1— 3 mol%
of FeCl3 was used, the reaction did not go to completion,
but a higher loading (5— 10 mol%) of the catalyst gave
very good results (Table 1, Entries 1, and 15— 17).
However, with an increased loading of the catalyst up to
15 mol%, there was no increase in the isolated yield of
the product (Table 1, Entry 18). It is important to note
that under solvent-free reaction conditions and at a rela-
tive low temperature (80, 60 ℃), 65% and 32% yields
of the expected products were isolated, respectively
(Table 1, Entries 19 and 20). Therefore, 5 mol% of
FeCl3 was considered as an efficient catalyst in the ab-
sence of any solvent or additive at 100 ℃ for the reac-
tion.
Entry Catalyst/mol% Solvent/Temp. (℃)
Yieldb/%
1
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl2 (10)
FeBr3 (10)
FeBr2 (10)
ZnCl2 (10)
FeCl3 (5)
1,2-Dibromoethane/100
1,2-Dichloroethane/80
CHCl3/62
56
45
42
16
10
2
3
4
Toluene/100
5
1,4-Dioxane/100
THF/68
6
＜
＜
5
5
7
NMP/100
8
DMF/100
NR
NR
91
9
CH3CN/80
10
11
12
13
14
15
16
17
18
19
Solvent-free/100
Solvent-free/100
Solvent-free/100
Solvent-free/100
Solvent-free/100
Solvent-free/100
Solvent-free/100
Solvent-free/100
Solvent-free/100
Solvent-free/80
Solvent-free/60
＜
5
68
12
25
91
80
43
91
65
32
FeCl3 (3)
FeCl3 (1)
FeCl3 (15)
FeCl3 (5)
20
FeCl3 (5)
a
Reaction conditions: 2-naphthol (1.0 mmol), benzaldehyde (0.5
b
mmol), solvent (1.0 mL) or without solvent for 10 h. Isolated
yield.
used as substrates for the reactions, slightly lower reac-
tivity was found (Table 2, Entries 7, 8 and 13). It is im-
portant to note that aliphatic aldehydes were also suc-
cessfully reacted with 2-naphthol to give the desired
products in good yields (Table 2, Entries 15 and 16). In
addition, we also investigated the reactivity of
2-pyridinecarboxaldehyde, and the reaction provided the
corresponding product in good yield (Table 2, Entry
14).
Based on the Lewis acid catalyzed condensation
protocol, a tentative mechanism for the formation of
benzoxanthenes was proposed (Scheme 2). A carboca-
tion was initially formed and aryl-methanebisnaphthol
was then formed in the second step, which then under-
went dehydration to give the final product, benzoxan-
thene.
Under the optimized reaction conditions, a series of
benzaldehydes were examined to probe the generality of
this reaction. The results are shown in Table 2. In the
presence of FeCl3 (5 mol%) and in the absence of any
solvent at 100 ℃, without any acid, base, ligand or ad-
ditive, reactions of a variety of substituted benzalde-
hydes containing electron-withdrawing or electron-
donating groups on the benzene rings with 2-naphthol
underwent smoothly, and the corresponding products
were obtained in good to excellent yields (Table 2, En-
tries 1— 14). When hindered benzaldehydes were
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Chin. J. Chem. 2010, 28, 2463— 2468

FeCl3-Catalyzed Condensation of 2-Naphthol and Aldehydes
Table 2 Reactions of aldehydes with 2-naphthola
Continued
Yieldb/%
Entry
14
Aldehyde
Product
3n
84
81
83
15
3o
16
3p
a Reaction conditions: 2-naphthol (1 mmol), aldehyde (0.5 mmol),
FeCl3 (5 mol%), at 100 ℃ for 10 h under solvent- and addi-
tive-free reaction conditions. b Isolated yield.
