Domino reaction of arylamine, methyl propiolate, aromatic aldehyde, and indole for facile synthesis of functionalized indol-3-yl acrylates

Article abstract of DOI:10.1016/j.tetlet.2012.10.043

In the presence of FeCl₃ as catalyst the one-pot domino reactions of arylamines, methyl propiolate, aromatic aldehydes, and indole in ethanol at room temperature proceeded smoothly to give methyl 2-(1H-indol-3-yl)arylmethyl-3-arylamino)acrylate

Full text of DOI:10.1016/j.tetlet.2012.10.043

Tetrahedron Letters 53 (2012) 6965–6967
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Domino reaction of arylamine, methyl propiolate, aromatic aldehyde,
and indole for facile synthesis of functionalized indol-3-yl acrylates
⇑
Li-Li Zhang, Jing Sun, Chao-Guo Yan
College of Chemistry & Chemical Engineering, Yangzhou University, Yangzhou 225002, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 July 2012
Revised 19 September 2012
Accepted 9 October 2012
Available online 17 October 2012
In the presence of FeCl3 as catalyst the one-pot domino reactions of arylamines, methyl propiolate,
aromatic aldehydes, and indole in ethanol at room temperature proceeded smoothly to give methyl
2-(1H-indol-3-yl)arylmethyl-3-arylamino)acrylates in good yields. 1H NMR spectra and single crystal
structures indicated that (Z)-acrylates were stereoselectively formed in the reactions.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
One-pot reaction
Domino reaction
b-Enamino ester
Electron-deficient alkyne
Indole
These years the use of domino reaction has emerged as one of
the powerful and efficient tools for the synthesis of structurally
diverse molecules and many newly designed domino reactions
have been successively reported.1,2 Recently the diverse reactivity
of Huisgen’s 1,4-dipoles, which are easily formed from the addition
of nitrogen-containing aromatic heterocycles to electron-deficient
alkynes, has been widely used in domino reactions to develop a
number of carbon–carbon bond formation reactions and versatile
heterocyclic constructions.3–5 On the other hand the addition of
aliphatic or aromatic primary amine to the activated alkynes
results in an active intermediate b-enamino ester, which is an
important synthetic building block for the synthesis of a wide vari-
ety of heterocycles and pharmaceutical compounds.6,7 A number of
domino reactions have been developed by using this kind of
b-enamino esters to react further with sequential adding of
nucleophilic or electrophilic reagents to give versatile nitrogen-
containing compounds and N,O-heterocycles.8–10 We also success-
fully reported several new domino reactions by using the in situ
formed b-enamino esters derived from the reactions of arylamines
with electron-deficient alkynes such as dimethyl acetylenedicar-
boxylate and methyl propiolate.11 We noted that the b-enamino
esters derived from the reactions of arylamines with dimethyl
acetylenedicarboxylate and methyl propiolate showed very differ-
ent reactivity and therefore different reaction patterns were usu-
ally encountered.12 Encouraged by these results and a hunt for
new domino reactions, we investigated FeCl3 catalyzed one-pot
domino reactions of arylamines, methyl propiolate, aromatic alde-
hydes, and indole and successfully developed a facile synthetic
procedure for the functionalized indol-3-yl acrylates.
In a preliminary experiment, the reaction conditions were
examined which included catalyst, solvent, temperature, molar
ratio of reactants, and adding sequences of substrates. The best
result was obtained by using domino reaction procedure and FeCl3
as catalyst. At first p-methoxyaniline reacted with methyl propio-
late in ethanol at room temperature overnight to give the desired
b-enamino ester according to the previously established reaction
conditions.12 Then p-chlorobenzaldehyde, indole, and anhydrous
FeCl3 (20 mol %) were added and the resulting mixture was stirred
at room temperature for additional 24 h. After workup we were
pleased to find that the polysubstituted acrylate (1c) was prepared
in 55% yield. Other solvents such as methanol, acetonitrile, and
Lewis acids such as I2 and ZnCl2 were also examined. If no catalyst
was added, the reaction could produce 1a in 14% yield. Under the
optimized reaction conditions, a variety of arylamines and aromatic
aldehydes were employed and the reaction proceeded smoothly to
give the corresponding methyl 2-(1H-indol-3-yl)arylmethyl-
3-arylamino)acrylates (1a–1r) in moderate yields (Table 1).13
Aromatic aldehydes with the different kinds of substituents showed
a marginal effect to the reactivity. But aliphatic aldehydes such as
propionaldhyde and butylaldehyde could not be used in this reac-
tion and no expected products were obtained. Arylamines with
electron-donating substituents such as alkyl and methoxyl groups
and with weak electron-withdrawing groups such as chloro and
bromo all gave good yields of products. It should be pointed out that
m-nitroaniline and p-nitroaniline could not be used in this domino
⇑
Corresponding author.
