Efficient synthesis of tetrahydrobenzo[b]pyrans under solvent-free conditions at room temperature

Article abstract of DOI:10.1080/00397910600640230

A range of tetrahydrobenzo[b]pyrans have been synthesized in very good yields under solvent-free conditions by grinding α-cyanocinnamonitrils or β-cyano-β-carbethoxy styrene and 5,5-dimethyl-1,3-cyclohexanedione in the presence of TEBA as catalyst. The sh

Full text of DOI:10.1080/00397910600640230

This article was downloaded by: [Fordham University]
On: 10 August 2013, At: 11:19
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office:
Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An International
Journal for Rapid Communication of
Synthetic Organic Chemistry
Publication details, including instructions for authors and subscription
information:
http://www.tandfonline.com/loi/lsyc20
Efficient Synthesis of
Tetrahydrobenzo[b]pyrans under
Solvent‐Free Conditions at Room
Temperature
Liangce Rong a b , Xiaoyue Li a , Haiying Wang a , Daqing Shi a b , Shujiang Tu
a b & Qiya Zhuang a b
a Department of Chemistry, Xuzhou Nornal University, Xuzhou, Jiangsu,
China
b Key Laboratory of Biotechnology on Medical Plant, Xuzhou, Jiangsu, China
Published online: 22 Sep 2006.
To cite this article: Liangce Rong , Xiaoyue Li , Haiying Wang , Daqing Shi , Shujiang Tu & Qiya Zhuang
(2006) Efficient Synthesis of Tetrahydrobenzo[b]pyrans under Solvent‐Free Conditions at Room Temperature,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
36:16, 2363-2369, DOI: 10.1080/00397910600640230
To link to this article: http://dx.doi.org/10.1080/00397910600640230
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”)
contained in the publications on our platform. However, Taylor & Francis, our agents, and our
licensors make no representations or warranties whatsoever as to the accuracy, completeness, or
suitability for any purpose of the Content. Any opinions and views expressed in this publication
are the opinions and views of the authors, and are not the views of or endorsed by Taylor &
Francis. The accuracy of the Content should not be relied upon and should be independently
verified with primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities
whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or
arising out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any substantial
or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or
distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use
can be found at http://www.tandfonline.com/page/terms-and-conditions

Synthetic Communicationsw, 36: 2363–2369, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600640230
Efficient Synthesis of
Tetrahydrobenzo[b]pyrans under Solvent-
Free Conditions at Room Temperature
Liangce Rong
Department of Chemistry, Xuzhou Nornal University, Xuzhou,
Jiangsu, China and Key Laboratory of Biotechnology on Medical Plant,
Xuzhou, Jiangsu, China
Xiaoyue Li and Haiying Wang
Department of Chemistry, Xuzhou Nornal University, Xuzhou,
Jiangsu, China
Daqing Shi, Shujiang Tu, and Qiya Zhuang
Department of Chemistry, Xuzhou Nornal University, Xuzhou,
Jiangsu, China and Key Laboratory of Biotechnology on Medical Plant,
Xuzhou, Jiangsu, China
Abstract: A range of tetrahydrobenzo[b]pyrans have been synthesized in very good
yields under solvent-free conditions by grinding a-cyanocinnamonitrils or b-cyano-
b-carbethoxy styrene and 5,5-dimethyl-1,3-cyclohexanedione in the presence of
TEBA as catalyst. The short reaction time, cleaner reaction, and easy workup make
this protocol practical and economically attractive.
