Regioselective opening of chalcone epoxides with nitrogen heterocycles using indium(III) chloride as an efficient catalyst

Article abstract of DOI:10.1080/00397911.2012.667291

Indium(III) chloride catalyzes regioselective ring opening of chalcone epoxides with nitrogen heterocycles such as indole, 2-methyl indole, and pyrrole under mild conditions at room temperature to afford 1,3-diaryl-2-hydroxy-3-(1H- 3-indolyl/2-pyrrolyl)propan-1-ones in good yields (60-88%) within 20-50 min. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications to view the free supplemental file.

Full text of DOI:10.1080/00397911.2012.667291

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Regioselective Opening of Chalcone
Epoxides with Nitrogen Heterocycles
Using Indium(III) Chloride as an Efficient
Catalyst
Naveen Kumar Konduru a & Naseem Ahmed a
a Department of Chemistry, Indian Institute of Technology Roorkee,
Roorkee, Uttarakhand, India
Accepted author version posted online: 27 Dec 2012.Published
online: 28 Apr 2013.
To cite this article: Naveen Kumar Konduru & Naseem Ahmed (2013): Regioselective Opening of
Chalcone Epoxides with Nitrogen Heterocycles Using Indium(III) Chloride as an Efficient Catalyst,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 43:15, 2008-2018
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Synthetic Communications1, 43: 2008–2018, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2012.667291
REGIOSELECTIVE OPENING OF CHALCONE EPOXIDES
WITH NITROGEN HETEROCYCLES USING INDIUM(III)
CHLORIDE AS AN EFFICIENT CATALYST
Naveen Kumar Konduru and Naseem Ahmed
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee,
Uttarakhand, India
GRAPHICAL ABSTRACT
Abstract Indium(III) chloride catalyzes regioselective ring opening of chalcone epoxides
with nitrogen heterocycles such as indole, 2-methyl indole, and pyrrole under mild con-
ditions at room temperature to afford 1,3-diaryl-2-hydroxy-3-(1H-3-indolyl/2-pyrrolyl)
propan-1-ones in good yields (60–88%) within 20–50 min.
Supplemental materials are available for this article. Go to the publisher’s online edition
of Synthetic Communications1 to view the free supplemental file.
Keywords Chalcone epoxide; 1,3-diaryl-2-hydroxy 3-(1H-3-indolyl=2-pyrrolyl)propan-
1-one; InCl3; indole; pyrrole
INTRODUCTION
Functionalized indole and pyrrole derivatives have a wide range of biological
and pharmaceutical importance.[1] In particular, 3-substituted indole derivatives
are found in various natural products and medicines.[2] For example, soraphinol
A,[3] actinopolymorphol B,[4] and kurasoin B[5] are known protein farnesyl transfer-
ase (PFTase) inhibitors and therefore have anticancer properties.[6] Sattazoline and
its derivatives have expressed antiviral activity against herpes simplex viruses type
Received December 9, 2011.
Address correspondence to Naseem Ahmed, Department of Chemistry, Indian Institute of
Technology Roorkee, Roorkee 247 667, Uttarakhand, India. E-mail: nasemfcy@iitr.ernet.in
2008

REGIOSELECTIVE EPOXIDE OPENING
2009
Figure 1. Indole containing biologically active compounds and natural products.
1 and 2 and selectively inhibited the protein synthesis in herpes virus–infected cells.[7]
Similarly, compounds 1 and 2 (Fig. 1) isolated from Xenorhabdus nematophilus and
Balasubramide isolated from Clausena indica have shown good antibacterial activi-
ties,[8] These compounds have indoles as basic moieties. Similarly, natural products
containing pyrrole moieties are also present in different organic functional materials,
drugs, pigments, and pharmaceuticals, for example, solsodomine A, chlorophyllone
a, porphyrin, and bile pigments.[9a] Some other natural products such as kurasoin A,
kurasoin B, kurasoin C, cytochalasian, sesquiterpene, secokotomolide, and steroidal
glycosides contain acyloin moieties and have pharmacological significance. Indole
and pyrrole moieties also have been used as synthons in various organic syntheses
of complex and biologically active molecules.
Chalcone and chalcone epoxide are natural products found as secondary pro-
ducts in higher plants. They are used as substrate in different organic syntheses hav-
ing biological and pharmaceutical importance.[9b] Because of ring strain in epoxides,
they undergo easy intramolecular and intermolecular nucleophilic addition reac-
tion[10] under mild catalytic conditions.[11] Under controlled reaction conditions,
epoxide ring opening had a highly regioselective synthetic strategy in carbon–carbon
bond formation.[12]
Different procedures have been reported for the ring opening of terminal epox-
ides with nitrogen heterocycles (nucleophile) under high pressure[13] and in the pres-
ence of catalysts such as SiO2,[14] lanthanide triflate,[15] chromium salen
complexes,[16] sulfated zirconia,[17] antimony trichloride=montmorillonite K-10,[18]
and InBr3.[19] Similarly, chalcone epoxide ring-opening reaction using indoles has
recently been reported in the presence of ZnCl2, K-10, and ultrasonication
(Scheme 1).[20] In this procedure, use of ZnCl2 or K-10 alone with ultrasonication
Scheme 1. Opening of chalcone epoxide with indole by using ZnCl2=K-10 in ultrasonication.