E-mail address: cgyan@yzu.edu.cn (C.-G. Yan).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.10.043

6966
L.-L. Zhang et al. / Tetrahedron Letters 53 (2012) 6965–6967
Table 1
Synthesis of the functionalized indol-3-yl acrylates
Ar
ArCHO +
CO2CH3
CH3O2C
N
EtOH
H
RNH2
FeCl3
N
H
RHN
Entry
Compound
R
Ar
Yield (%)
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
1m
1n
1o
1p
1q
1r
p-CH3OC6H4
p-CH3OC6H4
p-CH3OC6H4
p-CH3OC6H4
p-CH3C6H4
p-CH3C6H4
p-CH3C6H4
p-CH3C6H4
p-CH3C6H4
p-CH3C6H4
p-CH3C6H4
p-CH3C6H4
p-(CH3)2CHC6H4
p-(CH3)3CC6H4
C6H5
p-FC6H4
p-ClC6H4
p-BrC6H4
m-NO2C6H4
p-CH3OC6H4
m-CH3OC6H4
p-CH3C6H4
p-(CH3)2CHC6H4
C6H5
p-FC6H4
p-ClC6H4
p-BrC6H4
p-BrC6H4
53
55
60
58
62
72
64
67
59
54
53
51
61
63
66
58
57
52
41
51
9
10
11
12
13
14
15
16
17
18
19
20
Figure 2. Molecular structure of compound 1j.
p-BrC6H4
p-CH3OC6H4
p-CH3C6H4
p-CH3OC6H4
p-CH3OC6H4
p-ClC6H4
C6H5
p-ClC6H4
p-BrC6H4
C6H5CH2CH2
C6H5CH2CH2
OCH3
1u
1v
CO2CH3
CH3O2C
Ar'CHO
p-BrC6H4
O
H
EtOH
ArNH2
+
N
NHAr
Ar
reaction because they could not react smoothly with methyl propi-
olate to form the expected b-enamino ester. Aliphatic amine such as
2-phenylethylamine was also successfully employed in the reac-
tions to give the expected products 1u and 1v in relative lower
yields.
A
A'
)
(
)
(
OCH3
OCH3
OCH3
Ar'
Ar'
Ar'
N
H
FeCl3
O
H
O
H
O
H
OH
OH
FeCl3
_
FeCl3(H2O)
The structures of the above prepared 2-(1H-indol-3-yl)aryl-
methyl-3-arylamino)acrylates (1a–1v) were characterized by IR,
1H, 13C NMR, and HRMS spectra (see Supporting information)
and were further confirmed by single-crystal X-ray diffraction
determination of the two compounds 1g (Fig. 1) and 1j (Fig. 2).13
The 1H NMR spectra of compounds 1a–1v usually show one set
of characteristic peaks for each groups such as two singlets at
about 10.80 and 9.76 ppm for indolyl NH unit and arylamino NH
group and a singlet at 5.40 ppm for methine group, while the sign
of the vinyl proton is usually overlapped with the peaks of protons
of the aromatic groups. In the single crystal structures of com-
pounds 1g and 1j the arylamino group and the ester group exist
in the cis-position of C@C double bond. One intramolecular N–
Hꢀ ꢀ ꢀO hydrogen bond was formed between the amino group and
esteric carbonyl group. According to 1H NMR spectra and the single
crystal structures we could deduce that all prepared acrylate deriv-
N
Ar
N
Ar
N
Ar
N
H
B
(
C
( )
1
)
Scheme 1. The proposed mechanism for domino reaction.
atives 1a–1v are of Z-configuration (arylamino group and the ester
group in the cis-position of C@C double bond), which also indicates
that this domino reaction is a highly stereoselective reaction.
A reaction mechanism for this domino reaction is briefly out-
lined in Scheme 1 based on the similar domino reactions of the
in situ generated b-enamino ester.14 At first arylamine adds to
methyl propiolate to form the b-enamino ester, in which the
trans-isomer (A) and cis-isomer (A0) are in equilibrium.14 Secondly
the nucleophilic addition of b-enamino ester to carbonyl group of
aromatic aldehyde forms the adduct intermediate (B). Thirdly in
the presence of Lewis acid FeCl3 as the catalyst, Friedel–Crafts alkyl-
ation of indole with the newly formed electrophilic reagent (C) re-
sults in the final product 1a–1v. It might be due to the formation of
one intramolecular hydrogen bond, the thermodynamic stable
cis-isomer (A0) takes part in the domino reaction process and subse-
quently gives (Z)-2-(1H-indol-3-yl)arylmethyl-3-arylamino)acry-
late, in which the intramolecular hydrogen bond is retained.