Keywords: a-Cyanocinnamonitrils, b-cyano-b-carbethoxy styrene, solvent-free
conditions, tetrahydrobenzo[b]pyrans
The increasing attention during the past decades on environmental protection
has influenced both modern academic and industrial groups to develop
Received in R.O.C. September 8, 2005
Address correspondence to Liangce Rong, Key Laboratory of Biotechnology on
Medical Plant, Jiangsu, Xuzhou, Jiangsu 221116, China. E-mail: lcrong2005@
yahoo.com
2363

2364
L. Rong et al.
chemical processes with maximum yield and minimum cost while using
nontoxic reagents, catalysts, and solvents, or even better, no solvents. In
recent years, solid-state organic reactions have caused great interest. They
have many advantanges such as high efficiency and selectivity, easy separ-
ation and purification, and mild reaction conditions and benefit industry as
well as the environment.[1] Many articles about solid-state reactions with
grinding have been reported, such as such as the Grignard reaction,[2] Refor-
matsky reaction,[3] aldol condensations,[4] Dieckmann condensations,[5]
phenol coupling reaction,[6] reduction reaction,[7] and other reactions.[8]
Pyrans and their derivatives are versatile intermediates[9] in the fields of
pharmaceuticals, cosmetics, and perfumes. Pyran derivatives also act as
modulators of potassium channels, influencing the activity of the heart and
blood pressure.[10] Further, tetrahydrobenzo[b]pyrans are important deriva-
tives of pyrans, which have received considerable attention in recent years
because of their wide range of biological activities.[11] Compounds with
these ring systems have diverse pharmacological activities such as anticoagu-
lant, anticancer, spasmolytic, diuretic, and activities anti-ancaphylactia.[12]
Tetrahydrobenzo[b]pyrans also constitute the structural unit of a series of
natural products.[13] A number of 2-amino-4H-pyrans are useful as photoactive
materials.[14] Several methods have been reported for the synthesis of this
compounds; for example, Kamaljit et al.[15] reported that ethyl 2-amino-
5,6,7,8-tetrahydro-5-oxo-4-aryl-7,7-dime-thyl-4H-benzo-[b]-pyran-3-carbox-
ylates were prepared by the reaction of b-cyano-b-carbethoxy styrene with
1,3-cyclohexanedione in refluxing acetonitrile–acetic acid (10 : 1, V/V).
Wang et al.[16] reported synthesis of these compounds in DMF using piperidine
as catalyst. They both used organic solvents, made the workup procedure
complicated, and led to poor yields of the products besides polluting the
environment. Kaupp et al.[17] reported a novel method for the synthesis of
benzo[b]pyrans utilizing the reactants in solid or molten state. This reaction
has some limitations: the two-step reaction was performed at very high
temperature and required a longer period of time. Moreover, the reaction was
applied for the synthesis of only a few compounds. Ipsita et al.[18] and Tu
et al.[19] have reported synthesis of 4H-benzo[b]pyrans under microwave
irradiation conditions, but it has only been carried out in laboratory and is
difficult to apply in the industrial process until now. Shi et al.[20] has also
reported synthesis of those compounds in water, but used high reaction
temperatures and long reaction times. Herein, we describe an efficient, green,
and convenient procedure for the synthesis of tetrahydrobenzo[b]pyrans
under solvent-free conditions at room temperature.
Recently, in our research, we found phase-transfer catalysis (such as
triethylbenzylammonium chloride, TEBA) could be efficiently used in solid-
state organic reactions.[21] To extend our research, we chose TEBA as a
catalyst and tried to use in the synthesis of tetrahydrobenzo[b]pyrans from
the reaction of 5,5-dimethyl-1,3-cyclohexanedione with a-cyanocinnamoni-
trils; to our surprise, we found the reaction could be completed with high

Tetrahydrobenzo[b]pyrans
2365
yields in a very short time. When we chose b-cyano-b-carbethoxy styrene
instead of a-cyanocinnamonitrils, it reacted with 5,5-dimethyl-1,3-cyclohex-
anedione in similar conditions, and the outcomes of reaction were good also.
The experimental procedure was very simple. A mixture of a-cyanocin-
namonitrils or b-cyano-b-carbethoxy styrene 1 (1 mmol), 5,5-dimethyl-1,3-
cyclohexanedione 2 (1 mmol), and TEBA (2 mmol) was ground at room temp-
erature with the agate mortar and pestle under solvent-free conditions. Within
a few minutes, the reactions could be completed with high yields (Scheme 1).
