Three-component coupling reactions of isoquinolines, dimethyl acetylenedicarboxylate and indoles: a facile synthesis of 3-indolyl-1,2-dihydro-2-isoquinolinyl-2-butenedioate

Article abstract of DOI:10.1016/j.tetlet.2008.02.129

A three-component coupling of isoquinolines, dimethyl acetylenedicarboxylate (DMAD) and indoles is achieved for the first time to produce dimethyl (E)-2-[1-(1H-3-indolyl)-1,2-dihydro-2-isoquinolinyl]-2-butenedioates in excellent yields and with high selec

Full text of DOI:10.1016/j.tetlet.2008.02.129

Available online at www.sciencedirect.com
Tetrahedron Letters 49 (2008) 2815–2819
Three-component coupling reactions of isoquinolines,
dimethyl acetylenedicarboxylate and indoles: a facile synthesis
of 3-indolyl-1,2-dihydro-2-isoquinolinyl-2-butenedioate
J. S. Yadav *, B. V. Subba Reddy, Nagendra Nath Yadav, Manoj K. Gupta
Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Received 23 November 2007; revised 19 February 2008; accepted 22 February 2008
Available online 4 March 2008
Abstract
A three-component coupling of isoquinolines, dimethyl acetylenedicarboxylate (DMAD) and indoles is achieved for the first time to
produce dimethyl (E)-2-[1-(1H-3-indolyl)-1,2-dihydro-2-isoquinolinyl]-2-butenedioates in excellent yields and with high selectivity. The
reaction proceeds smoothly at room temperature without a catalyst. Quinoline, DMAD and indole also undergo smooth coupling to
furnish dimethyl (E)-2-[2-(1H-3-indolyl)-1,2-dihydro-1-quinolinyl]-2-butenedioate under similar conditions. This method is very useful
to functionalize both indoles and aza-aromatic compounds in a one-pot operation.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Isoquinoline/quinoline; Indole; Dimethyl acetylenedicarboxylate; 3-Indolyl-dihydroisoquinolines
Indole nucleus is frequently found in medicinal chemis-
try and is considered as ‘privileged scaffolds’.1 SUGEN
found an indolin-2-one as a pharmacophore for potent
KDR kinase inhibitors,2 and Merck recently reported a
class of potent KDR kinase inhibitors containing the
indol-2-yl quinolin-2-one structure (Fig. 1).3
Isoquinoline is also present in various natural products
such as cryptaustoline (i) and cryptowoline (ii) (Fig. 2).4
They are known to exhibit various biological activities such
as antileukaemic,5 tubulin polymerization inhibitory6 and
anti-tumour activities.7,8 Related synthetic acetoxy-substi-
tuted 5,6-dihydro[2,1-a]isoquinolines (iii) also exhibit
strong binding affinities for the oestrogen receptor of
O
O
N
MeO
-
MeO
HO
N
I
-
N
H
MeO
HO
I
H
Me
+
N
OMe
OMe
O
N
Me
+
O
N
H
N
O
O
H
O
N
N
Ms
(ii) Cryptowoline
(i) Cryptaustoline
N
H
O
N
AcO
H
N
Fig. 1. Merck KDR inhibitors.
OAc
(iii)
*
Corresponding author. Tel.: +91 40 27193030; fax: +91 40 27160512.
Fig. 2. Biologically active indolo[2,1-1]isoquinolines.
E-mail address: yadavpub@iict.res.in (J. S. Yadav).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.02.129

2816
J. S. Yadav et al. / Tetrahedron Letters 49 (2008) 2815–2819
MDA-MB 231 and MCF-7 mammary tumour cell lines.9 It
has also been reported that hydroxy-substituted indolo-
[2,1-a]isoquinolines bind to the colchicine binding site
and inhibit the polymerization of tubulin.9
Given this proven utility, it seems reasonable that the
synthesis of a novel series of indol-3-yl-1,2-dihydro quino-
CO2Me
CO2Me
CO2Me
CH2Cl2, r.t.
2 h
N
+
+
N
N
H
CO2Me
N
H
1
2
4a
3
Scheme 1. Preparation of product 4a.