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N. K. KONDURU AND N. AHMED
failed in the epoxide ring opening. Similarly, without ultrasonication, ZnCl2 or
montmorillonite K-10 also failed to give the products. In contrast to our finding,
in the later reaction procedure indole attacked at the a-position of the carbonyl
group, which afforded 3-aryl-3-hydroxy-2-(1H-indol-3-yl)-1-phenyl-1-propanone.
In continuation of our interest in Lewis acid catalysis[21] and the importance of
metal halides as inexpensive, easily available, and stable catalysts in epoxide ring
opening, herein we report an efficient method for regioselective ring opening of chal-
cone epoxides with nitrogen heterocycles in presence of indium(III) chloride catalyst.
In our method, regioselective indole nucleophilic attack at the b-position of the car-
bonyl group afforded 1,3-bis(4-chlorophenyl)-2-hydroxy-3-(1H-indol-3-yl)propan-1-
ones in significant yields (88%) within 20–50 min.
RESULTS AND DISCUSSION
Various chalcones were prepared following a reported procedure by the
condensation of acetophenones and aromatic aldehydes.[21a] Epoxidation of chal-
cones was carried out using sodium hydroxide and hydrogen peroxide in aqueous
tetrahydrofuran (THF) to give the corresponding epoxides 1a–u in good yields
(80–90%).[11b]
Initially, we examined epoxide ring opening with indole nucleophile under neat
grinding and silica-gel-supported grinding at room temperature. They failed to give
the products; however, a later case at elevated temperature (140 ꢀC) afforded the pro-
duct in 20% yield. Further, different Lewis acids (SnCl4, TaCl5, SnCl2 ꢁ 2H2O, AlCl3,
ZnCl2, ZnO, CuBr2, LaCl3, BiCl3, LiBr, InCl3, TiCl4, and FeCl3) and solvents [tolu-
ene, THF, dochloromethane (DCM), CHCl3, EtOAc, and diethyl ether] were used to
optimize the product yields. Among solvents and catalysts, DCM and indium(III)
chloride (Table 1, entry 5) were the best solvent and the most efficient catalyst
(20 mol% catalyst loading) respectively. The epoxide opening with indole gave the
optimal yield (85–88%) within 20–50 min in DCM and 20 mol% catalyst loading.
The other catalyst, BiCl3, gave good yields (75%) in 2 h, but showed moderate cata-
lytic activity (Table 1, entries 1 and 2). Similarly, TaCl5 and SnCl2 ꢁ 2H2O gave poor
yields (20–48%) after 28–38 h because of poor catalytic activity, and other catalysts
failed to give the product.
Catalytic loading has also influenced the rate of the reaction. To optimize the
catalytic loading, the reactions were carried out with 5, 10, 20, and 25 mol% catalyst
in DCM, and the efficiency of the catalyst loading was determined from the time
needed for the complete conversion of the epoxide 1a. InCl3 at 5 mol% loading gave
the complete conversion of epoxide 1a to 2a in 2 h. At increased catalytic loading,
Scheme 2. Synthesis of 1,3-bis(4-chlorophenyl)-2-hydroxy-3-(1H-indol-3-yl)propan-1-one.