The results are summarized in Table 1.
In conclusion, we have developed a new protocol for synthesizing tetra-
hydrobenzo[b]pyrans. To our knowledge, TEBA is first used as a catalyst in
solvent-free reactions. The present method describes an efficient and
practical alternative to the preparation of tetrahydrobenzo[b]pyrans that, in
contrast to most of the existing protocols, does not require any solvent and
consequently minimizes the generation of toxic waste. We believe that the
present methodology addresses the current trend toward green chemistry.
EXPERIMENTAL
Melting points were uncorrected. 1H NMR spectra were obtained for solutions
in CDCl3 with Me4Si as internal standard using an Inova-400 spectrometer.
Microanalyses were carried out using a Perkin-Elmer 2400 II analyzer. IR
spectra were recorded on an FTIR-8101 spectrometer in KBr.
General Procedure
a-Cyanocinnamonitrils or b-cyano-b-carbe-thoxy styrene 1 (1 mmol), 5,5-
dimethyl-1,3-cyclohexanedione 2 (1 mmol), and TEBA (2 mmol) were added
to a mortar. The mixture was ground with a pestle at room temperature. The
reaction was completed within a few minutes (monitored by TLC) and
poured into water. The product was filtered, dried, and recrystallized from
95% ethanol. All the products were characterized by comparison of their
spectroscopic and physical data with authentic samples synthesized by
reported procedures.[20]
Scheme 1.

2366
L. Rong et al.
Table 1. Synthesis of tetrahydrobenzo[b]pyrans under mild and solvent-free
conditions
Entry
Ar
X
Reaction time (min)
Yield (%)
3a
3b
3c
3d
3e
3f
C6H5
4-ClC6H4
4-FC6H4
CN
CN
CN
CN
CN
CN
CN
CN
CN
10
5
92
95
94
90
85
93
95
91
96
88
93
94
97
90
90
94
92
95
90
96
5
4-CH3C6H4
4-CH3OC6H4
2-ClC6H4
10
10
5
3g
3h
3i
3,4-OCH2OC6H4
4-BrC6H4
8
5
2,4-Cl2C6H4
C6H5
4-ClC6H4
4
3j
COOC2H5
COOC2H5
COOC2H5
COOC2H5
COOC2H5
COOC2H5
COOC2H5
COOCH3
COOCH3
COOCH3
COOCH3
15
8
3k
3l
4-FC6H4
8
3m
3n
3o
3p
3q
3r
3s
2,4-Cl2C6H4
4-CH3C6H4
4-CH3OC6H4
3,4-OCH2OC6H4
C6H5
5
15
15
10
10
8
4-ClC6H4
4-CH3C6H4
2,4-Cl2C6H4
10
8
3t
Spectral and Analytical Data of Some Selected Compounds
Compound 3a: mp: 232–2348C. IR (KBr) n: 3397, 3213, 3034, 2961, 2199,
1681, 1661, 1598, 1443, 1414, 1370, 1251, 1214, 1150, 1036, 843, 812,
1
745, 695 cm21. H NMR (DMSO-d6) d: 0.95 (3H, s, CH3), 1.04 (3H, s,
CH3), 2.10 (1H, d, J ¼ 16.0 Hz, C8-H), 2.25 (1H, d, J ¼ 16.0 Hz, C8-H),
2.47–2.55 (2H, m, C6-H), 4.16 (1H, s, C4-H), 6.99 (2H, s, NH2), 7.12–7.30
(5H, m, ArH). Anal. calcd. for C18H18N2O2: C, 73.45; H, 6.16; N, 9.52.
Found: C, 73.20; H, 6.43; N, 9.61%.
