A new and efficient domino strategy to indole derivatives synthesis and its C3-bisfunctionalization

Article abstract of DOI:10.1016/j.tetlet.2012.09.120

A series of new poly-functionalized indole derivatives were synthesized via domino reactions of alloxan monohydrate and N-aryl substituted enaminones in HOAc at room temperature. The direct C3-bisfunctionalization of indole ring was achieved in a one-pot operation. The reaction is easy to perform simply by mixing common reactants in acetic acid. The reaction proceeds at fast rates and can be finished within 24 min, which makes workup convenient to give good to excellent chemical yields.

Full text of DOI:10.1016/j.tetlet.2012.09.120

Tetrahedron Letters 53 (2012) 6611–6614
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
A new and efficient domino strategy to indole derivatives synthesis and its
C3-bisfunctionalization
⇑
⇑
Li-Yuan Xue, Bo Jiang , Man-Su Tu, Shu-Jiang Tu
School of Chemistry and Chemical Engineering, and Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Jiangsu Normal University, Xuzhou 211116, PR
China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new poly-functionalized indole derivatives were synthesized via domino reactions of alloxan
monohydrate and N-aryl substituted enaminones in HOAc at room temperature. The direct C3-bisfunc-
tionalization of indole ring was achieved in a one-pot operation. The reaction is easy to perform simply
by mixing common reactants in acetic acid. The reaction proceeds at fast rates and can be finished within
24 min, which makes workup convenient to give good to excellent chemical yields.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 14 August 2012
Revised 21 September 2012
Accepted 26 September 2012
Available online 2 October 2012
Keywords:
Indole derivatives synthesis
Bisfunctionalization
Domino reactions
The indole ring system represents a key structural component
that occurs ubiquitously in biologically active natural and unnatu-
ral compounds as well as in optoelectronic functional materials.1
Many indole alkaloids are recognized as one of the rapidly growing
groups of marine invertebrate metabolites for their broad spec-
trum of biological properties,2 such as anticancer, anti-tumor,3
anti-inflammatory, hypoglycemic, analgesic, and antipyretic activ-
ities.4 Consequently, practical and atom-economical synthesis of
indoles from simple starting materials is critical to the pharmaceu-
tical and fine chemical industries.5 On the other hand, urea deriv-
atives represent an important class of molecules that display
remarkable pharmacological activity such as NPY Y5 receptor
antagonists,6 2-adrenoreceptor agonists,7 CCR3 antagonists,8 H3
receptor,9 and p38 MAPK inhibitors.10 Thus, a hybrid of these
two motifs could potentially lead to a series of structurally and bio-
logically interesting compounds. Although many synthetic meth-
ods are known for the construction of the indole structure11 and
carbonylurea derivatives,6–10 respectively, to the best of our
knowledge, the formation of indole framework and its bisfunction-
alization residing in 3-position of indole ring via intermolecular
domino reactions have not been achieved so far.
‘green chemistry’ as well on account of avoiding time-consuming,
costly processes for purification of various precursors and tedious
steps of protection and deprotection of functional groups. Hence,
domino processes, in an environmentally benign and atom-eco-
nomic fashion, play an important role in organic syntheses, espe-
cially considering that certain complex compounds such as fused
polyheterocycles are of great significance and their synthesis still
remains a challenge for chemists.
In the past several years, we have developed unique domino
reactions that can provide efficient routes to useful functionalized
polyheterocycles of chemical and pharmaceutical interest.13,14
During our study of this topic, herein, we would like to report an-
other new synthetic strategy for the domino N-heteroannulations
of alloxan monohydrate 1 and enaminones 2 yielding the multi-
functionalized indole derivatives with high yields and regioselec-
tivity (Scheme 1). The notable feature of the present domino
strategy was shown by the fact that the construction of indole skel-
eton and its bisfunctionalization residing in C3-position of indole
ring were readily achieved through the metal-free ring-opening
On the other hand, the development of new methodologies
aimed at improving synthetic efficiency is an important goal in
contemporary organic synthesis. Domino strategy is used to im-
prove the efficiency of a chemical reaction whereby multiple bonds
are formed in a single reaction without the need to isolate interme-
diates.12 These reactions obey the principles of ‘atom economy’ and
O
O
O
NH2
O
O
N
HO
HO
HO
H
NH
HOAc
r.t.
+
O
Ar
N
H
N
H
1
O
O
N
Ar
3
2a-o
⇑
Corresponding authors. Tel./fax: +86 516 83500065.
