Phosphomolybdic acid-catalyzed efficient one-pot three-component aza-Diels-Alder reactions under solvent-free conditions: a facile synthesis of trans-fused pyrano- and furanotetrahydroquinolines

Article abstract of DOI:10.1016/j.tetlet.2006.04.085

trans-Fused pyrano- and furanotetrahydroquinoline derivatives have been synthesized via a one-pot three-component aza-Diels-Alder reaction of aryl imines formed in situ from aromatic amines and arylaldehydes with cyclic enol ethers,such as 3,4-dihydro-2H-

Full text of DOI:10.1016/j.tetlet.2006.04.085

Tetrahedron Letters 47 (2006) 4409–4413
Phosphomolybdic acid-catalyzed efficient one-pot three-component
aza-Diels–Alder reactions under solvent-free conditions: a
facile synthesis of trans-fused pyrano- and
furanotetrahydroquinolines
K. Nagaiah,* D. Sreenu, R. Srinivasa Rao, G. Vashishta and J. S. Yadav
Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad 500007, India
Received 17 February 2006; revised 10 April 2006; accepted 19 April 2006
Available online 11 May 2006
Abstract—trans-Fused pyrano- and furanotetrahydroquinoline derivatives have been synthesized via a one-pot three-component
aza-Diels–Alder reaction of aryl imines formed in situ from aromatic amines and arylaldehydes with cyclic enol ethers,such as
3,4-dihydro-2H-pyran and 2,3-dihydrofuran,in the presence of 1 mol % of phosphomolybdic acid under solvent-free conditions
at room temperature in good to excellent yields.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Pyrano- and furanoquinoline derivatives are an impor-
tant class of natural products and exhibit a wide spectrum
of biological activities, such as antiallergic, anti-inflam-
matory, antipyretic, analgesic, antiplatelet, psychotropic
and estrogenic activity.1 Many biologically active alkal-
oids, such as simulenoline 1, huajiaosimuline 2, zanthod-
ioline 3, flindersine 4, teclealbine 5 and flindersiamine 6,
contain pyranoquinoline and furanoquinoline moieties
(Fig. 1).1d,1e,2 Hence, the synthesis of pyranoquinoline
and furanoquinoline derivatives is, currently, of much
importance. Generally, the pyranoquinoline and furano-
quinoline derivatives are prepared by aza-Diels–Alder
reactions of imines (derived from various aromatic amines
and aromatic aldehydes) with different dienophiles, such
as 3,4-dihydro-2H-pyran and 2,3-dihydrofuran, in the
presence of different acid catalysts.3–6 However, many
of these reactions cannot be carried out in a one-pot oper-
ation with a carbonyl compound, amine and enol ether,
because the amines and water that exist during imine
formation can decompose or deactivate the Lewis acids.
Thus, more than stoichiometric amounts of the Lewis
acids are required because the acids can be trapped by
nitrogen of both the reactant and the product.1 Further-
more, most of the imines are hygroscopic, unstable at
high temperatures and are difficult to purify by distilla-
tion or column chromatography. One-pot procedures
have been developed for this transformation, using lan-
thanide chlorides4f and lanthanide triflates7 as catalysts.
Even though these procedures do not require the isolation
of unstable imines prior to the reactions, metal triflates
are not easily available or are expensive, and afford a
mixture of products with unsatisfactory yields. These lim-
itations prompted us to develop simple, convenient, effi-
cient, economic and environmentally benign approaches
for the single step synthesis of pyrano- and furanoquino-
line derivatives.
In view of the emerging importance of environmental
awareness in chemical and pharmaceutical industries,
the development of environmentally benign organic
reactions have become a crucial and demanding research
area in modern organic chemical research.8 Due to envi-
ronmental awareness, chemists are devoted towards
‘green chemistry’, which by definition is the design,
development and implementation of chemical products
and processes to reduce or eliminate the use and gener-
ation of substances hazardous to human health and the
environment. Heteropolyacids (HPAs) are environmen-
tally friendly and economically feasible solid acids
owing to their high catalytic activities and reactivities,
ease of handling; they allow cleaner reactions in compar-
ison to conventional catalysts and are non-toxic and,
Keywords: Arylimines; Phosphomolybdic acid; Aza-Diels–Alder reac-
tion; Solvent-free conditions; Tetrahydroquinolines.