Table 1
Three-component coupling reactions of isoluinolines, DMAD and indoles
Entry
Isoquinoline
1
DMAD
2
Indole
3
Producea
4
Time (h)
2.0
Yieldb (%)
CO2Me
CO2Me
N
R
a
90
N
H
N
N
N
N
N
H
CO2Me
CO2Me
N
R
b
c
4.0
2.0
1.5
78
92
85
N
CH2Ph
N
N
PhCH2
CO2Me
CO2Me
R
N
H
Me
Ph
Me
N
H
CO2Me
CO2Me
N
R
d
N
H
Ph
N
H
Br
CO2Me
CO2Me
Br
N
R
e
f
2.5
4.0
70
60
N
H
N
N
N
H
O2N
CO2Me
CO2Me
O2N
N
R
N
H
N
H
Br
CO2Me
CO2Me
Br
N
N
R
g
2.5
75
N
H
N
H
Br
CO2Me
CO2Me
Br
N
N
R
h
1.0
2.5
88
90
Me
N
H
Me
N
H
Br
CO2Me
CO2Me
Br
Br
N
N
R
i
N
H
Br
N
H

J. S. Yadav et al. / Tetrahedron Letters 49 (2008) 2815–2819
2817
Table 1 (continued)
Entry
Isoquinoline
DMAD
Indole
Producea
Time (h)
Yieldb (%)
1
2
3
4
Br
CO2Me
CO2Me
Br
N
R
j
3.0
82
N
H
Me
Ph
Me
N
N
H
Br
CO2Me
CO2Me
Br
N
N
R
R
k
2.0
3.5
3.5
2.0
90
70
73
82
N
H
Ph
N
N
H
NO2
l
N
H
N
N
H
NO2
CO2Me
CO2Me
NO2
N
R
m
Me
N
H
Me
N
N
H
Me
R
N
Me
N
n
N
H
N
H
CO2Me
a
All products were characterized by NMR, IR and spectrometry. R=
Isolated yields after purification.
.
CO2Me
b
line derivatives would provide additional lead molecules
for use in drug discovery. Aza-aromatic compounds acti-
vated by acyl chlorides or DMAD are important interme-
diates for the synthesis of a variety of biologically active
nitrogen containing alkaloids.10–12 Knowing the impor-
tance of isoquinoline/quinoline and indole derivatives, the
preparation of their new analogs is of prime importance
in both synthetic and medicinal chemistry.
In continuation of our interest on the functionalization
of aza-aromatic systems activated by acyl chlorides,13 we
herein report a simple and catalyst free method for the
direct coupling of indoles with quinoline and isoquinolines
activated by dimethyl acetylenedicarboxylate via a three-
component reaction. Accordingly, treatment of isoquino-
line (1) with dimethyl acetylenedicarboxylate (2) and indole
(3) in dichloromethane at room temperature for 2 h gave
the product, dimethyl 2-(1-(indolin-3-yl)isoquinolin-2(1H)-
yl)but-2-enedioate 4a in 90% yield (Scheme 1).
nucleophilic addition took place selectively at the 1-posi-
tion of isoquinoline, showing high regioselectivity. No
1,4-addition products were observed under these reaction
conditions. Like indoles, 4-bromo-, 5-bromo-, 5-nitro-
and 3-methyl-isoquinolines also reacted readily with
DMAD and indoles to afford the corresponding 1-substi-
tuted isoquinolines (Table 1, entries g–n). Mechanistically,
the reaction may proceed via the formation of a zwitter-
ionic intermediate,15 which reacts simultaneously with
indole to furnish the desired product (Scheme 2).
Like isoquinolines, the quinoline also coupled readily
with indole under identical conditions. The reaction
went to completion in 2.5 h and the product, dimethyl
CO2Me
(+)
+
CO2Me
CO2Me
N
N
CO2Me
(-)
Similarly, various indoles such as N-benzyl-, 2-methyl-,
2-phenyl-, 5-bromo- and 5-nitro-indole underwent smooth
coupling with activated isoquinolines to produce the corre-
sponding products in good to excellent yields (Table 1,
entries b–f). The geometry of alkene in product 4a was
found to be E, which was confirmed by comparison of
NMR data with authentic sample.14 In all the cases, the
CO2Me
CO2Me
N
Indole
N
H
Scheme 2. A plausible reaction mechanism.

2818
J. S. Yadav et al. / Tetrahedron Letters 49 (2008) 2815–2819
Acknowledgement
CO2Me
+
CH2Cl2, r.t.
2.5 h, 75 %
+
N
NH
CO2Me
N
N
N.N.Y. and M.K.G. thank CSIR, New Delhi, for the
award of fellowships.