Entry
1
Aldehyde
Product
Yieldb/%
91
Scheme 2
3a
2
3
4
5
6
7
3b
3c
3d
3e
3f
91
92
96
95
97
87
3g
8
3h
3i
81
97
93
93
94
9
Conclusion
10
11
12
3j
3k
3l
In summary, we have developed an efficient proto-
col for the synthesis of 14-aryl(alkyl)-14-H-dibenzo-
[a,j]xanthenes. This protocol involves using FeCl3 (5
mol%) as an eco-friendly, inexpensive, and efficient
catalyst without any acid, base, ligand or additive under
thermal, solvent-free reaction conditions. The reactions
of 2-naphthol with both of aliphatic and aromatic alde-
hydes underwent smoothly to generate the correspond-
ing products in good to excellent yields. Simple, neutral,
green and safe experimental conditions are the charac-
teristics of this protocol.
Experimental
13
3m
86
Physical measurements and materials
All 1H NMR and 13C NMR spectra were recorded on
Chin. J. Chem. 2010, 28, 2463— 2468
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
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Wang et al.
FULL PAPER
a 400 MHz Bruker FT-NMR spectrometers. All chemi-
cal shifts (δ) are given with reference to tetramethylsi-
lane (TMS) as an internal standard. Products were puri-
fied by flash chromatography on 230— 400 mesh silica
gel.
The chemicals and solvents were purchased from
commercial suppliers either from Aldrich, Fluka, USA
or Shanghai Chemical Company, China and were used
without purification prior to use.
131.03, 129.83, 129.07, 128.88, 126.88, 124.34, 122.36,
120.18, 117.97, 116.63, 37.41.
14-(p-Nitrophenyl)-14-H-dibenzo[a,j]xanthene
(3f)11b 1H NMR (CDCl3, 400 MHz) δ: 8.28 (s, 1H),
8.26 (s, 1H), 8.00— 7.96 (m, 2H), 7.85 (s, 1H), 7.83 (s,
2H),7.81 (s, 1H), 7.68— 7.64 (m, 2H), 7.61— 7.57 (m,
2H), 7.51 (s, 1H), 7.48 (s, 1H), 7.45— 7.41 (m, 2H),
6.58 (s, 1H); 13C NMR (CDCl3, 100 MHz) δ: 151.97,
148.76, 131.06, 131.05, 129.56, 129.03, 128.93, 127.16,
124.55, 123.83, 122.01, 118.03, 115.74, 37.84.
14-(o-Chlorophenyl)-14-H-dibenzo[a,j]xanthene
(3g)11b 1H NMR (CDCl3, 400 MHz) δ: 8.69 (d, J＝
8.53 Hz, 2H), 7.78— 7.73 (m, 4H), 7.58 (t, J＝ 7.38 Hz,
2H), 7.45— 7.33 (m, 5H), 7.22 (s, 1H), 6.89— 6.81 (m,
2H), 6.75 (s, 1H); 13C NMR (CDCl3, 100 MHz) δ:
148.89, 143.52, 131.75, 131.71, 130.84, 130.09, 129.53,
129.01, 128.58, 127.87, 127.79, 126.86, 124.37, 123.40,
34.58.
14-(o-Nitrophenyl)-14-H-dibenzo[a,j]xanthene
(3h)25 1H NMR (CDCl3, 400 MHz) δ: 8.51 (d, J＝ 8.09
Hz, 2H), 7.81— 7.78 (m, 5H), 7.61— 7.57 (m, 2H), 7.54
(s, 1H), 7.50— 7.46 (m, 3H), 7.43— 7.39 (m, 2H),
7.22— 7.18 (m, 1H), 7.06— 7.01 (m, 1H); 13C NMR
(CDCl3, 100 MHz) δ: 149.36, 146.99, 140.83, 134.08,
132.21, 131.68, 130.94, 129.42, 128.68, 127.54, 127.36,
124.87, 124.63, 122.54, 117.98, 117.53, 32.48.