*
Corresponding author. Tel.: +91 40 27160123; fax: +91 40
27160512; e-mail: nagaiah@iict.res.in
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.04.085

4410
K. Nagaiah et al. / Tetrahedron Letters 47 (2006) 4409–4413
O
O
OH
O
O
HO
O
HO
N
N
N
OMe
O
O
CH3
CH3
1 simulenoline
2 huajiaosimuline
3 zanthodioline
OMe
OMe
O
O
O
MeO
O
N
O
N
N
H
O
OMe
O
4 flindersine
5 teclealbine
6 flindersiamine
Figure 1.
O
O
H
H
NH2
PMA (1 mol%)
H
R
R
H
ArCHO
+
+
R
+
O
solvent-free, r.t.
3-6 h
Ar
N
N
H
Ar
H
1
DHF
2
3 trans-isomer
4 cis-isomer
major
minor
Scheme 1.
O
H
O
H
NH2
PMA (1 mol%)
R
H
R
H
ArCHO
+
+
R
+
O
DHP
N
H
Ar
N
H
solvent-free, r.t.
3-6 h
Ar
1
2
5 trans-isomer
6 cis-isomer
major
minor
Scheme 2.
hence, are regarded as green catalysts.9 Also, heteropoly-
acids are promising redox and bifunctional catalysts in
homogeneous as well as heterogeneous conditions.10
Among the heteropolyacids, phosphomolybdic acid
(PMA, H3PMO12O40) is one of the less expensive, com-
mercially available catalysts. Hence, its important cata-
lytic properties in many organic transformations, such
as the dehydration of alcohols,11 tetrahydropyranylation
of phenols,12 Friedel–Crafts C-alkylation of aromatic
compounds,13 aziridination of olefins,14 ring opening of
aziridines15 and in the synthesis of homoallylic amines,16
have been explored. However, there are no reports on the
use of phosphomolybdic acid for the synthesis of pyrano-
and furanoquinoline derivatives.
In a similar manner, treatment of anilines 1 and benz-
aldehydes 2 with 3,4-dihydro-2H-pyran (DHP) in the
presence of 1 mol % of phosphomolybdic acid under
solvent-free conditions gave the corresponding pyrano-
quinolines 5 and 6 in 90% yield (Scheme 2).
Table 1. Optimisation of the catalytic and solvent conditions on the
reaction of aniline 1 g, benzaldehyde 2 g and 3,4-dihydro-2H-pyrana
Entry Solvent
Catalyst Time Yieldb Productc
(mol %) (h)
trans:cis
1
2
3
4
5
6
7
8
9
CH2Cl2
CHCl3
1,2-Dichloroethane
CH3CN
n-Hexane
None
None
None
None
None
1.0
1.0
1.0
1.0
1.0
None
1.0
2.0
5.0
10.0
12
12
12
12
12
24
3
3
3
3
60
62
69
71
75
—
92
87
75
72
57:43
60:40
65:35
68:32
75:25
—
90:10
88:12
85:15
82:18
In this letter, we describe a mild and efficient approach
for the synthesis of pyrano- and furanoquinoline deriv-
atives via aza-Diels–Alder reactions, using phosphomo-
lybdic acid as catalyst, in good to excellent yields.
Accordingly, treatment of anilines 1 and benzaldehydes
2 with 2,3-dihydrofuran (DHF) in the presence of
1 mol % of phosphomolybdic acid under solvent-free
conditions gave the corresponding furanoquinolines 3
and 4 in 92% yield (Scheme 1).
10
a Reaction conditions: Benzaldehyde (1 mmol), aniline (1 mmol), 3,4-
dihydro-2H-pyran (2 mmol), solvent (5 ml) or no solvent.
b Isolated and unoptimized yields.
c Ratio of the products was determined from the crude 1H NMR spectra.

K. Nagaiah et al. / Tetrahedron Letters 47 (2006) 4409–4413
4411
Initially, a systematic study was carried out for the cata-
lytic evaluation of phosphomolybdic acid in the reaction
of aniline 1g and benzaldehyde 2g with 3,4-dihydro-2H-
pyran (DHP) with different solvents and catalytic loads
(Table 1). The best result was obtained with 1 mol % of
the catalyst under solvent-free conditions in terms of
reaction times, yields and diastereoselectivity. However,
in the absence of the catalyst, the reaction did not
proceed even after a longer reaction time (24 h).
