An efficient and green one-pot synthesis of 12-aryl-8,9,10,12- tetrahydrobenzo[a]xanthen-11-one derivatives promoted by sulfamic acid in [BMIM]BF4 ionic liquid

Article abstract of DOI:10.1002/cjoc.201180488

An efficient and green procedure for the synthesis of novel 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one derivatives has been described through one-pot condensation of 2-naphthol, arylaldehyde and 5,5-dimethyl-cyclohexane-1,3-dione in the presence o

Full text of DOI:10.1002/cjoc.201180488

FULL PAPER
DOI: 10.1002/cjoc.201180488
An Efficient and Green One-pot Synthesis of
12-Aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one Deriva-
tives Promoted by Sulfamic Acid in [BMIM]BF4 Ionic Liquid
Zang, Hongjun*(臧洪俊)
Zhang, Weiwei(张维维)
Zhang, Yong(张勇)
Xu, Xianlin(徐先林)
Cheng, Bowen(程博闻)
Ren, Yuanlin(任元林)
Department of Enviromental and Chemistry Engineering, Tianjin Polytechnic University, State Key Laboratory of
Hollow Fiber Membrane Materials and Processes, 300160 Tianjin, China
An efficient and green procedure for the synthesis of novel 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-
one derivatives has been described through one-pot condensation of 2-naphthol, arylaldehyde and 5,5-dimethyl-
cyclohexane-1,3-dione in the presence of sulfamic acid (NH2SO3H) in ionic liquid 1-n-butyl-3-methylimidazolium
tetrafluoroborate ([BMIM]BF4). These reactions proceed with good yields under short reaction time. Furthermore,
the green catalytic system can be recycled specific times with no decreases in yields and reaction rates.
Keywords one-pot reaction, xanthenes, ionic liquid, sulfamic acid
Introduction
methods for the one-pot synthesis of benzoxanthenes in
terms of high yield, shorter reaction time, environmen-
tally benign design, operational simplicity and reusabil-
ity of catalyst remains desirable.
The development of new methods for the synthesis
of xanthenes and benzoxanthenes derivatives is an im-
portant area of synthetic research because of the broad
spectrum of their biological and pharmaceutical proper-
ties such as anti-inflammatory,[1] antiviral[2] and anti-
bacterial.[3] Some of xanthenes derivatives have been
used as antagonists for paralyzing the action of zoxa-
zolamine[4] and in photodynamic therapy.[5] Furthermore,
these compounds can be employed as dyes,[6]
pH-sensitive fluorescent materials for visualization of
biomolecules[7] and in laser technologies.[8] Thus, the
synthesis of a variety of xanthene derivatives is of great
importance.
Recently, only a few reports on synthesis of 12-aryl-
8,9,10,12-tetrahydrobenzo[a]xanthen-11-one derivatives
have appeared on the use of NaHSO4•SiO2 in CH2Cl2,[9]
Sr(OTf)2 in 1,2-dichloroethane,[10] TBAF in water,[11]
pTSA in [BMIM]BF4,[12] chlorosulphonic acid (ClSO3H)
under ultrasound,[13] 12-tungstophosphoric acid
(H3PW12O40) under solvent-free conditions,[14] cyanuric
chloride (TCT) under solvent-free conditions,[15]
HClO4-SiO2 under solvent-free conditions[16] and
RuCl3•nH2O in ethanol.[17] However, these methods are
not entirely satisfactory, with disadvantages such as
relatively long reaction times, low yield, unfriendliness
to environment, using a catalyst that cannot be recycled,
tedious workup procedures and co-occurrence of side
reactions, and so on. Therefore, development of better
Green chemistry has emerged as a discipline that
permeates all aspects of synthetic chemistry. There are a
variety of approaches for the development of greener
protocols, which reflect the enormity and complexity of
this field. Alternative reaction media are some of the
ways to make a protocol greener.[18] In this regard, over
the past decade, ionic liquids have gradually emerged as
a novel environmentally benign alternative to traditional
organic solvents. Recently, the use of room temperature
ionic liquids as green solvents in organic synthetic
processes has gained considerable importance due to
their negligible vapour pressure, solvating ability and
easy recyclability.[19]
Sulfamic acid (NH2SO3H, SA) has emerged as a
promising substitute for conventional Bronsted acid and
Lewis acid catalysts. It is a nonvolatile, non-hygros-
copic, odorless, uncorrodible, crystalline solid with out-
standing physical stability and is a commercially avail-
able, cheap material.[20] It possesses distinctive catalytic
features related to its zwitterionic nature and displays an
excellent activity over a vast array of acid-catalyzed
organic transformations. Sulfamic acid has been intro-
duced as a promising solid-acid catalyst for various or-
ganic transformations.[21]
In continuation of our endeavor in green synthesis
and using ionic liquid as a recyclable eco-friendly reac-
*
E-mail: Chemhong@126.com
Received December 1, 2010; accepted September 27, 2011.