E-mail addresses: jiangchem@jsnu.edu.cn (B. Jiang), laotu@jsnu.edu.cn (S.-J. Tu).
Scheme 1. The domino reaction of 1 with 2a–2o.
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.09.120

6612
L.-Y. Xue et al. / Tetrahedron Letters 53 (2012) 6611–6614
Table 2
of alloxan monohydrate in a one-pot operation. The present work
represents the special examples for synthesizing such important
types of indole-substituted carbonylurea derivatives.
Syntheses of indole derivatives16
Entry
3Ar
Time (min)
Yielda (%)
We have planned to link two biologically important nuclei,
indoles and urea derivatives, to generate a new set of compounds,
indole-substituted carbonylureas, using domino heterocyclization
of alloxan monohydrate 1 and enaminones 2. It should be men-
tioned that enaminones are versatile and readily obtainable re-
agents, and their chemistry has received considerable attention
in recent years.15 Recently, we have also established a new
three-component domino reaction of enaminones for the synthesis
of polysubstituted fused pyrrole derivatives through allylic func-
tionalization.13a–d In this Letter, we devoted our efforts to the study
of the reaction of a preformed enaminone 2a and alloxan monohy-
drate 1 as a model reaction. Experiments were first examined in
DMF at room temperature, using NaOH or t-BuOK as a base
(1.0 equiv). The reaction scarcely proceeded in basic conditions
(Table 1, entries 1–2). The indole-substituted carbonylureas 3
was also not generated in DMF without base. So we attempted to
change the reaction condition to acidic condition. When HOAc
was used as the solvent, the reaction proceeded smoothly to give
the product 3a in 92% chemical yield. A similar outcome (88%
yield) was obtained when the reaction was performed in acetic
anhydride at room temperature (Table 1, entry 5).
We next explored the scope of this domino reaction of enami-
nones 2 with alloxan monohydrate 1 under the optimized condi-
tions (HOAc, rt). The results are summarized in Table 2. We
found that the substituents on the aromatic ring of enaminones 2
did not hamper the reaction process. Reactions of methyl-, meth-
oxy-, bromo-, chloro-, or fluoro-substituted N-phenyl enaminones
2 with alloxan monohydrate 1 all worked well to afford the desired
products in good yields. N-4-Nitrophenyl enaminones also gave the
4-nitrophenyl substituted indoles 3i in 85% yield. In addition, the
bulkily o-substituted N-phenyl enaminones 2 was converted into
the corresponding indole derivatives 3l with acetyl urea group reg-
iospecifically residing in C3-position. The results exhibit the scope
and generality of the new domino reaction with respect to a range
of enaminone substrates. Furthermore, halogen functional groups
(Cl and Br) were tolerated well. These functional groups provide
ample opportunity for further functional group manipulations,
for example, by modern cross-coupling reactions.
1
2
3
4
5
6
7
8
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
4-Fluorophenyl (2a)
4-Chloropheny (2b)
3-Chloropheny (2c)
3,4-Dichlorophenyl (2d)
3,5-Dichlorophenyl (2e)
4-Bromophenyl (2f)
3-Bromophenyl (2g)
3-Bromo-4-methylphenyl (2h)
4-Nitrophenyl (2i)
Phenyl (2j)
p-Tolyl (2k)
o-Tolyl (2l)
4-Methoxyphenyl (2m)
3,4-Dimethoxyphenyl (2n)
Benzo[d][1,3]dioxol-5-yl (2o)
18
15
17
15
13
16
17
18
23
19
18
20
18
23
24
92
93
92
86
90
91
85
84
85
94
89
83
87
86
87
9
10
11
12
13
14
15
a
Isolated yield.
Ar
NH
O
O
O
O
O
HO
HOAc
+
NH
O
HO
NH
O
r. t.
NH
Ar
HO
O
O
N
H
1
O
N
H
4
2p-t
Scheme 2. The domino reaction of 1 with 2p–2t.
Table 3
Syntheses of pyrimidine-2,4,6-triones 416
Entry
4
Ar
Time (min)
Yielda (%)
1
2
3
4
5
4a
4b
4c
4d
4e
3,4-Dichlorophenyl 3(2p)
3-Bromo-4-methylphenyl (2q)
Phenyl (2r)
p-Tolyl (2s)
4-Chloropheny (2t)
16
18
17
20
22
92
94
92
93
89
a
Isolated yield.