the results are summarized in Table 2. Various imines,
generated in situ from aldehydes and amines, immedi-
ately react with dihydrofuran or dihydropyran afforded
furano- and pyranoquinolines via one-pot without the
need of preformation of the imines. In most cases, the
product was obtained as a mixture of cis- and trans-iso-
mers favoring the trans-isomer. In all cases, the products
were obtained in good yields with high diastereoselectiv-
ity. The diastereomers could be easily separated by col-
umn chromatography on silica gel. The ratio of the
1
To investigate the scope of the phosphomolybdic acid
catalysed synthesis of pyrano- and furanoquinolines,
several aldimines (formed in situ from aromatic alde-
hydes and anilines in acetonitrile) were examined, and
diastereomers was determined from H NMR spectra
of the crude products, and the structures were estab-
lished from the spectral (1H NMR and MS) data of
the pure compounds. This method is equally effective
Table 2. Phosphomolybdic acid catalyzed synthesis of pyrano- and furanoquinolinesa
Entry
R
Ar
Enol ether
Time [h]
3.0
Yield [%]b
92
Product trans/cisc
a
H
C6H5
8:12
O
O
O
O
O
O
b
c
d
e
f
H
4-MeOC6H4
4-FC6H4
4-ClC6H4
H
4.0
3.0
3.5
4.5
4.0
3.5
3.0
3.5
5.0
6.0
4.5
4.0
3.5
6.0
4.0
90
89
85
87
92
90
87
89
83
80
81
85
87
90
89
87:13
85:15
78:22
88:12
75:25
90:10
85:15
88:12
83:17
80:20
82:18
78:22
85:15
73:27
75:25
H
4-Me
4-MeO
4-MeO
H
4-FC6H4
C6H5
g
h
i
O
O
O
O
O
O
O
O
O
O
H
4-ClC6H4
4-FC6H4
C6H5
H
j
4-Me
4-Me
2-Me
4-MeO
4-F
k
l
4-MeOC6H4
C6H5
m
n
o
p
C6H5
C6H5
1-Naphthyl
1-Naphthyl
C6H5
4-FC6H4
a Reaction conditions: aldehyde (1 mmol), amine (1.5 mmol), enol ether (2 mmol), PMA (1 mol %), solvent-free.
b All products were characterized by 1H and 13C NMR, IR and mass spectroscopy.
c Product ratio was determined from the 1H NMR spectra of the crude products.

4412
K. Nagaiah et al. / Tetrahedron Letters 47 (2006) 4409–4413
1995, 233–234; (c) Kobayashi, S.; Ishitani, H.; Nagayama,
S.; Hachiya, I. Synlett 1995, 1195–1202; (d) Nagarajan, R.;
Chitra, S.; Perumal, P. T. Tetrahedron 2001, 57, 3419–
3423.
for both electron-rich as well as electron deficient aryl
imines. Also, this method offers several advantages, such
as higher yields, shorter reaction times, high trans-selec-
tivity, cleaner reaction profiles and simple experimental
and work-up procedures. All the products were charac-
8. (a) Anastas, P.; Williamson, T. Green Chemistry. In
Frontiers in Benign Chemical Synthesis and Procedures;
Oxford Science Publications: Oxford, 1998; (b) Ritter, S.
K. Chem. Eng. News 2001, 27–34.
9. (a) Clark, J. H. Acc. Chem. Res. 2002, 35, 791; (b) Misono,
M.; Ono, I.; Koyano, G.; Aoshima, A. Pure Appl. Chem.
2000, 72, 1305.
10. (a) Kozhevnikov, I. V. Chem. Rev. 1998, 98, 171; (b)
Mizuno, N.; Misono, M. Chem. Rev. 1998, 98, 199; (c)
Mizuno, N.; Misono, M. Chem. Rev. 1998, 98, 199.
11. Vazquez, P.; Pizzio, L.; Caceres, C.; Blanco, M.; Thomas,
H.; Alesso, E.; Finkielsztein, L.; Lantano, B.; Moltrasio,
G.; Aguirre, J. J. Mol. Cat. A 2000, 161, 223–232.
12. Romanelli, G.; Vazquez, P.; Pizzio, L.; Quaranta, N.;
Autino, J.; Blanco, M.; Caceres, C. Appl. Catal. A 2004,
261, 163–170.