362
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, 30, 362—366

One-pot Synthesis of 12-Aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one Derivatives
tion medium, herein we report the results of the synthe-
sis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-
11-one derivatives from correspondding aldehydes,
2-naphthol and dimedone using sulfamic acid as a cata-
lyst in ionic liquid [BMIM]BF4 (Scheme 1). This
method has the advantages of high yields, simple meth-
odology, environmental friendliness and easy work-up.
The [BMIM]BF4 can be recovered by simple rotary
evaporation and reused delivering good yields.
(Table 1, Entries 1, 2). Next, we also examined the ef-
fect of different solvents such as [BMIM]BF4,
[BMIM]PF6, [HMIM]HSO4, dichloromethane (CH2Cl2),
dichloroethane (ClCH2CH2Cl) and under solvent-free
conditions on a model reaction using NH2SO3H as the
catalyst. As shown in Table 1, in various solvents or
under solvent-free conditions, the yield of product was
low. We found that the best result was obtained in
[BMIM]BF4 (Table 1). [BMIM]BF4 gave the highest
yields for 4a (86%, Table 1, Entry 3) within the shortest
reaction time at 80 ℃. When the reaction was per-
formed at 80 ℃ in [BMIM]PF6 or [HMIM]HSO4, it
gave a mixture of 4a and 5a (by-product 1,8-dioxo-do-
decahydroxanthene derivative). This result was compa-
Scheme 1
rable with that in [BMIM]BF4, indicating that BF－ of
4
the ionic liquid [BMIM]BF4, played a significant role in
the reaction. However the precise effect of BF－ on the
4
reaction awaits further studie. Moreover, ionic liquid
[BMIM]BF4 is chosen as the most suitable reaction me-
dium for successive reactions. Effects of reaction tem-
perature and time on the yields of the products were also
studied by processing the condensation reaction at dif-
ferent temperature (Table 1, Entries 3, 9) and different
times (Table 1, Entries 3, 11, 12). The results showed
that the reaction at 80 ℃ for 1 h proceeded in highest
yield. In the process, ultrasonic irradiation did not ac-
celerate the reaction rate and shorten the reaction time
(Table 1, Entry 10). Therefore, we selected theionic liq-
uid [BMIM]BF4 as solvent and NH2SO3H as the catalyst
for the one-pot reaction of aldehydes, 2-naphthol and
dimedone at 80 ℃ to give correspond ing 12-aryl-
Results and Discussion
In our initial research, benzaldehyde was selected as
a representative reactant in order to optimize the reac-
tion conditions. We conducted the three-component
condensation reaction of 2-naphthol, benzaldehyde and
dimedone in the presence of various catalysts and sol-
vents and the results were listed in Table 1. In the ab-
sence of the catalyst, no product formation was ob-
served at 80 ℃ for 2 h in [BMIM]BF4 and [BMIM]PF6
8,9,10,12-tetrahydrobenzo[a]xanthen-11-one
deriva-
tives.