14-(m-Chlorophenyl)-14-H-dibenzo[a,j]xanthene
(3i)11b 1H NMR (CDCl3, 400 MHz) δ: 8.31 (s, 1H),
8.29 (s, 1H), 7.82 (s, 1H), 7.80 (s, 1H), 7.79 (s, 1H),
7.77 (s, 1H), 7.57 (t, J＝ 7.42 Hz, 2H), 7.48— 7.38 (m,
6H), 7.05 (t, J＝ 8.05 Hz, 1H), 6.96— 6.93 (m, 1H), 6.43
(s, 1H); 13C NMR (CDCl3, 100 MHz) δ: 148.74, 146.84,
134.38, 131.22, 131.02, 129.56, 129.12, 128.86, 128.29,
126.92, 126.71, 126.36, 124.34, 122.36, 118.04, 116.53,
37.72.
14-(m-Bromophenyl)-14-H-dibenzo[a,j]xanthene
(3j)11a 1H NMR (CDCl3, 400 MHz) δ: 8.25 (d, J＝
8.40 Hz, 2H), 7.78— 7.72 (m, 4H), 7.58— 7.52 (m, 3H),
7.46— 7.42 (m, 3H), 7.38— 7.34 (m, 2H), 7.08— 7.05
(m, 1H), 6.95 (t, J＝ 7.60 Hz, 1H), 6.36 (s, 1H); 13C
NMR (CDCl3, 100 MHz) δ: 148.66, 147.10, 131.17,
131.09, 130.97, 129.85, 129.59, 129.10, 128.83, 126.88,
126.82, 124.31, 122.69, 122.31, 117.99, 116.45, 37.66.
14-(m-Methoxyphenyl)-14-H-dibenzo[a,j]xanthe-
ne (3k)26 1H NMR (CDCl3, 400 MHz) δ: 8.35 (s, 1H),
8.33 (s, 1H), 7.77 (s, 1H), 7.75 (s, 1H), 7.73 (s, 1H),
7.71 (s, 1H), 7.53 (t, J＝ 7.75 Hz, 2H), 7.44 (s, 1H), 7.42
(s, 1H), 7.35 (t, J＝ 7.36 Hz, 2H), 7.12 (d, J＝ 7.55 Hz,
1H), 7.03— 7.00 (m, 2H), 6.47 (dd, J＝ 1.90, 1.86 Hz,
1H), 6.40 (s, 1H), 3.56 (s, 3H); 13C NMR (CDCl3, 100
MHz) δ: 159.54, 148.67, 146.44, 131.40, 130.99, 129.21,
128.78, 128.70, 126.70, 124.16, 122.66, 120.72, 117.93,
117.11, 114.90, 110.88, 54.95, 37.89.
General procedure for synthesis of benzoxanthenes
A mixture of an aldehyde (0.5 mmol), 2-naphthol
(1.0 mmol) and FeCl3 (4 mg, 5 mol%) was heated at
100 ℃ for 10 h. The progress of the reaction was moni-
tored by TLC. After completion of the reaction, water (3
mL) was added and the product was extracted with ethyl
acetate (3 mL× 3). The organic layer was dried (MgSO4)
and evaporated, and the crude product was purified by
flash chromatography (ethyl acetate/petroleum ether as
eluent) to provide the pure product.
14-Phenyl-14-H-dibenzo[a,j]xanthene (3a)24 1H
NMR (CDCl3, 400 MHz) δ: 8.37 (s, 1H), 8.35 (s, 1H),
7.80 (s, 1H), 7.78 (s, 1H), 7.76 (s, 1H), 7.74 (s, 1H),
7.56— 7.49 (m, 4H), 7.47 (s, 1H), 7.44 (s, 1H), 7.39—
7.35 (m, 2H), 7.11 (t, J＝ 8.07 Hz, 2H), 6.98— 6.93 (m,
1H), 6.45 (s, 1H); 13C NMR (CDCl3, 100 MHz) δ:
148.69, 144.94, 131.41, 131.01, 128.79, 125.74, 128.42,
128.20, 126.73, 126.32, 124.18, 122.64, 117.96, 117.28,
37.97.