Compound 3b: mp 237–2498C. IR (KBr) n: 3375, 3181, 2958, 2188, 1664,
1596, 1490, 1495, 1398, 1364, 1234, 1215, 1132, 1087, 1032, 854, 825, 770,
1
685 cm21. H NMR (CDCl3, 400 MHz) d: 0.94 (s, 3H, CH3), 1.03 (s, 3H,
CH3), 2.10 (d, J ¼ 16.0 Hz, 1H, C8-H), 2.24 (d, J ¼ 16.0 Hz, 1H, C8-H),
2.46–2.55 (m, 2H, C6-H), 4.19 (s, 1H, C4-H), 7.05 (s, 2H, NH2), 7.16
(d, J ¼ 7.2 Hz, 2H, ArH), 7.34 (d, J ¼ 7.2 Hz, 2H, ArH). Anal. calcd. for
C18H17ClN2O2: C, 65.75; H, 5.21; N, 8.52. Found: C, 65.50; H, 5.40; N, 8.65%.
Compound 3c: mp 192–1948C. IR (KBr) n: 3367, 3179, 2960, 2190, 1675,
1628, 1593, 1506, 1406, 1367, 1253, 1216, 1156, 1131, 1033, 975, 859,

Tetrahydrobenzo[b]pyrans
2367
1
838, 775, 706 cm21. H NMR (CDCl3, 400 MHz) d: 0.94 (s, 3H, CH3), 1.03
(s, 3H, CH3), 2.10 (d, J ¼ 16.0 Hz, 1H, C8-H), 2.24 (d, J ¼ 16.0 Hz, 1H,
C8-H), 2.45–2.57 (m, 2H, C6-H), 4.19 (s, 1H, C4-H), 7.02 (s, 2H, NH2),
7.07–7.19 (m, 4H, ArH). Anal. calcd. for C18H17FN2O2: C, 69.22; H, 5.49;
N, 8.97. Found: C, 69.17; H, 5.34; N, 9.10%.
Compound 3d: mp 220–2228C. IR (KBr) n: 3426, 3331, 2957, 2192, 1676,
1640, 1601, 1510, 1459, 1404, 1369, 1318, 1242, 1205, 1157, 1136, 1033,
1
971, 909, 842, 765 cm21. H NMR (CDCl3, 400 MHz) d: 0.95 (s, 3H, CH3),
1.04 (s, 3H, CH3), 2.09 (d, J ¼ 16.0 Hz, 1H, C8-H), 2.24 (d, J ¼ 16.0 Hz,
1H, C8-H), 2.25 (s, 3H, CH3), 2.45–2.56 (m, 2H, C6-H), 4.12 (s, 1H, C4-
H), 6.96 (s, 2H, NH2), 7.02 (d, J ¼ 8.0 Hz, 2H, ArH), 7.08 (d, J ¼ 8.0 Hz,
2H, ArH); Anal. calcd. for C19H20N2O2: C, 74.00; H, 6.54; N 9.08. Found
C, 74.30; H, 6.77; N, 9.31%.
Compound 3e: mp 196–1988C. IR (KBr) n: 3377, 3186, 2964, 2198, 1681,
1655, 1596, 1509, 1456, 1406, 1369, 1249, 1209, 1171, 1157, 1137, 1037,
.
1034, 968, 843, 768 cm21 1H NMR (CDCl3, 400 MHz) d: 0.95 (s, 3H,
CH3), 1.03 (s, 3H, CH3), 2.09 (d, J ¼ 16.0 Hz, 1H, C8-H), 2.24
(d, J ¼ 16.0 Hz, 1H, C8-H), 2.46–2.56 (m, 2H, C6-H), 3.71 (s, 3H, OCH3),
4.12 (s, 1H, C4-H), 6.84 (d, J ¼ 8.0 Hz, 2H, ArH), 6.95 (s, 2H, NH2), 7.05
(d, J ¼ 8.0 Hz, 2H, ArH). Anal. calcd. for C19H20N2O3: C, 74.35; H, 6.21;
N, 8.64. Found: C, 74.25; H, 6.77; N, 8.31%.