Table 1 The effect of solvent and catalyst on the reaction for the synthesis of novel 12-phenyl-8,9,10,12-tetrahydrobenzo[a]xanthen-
11-one
Yieldb/%
Entrya
Solvent
Catalyst
Temperature
Time/min
4a
5a
1
[BMIM]BF4
[BMIM]PF6
[BMIM]BF4
Solvent-free
[BMIM]PF6
[HMIM]HSO4
ClCH2CH2Cl
CH2Cl2
―
80 ℃
80 ℃
80 ℃
80 ℃
80 ℃
80 ℃
80 ℃
80 ℃
r.t.
120
120
60
―
―
2
―
―
―
3
NH2SO3H
NH2SO3H
NH2SO3H
NH2SO3H
NH2SO3H
NH2SO3H
NH2SO3H
NH2SO3H
NH2SO3H
NH2SO3H
NaHSO4•SiO2
Sr(OTf)2
pTSA
86
Trace
Trace
15
4
60
67
5
60
64
6
60
22
47
7
60
58
Trace
Trace
Trace
Trace
Trace
Trace
―
8
60
62
9
[BMIM]BF4
[BMIM]BF4
[BMIM]BF4
[BMIM]BF4
ClCH2CH2Cl
ClCH2CH2Cl
[BMIM]BF4
60
36
10
11
12
13
14
15
﴾﴾﴾
60
42
80 ℃
80 ℃
80 ℃
80 ℃
80 ℃
30
61
240
180
400
180
85
879
8510
90 12
―
―
a Reaction conditions: 1 mmol 2-naphthol, 1 mmol benzaldehyde and 1.1 mmol dimedone, 1 mmol catalyst and 1 mL solvent. b Isolated yield.
Chin. J. Chem. 2012, 30, 362—366
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
363

Zang et al.
FULL PAPER
Table 2 Preparation of 12-aryl-8,9,10,12-tetrahydrobenzo[a]-
xanthen-11-one derivatives using NH2SO3H in [BMIM]BF4
To show the merit of the present work in comparison
with the reported results in the literature, we compared
the results of NaHSO4•SiO2,[9] Sr(OTf)2[10] and pTSA[12]
in the synthesis of 12-phenyl-8,9,10,12-tetrahydro-
benzo[a]xanthen-11-one. As shown in Table 1, the sul-
famic acid combined with ionic liquid can act as suit-
able catalyst system with respect to reaction times.
Moreover, reusability of the catalyst was also studied to
minimize costs and inorganic waste.
To generalize the method, we performed the reaction
of variety of aldehydes at 80 ℃ in [BMIM]BF4 using
NH2SO3H as catalyst. As shown in Table 2, in all cases,
12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one
derivatives were obtained in good yields, and it was
observed to be a general method that tolerates both elec-
tron-withdrawing and electron-donating substituents. It
was expected that the reaction mechanism was similar
to the previously reported catalyzed mechanism.[9,10]
The suggested mechanism of the NH2SO3H catalyzed
transformation was shown in Scheme 2.
Finally, the feasibility of reuse and recycling of the
NH2SO3H was examined through a series of sequential
reactions of benzaldehyde, 2-naphthol with 5,5-dime-
thylcyclohexane-1,3-dione as a model reaction to give
4a. In a typical reaction, the catalyst was recovered by
extracting the product with diethyl ether, leaving behind
NH2SO3H immobilized in ionic liquid [BMIM]BF4. The
recovered catalyst was reused for five cycles. The cata-
lyst could be used for five times with negligible loss of
catalytic activity and there was no need of regeneration
of the catalyst (Table 3).
Entry
Aldehyde
PhCHO
Time/hYielda/%
m.p./℃
a
b
c
d
e
f
1
1
2
86 152—154 (154—155)[10]
88 180—181 (181—182)[10]
81 181—182
4-ClC6H4CHO
2-ClC6H4CHO
2,4-Cl2C6H3CHO 1.5
80 183—1859
4-MeOC6H4CHO
2-MeOC6H4CHO
3-NO2C6H4CHO
4-NO2C6H4CHO
2-BrC6H4CHO
1
2
83 204—206 (205—206)[10]
76 165—167
g
h
i
2
81 171—172 (169—170)[10]
84 185—186 (183—185)[11]
75 172—174[9]
1
1.5
2
j
4-OHC6H4CHO
79 211—213 (213—214)[9]
a Isolated yield.