1
terized by H NMR, 13C NMR, IR and mass spectro-
scopic data and also by comparison with authentic
samples.17
In conclusion, we have described a simple, mild and effi-
cient protocol for the synthesis of trans-fused furano-
and pyranoquinolines via a three-component one-pot
aza-Diels–Alder reaction of aldehydes, amines and cyc-
lic enol ethers, using 1 mol % of commercially available
and cheap phosphomolybdic acid (PMA) as catalyst.
Acknowledgements
13. Pizzio, L. R.; Vazquez, P. G.; Caceres, C. V.; Blanco, M.
N.; Alesso, E. N.; Torviso, M. R.; Lantano, B.; Moltra-
sio, G. Y.; Aguirre, J. M. Appl. Catal. A 2005, 287, 1–8.
14. Kishore Kumar, G. D.; Baskaran, S. Chem. Commun.
2004, 1026–1027.
D.S. and R.S.R. thank CSIR, New Delhi, for the award
of fellowships.
15. Kishore Kumar, G. D.; Baskaran, S. Synlett 2004, 1719–
1722.
References and notes
16. Smitha, G.; Bruhaspathy, M.; Williamson, J. S. Synlett
2005, 839–841.
17. Experimental procedure: A mixture of aryl amine 1
1. (a) Faber, K.; Stueckler, H.; Kappe, T. J. Hetercycl.
Chem. 1984, 21, 1177–1178; (b) Johnson, J. V.; Rauck-
man, S.; Baccanari, P. D.; Roth, B. J. Med. Chem. 1989,
32, 1942–1949; (c) Yamada, N.; Kadowaki, S.; Takahashi,
K.; Umezu, K. Biochem. Pharmacol. 1992, 44, 1211; (d)
McLaughlin, M. J.; Hsung, R. P. J. Org. Chem. 2001, 66,
1049–1053; (e) Michael, J. P. Nat. Prod. Rep. 2005, 22,
627–646.
(1.0 mmol), aromatic aldehyde
2
(1.0 mmol), 2,3-
dihydrofuran or 3,4-dihydro-2H-pyran (2.0 mmol) and
phosphomolybdic acid (PMA) (18 mg, 1 mol %), under
solvent-free conditions, was stirred at ambient tempera-
ture for the appropriate time (Table 2). The progress of the
reaction was monitored by TLC. After completion, the
reaction mixture was extracted with diethyl ether
(3 · 10 mL). The combined organic layers were dried over
anhydrous Na2SO4, concentrated in vacuo and purified by
column chromatography over silica gel to yield the
corresponding furano- and pyranoquinolines. All prod-
2. Ramesh, M.; Mohan, P. S.; Shanmugam, P. Tetrahedron
1984, 40, 4041.
3. (a) Boger, D. L.; Weinreb, S. M. J. Hetero Diels–Alder
Methodology in Organic Synthesis; Academic Press: San
Diego, 1987; Chapters 2 and 9; (b) Weinreb, S. M. In
Comprehensive Organic Synthesis; Trost, B. M., Fleming,
I., Eds.; Pergamon: Oxford, 1991; Vol. 5, pp 401–449.
4. (a) Povarov, L. S. Russ. Chem. Rev. 1967, 36, 656–670; (b)
Cabral, J.; Laszlo, P. Tetrahedron Lett. 1989, 30, 7237–
7238; (c) Babu, G.; Perumal, P. T. Tetrahedron Lett. 1998,
39, 3225–3228; (d) Baudelle, R.; Melnyk, P.; Deprez, B.;
Tartar, A. Tetrahedron 1998, 54, 4125–4140; (e) Crousse,
B.; Begue, J. P.; Delpon, D. B. Tetrahedron Lett. 1998, 39,
5765–5768; (f) Ma, Y.; Qian, C.; Xie, M.; Sun, J. J. Org.
Chem. 1999, 64, 6462–6467.
5. (a) Babu, G.; Nagarajan, R.; Perumal, P. T. Synthesis
2000, 661–666; (b) Yadav, J. S.; Reddy, B. V. S.; Madhuri,
Ch.; Sabitha, G. Synthesis 2001, 1065–1068; (c) Yadav, J.
S.; Reddy, B. V. S.; Srinivas, R.; Madhuri, Ch.; Rama-
lingam, T. Synlett 2001, 240; (d) Buonora, P.; Olsen, J. C.;
Oh, T. Tetrahedron 2001, 57, 6099–6138.