In summary we have provided a convenient procedure for the
stereoselective preparation of the functionalized acrylates in good
yields by one-pot domino reaction of arylamines, methyl propio-
late, aromatic aldehydes, and indole. The short reaction time, read-
ily variable substrates, and easiness of handling render this domino
reaction applicable to the synthesis of structurally diverse hetero-
cyclic compounds. The potential uses of the reaction in synthetic
and medicinal chemistry might be quite significant. Further expan-
sion of the reaction scope and synthetic applications of this meth-
odology are in progress in our laboratory.
Figure 1. Molecular structure of compound 1g.

L.-L. Zhang et al. / Tetrahedron Letters 53 (2012) 6965–6967
filtration and washed with cold alcohol to give the pure product.
6967
Acknowledgments
Methyl (Z)-2-((1H-indol-3-yl)(p-fluorophenyl)methyl)-3-(p-methoxyphenylamino)
acrylate (1a): White solid, 53%, mp 206–208 °C; 1H NMR (600 MHz, DMSO-d6)
d: 10.87 (s, 1H, NH), 9.76 (d, J = 12.6 Hz, 1H, NH), 7.37 (d, J = 7.8 Hz, 1H, ArH), 7.31–
7.28 (m, 3H, ArH), 7.13–7.10 (m, 2H, ArH), 7.09–7.06 (m, 1H, ArH), 6.95–6.91 (m,
2H, CH, ArH), 6.78 (d, J = 9.0 Hz, 2H, ArH), 6.72–6.69 (m, 3H, CH, ArH), 5.47 (s, 1H,
CH), 3.65 (s, 3H, OCH3), 3.62 (s, 3H, OCH3); 13C NMR (150 MHz, DMSO-d6) d: 169.0,
This work was financially supported by the National Natural
Science Foundation of China (Grant No. 21172189) and the Priority
Academic Program Development of Jiangsu Higher Education
Institutions.
1
3
160.6 (d, JCF = 241.5 Hz), 154.8, 143.5, 140.6, 136.8, 129.9 (d, JCCCF = 7.8 Hz),
2
126.1, 124.4, 121.2, 118.9, 118.5, 117.4, 116.8, 114.7 (d, JCCF = 21.9 Hz), 111.6,
100.5, 55.2, 50.8, 40.9; IR (KBr) m: 3314, 3060, 2996, 2945, 2835, 1899, 1656, 1613,
1511, 1437, 1362, 1279, 1218, 1110, 1036, 1006, 945, 852, 823 cmꢁ1; HRMS (ESI)
Anal. Calcd for C26H23FN2NaO3 ([M+Na]+): 453.1585. Found: 453.1589.
Supplementary data
Methyl (Z)-2-((1H-indol-3-yl)(p-chlorophenyl)methyl)-3-(p-methoxyphenylamino)
acrylate (1b): White solid, 55%, mp 185–187 °C; 1H NMR (600 MHz, DMSO-d6) d:
10.89 (s, 1H, NH), 9.77 (d, J = 13.2 Hz, 1H, NH), 7.38–7.34 (m, 3H, ArH), 7.31–7.28
(m, 3H, ArH), 7.09–7.07 (m, 1H, ArH), 6.95–6.93 (m, 2H, CH, ArH), 6.78 (d,
J = 8.4 Hz, 2H, ArH), 6.73–6.70(m, 3H, CH, ArH), 5.45(s, 1H, CH), 3.65(s, 3H, OCH3),
3.61 (s, 3H, OCH3); 13C NMR (150 MHz, DMSO-d6) d: 168.9, 154.8, 143.6, 143.5,
136.8, 134.5, 130.4, 130.0, 128.0, 126.1, 124.4, 121.3, 118.9, 118.5, 116.9, 116.8,
The Detailed experiments and characterization data for all com-
pounds can be found in Supporting Information. Crystallographic
data 1f (CCDC 890917), 1i (CCDC 890918) has been deposited at
the Cambridge Crystallographic Database Centre. Supplementary
data associated with this article can be found, in the online version,
at http://dx.doi.org/10.1016/j.tetlet.2012.10.043.