Compound 3j: mp: 151–1538C. IR (KBr) n: 3403, 3290, 3027, 2956, 1693,
1655, 1606, 1524, 1475, 1453, 1371, 1288, 1202, 1165, 1081, 1039, 835,
1
796, 725, 697 cm21. H NMR (DMSO-d6) d: 0.89 (3H, s, CH3), 1.04 (3H,
s, CH3), 1.09 (3H, t, J ¼ 7.2 Hz CH3), 2.06 (1H, d, J ¼ 16.0 Hz, C8-H),
2.26 (1H, d, J ¼ 16.0 Hz, C8-H), 2.46 (1H, d, J ¼ 17.6 Hz, C6-H), 2.55 (1H,
d, J ¼ 17.6 Hz, C6-H), 3.94 (2H, q, J ¼ 7.2 Hz, CH2O), 4.50 (1H, s, C4-H),
7.02–7.22 (5H, m, ArH), 7.54 (2H, s NH2). Anal. calcd. for C20H23NO4: C,
70.36; H, 6.79; N, 4.10. Found: C, 70.53; H, 6.63; N, 3.97%.
Compound 3k: mp: 153–1548C. IR (KBr) n: 3480, 3327, 2976, 1681, 1665,
1
1524, 1485, 1371, 1302, 1298, 1202, 1165, 1081, 1039, 915, 835 cm21. H
NMR (DMSO-d6) d: 0.89 (3H, s, CH3), 1.04 (3H, s, CH3), 1.09 (3H, t,
J ¼ 7.2 Hz CH3), 2.06 (1H, d, J ¼ 16.0 Hz, C8-H), 2.26 (1H,
d, J ¼ 16.0 Hz, C8-H), 2.46 (1H, d, J ¼ 17.6 Hz, C6-H), 2.55 (1H, d,
J ¼ 17.6 Hz, C6-H), 3.94 (2H, q, J ¼ 7.2 Hz, CH2O), 4.50 (1H, s, C4-H),
7.12–7.22 (5H, m, ArH), 7.56 (2H, s NH2). Anal. calcd. for C20H22ClNO4:
C, 63.91; H, 5.90; N, 3.73. Found: C, 64.08; H, 5.71; N, 3.58%.
Compound 3n: mp: 165–1668C. IR (KBr) n: 3408, 3289, 2976, 1692, 1665,
1
1625, 1520, 1485, 1370, 1298, 1202, 1081, 1039, 835, 789 cm21. H NMR
(DMSO-d6) d: 0.89 (3H, s, CH3), 1.04 (3H, s, CH3), 1.09 (3H, t, J ¼ 7.2 Hz

2368
L. Rong et al.
CH3), 2.06 (1H, d, J ¼ 16.0 Hz, C8-H), 2.20 (3H, s, CH3), 2.26 (1H,
d, J ¼ 16.0 Hz, C8-H), 2.46 (1H, d, J ¼ 17.6 Hz, C6-H), 2.55 (1H, d,
J ¼ 17.6 Hz, C6-H), 2.53 (1H, d, J ¼ 17.6 Hz, C6-H), 3.94 (2H, q,
J ¼ 7.2 Hz, CH2O), 4.50 (1H, s, C4-H), 6.92–7.02 (4H, m, ArH), 7.50 (2H,
s NH2). Anal. calcd. for C21H25NO4: C, 70.96; H, 7.09; N, 3.94. Found: C,
70.41; H, 6.83; N, 3.94%.