Table 3 Reuse studies of NH2SO3H immobilized in ionic liquid
[BMIM]BF4 for the synthesis of 4a
Run
1
2
3
4
5
In conclusion, NH2SO3H has been employed for the
first time as a novel and efficient catalyst for the syn-
thesis of 12-aryl-8,9,10,12-tetrahydro-benzo[a]xanthen-
11-one derivatives by the reaction of aldehydes,
2-naphthol with 5,5-dimethylcy-clohexane-1,3-dione
using [BMIM]BF4 as the solvent. The salient features of
this protocol are mild reaction conditions, high yields of
Yielda/%
a Isolated yield.
86
84
85
83
84
products, cheapness and easy availability of the reagent,
high selectivity of products, recyclable ionic liquid and
short reaction times.
Scheme 2
364
www.cjc.wiley-vch.de
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, 30, 362—366

One-pot Synthesis of 12-Aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one Derivatives
Experimental
MHz) δ: 8.28 (d, J＝8.4 Hz, 1H, Ar-H), 7.75—7.67 (m,
3H, Ar-H), 7.43—7.25 (m, 4H, Ar-H), 7.01—6.78 (m,
3H, Ar-H), 5.96 (s, 1H, CH), 3.95 (s, 3H, CH3), 2.59 (s,
2H, CH2), 2.31 (d, J＝16.0 Hz, 1H, CH2), 2.20 (d, J＝
16.3 Hz, 1H, CH2), 1.12 (s, 3H, CH3), 0.99 (s, 3H, CH3);
13C NMR (CDCl3, 300 MHz) δ: 196.8, 163.6, 157.9,
145.3, 137.1, 131.5, 131.2, 130.1, 129.4, 128.4, 127.9,
127.2, 124.8, 123.3, 117.6, 117.1, 114.2, 113.5, 55.8,
51.1, 41.3, 34.1, 31.9, 29.2, 27.1; IR (KBr) νmax: 3120,
2952, 1652, 1601, 1517, 1453, 1391, 1213, 1122, 1016,
Melting points were recorded on an electrothermal
apparatus and were uncorrected. The H NMR spectra
1
were measured on a Bruker AVANCE 300 spectrometer
using TMS as internal standard in CDCl3. IR spectra
were measured with a BIO-RAD FTS3000 spectrometer
using KBr optics. Elemental analyses were obtained
using a Perkin-Elmer auto-analyzer. 1-n-Butyl-3-me-
thylimidazolium tetrafluoroborate ([BMIM]BF4), 1-n-
－
1
butyl-3-methylimidazolium
hexafluorophosphate
742, 668, 525 cm . Anal. calcd for C26H24O3: C 81.21,
H 6.28; found C 81.29, H 6.31.
([BMIM]PF6) and 1-hexyl-3-methylimidazolium hy-
drogen sulfate ([HMIM]HSO4) were prepared according
to the literature.[22,23]
Acknowledgement
General procedure for the synthesis of 12-aryl-
8,9,10,12-tetrahydrobenzo[a]xanthen-11-one deriva-
tives
The work was supported by the Tianjin National
Natural Science Foundation (Nos. 11JCZDJC21300 and
10JCZDJC22200) and NSFC (No. 51076174).
A mixture of aldehydes (1 mmol), 2-naphthol (1
mmol), cyclic 1,3-dicarbonyl compound (1.1 mmol),
NH2SO3H (0.2 mmol) and [BMIM]BF4 (1 mL) was
heated at 80 ℃ for a specified time. After completion
of the reaction as indicated by TLC, the system was
cooled to room temperature. The mixture was washed
with water (10 mL) and extracted with ethyl acetate (15
mL×3). The combined organic layers were dried over
anhydrous sodium sulfate, filtered, and evaporated to
dryness in vacuo. The water in the ionic liquid was
evaporated under reduced pressure. The residual ionic
liquid was washed with small amount of diethyl ether,
dried under vacuum at 80 ℃ for 2 h and reused. The
product was purified by chromatography on silica
(200–300 mesh). Elution with a mixture of petroleum
ether and ethyl acetate (10/1, V/V) afforded the
12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one
derivatives 4a—4j. All the known products 4a, 4b, 4d,
References
[1] Poupelin, J. P.; Saint-Ruf, G.; Foussard-Blanpin, O.; Narcisse, G.;
Uchida -Ernouf, G.; Lacroix, R. Eur. J. Med. Chem. 1978, 13, 67.