114.8, 111.7, 100.1, 55.2, 50.8, 41.1; IR (KBr) m: 3302, 3003, 2951, 2833, 1656,
1616, 1582, 1514, 1453, 1403, 1360, 1279, 1223, 1099, 1035, 1005, 948, 857, 821,
792 cmꢁ1; HRMS (ESI) Anal. Calcd for C26H23ClN2NaO3 ([M+Na]+): 469.1289.
Found: 460.1292.
References and notes
Methyl (Z)-2-((1H-indol-3-yl)(p-iso-propylphenyl)methyl)-3-(p-methlyphenylamino)
acrylate (1h): white solid, 67%, mp 214–216 °C; 1H NMR (600 MHz, DMSO-d6) d:
10.83 (s, 1H, NH), 9.77 (d, J = 12.6 Hz, 1H, NH), 7.37 (d, J = 7.8 Hz, 1H, ArH), 7.29 (d,
J = 7.8 Hz, 1H, ArH), 7.20–7.16 (m, 4H, ArH), 7.06 (t, J = 7.4 Hz, 1H, ArH), 6.98–6.96
(m, 3H, CH, ArH), 6.92 (t, J = 7.4 Hz, 1H, ArH), 6.70 (s, 1H, CH), 6.65 (d, J = 8.4 Hz, 2H,
ArH), 5.45 (s,1H, CH), 3.63(s, 3H,OCH3), 2.86 (t, J = 7.2 Hz,1H,CH), 2.16 (s,3H, CH3),
1.20 (d, J = 6.6 Hz, 6H, CH3); 13C NMR (150 MHz, DMSO-d6) d: 169.1, 145.8, 142.6,
141.7, 138.6, 136.8, 130.9, 129.9, 128.1, 126.2, 125.9, 124.2, 121.1, 119.0, 118.4,
1. Zhu, J.; Bienayme, H. Multicomponent Reactions; Wiley: Weinheim, 2005.
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117.7, 115.1, 111.6, 101.5, 50.8, 41.1, 33.0, 23.9, 20.1; IR (KBr) m: 3336, 2957, 2866,
1892, 1660, 1613, 1579, 1516, 1447, 1362, 1274, 1228, 1195, 1120, 1052, 1007, 954,
860, 815 cmꢁ1; HRMS (ESI) Anal. Calcd for C29H30N2NaO2 ([M+Na]+): 461.2199.
Found: 461.2203.
Methyl
(Z)-2-((1H-indol-3-yl)(p-bromophenyl)methyl)-3-(p-methylphenylamino)
acrylate (1l): White solid, 51%, mp 212–214 °C; 1H NMR (600 MHz, DMSO-d6) d:
10.91 (s, 1H, NH), 9.80 (d, J = 12.6 Hz, 1H, NH), 7.48 (d, J = 7.4 Hz, 2H, ArH), 7.38 (d,
J = 7.5 Hz, 1H, ArH), 7.29–7.24 (m, 3H, ArH), 7.09–7.07 (m, 1H, ArH), 7.03–6.98 (m,
3H, CH, ArH), 6.95–6.93 (m, 1H, ArH), 6.72 (s, 1H, CH), 6.66 (d, J = 7.3 Hz, 2H, ArH),
5.45 (s, 1H, CH), 3.62 (s, 3H, OCH3), 2.16 (s, 3H, CH3); 13C NMR (150 MHz, DMSO-d6)
d: 168.9, 144.0, 142.9, 138.5, 136.8, 131.1, 130.9, 130.4, 129.9, 126.1, 124.5, 121.3,
118.9, 118.5, 116.7, 115.3, 111.7, 100.7, 50.8, 41.3, 20.1; IR (KBr) m: 3284, 3026,
2946, 2858, 1886, 1659, 1609, 1579, 1518, 1484, 1439, 1403, 1364, 1279, 1222,
1124, 1005, 950, 813, 790 cmꢁ1; HRMS (ESI) Anal. Calcd for C26H23BrN2NaO2
([M+Na]+): 497.0853. Found: 497.0836.