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Delpon, D.; Begue, J. P. Tetrahedron Lett. 2003, 44, 217–
219; (b) Yadav, J. S.; Reddy, B. V. S.; Reddy, J. S. S.; Rao,
R. S. Tetrahedron 2003, 59, 1599–1604; (c) Yadav, J. S.;
Reddy, B. V. S.; Sunitha, V.; Reddy, K. S. Adv. Synth.
Catal. 2003, 345, 1203–1206; (d) Ravindranath, N.;
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2003, 32, 222–223; (e) Srinivas, K. V. N. S.; Das, B. Synlett
2004, 1715–1718, and references cited therein.
1
ucts were characterized by H NMR, 13C NMR, IR and
mass spectroscopic data and also by comparison with
authentic samples. The spectroscopic data of known
products were identical with the data reported in the
literature.3–6 Spectral data for selected products:
Compound 3a: trans-4-Phenyl-2,3,3a,4,5,9b-hexahydro-furo-
[3,2-c]quinoline:viscous oil, IR (KBr):mmax: 3329, 2952, 1610,
1055 cmÀ1; 1H NMR (200 MHz, CDCl3): d 1.72(m, 1H), 2.00
(m, 1H), 2.45 (m, 1H), 3.85 (m, 3H), 4.10 (m, 1H), 4.60 (d,
J = 5.2 Hz, 1H), 6.64 (d, J = 8.2 Hz, 1H), 6.80 (td, J = 7.9,
0.9 Hz, 1H,), 7.18 (td, J = 7.9, 0.9 Hz, 1H), 7.24–7.46(m, 6H).
13C NMR (50 MHz, CDCl3): d 145.5, 141.6, 131.0, 128.9,
128.6, 128.2, 128.0, 120.0, 118.0, 114.4, 76.0, 65.2, 57.4, 43.3,
28.6. EIMS (EI, 70 eV): m/z: 251 M+, 206.
Compound 4a: cis-4-Phenyl-2,3,3a,4,5,9b-hexahydro-furo-
[3,2-c]quinoline: white solid, mp 93–95 ꢁC; IR (KBr): mmax
:
3350, 2975, 2855, 1612, 1485, 1072 cmÀ1 1H NMR
,
(200 MHz, CDCl3): d 1.55 (m, 1H), 2.25 (m, 1H), 2.75 (m,
1H), 3.82 (m, 3H), 4.70 (d, J = 2.9 Hz, 1H), 5.25 (d,
J = 8.2 Hz, 1H), 6.60 (d, J = 8.2 Hz, 1H), 6.80 (d, J =
8.2 Hz, 1H), 7.05 (t, J = 8.2 Hz, 1H), 7.35–7.55 (m, 6H). 13
C
NMR (50 MHz, CDCl3): d 144.7, 142.3, 130.0, 128.7, 128.2,
127.5, 126.2, 122.5, 119.0, 114.8, 75.8, 66.6, 57.4, 45.7, 24.4.
EIMS (EI, 70 eV): m/z: 251 M+, 206, 174, 130, 91. Anal.
Calcd for C17H17NO (251.32): C, 81.24; H, 6.82; N, 5.57.
Found: C, 81.27; H, 6.85; N, 5.60.
Compound 5g: trans-5-Phenyl-3,4,4a,5,6,10b-hexahydro-2H-
pyrano[3,2-c]quinoline: Pale yellow oil; IR (KBr): mmax: 3325,
7. (a) Makioka, Y.; Shindo, T.; Taniguchi, Y.; Takaki, K.;
Fujwara, Y. Synthesis 1995, 801–804; (b) Kobayashi, S.;
Araki, M.; Ishitani, H.; Nagayama, S.; Hachiya, I. Synlett

K. Nagaiah et al. / Tetrahedron Letters 47 (2006) 4409–4413
4413
2940, 2864, 1605, 1480, 1080 cmÀ1
,
1H NMR (200 MHz,
(265.35): C, 81.48; H, 7.22; N, 5.28. Found: C, C, 81.50; H,
7.24; N, 5.30.
CDCl3): d 1.25–1.60 (m, 3H), 1.80–1.90 (m, 1H), 2.00–2.10
(m, 1H), 3.75 (dt, J = 11.5, 2.5 Hz, 1H), 4.00–4.10 (m, 2H),
4.40 (d, J = 2.5 Hz, 1H), 4.75 (d, J = 10.8 Hz, 1H), 6.50 (d,
J = 8.0 Hz, 1H), 6.70 (t, J = 7.5 Hz, 1H), 7.10 (t, J = 7.5 Hz,
1H), 7.25 (d, J = 8.0 Hz, 1H), 7.45–7.55 (m, 5H). 13C NMR
(50 MHz, CDCl3): d 144.5, 142.2, 130.9, 129.5, 128.5, 127.9,
127.7, 120.5, 117.2, 114.2, 74.5, 69.2, 55.0, 39.2, 24.2, 22.2.