Compound 3q: mp: 144–1468C. IR (KBr) n: 3405, 3304, 2955, 1693, 1655,
1536, 1438, 1370, 1286, 1204, 1164, 1075, 1036, 838, 792, 766, 728,
1
704 cm21. H NMR (DMSO-d6) d: 0.88 (3H, s, CH3), 1.03 (3H, s, CH3),
2.06 (1H, d, J ¼ 16.0 Hz, C8-H), 2.26 (1H, d, J ¼ 16.0 Hz, C8-H), 2.45 (1H,
d, J ¼ 16.0 Hz, C6-H), 2.53 (1H, d, J ¼ 16.0 Hz, C6-H), 3.50 (3H, s,
CH2O), 4.52 (1H, s, C4-H), 7.06–7.22 (5H, m, ArH), 7.52 (2H, s NH2).
Anal. calcd. for C19H21NO4: C, 69.71; H, 6.47; N, 4.28. Found: C, 69.77;
H, 6.34; N, 4.66%.
Compound 3r: mp: 160–1618C. IR (KBr) n: 3478, 3319, 2960, 1693, 1655,
1536, 1488, 1370, 1286, 1204, 1164, 1075, 1036, 838, 792, 766, 728,
1
704 cm21. H NMR (DMSO-d6) d: 0.88 (3H, s, CH3), 1.03 (3H, s, CH3),
2.06 (1H, d, J ¼ 16.0 Hz, C8-H), 2.26 (1H, d, J ¼ 16.0 Hz, C8-H), 2.45 (1H,
d, J ¼ 16.0 Hz, C6-H), 2.53 (1H, d, J ¼ 16.0 Hz, C6-H), 3.50 (3H, s,
CH2O), 4.52 (1H, s, C4-H), 7.15 (2H, J ¼ 8.0 Hz, ArH), 7.25 (2H,
J ¼ 8.0 Hz), 7.58 (5H, m, ArH), 7.55 (2H, s NH2). Anal. calcd. for
C19H20ClNO4: C, 63.07; H, 5.57; N, 3.87. Found: C, 63.28; H, 5.46; N, 3.88%.
Compound 3s: mp: 190–1928C. IR (KBr) n: 3412, 3309, 2960, 1693, 1655,
1653, 1520, 1438, 1370, 1286, 1204, 1164, 1081, 1036, 907, 845, 792, 766,
740, 704 cm21. 1H NMR (DMSO-d6) d: 0.88 (3H, s, CH3), 1.03 (3H, s, CH3),
2.06 (1H, d, J ¼ 16.0Hz, C8-H), 2.26 (1H, d, J ¼ 16.0Hz, C8-H), 2.45 (1H,
d, J ¼ 16.0Hz, C6-H), 2.53 (1H, d, J ¼ 16.0Hz, C6-H), 3.50 (3H, s, CH2O),
4.52 (1H, s, C4-H), 6.98–7.03 (4H, m, ArH), 7.48 (2H, s NH2). Anal. calcd.
for C20H23NO4: C, 70.36; H, 6.79; N, 4.10. Found: C, 70.65; H, 6.52; N, 3.95%.
ACKNOWLEDGMENT
We are grateful to Natural Science Foundation (04XLB14) of Xuzhou Normal
University and the Foundation of the Key Laboratory of Biotechnology on
Medical Plants of Jiangsu Province for financial support.
REFERENCES
1. Tanaka, K.; Toda, F. Chem. Rev. 2000, 100, 1025.
2. Toda, F.; Takumi, H.; Yamaguchi, H. Chem. Exp. 1989, 4, 507.

Tetrahydrobenzo[b]pyrans
2369
3. Tanaka, K.; Kishigami, S.; Toda, F. J. Org. Chem. 1991, 56, 4333.
4. Toda, F.; Tanaka, K.; Hamai, K. J. Chem. Soc. Perkin Trans. 1 1990, 3207.
5. Toda, F.; Suzuki, T.; Higa, S. J. Chem. Soc. Perkin Trans. 1 1998, 3521.
6. Toda, F.; Tanaka, K.; Iwata, S. J. Org. Chem. 1989, 54, 3007.
7. Toda, F.; Kiyoshige, K.; Yagi, M. Angew. Chem. Int. Ed. Engl. 1989, 28, 320.
8. (a) Schmeyers, T.; Toda, F.; Boy, J.; Kaupp, G. J. Chem., Soc. Perkin Trans. 2
1998, 989; (b) Hagiwara, H.; Obtsubo, S.; Kato, M. Mol. Cryst. Liq. Cryst.