(Z)-methyl 2-((1H-indol-3-yl)(p-bromophenyl)methyl)-3-(p-tert-butylphenylamino)
acrylate (1n): White solid, 63%, mp 233–235 °C; 1H NMR (600 MHz, DMSO-d6) d:
10.92 (s, 1H, NH), 9.83 (d, J = 12.6 Hz, 1H, NH), 7.48 (d, J = 6.6 Hz, 2H, ArH), 7.38 (d,
J = 6.6 Hz, 1H, ArH), 7.29 (d, J = 6.6 Hz, 1H, ArH), 7.25 (d, J = 6.6 Hz, 2H, ArH), 7.19 (d,
J = 6.6 Hz, 2H, ArH), 7.08 (br s, 1H, ArH), 7.02 (d, J = 12.6 Hz, 1H, CH), 6.94 (br s, 1H,
ArH), 6.71–6.68 (m, 3H, CH, ArH), 5.45 (s, 1H, CH), 3.62 (s, 3H, OCH3), 1.18 (s, 9H,
CH3); 13C NMR (150 MHz, DMSO-d6) d: 168.9, 144.6, 144.0, 142.9, 138.4, 137.0,
130.9, 130.4, 126.2, 126.1, 124.5, 121.3, 118.9, 118.5, 116.7, 115.0, 111.7, 100.8,
50.8, 41.2, 33.8, 31.1; IR (KBr)
m: 3352, 3042, 2957, 2866, 1907, 1661, 1606, 1574,
1517, 1484, 1439, 1362, 1306, 1270, 1229, 1202, 1116, 1071, 1007, 957, 818 cmꢁ1
;
HRMS (ESI) Anal. Calcd for
539.1306.
C
29H29BrN2NaO2 ([M+Na]+): 539.1305. Found:
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Y.; Gao, H.; Yan, C. G. Eur. J. Org. Chem. 2012, 1976–1983.
(Z)-methyl 2-((1H-indol-3-yl)(p-methylphenyl)methyl)-3-phenylaminoacrylate (1p):
White solid, 58%, mp 214–216 °C; 1H NMR (600 MHz, DMSO-d6) d: 10.86 (s, 1H,
NH), 9.86 (d, J = 12.6 Hz, 1H, NH), 7.37 (d, J = 7.2 Hz, 1H, ArH), 7.28 (d, J = 7.2 Hz, 1H,
ArH), 7.17–7.16 (m, 4H, ArH), 7.12–7.11 (m, 2H, ArH), 7.08–7.06 (m, 1H, ArH), 7.02
(d, J = 12.6 Hz, 1H, CH), 6.93–6.92 (m, 1H, ArH), 6.89–6.88 (m, 1H, ArH), 6.75–6.74
(m, 2H, ArH), 6.71 (s, 1H, CH), 5.45 (s, 1H, CH), 3.63 (s, 3H, OCH3), 2.28 (s, 3H, CH3);
13C NMR (150 MHz, DMSO-d6) d: 169.1, 142.1, 141.2, 140.9, 136.8, 134.8, 129.5,
128.7, 128.1, 126.2, 124.3, 121.9, 121.2, 118.9, 118.4, 117.5, 115.0, 111.6, 102.2,
12. (a) Sun, J.; Sun, Y.; Xia, E. Y.; Yan, C. G. ACS Comb. Sci. 2011, 13, 436–441; (b)
Sun, J.; Sun, Y.; Gao, H.; Yan, C. G. Synthesis 2012, 1069–1073; (c) Sun, Y.; Sun,
J.; Yan, C. G. Mol. Divers. 2012, 16, 163–171.
50.9, 41.2, 20.6; IR (KBr)
1309, 1269, 1224, 1195, 1100, 1000, 942, 794 cmꢁ1; HRMS (ESI) Anal. Calcd for
26H24N2NaO2 ([M+Na]+): 419.1730. Found: 419.1734.
m: 3366, 3046, 2949, 1658, 1624, 1600, 1505, 1434, 1362,
C
13. General procedure for domino reactions of arylamine, methyl propiolate,
aromatic aldehydes, and indoles 1a–1v: In a round bottom flask a mixture of
arylamine (2.2 mmol) and methyl propiolate (2.2 mmol) in ethanol (5.0 mL)
was stirred at room temperature for 12 h. Then aromatic aldehyde (2.0 mmol),
indole (2.0 mmol), and FeCl3 (0.2 mmol, g) were added to it. The solution was
stirred at room temperature for 18 h. The resulting precipitate was collected by
14. (a) Kandeel, A. K.; Vernon, J. M. M. J. Chem. Soc., Perkin. Trans. 1 1987, 2023–
2026; (b) Cho, C. S. Tetrahedron Lett. 2005, 46, 1415–1417; (c) Ziyaei-
Halimehjani, A.; Saidi, M. R. Tetrahedron Lett. 2008, 49, 1244–1248; (d) Zhu,
Q. H.; Jiang, H. F.; Li, J. H.; Zhang, M.; Wang, X. J.; Qi, C. R. Tetrahedron 2009, 65,
4604–4613.