H
CO2Me
CO2Me
5
References and notes
Scheme 3. Preparation of product 5.
1. (a) Indoles; Sundberg, R. J., Ed.; Academic Press: San Diego, 1996;
(b) Gribble, G. W. Perkin Trans. 1 2000, 1045; (c) Cacchi, S.; Fabrizi,
G. Chem. Rev. 2005, 105, 2873; (d) Humphrey, G. R.; Kuethe, J. T.
Chem. Rev. 2006, 106, 2875.
CH2Cl2, 6 h
2. (a) Sun, L.; Tran, N.; Liang, C.; Tang, F.; Rice, A.; Schreck, R.;
Waltz, K.; Shawver, L. K.; McMahon, G.; Tang, C. J. Med. Chem.
1999, 42, 5120; (b) Shaheen, R. M.; Davis, D. W.; Liu, W.;
Zebrowski, B. K.; Wilson, M. R.; Bucana, C. D.; McConkey, D. J.;
McMahon, G.; Ellis, L. M. Cancer Res. 1999, 59, 5412.
3. (a) Kuethe, J. T.; Wong, A.; Qu, C.; Smitrovich, J.; Davies, I. W.;
Hughes, D. L. J. Org. Chem. 2005, 70, 2555; (b) Payack, J. F.;
Vazquez, E.; Matty, L.; Kress, M. H.; McNamara, J. J. Org. Chem.
2005, 70, 175; (c) Wong, A.; Kuethe, J. T.; Davies, I. W.; Hughes, D.
L. J. Org. Chem. 2004, 69, 7761; (d) Kuethe, J. T.; Wong, A.; Davies,
I. W. Org. Lett. 2003, 5, 3975; (e) Fraley, M. E.; Arrington, K. L.;
Buser, C. A.; Ciecko, P. A.; Coll, K. E.; Fernandes, C.; Hartman, G.
D.; Hoffman, W. F.; Lynch, J. J.; McFall, R. C.; Rickert, K.; Singh,
R.; Smith, S.; Thomas, K. A.; Wong, B. K. Bioorg. Med. Chem. Lett.
2004, 14, 351.
+
+
N
N
r.t.
H
COR
NH
N
+
COR
COR
N
N
H
H
Major (6 and 8)
Minor (7 and 9)
R = OMe; Yield = 85%; Ratio of 6 and 7 = 7:3
R = Ph; Yield = 80%; Ratio of 8 and 9 = 7:3
Scheme 4. Preparation of products 6–9.
4. Ewing, J.; Hughes, G.; Ritchie, E.; Taylor, W. C. Nature 1952, 169,
618.
5. Anderson, W. K.; Heider, A. R.; Raju, N.; Yucht, J. A. J. Med.
Chem. 1988, 31, 2097.
6. Goldbrunner, M.; Loidl, G.; Polossek, T.; Mannschreck, A.; von
Angerer, E. J. Med. Chem. 1997, 40, 3524.
2-(2-(1H-indol-3-yl)quinolin-1(2H)-yl)but-2-enedioate 5,
was obtained in 75% yield (Scheme 3).16
This method worked well for both electron rich and
electron deficient substrates. Various functional groups
such as halides, esters and nitro derivatives are well toler-
ated under the reaction conditions (Table 1). This method
offers several advantages such as high yields of products,
mild reaction conditions, greater selectivity, cleaner reac-
tion profiles and operational simplicity. No additives or
catalysts were required to effect the reaction. It should be
noted that isoquinolines gave higher yields of products
when compared to quinolines. The scope and generality
of this process is illustrated with respect to various isoquino-
lines and indoles and the results are presented in Table 1.17
It is noteworthy to mention that isoquinoline was also acti-
vated by methyl propiolate and 1-ethynylphenyl ketone
(Scheme 4). However, the products were obtained as
mixtures in each reaction, the structures of which were
7. Ambros, R.; von Angerer, S.; Wiegrebe, W. Arch. Pharm. (Weinheim,
Ger.) 1988, 321, 743.
8. Ambros, R.; von Angerer, S.; Wiegrebe, W. Arch. Pharm. 1988, 321,
481.
9. Ambros, R.; Schneider, M. R.; von Angerer, S. J. Med. Chem. 1990,
33, 153.
10. (a) Magnus, P.; Rodroaguez-lopez, J.; Mulholland, K.; Matthews, I.