[2] Lambert, R. W.; Martin, J. A.; Merrett, J. H.; Parkes, K. E. B.;
Thomas, G. J. WO 9706178, 1997 [Chem. Abstr. 1997, 126,
212377y].
[3] Hideo, T.; Teruomi, J. JP 56005480, 1981 [Chem. Abstr. 1981, 95,
80922b].
[4] Saint-Ruf, G.; Hieu, H. T.; Poupelin, J. P. Naturwissenschaften 1975,
62, 584.
[5] Ion, R. M.; Planner, A.; Wiktorowicz, K.; Frackowiak, D. Acta Bio-
chim. Pol. 1998, 45, 833.
[6] (a) Banerjee, A.; Mukherjee, A. K. Stain Technol. 1981, 56, 83; (b)
Menchen, S. M.; Benson, S. C.; Lam, J. Y. L.; Zhen, W.; Sun, D.;
Rosenblum, B. B.; Khan, S. H.; Taing, M. US 6583168, 2003 [Chem.
Abstr. 2003, 139, p54287f].
[7] Knight, C. G.; Stephens, T. Biochem. J. 1989, 258, 683.
[8] Ahmad, M.; King, T. A.; Ko, D.-K.; Cha, B. H.; Lee, J. J. Phys. D:
Appl. Phys. 2002, 35, 1473.
[9] Biswanath, D.; Keetha, L.; Maddeboina, K.; Yallamalla, S. Synlett
2007, 3107.
[10] Li, J. J.; Tang, W. Y.; Lu, L. M.; Su, W. K. Tetrahedron Lett. 2008,
49, 7117.
[11] Gao, S.; Tsai, C. H.; Yao, C. F. Synlett 2009, 949.
[12] Khurana, J. M.; Magoo, D. Tetrahedron Lett. 2009, 50, 4777.
[13] Nazeruddin, G. M.; Al-Kadasi, A. M. A. Res. J. Pharm. Biol. Chem.
Sci. 2011, 2, 71.
[14] Wang, H. J.; Ren, X. Q.; Zhang, Y. Y.; Zhang, Z. H. J. Braz. Chem.
Soc. 2009, 20, 1939
[15] Zhang, Z. H.; Zhang, P.; Yang, S. H.; Wang, H. J.; Deng, J. J. Chem.
Sci. 2010, 22, 427
1
4e and 4g—4j were fully characterized by IR and H
NMR spectroscopy, and melting points, which were
consistent with the literature data.[9-11] The new com-
1
pounds 4c and 4f were identified by IR, H NMR spec-
troscopy and elemental analysis.
12-(2-Chlorophenyl)-9,9-dimethyl-p-tolyl-8,9,10,12-
tetrahydrobenzo[a]xanthen-11-one (4c): White solid;
1
m.p. 181—182 ℃; yield 81%. H NMR (CDCl3, 300
MHz) δ: 8.26 (d, J＝8.4 Hz, 1H, ArH), 7.82—7.77 (m,
2H, ArH), 7.52—7.30 (m, 4H, ArH), 7.10—7.03 (m, 3H,
ArH), 6.03 (s, 1H, CH), 2.66 (s, 2H, CH2), 2.36 (d, J＝
16.1 Hz, 1H, CH2), 2.27 (d, J＝16.3 Hz, 1H, CH2), 1.18
[16] Mo, L. P.; Chen, H. L. Chin. Chem. Soc. 2010, 57, 157.