14-(p-Methylphenyl)-14-H-dibenzo[a,j]xanthene
(3b)11b 1H NMR (CDCl3, 400 MHz) δ: 8.34 (d, J＝
8.38 Hz, 2H), 7.77— 7.71 (m, 4H), 7.52 (t, J＝ 7.03 Hz,
2H), 7.44— 7.33 (m, 6 H), 6.90 (d, J＝ 8.02 Hz, 2H),
6.39 (s, 1H), 2.07 (s, 3H); 13C NMR (CDCl3, 100 MHz)
δ: 148.60, 142.06, 135.81, 131.39, 131.01, 129.10,
128.71, 128.68, 128.03, 126.67, 124.13, 122.65, 117.92,
117.38, 37.54, 20.81.
14-(p-Fluorophenyl)-14-H-dibenzo[a,j]xanthene
(3c)11a 1H NMR (CDCl3, 400 MHz) δ: 8.29 (d, J＝
8.61 Hz, 2H), 7.80— 7.74 (m, 4H), 7.56— 7.52 (m, 2H),
7.45— 7.36 (m, 6 H), 6.78 (t, J＝ 8.87 Hz, 2H), 6.42 (s,
1H); 13C NMR (CDCl3, 100 MHz) δ: 148.64, 140.73,
131.23, 131.01, 129.61, 129.53, 128.93, 128.84, 126.81,
124.27, 122.43, 117.96, 117.02, 115.37, 115.16, 37.13.
14-(p-Chlorophenyl)-14-H-dibenzo[a,j]xanthene
(3d)11b 1H NMR (CDCl3, 400 MHz) δ: 8.29 (d, J＝
8.46 Hz, 2H), 7.83— 7.77 (m, 4H), 7.58— 7.54 (m, 2H),
7.47 (s, 1H), 7.45— 7.38 (m, 5H), 7.10— 7.07 (m, 2H),
6.44 (s, 1H); 13C NMR (CDCl3, 100 MHz) δ: 148.66,
143.43, 132.05, 131.22, 131.02, 129.45, 129.05, 128.87,
128.60, 126.87, 124.33, 122.37, 117.97, 116.72, 37.38.
14-(p-Bromophenyl)-14-H-dibenzo[a,j]xanthene
(3e)11b 1H NMR (CDCl3, 400 MHz) δ: 8.30 (s, 1H),
8.28 (s, 1H), 7.83 (s, 1H), 7.81 (s, 1H), 7.79 (s, 1H),
7.77 (s, 1H), 7.56 (t, J＝ 6.96 Hz, 2H), 7.47 (s, 1H), 7.45
(s, 1H), 7.42 (s, 1H), 7.40 (s, 1H), 7.38 (s, 1H), 7.36 (s,
1H), 7.24 (d, J＝ 2.93 Hz, 2H), 6.43 (s, 1H); 13C NMR
(CDCl3, 100 MHz) δ: 148.66, 143.95, 131.55, 131.22,
14-(p-Chloro-m-nitrophenyl)-14-H-dibenzo[a,j]-
xanthene (3l)27 1H NMR (CDCl3, 400 MHz) δ: 8.21
(d, J＝ 8.44 Hz, 2H), 8.01 (d, J＝ 1.92 Hz, 1H), 7.85 (s,
1H), 7.83 (s, 2H),7.81 (s, 1H), 7.61 (t, J＝ 7.42 Hz, 3H),
7.49— 7.42 (m, 4H), 7.26 (d, J＝ 8.27 Hz, 1H), 6.25 (s,
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Chin. J. Chem. 2010, 28, 2463— 2468

FeCl3-Catalyzed Condensation of 2-Naphthol and Aldehydes
1H); 13C NMR (CDCl3, 100 MHz) δ: 148.80, 145.21,
132.68, 131.98, 131.05, 130.88, 129.70, 129.12, 127.32,
125.12, 124.80, 124.65, 121.78, 118.04, 115.37, 37.05.