EIMS (EI, 70 eV): m/z: 265 M+, 205, 150, 109, 77, 43. Anal.
Calcd for C18H19NO (265.35): C, 81.48; H, 7.22; N, 5.28.
Found: C, C, 81.51; H, 7.24; N, 5.34.
Compound 5p: trans-12-(4-Fluoro-phenyl)-2,3,4a,11,12,12a
hexahydro-1H-4-oxa-11-aza-chrysene: Brown solid, mp
179–181 ꢁC; IR (KBr): mmax: 3378, 2947, 2870, 1668, 1575,
1468, 1081 cmÀ1, 1H NMR (200 MHz, CDCl3): d 1.30–1.45
(m, 2H), 1.60–1.80 (m, 2H), 2.10 (m, 1H), 3.75 (dt, J = 11.5,
2.7 Hz, 1H), 4.10 (d, J = 2.7 Hz, 1H), 4.452 (d, J = 2.7 Hz,
1H), 4.65 (br s, NH, 1H), 4.80 (d, J = 10.8 Hz, 1H), 7.05–
7.15 (m, 2H), 7.20–7.40 (m, 4H), 7.45–7.50 (m, 2H), 7.70–
7.80 (m, 2H). Anal. Calcd for C22H20FNO (333.40): C,
79.26; H, 6.05; F, 5.70, N, 4.20. Found: C, 79.28; H, 6.10; F,
5.74, N, 4.22.
Compound 6p: cis-12-(4-Fluoro-phenyl)-2,3,4a,11,12,12a-
hexahydro-1H-4-oxa-11-aza-chrysene: Brown solid, mp 138–
140 ꢁC; IR (KBr): mmax: 3370, 2945, 2860, 1665, 1570, 1465,
1080 cmÀ1, 1H NMR (200 MHz, CDCl3): d1.20–1.35 (m, 2H),
1.40–1.55 (m, 2H), 2.10 (m, 1H), 3.25 (dt, J = 11.5, 2.5 Hz,
1H), 3.50 (dd, J = 11.5, 2.5 Hz, 1H), 4.00 (br s, NH, 1H), 4.70
(d, J = 2.7 Hz, 1H), 5.40 (d, J = 5.7 Hz, 1H), 7.00 (m, 2H),
7.20 (m, 1H), 7.35 (m, 2H), 7.40–7.50 (m, 3H). 7.65 (m, 2H).
Anal. Calcd for C22H20FNO (333.40): C, 79.26; H, 6.05; F,
5.70; N, 4.20. Found: C, 79.30; H, 6.09; F, 5.76; N, 4.24.
Compound 6g: cis-5-Phenyl-3,4,4a,5,6,10b-hexahydro-2H-
pyrano[3,2-c]quinoline: White solid, mp 128–129 ꢁC; IR
(KBr): mmax: 3340, 2970, 2850, 1610, 1490, 1090 cmÀ1, H
1
NMR (200 MHz, CDCl3): d 1.25 (m, 1H), 1.50–1.70 (m,
3H), 2.15–2.20 (m, 1H), 3.40 (dt, J = 11.3, 2.4 Hz, 1H), 3.55
(dd, J = 11.3, 2.4 Hz, 1H), 3.80 (br s, NH, 1H), 4.70 (d, J =
2.7 Hz, 1H), 5.30 (d, J = 5.6 Hz, 1H), 6.55 (d, J = 8.0 Hz,
1H), 6.78 (t, J = 8.0 Hz, 1H), 7.05 (t, J = 7.8 Hz, 1H), 7.25–
7.45 (m, 6H). 13C NMR (50 MHz, CDCl3): d 145.2, 141.2,
128.2, 128.0, 127.7, 127.5, 126.9, 120.4, 118.0, 114.4, 72.8,
60.7, 59.3, 39.0, 25.7, 18.2. EIMS (EI, 70 eV): m/z: 265 M+,
234, 220, 194, 129, 117, 91, 77. Anal. Calcd for C18H19NO