[17] Tabatabaeian, K.; Khorshidi, A.; Mamaghani, M.; Dadashi, A.;
Jalali, M. K. Can. J. Chem. 2011, 89, 623
13
(s, 3H, CH3), 1.04 (s, 3H, CH3); C NMR (CDCl3, 300
MHz) δ: 196.9, 163.7, 147.5, 143.4, 133.1, 131.7, 131.4,
131.1, 129.3, 128.3, 128.1, 127.7, 127.1, 124.8, 123.5,
117.4, 117.1, 114.5, 51.2, 41.8, 34.3, 29.1, 27.2; IR
(KBr) νmax: 3122, 2927, 1652, 1592, 1446, 1402, 1371,
1202, 1133, 996, 756, 523 cm－ 1. Anal. calcd for
C25H21ClO2: C 77.21, H 5.43; found C 77.23, H 5.48.
12-(2-Methoxyphenyl)-9,9-dimethyl-p-tolyl-8,9,10,
12-tetrahydrobenzo[a]xanthen-11-one (4f): White solid;
[18] (a) Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Prac-
tice, Oxford University Press, Oxford, 2000; (b) Polshettiwar, V.;
Varma, R. S. Chem. Soc. Rev. 2008, 37, 1546; (c) Sinou, D. Adv.
Synth. Catal. 2002, 344, 221; (d) Rogers, R. D.; Seddon, K. R. Sci-
ence 2003, 302, 792.
[19] (a) Welton, T. Chem. Rev. 1999, 99, 2071; (b) Wasserscheid, P.;
Keim, W. Angew. Chem., Int. Ed. 2000, 39, 3772; (c) Sheldon, R.
Chem. Commun. 2001, 23, 2399; (d) Gordon, C. M. Appl. Catal. A
2001, 222, 101; (e) Dupont, J.; Souza, R. F. D.; Suarez, P. A. Z.
Chem. Rev. 2002, 102, 3667.
1
m.p. 165—167 ℃; yield 81%; H NMR (CDCl3, 300
Chin. J. Chem. 2012, 30, 362—366
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
365

Zang et al.
FULL PAPER
[20] Wang, B. Synlett 2005, 1342.
Zhang, Y. Tetrahedron Lett. 2007, 48, 4297; (h) Upadhyaya, D. J.;
Barge, A.; Stefania, R.; Cravotto, G. Tetrahedron Lett. 2007, 48,
8318; (i) Madhav, J. V.; Reddy, Y. T.; Reddy, P. N.; Crooks, P. A.;
Kumar, V. N.; Rajitha, B. J. Heterocyclic Chem. 2009, 46, 289; (j)
Reddy, Y. T.; Reddy, P. R.; Reddy, M. N.; Rajitha, B.; Crooks, P. A.
Syn. Commun. 2008, 38, 3201.
[21] (a) Jin, T. S.; Sun, G.; Li, Y. W.; Li, T. S. Green Chem. 2002, 4, 255;
(b) Li, J. T.; Han, J. F.; Yang, J. H.; Li, T. S. Ultrason. Sonochem.
2003, 10, 119; (c) Patil, S. B.; Singh, P. R.; Surpur, M. P.; Samant, S.
D. Ultrason. Sonochem. 2007, 14, 515; (d) Wang, B.; Gu, Y. L.; Luo,
C.; Yang, T.; Yang, L. M.; Suo, J. S. Tetrahedron Lett. 2004, 45,
3369; (e) Yadav, J. S.; Rao, P. P.; Sreenu, D.; Rao, R. S.; Kumar, V.
N.; Nagaiah, K.; Prasad, A. R. Tetrahedron Lett. 2005, 46, 7249; (f)
Heydari, A.; Khaksar, S.; Pourayoubi, M.; Mahjoub, A. R. Tetrahe-
dron Lett. 2007, 48, 4059; (g) An, L. T.; Zou, J. P.; Zhang, L. L.;
[22] Owens, G. S.; Abu Omer, M. M. J. Mol. Catal. Chem. 2002, 187,
215.
[23] Fraga-Dubreuil, J.; Bourahla, K.; Rahmouni, M.; Bazureau, J. P.;
Hamelin, J. Catal. Commun. 2002, 3, 185.
(E1012011 Lu, Y.; Lu, Z.)
366
www.cjc.wiley-vch.de
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, 30, 362—366