J. Am. Chem. Soc. 1992, 114, 382; (b) Comins, D. L.; Sajan, P. J. In
Comprehensive Heterocyclic Chemistry II; Katritzky, A. P., Rees, V.
W., Scriven, E. F., Eds.; Pyridines and their Benzo Derivatives:
Reactivity at the Ring; Pergamon Press: Oxford, 1996; Vol. 5, pp 37–
38; (c) Katritzky, A. R.; Rachwal, S.; Rachwal, S. Tetrahedron 1996,
52, 15031; (d) Itoh, T.; Miyazaki, M.; Nagata, K.; Ohsawa, A.
Tetrahedron 2000, 56, 4383.
11. Yavari, I.; Hossaini, Z.; Sabbaghan, M.; Ghazanfarpour-Darjani, M.
Tetrahedron 2007, 63, 9423.
12. (a) Nair, V.; Devipriya, S.; Eringathodi, S. Tetrahedron Lett. 2007, 48,
3667. and references cited therein; (b) Nair, V.; Vidya, N.; Biju, A. T.;
Deepthi, A.; Abhilash, K. G.; Suresh, E. Tetrahedron 2006, 62, 10136.
13. (a) Yadav, J. S.; Reddy, B. V. S.; Gupta, M. K.; Prabhakar, A.;
Jagadeesh, B. Chem. Commun. 2004, 2124; (b) Yadav, J. S.; Reddy, B.
V. S.; Srinivas, M.; Sathaiah, K. Tetrahedron Lett. 2005, 46, 3489; (c)
Yadav, J. S.; Reddy, B. V. S.; Srinivas, M.; Sathaiah, K. Tetrahedron
Lett. 2005, 46, 8905; (d) Yadav, J. S.; Reddy, B. V. S.; Gupta, M. K.;
Prathap, I.; Dash, U. Synthesis 2007, 1077.
14. (a) Hayakawa, K.; Fujii, I.; Kanematsu, K. J. Org. Chem. 1983, 48,
166; (b) Carboni, B.; Toupet, L.; Carrie, R. Tetrahedron 1987, 43,
2293.
15. (a) Winterfeldt, E. Angew. Chem., Int. Ed. Engl. 1967, 6, 424; (b)
Johnson, A. W.; Tebby, J. C. J. Chem. Soc. 1961, 2126; (c) Tebby, J.
C.; Wilson, I. F.; Griffiths, D. V. J. Chem. Soc., Perkin Trans. 1 1979,
2133; (d) Butterfield, P. J.; Tebby, J. C.; Griffiths, D. V. J. Chem. Soc.,
Perkin Trans. 1 1979, 1189.
established by NMR, IR and mass spectrometry.18
A
similar method has been reported using chlorovinyl phenyl
ketone instead of 1-ethynylphenyl ketone for the prepara-
tion of 9.19
In summary, we have developed a novel multi-compo-
nent reaction capable of coupling of indoles with quinoline
and isoquinolines activated by dimethyl acetylenedicarbox-
ylate at room temperature without a catalyst to produce
indolyl-dihydroquinoline and isoquinolines. In addition
to its simplicity and mild reaction conditions, this method
provides high yields of products with high selectivity,
which makes it a useful and attractive process for the syn-
thesis of indolyl quinoline and isoquinolines in a single step
operation.
16. Compound 5: Dark yellow solid, mp 114–116 °C, IR (KBr): m 3410,
2924, 2853, 1741, 1603, 1494, 1453, 1288, 1159, 745 cmÀ1 1H NMR
.

J. S. Yadav et al. / Tetrahedron Letters 49 (2008) 2815–2819
2819
(200 MHz, CDCl3): d 7.55–7.51 (m, 1H), 7.32–7.00 (m, 7H), 6.75 (d,
J = 9.4 Hz, 1H), 6.66 (d, J = 3.3 Hz, 1H), 6.50 (d, J = 5.4 Hz, 1H),
6.37–6.34 (m, 1H), 6.05 (dd, J = 9.4, 5.6 Hz, 1H), 5.58, 3.68 (s, 3H),
3.65 (s, 3H). 13C NMR (75 MHz, CDCl3): d: 51.6, 52.9, 68.5, 103.8,
106.2, 109.1, 119.3, 120.1, 121.3, 122.3, 122.4, 123.9, 124.6, 125.9,
127.6, 129.1, 133.6, 136.5, 150.2, 164.9, 166.0; LCMS: m/z: 411.0
(M++Na), 304.1, 272.0; HRMS (ESI) calcd for C23H20N2O4:
411.1320. Found: 411.1324.
J = 7.8 Hz, 1H), 5.58 (d, J = 7.8 Hz, 1H), 4.76 (s, 1H), 3.73 (s, 3H),
3.46 (s, 3H);13C NMR (75 MHz, CDCl3): d 50.8, 52.9, 54.9, 91.6,
106.8, 110.9, 114.5, 120.1, 120.4, 122.5, 124.8, 126.5, 126.7, 127.0,
127.4, 128.8, 129.2, 132.2, 132.4, 135.1, 135.3, 149.8, 165.1, 167.3;
LCMS: m/z: 487.1 (M++Na), 463.1, 335.1, 279.1; HRMS (ESI) calcd
for C29H23N2O4: 463.1657. Found: 463.1640.
18. Compound 6 (major): light yellow solid, mp 88–90 °C; IR (KBr): m
3319, 2924, 2854, 1681, 1606, 1568, 1457, 1425, 1264, 1162, 1109,
17. General procedure: To a stirred solution of indole (1 mmol) and
DMAD (1 mmol) in 5 mL dichloromethane was added isoquinoline.
The mixture was stirred at the room temperature for appropriate time
(see Table 1). After complete conversion as indicated by TLC, the
reaction mixture was quenched with water (10 mL) and extracted with
dichloromethane (2 Â 15 mL). The combined extracts were dried over
anhydrous Na2SO4, and concentrated in vacuo. The resulting product
was purified by column chromatography on silica gel (Merck, 60–120
mesh, ethyl acetate–hexane, 1:9) to afford pure products as a yellow
solid. Spectroscopic data for selected compound: Compound (4a):
Pale yellow solid, mp 145–147 °C, IR (KBr): m 3445, 3046, 2948, 2850,
748 cmÀ1 1H NMR (300 MHz, CDCl3): d 8.19 (br s, 1H), 7.62 (d,
;
J = 8.3 Hz, 1H), 7.50 (d, J = 13.5 Hz, 1H), 7.25 (d, J = 7.5 Hz, 1H),
7.13–7.02 (m, 6H), 6.93 (br s, 1H), 6.45 (d, J = 7.5 Hz, 1H), 6.14 (d,
J = 1.5 Hz, 1H), 5.90 (d, J = 7.5 Hz, 1H), 5.13 (d, J = 13.5 Hz, 1H),
3.62 (s, 3H); 13C NMR (75 MHz, CDCl3): d 50.8, 67.4, 90.4, 106.9,
111.4, 116.8, 119.2, 119.7, 121.9, 122.6, 124.6, 126.6, 126.8, 127.4,
129.2, 131.4, 136.3, 147.5, 169.5; LCMS: m/z: 353.1 (M++Na), 329.1.
HRMS (ESI) calcd for C21H18N2O2Na: 353.1265. Found: 353.1264.
Compound 7 (minor): orange solid, mp 65–68 °C; IR (KBr): m 3415,
2924, 2854, 1696, 1618, 1570, 1456, 1268, 1163, 768, 746 cmÀ1 1H
;
NMR (300 MHz, CDCl3): d 7.58 (d, J = 8.3 Hz, 1H), 7.53 (d,
J = 13.5 Hz, 1H), 7.51 (br s, 1H), 7.27–7.15 (m, 2H), 7.15–7.05 (m,
5H), 6.96 (d, J = 3.0 Hz, 1H), 6.63 (d, J = 7.5 Hz, 1H), 6.38 (d,
J = 3.0 Hz, 1H), 6.01 (d, J = 7.5 Hz, 1H), 5.15 (d, J = 13.5 Hz, 1H),
3.60 (s, 3H); 13C NMR (75 MHz, CDCl3): d 51.1, 67.2, 94.2, 103.7,
105.8, 109.2, 120.1, 121.3, 122.5, 125.2, 125.3, 126.6, 127.4, 127.6,
128.4, 128.6, 129.2, 134.6, 146.5, 168.0; LCMS: m/z: 353.1 (M++Na),