In view of these results, we then investigated several differently
substituted enaminones. The reactions of N-substituted 4-aminofu-
ran-2(5H)-ones2p–2t with 1 were carried out under the above condi-
tions for a short period (16–22 min). In these reactions, only
nucleophilic substitutions between2p–2t and 1 occurred and resulted
in structurally diverse furan-3-yl-substituted pyrimidine-2,4,6-tri-
ones4a–4e (Scheme 2). This substitution reaction also exhibits a good
scope of enaminone substrates (Table 3), providing a straightforward
pathway to construct highly substituted pyrimidine-2,4,6-triones
with a quaternary center. The structural elucidations were unequivo-
cally determined by NMR spectroscopic analysis and X-ray diffraction
of single crystals 3e and 4e (Figs. 1 and 2).17
reaction rates which enable the reaction to be completed within
13–24 min; (2) the environmentally friendly process in which
water is the major by-product; (3) the convenient work-up which
only needs simple filtration since the products directly precipitate
out after the reaction is finished and when its mixtures are diluted
with cold water; (4) readily available starting materials of pre-
formed N-substituted enaminones and alloxan monohydrate.
Moreover, during these domino processes, C3-bisfunctionalization
of indole ring including a quaternary hydroxyl functionality was
realized accompanied by C–O and C–N bonds cleavage of the allox-
an monohydrate. This observation is very useful and important in
organic chemistry.
On the basis of all the above results, possible mechanism has
been proposed for the formation of indole-substituted carbonylu-
rea derivatives as shown in Scheme 3. The reaction involves the
ring closure cascade reactions that consist of initial nucleophilic
substitutions (1 to A), cyclization/ring-opening of alloxan monohy-
drate (addition-elimination A to 3).
Similar to our previous domino process,13,14 the present reac-
tion also showed the following attractive characteristics: (1) fast
Table 1
Optimization of reaction conditions
Entry
Solvent
Base
Time (min)
Yielda (%)
In conclusion, we have described a new domino reaction as an
alternative and atom-economic strategy for indole synthesis and
its C3-bisfunctionalization with concomitant ring-opening of allox-
an monohydrate in one-pot manner. The reaction proceeds by
domino [3 + 2] heterocyclization obtaining indoles in good yields,
showing that the synthetic route allows us to build blocks of indole
derivatives with a wide diversity in substituents. Features of this
1
2
3
4
5
DMF
DMF
DMF
HOAc
Ac2O
NaOH
t-BuOK
—
—
—
18
18
18
18
18
N.R.
N.R.
N.R
92
88
a
Isolated yield.

L.-Y. Xue et al. / Tetrahedron Letters 53 (2012) 6611–6614
6613
Figure 1. X-ray structure of 3e.17
Figure 2. X-ray structure of 4e.17
O
H
N
O
O
O
O
+
HO
HO
HO
OH2
HN
Ar
O
H+
NH
2
HN
NH
OH
O
O
N
H
O
OH
O
N
H
NH
Ar
A
1
HO
O
HO
O
O
NH
NH
NH
OH+
O
-H+
tautomerization
HO
N
H
OH+
H+
N
Ar
OH
N
Ar
B
C
O
O
NH2
O
HO
N
H
O
N
Ar
3
Scheme 3. The possible mechanism of formation of indoles 3,
strategy include the mild condition, convenient one-pot operation,
and high regioselectivity. Efforts are actually directed toward the
extension of this methodology to natural products and drug
synthesis.

6614
L.-Y. Xue et al. / Tetrahedron Letters 53 (2012) 6611–6614
Neuschütz, K.; Velker, J.; Neier, R. Synthesis 1998, 227; (f) Poli, G.; Giambastiani,
Acknowledgments
G.; Heumann, A. Tetrahedron 2000, 56, 5959; (g) McCarroll, A. J.; Walton, J. C.
Angew. Chem. 2001, 113, 2282–2307
We are grateful for the financial support from the National Sci-
ence Foundation of China (Nos. 21232004, 21272095, 21072163,
and 21102124), the Priority Academic Program Development
(PAPD) of Jiangsu Higher Education Institutions, Science Founda-
tion in Interdisciplinary Major Research Project of Xuzhou Normal
University (No. 09XKXK01), the NSF of Jiangsu Education Commit-
tee (11KJB150016) and Jiangsu Science and Technology Support
Program (No. BE2011045), and Doctoral Research Foundation of
Xuzhou Normal Univ. (XZNU, No. 10XLR20).
13. (a) Jiang, B.; Yi, M.-S.; Shi, F.; Tu, S.-J.; Pindi, S.; McDowell, P.; Li, G. Chem.
Commun. 2012, 48, 808; (b) Jiang, B.; Li, Q.-Y.; Zhang, H.; Tu, S.-J.; Pindi, S.; Li, G.