REGIOSELECTIVE EPOXIDE OPENING
2011
Table 1. Optimization of reaction conditions
Entrya
Lewis acid
Solvent
Reaction time
Yield (%)b
c
1
2
3
4
5
BiCl3
CH2Cl2
CH2Cl2
CH2Cl2
EtOAc
CH2Cl2
4 h
2 h
75
75
85
76
85
d
BiCl3
InCl3
c
1 h
1 h
d
InCl3
d
InCl3
40 min
a1 equiv of epoxide and 1 equiv indole were used.
bIsolated yield.
cCatalyst 10 mol % used.
dCatalyst 20 mol % used.
10 mol% reaction time decreased to 1 h. Further, increase in catalytic loading to
20 mol% serendipitously reduced reaction time to 40 min, and moreover we increased
catalytic loading from 20 to 25 mol%, but there is no increase in rate of reaction. As a
result, catalytic loading has influence on the rate of reaction but not on product
yields.
Under optimal reaction condition, we carried out reactions using a variety of
chalcone epoxides with nitrogen heterocycles such as indole (3a), 2-methyl indole
(3b), pyrrole (3c), imidazole (3d), and pyrazole (3e) using InCl3 catalyst in DCM
(Scheme 3). Nitrogen heterocycles 3a, 3b, and 3c have successfully opened chalcone
epoxide (Table 2); however, 3d and 3e failed in epoxide ring opening, which might be
due to poor nucleophilicity.
We also observed that the substituents on the aromatic rings have influence on
the reaction rate and product yields. For example, electron-donating groups such as
methoxy and methyl groups on Ar2 afforded the product in poor yields but at a fas-
ter rate (Table 2; 2c, 2i, 2j, 2p, 2q). Similarly, electron-withdrawing groups such as
chloro, bromo, and nitro on Ar2 gave products in good yields but took longer
Scheme 3. Opening of chalcone epoxide with different nitrogen heteronucleophiles.

2012
N. K. KONDURU AND N. AHMED
Table 2. Synthesis of 1,3-diaryl-2-hydroxy-3-(1H-3-indolyl=2-pyrrolyl)propan-1-one
Reaction time
(min)
Yield
(%)
Entry Nucleophile
Reactant
Product
Product
1
2a
35
85
82
72
2
3
3a
3a
2b
2c
40
25
4
3a
2d
40
81
5
6
3a
3a
3a
3a
3a
3a
2e
2f
2g
2h
2i
50
40
40
40
30
30
86
86
82
85
72
71
7
8
9
10
2j
11
3a
2k
45
85
(Continued )

REGIOSELECTIVE EPOXIDE OPENING
2013
Table 2. Continued
Reaction time
(min)
Yield
(%)
Entry Nucleophile
Reactant
Product
Product
12
3a
2l
40
82
13
14
15
3a
3a
3a
2m
2n
2o
35
40
40
80
88
86
16
17
3a
3a
2p
2q
30
20
73
60
18
19
2r
2s
40
40
74
75
3b
20
21
2t
50
50
70
70
3c
2u
reaction time (Table 2; 2a, 2e, 2f, 2h, 2k, 2o). However, substituent effect on Ar1 has
no significant influence on rate of reaction and product yields (Table 2; 2f, 2g, 2l,
2m). Treatment of chalcone epoxides with 2-methyl indole afforded 1,3-diaryl-2-
hydroxy-3-(2-methyl-1H-indol-3-yl)propan-1-ones in poor yields (Table 2; 2r, 2s)
because of steric hindrance of the methyl group. The reaction of pyrrole with

2014
N. K. KONDURU AND N. AHMED
Scheme 4. Reaction of pyrrole with chalcone epoxide.
chalcone epoxide might need to be performed under controlled conditions, because
a mixture of products was obtained using 1 to 2 equiv. pyrrole in the reaction. To
avoid this, we used 3 equiv. of pyrrole and got 2-sustituted and 3-sustituted products
in 70% and 27% yields, respectively.
The assigned structures of products 2a–u were confirmed on the basis of their
1
spectral analysis [infrared (IR), H and 13C NMR, and high-resoultion mass spec-
trometry (HR-MS)] and further compared with reported data in the literature.[14,19]
The trans-configuration of 2a–u was confirmed by the coupling constants of protons
at 2- and 3-positions in the 1H NMR spectrum. In indole derivative 2g, the 1H NMR
spectrum has peaks at d 4.75 ppm (d, 1H, J ¼ 7.5 Hz, H3) and 5.81 ppm (d, 1H,
J ¼ 7.5 Hz, H2), in which the coupling constant (J ¼ 7.5 Hz) indicated a trans-
configuration. The 13C NMR spectrum gave peaks at d 47.2 (C-indole), 76.17
=
(C-OH), and 199.36 (C O). The characteristic IR peaks at 3420 (NH), 3376
ꢂ1
=
(OH), and 1679 (C O) cm showed the presence of saturated carbonyl groups.
Electrospray ionization—mass spectrometry (ESI-MS) also gave the molecular ion
peak at 398.1000 (M þ Naþ).
Pyrrole-containing derivative 2t was also characterized by spectral data, for
example, the 1H NMR spectrum has peaks at d 6.02 ppm (dd, 1H, J ¼ 5.5,
3.5 Hz), d 6.13 ppm (dd, 1H, J ¼ 5.5, 2.5 Hz), and d 6.71 ppm (dd, 1H, J ¼ 3.5,
2.5 Hz) for pyrrole ring protons. Also, the 13C NMR spectrum has peaks at d
106.0, 108.4, 118, and 132.1 ppm, indicating the formation of 2-substituted pyrrole
derivative. The characteristic IR peaks at 3422 (NH), 3365 (OH) 3124, 2923, and
ꢂ1
=
1680 (C O) cm showed the presence of saturated carbonyl groups. ESI-MS also
Scheme 5. Proposed mechanism for opening of chalcones epoxide with indole.