14-(2-Chloro-5-nitrophenyl)-14-H-dibenzo[a,j]-
xanthene (3m)27 1H NMR (CDCl3, 400 MHz) δ: 8.57
(d, J＝ 8.47 Hz, 2H), 8.22 (d, J＝ 2.55 Hz, 1H), 7.84—
7.80 (m, 4H), 7.73 (dd, J＝ 2.59, 6.26 Hz, 1H), 7.63—
7.58 (m, 2H), 7.54 (s, 1H), 7.51 (s, 1H), 7.45— 7.40 (m,
3H), 6.84 (s, 1H); 13C NMR (CDCl3, 100 MHz) δ:
149.13, 147.56, 145.48, 136.31, 131.37, 130.93, 130.59,
129.70, 128.91, 127.17, 126.96, 124.65, 122.71, 122.56,
118.38, 116.57, 34.89.
6
7
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14-(o-Pyridyl)-14-H-dibenzo[a,j]xanthene (3n)11a
1H NMR (CDCl3, 400 MHz) δ: 8.67 (d, J＝ 8.62 Hz,
2H), 8.50 (d, J＝ 4.52 Hz, 1H), 7.78 (s, 2H), 7.76 (s, 2H),
7.55 (t, J＝ 7.69 Hz, 2H), 7.45 (d, J＝ 8.88 Hz, 2H), 7.37
(t, J＝ 7.79 Hz, 2H), 7.28 (t, J＝ 7.41 Hz, 1H), 7.12 (d,
J＝ 7.85 Hz, 1H), 6.68 (t, J＝ 5.45 Hz, 1H), 6.73 (s, 1H);
13C NMR (CDCl3, 100 MHz) δ: 164.46, 148.15, 137.25,
131.84, 130.85, 129.18, 128.34, 126.92, 126.34, 124.36,
123.91, 121.26, 117.84, 115.87, 41.67.
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14-(n-Propyl)-14-H-dibenzo[a,j]xanthene (3o)11b
1H NMR (CDCl3, 400 MHz) δ: 8.20 (s, 1H), 8.18 (s,
1H), 7.80 (d, J＝ 8.11 Hz, 2H), 7.70 (d, J＝ 8.90 Hz, 2H),
7.57— 7.53 (m, 2H), 7.40— 7.36 (m, 2H), 7.33 (s, 1H),
7.31 (s, 1H), 5.47 (t, J＝ 4.45 Hz, 1H), 1.99— 1.94 (m,
2H), 1.03— 0.95 (m, 2H), 0.55 (t, J＝ 7.27 Hz, 3H); 13C
NMR (CDCl3, 100 MHz) δ: 149.89, 131.40, 130.97,
128.78, 128.09, 126.49, 123.99, 122.40, 117.49, 116.64,
38.16, 30.98, 18.09, 14.03.
13 (a) Mancheňo, O. G.; Bolm, C. Org. Lett. 2006, 8, 2349.
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14-(iso-Butyl)-14-H-dibenzo[a,j]xanthene (3p)28
1H NMR (CDCl3, 400 MHz) δ: 8.22 (s, 1H), 8.19 (s,
1H), 7.80 (s, 1H), 7.78 (s, 1H), 7.70 (s, 1H), 7.68 (s, 1H),
7.58— 7.53 (m, 2H), 7.40— 7.35 (m, 4H), 5.42 (t, J＝
5.72 Hz, 1H), 1.80 (t, J＝ 5.80 Hz, 2H), 1.50— 1.40 (m,
1H), 0.70 (d, J＝ 6.56 Hz, 6H); 13C NMR (CDCl3, 100
MHz) δ: 150.14, 131.56, 130.92, 128.75, 127.99, 126.46,
124.01, 122.23, 118.63, 117.69, 46.79, 29.56, 25.02,
23.57.
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