Org. Lett. 2012, 14, 700; (c) Jiang, B.; Li, Y.; Tu, M.-S.; Wang, S.-L.; Tu, S.-J.; Li, G.
J. Org. Chem. 2012, 77, 7497; (d) Jiang, B.; Yi, M.-S.; Tu, M.-S.; Wang, S.-L.; Tu, S.-
J. Adv. Synth. Catal. 2012, 354, 2504; (e) Jiang, B.; Tu, S.-J.; Kaur, P.; Wever, W.;
Li, G. J. Am. Chem. Soc. 2009, 131, 11660.
14. (a) Jiang, B.; Zhang, G.; Ma, N.; Shi, F.; Tu, S.-J.; Kaur, P.; Li, G. Org. Biomol. Chem.
2011, 9, 3834; (b) Jiang, B.; Wang, X.; Shi, F.; Tu, S.-J.; Li, G. Org. Biomol. Chem.
2011, 9, 4205; (c) Jiang, B.; Hao, W.-J.; Zhang, J.-P.; Tu, S.-J.; Shi, F. Org. Biomol.
Chem. 2009, 7, 1171; (d) Jiang, B.; Shi, F.; Tu, S.-J. Curr. Org. Chem. 2010, 14, 357;
(e) Jiang, B.; Liu, Y.-P.; Tu, S.-J. Eur. J. Org. Chem. 2011, 3026; (f) Wang, S.-L.; Wu,
F.-Y.; Cheng, C.; Zhang, G.; Liu, Y.-P.; Jiang, B.; Shi, F.; Tu, S.-J. ACS Comb. Sci.
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15. (a) Stanovnik, B.; Svete, J. Chem. Rev. 2004, 104, 2433; (b) White, J. D.; Ihle, D. C.
Org. Lett. 2006, 8, 1081; (c) Tu, S. J.; Jiang, B.; Jia, R. H.; Zhang, J. Y.; Zhang, Y.;
Yao, C. S.; Shi, F. Org. Biomol. Chem. 2006, 4, 3664; (d) Huang, J.; Liang, Y.; Pan,
W.; Dong, D. Org. Lett. 2007, 9, 5345; (e) Yavari, I.; Hossaini, Z.; Sabbaghan, M.
Tetrahedron Lett. 2008, 49, 844; (f) Wang, G. W.; Miao, C. B. Green Chem. 2006, 8,
1080; (g) Wu, X. J.; Xu, X. P.; Su, X. M.; Chen, G.; Zhang, Y.; Ji, S. J. Eur. J. Org.
Chem. 2009, 4963; (h) Wu, X. J.; Jiang, R.; Wu, B.; Su, X. M.; Xu, X. P.; Ji, S. J. Adv.
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Supplementary data
Supplementary data (experimental details and spectroscopic
characterization of all compounds along with 1H, IR and mass spec-
tra) associated with this article can be found, in the online version,
at http://dx.doi.org/10.1016/j.tetlet.2012.09.120.
16. General procedure for the synthesis of compounds 3 and 4. Synthesis of indoles 3:
In a 10-mL reaction vial, alloxan monohydrate 1 (1.1 mmol, 1.1 equiv),N-
substituted enaminones 2a–2o (1 mmol, 1.0 equiv), and HOAc (4.0 mL) were
stirred at room temperature for 13–24 min. Upon completion, monitored by
TLC, the mixture was poured into the cold water, and a solid product was
collected by Büchner filtration. The crude solid was purified by
recrystallization from EtOH (95%) to give the pure products 3a–3o. N-
Carbamoyl-1-(4-fluorophenyl)-3-hydroxy-6,6-dimethyl-2,4-dioxo-2,3,4,5,6,7-
hexahydro-1H-indole-3-carboxamide (3a) White solid, mp: 203–204 °C; IR
References and notes
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Shibata, T.; Suga, T.; Takahashi, H.; Hirohashi, T.; Sakuraba, A.; Gomori, A.;
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9. Ceras, J.; Cirauqui, N.; Pérez-Silanes, S.; Aldana, I.; Monge, A.; Galiano, S. Eur. J.
Med. Chem. 2012, 52, 113.
10. Lopes, R. O.; Romeiro, N. C.; de Lima, C. K. F.; Louback da Silva, L.; Palhares de
Miranda, A. L.; Nascimento, P. G. B. D.; Cunha, F. Q.; Barreiro, E. J.; Lima, L. M.