REGIOSELECTIVE EPOXIDE OPENING
2015
gave the molecular ion peak at 375.1053. Similarly, other derivatives 2b–2s and 2u
were confirmed by their spectral analysis.
The proposed mechanism for the opening of chalcone epoxide with nitrogen
heterocycles is presented in Scheme 5. Ligation of InCl3 catalyst with oxygen of chal-
cone epoxide followed by nucleophilic attack led to the cleavage of the C-O bond. It
might cleave in two different ways, but route 2 will be preferred to route 1 because of
stable carbocation formation. The nucleophilic attack of indoles and pyrrole on
carbocation and subsequent hydrogen transfer produced the title compounds with
concurrent liberation of InCl3 for the next catalytic cycle.
EXPERIMENTAL
Organic solvents were dried by standard methods when necessary. Commer-
cially available reagents were used without further purification unless mentioned.
All reactions were monitored by thin-layer chromoptography (TLC) using precoated
silica gel–aluminum plates. Visualization of TLC plates was accomplished with
ultraviolet (UV) lamp or in an iodine chamber. The column chromatography was
performed using silica gel (100–200 mesh, SD Fine-Chem Limited) with ethyl
acetate=hexane as eluent system. Melting points were recorded on a Perfit apparatus
and are uncorrected. The IR spectrum was recorded with KBr on a Thomso Nicolet
Fourier transform (FT)-IR spectrophotometer. 1H and 13C NMR spectra were
obtained in CDCl3 on a Bruker Spectrospin 500=125-MHz spectrometer using
1
TMS as internal standard. Chemical shifts of H NMR spectra were given in parts
per million with respect to TMS, and the coupling constant J was measured
in hertz (Hz). Data are reported as follows: chemical shifts, multiplicity (s ¼ singlet,
singlet, d ¼ doublet, t ¼ triplet, q ¼ quartet, m ¼ multiplet, dd ¼ double of doublet).
HRMS were recorded on a Bruker instrument.
Synthesis of 1,3-Diaryl-2-hydroxy-3-(1H-3-indolyl/1H-2-
pyrrolyl)propan-1-one
Indole or 2-methyl indole (1 mmol) and pyrrole (3 mmol) were added to a stir-
red mixture of chalcone epoxides (1 mmol) and indium(III) chloride (4.43 mg,
20 mol%) in dichloromethane. The resulting reaction mixture was stirred at room
temperature for an appropriate time (20–50 min). After TLC monitoring, the reac-
tion mixture was quenched with water and brine. The aqueous layer was extracted
with dichloromethane (3 ꢃ 15 mL). The combined organic layer was washed with
brine solution and dried over anhydrous Na2SO4, and the solvent was evaporated
under reduced pressure to give the crude product. Further purification by silica-gel
column chromatography gave 1,3-diaryl-2-hydroxy-3-(1H-3-indolyl=1H-2-pyrrolyl)
propan-1-one.
1-(4-Chlorophenyl)-2-hydroxy-3-(1H-indol-3-yl)-3-phenylpropan-
1-one (2g)
1
Yield: 82%; yellow semisolid; H NMR (CDCl3, 500 MHz): d (ppm): 3.65 (br,
1H, D2O-exchangeable, OH), 4.75 (d, 1H, J ¼ 7.5 Hz), 5.81 (dd, 1H, J ¼ 7.5, 2 Hz),
6.94–6.99 (m, 3H), 7.12–7.18 (m, 5H), 7.34 (d, 1H, J ¼ 8.5 Hz), 7.67–7.78 (m, 3H),