1996, 279, 291; (c) Tanaka, M.; Kobayashi, K. J. Chem. Soc., Chem.
Coummun. 1998, 1965; (d) Im, J.; Kim, J.; Kim, S.; Hahu, B.; Toda, F. Tetra-
hedron Lett. 1997, 38, 451.
9. (a) Dean, F. M. Naturally Occuring Oxygen Ring Compounds; Butterworth:
London, 1963; (b) Bigi, F.; Chesini, L.; Maggi, R.; Sartori, G. J. Org. Chem.
1999, 64, 1033.
10. (a) Evans, J. M.; Fake, C. S.; Hamilton, T. C.; Poyser, R. H.; Watts, E. A. J. Med.
Chem. 1990, 33, 492; (b) Bergmann, R.; Gericke, R. J. Med. Chem. 1990, 33, 492;
(c) Arnoldi, A.; Bonsignori, A.; Melloni, P.; Merlini, L.; Quadri, M. L.;
Rossi, A. C.; Valsecchi, M. J. Med. Chem. 1990, 33, 2865.
11. Green, G. R.; Evans, J. M.; Vong, A. K. In Comprehensive Heterocyclic Chemistry
II; Katritzky, A. R., Rees, C. W., Scriven, E. F. V., Eds.; Pergamon Press: Oxford,
1995; Vol. 5, p. 469.
12. (a) Foye, W. O. Prinicipi di Chemico Farmaceutica; Piccin: Padova, Italy; 1991;
416; (b) Andreani, L. L.; Lapi, E. Bull. Chim. Farm. 1960, 99, 583;
(c) Zhang, Y. L.; Chen, B. Z.; Zheng, K. Q.; Xu, M. L.; Lei, X. H. Yao. Xue.
Xue. Bao. 1982, 17, 17; Chem. Abstr. 1982, 96, 135383e; (d) Bonsignore, L.;
Loy, G.; Secci, D.; Calignano, A. Eur. J. Med. Chem. 1993, 28, 517;
(e) Witte, E. C.; Neubert, P.; Roesch, A. Ger. Offen. DE 1986; Chem. Abstr.
1986, 104, 224915f.
13. (a) Hatakeyama, S.; Ochi, N.; Numata, H.; Takano, S.. J. Chem. Soc., Chem.
Commun. 1988, 1202; (b) Gonzalez, R.; Martin, N.; Seoane, C.; Soto, J. J.
Chem. Soc., Perkin Trans. 1 1985, 1202.
14. Arnetso, D.; Horspool, W. M.; Martin, N.; Ramos, A.; Seaone, C.. J. Org. Chem.
1989, 54, 3069.
15. Kamaljit, S.; Jasbir, S.; Harjit, S. Tetrahedron 1996, 52, 14273.
16. Wang, X. S.; Shi, D. Q.; Tu, S. J.; Yao, C. S. Synth. Commun. 2003, 33, 119.
17. Kaupp, G.; Naimi-Zamal, M. R.; Schmeyers, J. Tetrahedron 2003, 59, 3753.
18. Ipsita, D.; Pulak, J. B. Tetrahedron Lett. 2004, 45, 8625.
19. Tu, S. J.; Zhou, J. F.; Cai, P. J.; J Feng, C. Synth. Commun. 2001, 31, 3729.
20. Shi, D. Q.; Zhang, S.; Zhuang, Q. Y.; Tu, S. J. Chin. J. Org. Chem. 2003, 23 (8),
877.
21. Our unpublished works.