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(KBr, m
, cmÀ1): 3473, 3286, 2971, 2850, 1764, 1727, 1708, 1513, 1403, 1213,
1007, 819, 693, 569; 1H NMR (400 MHz, DMSO-d6) (d, ppm): 10.97 (d,
J = 12.8 Hz, 2H, NH2), 9.77 (s, 1H, NH), 7.87 (d, J = 13.6 Hz, 1H, OH), 7.10–7.07
(m, 2H, ArH), 7.03–6.99 (m, 2H, ArH), 2.27 (s, 2H, CH2), 1.99 (s, 2H, CH2), 0.92 (s,
6H, 2CH3); 13C NMR (100 MHz, DMSO-d6) (d, ppm): 193.5, 170.7, 162.9,
159.9(1JCF = 247.2 Hz), 150.5, 134.0(4JCF = 2.9 Hz), 127.2(3JCF = 8.3 Hz), 127.2,
115.7(2JCF = 22.5 Hz), 115.5, 106.1, 74.8, 48.8, 32.5, 27.4; HRMS (ESI) m/z:
calculated. for C18H18FN3O5Na: 398.1122 [M+Na]+; found: 398.1096. Synthesis
of pyrimidines 4: In a 10-mL reaction vial, alloxan monohydrate 1 (1.1 mmol,
1.1 equiv), N-substituted 4-aminofuran-2(5H)-ones 2p–2t (1 mmol, 1.0 equiv),
and HOAc (4.0 ml) were stirred at room temperature for 16–22 min. Upon
completion, monitored by TLC, the mixture was poured into the cold water,
and a solid product was collected by Büchner filtration. The crude solid was
purified by recrystallization from EtOH (95%) to give the pure products 4a–4e.
5-(4-((3,4-Dichlorophenyl)amino)-2-oxo-2,5-dihydrofuran-3-yl)-5-
hydroxypyrimidine-2,4,6(1H,3H,5H)-trione (4a) White solid, mp: 241–243 °C;
IR (KBr, m
, cmÀ1): 3536, 3309, 3210, 2860, 1735, 1701, 1631, 1588, 1380, 1032,
765, 673; 1H NMR (400 MHz, DMSO-d6) (d, ppm): 11.51 (s, 2H, 2NH), 9.17 (s,
1H, OH), 7.55 (d, J = 12.0 Hz, 1H, ArH), 7.50 (s, 1H, ArH), 7.30 (s, 1H, NH), 7.21
(d, J = 8.0 Hz, 1H, ArH), 5.15 (s, 2H, CH2); 13C NMR (100 MHz, DMSO-d6) (d,
ppm): 170.8, 169.3, 163.9, 150.0, 138.3, 131.7, 131.1, 126.6, 123.0, 121.5, 94.1,
72.0, 66.6, 56.5; HRMS (ESI) m/z: calculated. for C14H9Cl2N3NaO6: 407.9760
[M+Na]+; found: 407.9772.
17. The single-crystal growth was carried out in a co-solvent of EtOH and DMF at
room temperature. Crystal data for 3e (CCDC-901502): C18H17Cl2N3O5, crystal
dimension 0.38 Â 0.30 Â 0.15 mm, Monoclinic, space group P2(1)/n,
11. The selected examples: (a) Bernini, R.; Fabrizi, G.; Sferrazza, A.; Cacchi, S.
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2011, 17, 7298.
a = 10.1811(12) Å, b = 6.7301(7) Å, c = 29.352(2) Å,
a
= 90o, b = 93.4730(10)o,
c
= 90o, V = 2007.5(4) Å3, Mr = 426.25, Z = 4, k = 0.71073 Å,
l
(Mo
K ) = 0.358 mmÀ1, F(000) = 880, R1 = 0.0601, wR2 = 0.1410. Crystal data for 4e
a
(CCDC-901503):
Orthorhombic, space group P2(1)2(1)2(1), a = 6.9537(6) Å, b = 12.7504(11) Å,
c = 20.7039(17) Å, = b =
= 90o, V = 1835.7(3) Å3, Mr = 424.80, Z = 4,
(Mo F(000) = 880, R1 = 0.0538,
K ) = 0.259 mmÀ1
C
17H17ClN4O7, crystal dimension 0.36 Â 0.23 Â 0.20 mm,
a
c
k = 0.71073 Å,
wR2 = 0.1120.
l
,
a
12. Reviews: (a) Tiete, L. F. Chem. Rev. 1996, 96, 115; (b) Denmark, S. E.;
Thorarensen, A. Chem. Rev. 1996, 96, 137; (c) Malacria, M. Chem. Rev. 1996,
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