2016
N. K. KONDURU AND N. AHMED
7.86 (d, 2H, J ¼ 8.5 Hz), 8.16 (br, 1H, D2O-exchangeable, NH). 13C NMR (CDCl3,
125 MHz): d (ppm): 47.20, 76.17, 111.17, 116.56, 118.93, 119.54, 122.22, 123.10,
126.89, 127.20, 128.02, 129.23, 129.45, 130.05, 132.62, 136.05, 137.65, 140.53,
=
199.36. IR (KBr) v: 3420 (NH), 3376 (OH), 3058, 2923, 1679 (C O), 1589, 1400,
1262, 1093, 742, 704 cmꢂ1. HR-MS (m=z) for C23H18ClNNaO2 (M þ Naþ). Anal.
calcd. 398.1026; found 398.1000.
3-(4-Chlorophenyl)-2-hydroxy-3-(2-methyl-1H-indol-3-yl)-1-
(naphthalen-2-yl)propan-1-one (2r)
1
Yield: 74%; yellow semisolid; H NMR (CDCl3, 500 MHz): d (ppm): 2.17 (s,
3H), 3.72 (br, 1H, D2O-exchangeable, OH), 4.60 (d, 1H, J ¼ 7 Hz), 6.02 (d, 1H,
J ¼ 7 Hz), 6.89–6.95 (m, 3H), 7.12–7.19 (m, 3H), 7.33 (d, 1H, J ¼ 9.5 Hz), 7.51 (t,
1H, J ¼ 7 Hz), 7.67 (t, 1H, J ¼ 7.5 Hz), 7.79 (s, 1H), 7.96–8.03 (m, 5H), 8.21 (br,
1H, D2O-exchangeable, NH). 13C NMR (CDCl3, 125 MHz): d (ppm): 11.94,
47.18, 73.59, 99.95, 110.24, 111.23, 119.16, 119.55, 119.85, 120.72, 121.38, 123.23,
126.66, 127.51, 128.14, 128.79, 129.64, 130.44, 131.10, 131.89, 131.91, 132.13,
135.29, 135.53, 138.69, 202.17. IR (KBr) v: 3522 (OH), 3421 (NH), 3075, 2931,
1686 (C O), 1492, 1434, 1299, 1093, 1017 cmꢂ1. HR-MS (m=z) for C28H22ClNNaO2
=
(M þ Naþ). Anal. calcd. 462.1399; found. 462.1376.
3-(4-Chlorophenyl)-2-hydroxy-1-(naphthalen-2-yl)-3-(1H-pyrrol-
2-yl)propan-1-one (2t)
Yield: 70%; light yellow semisolid; 1H NMR (CDCl3, 500 MHz): d (ppm): 3.79
(br, 1H, D2O-exchangeable, OH), 4.79 (d, 1H, J ¼ 7.5 Hz), 5.87 (dd, 1H, J ¼ 7.5,
1.5 Hz), 6.02 (dd, 1H, J ¼ 5.5, 3.5 Hz), 6.13 (dd, 1H, J ¼ 5.5, 2.5 Hz), 6.4–6.54 (m,
1H), 6.71 (dd, 1H, J ¼ 3.5, 2.5 Hz), 6.77 (dd, 2H, J ¼ 6.5, 2 Hz), 6.95 (t, 1H, J ¼ 8 Hz),
7.01–7.04 (m, 2H), 7.05–7.11 (m, 1H), 7.16–7.18 (m, 1H), 7.30–7.38 (m, 2H), 7.51 (t,
1H, J ¼ 8 Hz), 8.19 (br, 1H, D2O-exchangeable, NH). 13C NMR (CDCl3, 125 MHz):
d (ppm): 47.12, 76.15, 100.89, 106.0, 108.4, 116.82, 118.0, 122.12, 123.12, 126.97,
127.90, 128.70, 129.31, 131.91, 132.1, 134.01, 136.08, 137.74, 165.31, 200.44. IR
=
(KBr) v: 3422 (NH), 3365 (OH) 3124, 2923, 1680 (C O), 1626, 1452, 1258, 1106,
744, 697 cmꢂ1. HR-MS (m=z) for C23H18ClNO2 calcd. 375.1026; found 375.1053.
Complete experimental details are available in the Supporting Information,
available online.
CONCLUSION
In conclusion, we have developed a mild and efficient procedure for regioselec-
tive ring opening of chalcone epoxide with nitrogen heterocycles using indium(III)
chloride as a catalyst to afford 1,3-diaryl-2-hydroxy-3-(1H-3-indolyl=2-pyrrolyl)
propan-1-ones.
ACKNOWLEDGMENT
N. K. K. thanks the Council of Scientific and Industrial Research, New Delhi,
for the award of a junior reaserch fellowship (NET).

REGIOSELECTIVE EPOXIDE OPENING
2017
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