329.1. HRMS (ESI) calcd for C21H18N2O2Na: 353.1265. Found:
353.1280. Compound 8 (major): dark yellow solid, mp 202–204 °C; IR
(KBr): m 3216, 2923, 1638, 1581, 1532, 1455, 1383, 1346, 1267, 1208,
1736, 1601, 1458, 1430, 1283, 1212, 1171, 1035, 922, 767, 714 cmÀ1
;
1H NMR (200 MHz, CDCl3): d 7.66 (d, J = 7.4 Hz, 1H), 7.51 (d,
J = 7.4 Hz, 1H), 7.32–7.03 (m, 8H), 6.60 (d, J = 7.4 Hz, 1H), 6.38 (d,
J = 3.3 Hz, 1H), 6.07 (d, J = 8.3 Hz, 1H), 5.31 (s, 1H), 3.70 (s, 3H),
3.59 (s, 3H). 13C NMR (75 MHz, CDCl3): d 51.4, 53.3, 66.3, 95.4,
104.3, 107.5, 109.0, 120.1, 121.4, 122.6, 124.6, 125.3, 125.7, 126.0,
127.6, 128.0, 128.4, 129.2, 134.3, 149.3, 164.8, 166.4; LCMS: m/z:
411.1 (M++Na), 387.1, 290.1, 245.1. HRMS (ESI) calcd for
C23H20N2O4Na: 411.1320. Found: 411.1315. Compound (4b): Yellow
solid, mp 167–169 °C, IR (KBr): m 3385, 2923, 2852, 1742, 1701, 1587,
1110, 1045, 911, 769, 745, 701, 658, 569 cmÀ1 1H NMR (200 MHz,
;
1563, 1459, 1208, 1158, 743 cmÀ1
;
1H NMR (200 MHz, CDCl3): d
CDCl3): d 10.79–10.65 (br s, 1H), 7.88–7.66 (m, 3H), 7.75 (d,
J = 13.2 Hz, 1H), 7.49–7.21 (m, 4H), 7.19–6.92 (m, 6H), 6.79
(d, J = 7.8 Hz, 1H), 6.50 (br s, 1H), 6.42 (d, J = 2.3 Hz, 1H), 6.41
(d, J = 13.2 Hz, 1H), 6.01 (d, J = 7.8 Hz, 1H); 13C NMR (75 MHz,
DMSO): d 96.7, 111.6, 115.5, 116.6, 118.9, 119.2, 121.1, 122.6, 123.0,
123.5, 124.5, 126.7, 126.8, 127.3, 127.4, 128.2, 131.6, 136.2, 139.0,
148.3, 186.8; LCMS: m/z: 377.1 (M++H), 260.1, 245.1; HRMS (ESI)
calcd for C26H20N2ONa: 399.1473. Found: 399.1470.
7.74–7.70 (m, 1H), 7.30–6.89 (m, 13H), 6.41 (d, J = 8.0 Hz, 1H), 6.19
(s, 1H), 5.93 (d, J = 8.0 Hz, 1H), 5.23 (s, 1H), 5.19 (s, 2H), 3.86 (s,
3H), 3.59 (s, 3H). 13C NMR (75 MHz, CDCl3): d 50.0, 51.1, 53.1,
56.0, 90.8, 109.3, 110.0, 115.3, 119.5, 119.9, 122.0, 124.9, 125.4, 125.9,
126.1, 126.3, 126.4, 127.2, 127.5, 127.6, 128.6, 131.8, 136.5, 136.9,
150.2, 165.3, 167.3; LCMS: m/z: 501.2 (M++Na), 477.2, 335.1;
HRMS (ESI) calcd for C30H26N2O4Na: 501.1790. Found: 501.1785.
Compound (4d): Orange solid, mp 182–184 °C, IR (KBr): m 3313,
19. For compound 9 (minor), see reference: Sheinkman, A. K.; Prileps-
kaya, A. N.; Ginzburg, A. O.; Tokarev, A. K.; Deikalo, A. A. Khim.
Geterotsiklich. Soedin. 1971, 421 [Chem. Heterocycl. Compd. (Engl.
Transl.) 1971, 7, 389].
2923, 2852, 1742, 1671, 1565, 1457, 1207, 1168, 904, 743, 697 cmÀ1
;
1H NMR (200 MHz, CDCl3): d 8.06 (s, 1H), 7.75 (d, J = 7.8 Hz, 1H),
7.57–7.39 (m, 5H), 7.30–6.89 (m, 7H), 6.46 (s, 1H), 6.03 (d,