Facile and efficient michael addition of indole to nitroolefins catalyzed by zn(OAc)22H2O

Article abstract of DOI:10.1080/00397910903576610

The Zn(OAc)₂2H₂O-catalyed Michael addition reaction of indole to electron-deficient nitroolefins to afford the corresponding adducts in good to excellent yields with high selectivity is reported.

Full text of DOI:10.1080/00397910903576610

This article was downloaded by: [Dalhousie University]
On: 01 October 2013, At: 01:51
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
Facile and Efficient Michael Addition
of Indole to Nitroolefins Catalyzed by
Zn(OAc)2 · 2H2O
Xiang Ji a , Haibo Tong a & Yu Yuan a
a College of Chemistry and Chemical Engineering, Yangzhou
University, Yangzhou, China
Published online: 13 Jan 2011.
To cite this article: Xiang Ji , Haibo Tong & Yu Yuan (2011) Facile and Efficient Michael
Addition of Indole to Nitroolefins Catalyzed by Zn(OAc)2 · 2H2O, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 41:3, 372-379, DOI:
10.1080/00397910903576610
To link to this article: http://dx.doi.org/10.1080/00397910903576610
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Synthetic Communications1, 41: 372–379, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903576610
FACILE AND EFFICIENT MICHAEL ADDITION OF
INDOLE TO NITROOLEFINS CATALYZED BY
Zn(OAc)2 ꢀ 2H2O
Xiang Ji, Haibo Tong, and Yu Yuan
College of Chemistry and Chemical Engineering, Yangzhou University,
Yangzhou, China
The Zn(OAc)22H2O-catalyed Michael addition reaction of indole to electron-deficient
nitroolefins to afford the corresponding adducts in good to excellent yields with high
selectivity is reported.
Keywords: Indole; Michael addition; nitroolefins
INTRODUCTION
The Michael reaction has attracting much attention as one of the most
important CꢁC bond-forming reactions.[1] Among the Michael addition substrates,
indole is important, because a number of its derivatives occur in nature and show
versatile biological activities.[2] The 3-position of indole is one of the building blocks
for biologically active compounds. Addition of indole to nitroolefins fulfills the syn-
thesis of 3-substituted indole. Traditionally the Michael addition of indole to
nitroalkenes is catalyzed by a strong base and Brønsted acid.[3] In recent years, it
has been reported that these reactions can also be promoted by Lewis acid.[4,5]
Herein, we report that Zn(OAc)2 ꢀ 2H2O catalyzes these reactions in mild conditions
to afford the corresponding Michael adducts in good to excellent yields (Scheme 1).
RESULTS AND DISCUSSION
In a preliminary experiment, treatment of indole 1 with nitrostyrene 2a using
10 mol% Zn(OAc)2 ꢀ 2H2O as catalyst in cyclohexane at 80 ꢂC for 14 h afforded 3a
in 97% yield after column chromatography of the reaction mixture on silica gel.
Encouraged by this result, we carried out the reaction in different conditions
(Table 1).
The reaction resulted in excellent yields when a nonpolar solvent was used
(Table 1, entries 1–3). Cyclohexane was the most efficient among the nonpolar sol-
vents (Table 1, entry 1). Compared to the nonpolar solvents, the effect of the polar
Received August 10, 2009.
Address correspondence to Yu Yuan, College of Chemistry and Chemical Engineering, Yangzhou
University, 225002 Yangzhou, China. E-mail: yyuan@yzu.edu.cn
372

MICHAEL ADDITION OF INDOLE
373
Scheme 1. Zn(OAc)2-catalyzed Michael addition of indole to nitroolefins.
solvent seemed to be weaker (Table 1, entries 4–6). Moreover, it was found that this
reaction could also be carried out in water with 86% yield (Table 1, entry 7). The best
result was obtained while the reaction was carried out in the presence of 10 mol%
Zn(OAc)2 ꢀ 2H2O at 80 ꢂC using cyclohexane as solvent (97%; Table 1, entry 1).
However, decreasing the temperature or the amount of the catalyst reduced the
yields (Table 1, entries 10 and 8).
Under the optimized reaction conditions, a variety of b-nitrostyrenes were
tested, and the results are summarized in Table 2. All the reactions could proceed
smoothly under the optimized conditions. The b-nitrostyrenes with the halogen
group at the phenyl ring afforded excellent yields within 14 h (Table 2, entries
2–4). In contrast, the acceptable yields were achieved after prolonging the reaction
time using the b-nitrostyrenes bearing electron-donating groups at the phenyl as
the substrate (Table 2, entries 5–8). Using 2-nitrovinyl furan derived from 2-furalde-
hyde instead of b-nitrostyrene also gave the corresponding product 3i in good yield
(Table 2, entry 9).
Table 1. Screening for optimum reaction conditionsa
Entry
Catalyst (mol%)
Solvent
Temp (ꢂC)
Yieldb (%)
1
2
10
10
10
10
10
10
10
7
Cyclohexane
CCl4
80
80
80
80
80
80
80
80
80
60
97
92
94
87
83
87
86
82
0
3
1,4-Dioxane
CH3CN
4
5
CH3NO2
C2H5 OH
H2O
6
7
8
Cyclohexane
Cyclohexane
Cyclohexane
9
10
0
10
81
aConditions: 1 (0.3 mmol), 2a (0.36 mmol), and solvent (2 mL).
bYield after column chromatography.

374
X. JI, H. TONG, AND Y. YUAN
Table 2. Michael addition of indole to nitroolefins catalyzed by Zn(OAc)2 ꢀ 2H2Oa
Entry
Indole
Nitroolefins
Products
Time (h)
Yieldb (%)
1
3a
14
97
2
1
3b
14
98
3
4
5
1
1
1
3c
3d
3e
14
14
18
99
99
99
6
1
3f
18
92
7
8
1
1
3g
3h
18
18
90
83
9
1
3i
18
93
aConditions: 1 (0.3 mmol), 2a–i (0.36 mmol), and solvent (2 mL).
bYield after column chromatography.

MICHAEL ADDITION OF INDOLE
375
CONCLUSIONS
In summary, we have demonstrated an efficient and novel method for the
Michael addition reaction of indole to electron-deficient nitroolefins using Zn(OAc)2 ꢀ
2H2O as a new effective catalyst. The reactions were clean, and the products were
obtained in excellent yields without the formation of any side products.
EXPERIMENTAL
1H NMR and 13C NMR spectra were obtained with a Bruker Avance 600 spec-
trometer in CDCl3 with tetramethylsilane (TMS) or dimethylsulfoxide (DMSO-d6)
as an internal standard. Infrared (IR) spectra were recorded with a Bruker Tensor
27 Fourier transform (FT)–IR spectrophotometer using KBr pellets. Gas chromato-
graphy–mass spectrometry (GC-MS) was performed on a Finnigan Trace DSQ
chromatograph. The analytical data for the known compounds matched the
literature data.
General Procedure for the Michael Addition of Indole
to b-Nitrostyrenes
The indole (0.3 mmol), the b-nitrostyrenes (0.36 mmol), Zn(OAc)2 ꢀ 2H2O
(0.03 mmol), and cyclohexane (2 mL) were heated at 80 ꢂC for the appropriate time.
After the completion of the reaction, monitored by thin-layer chromatography
(TLC), the solvent was evaporated, and the product was extracted into ethyl acetate
(3 ꢃ 5 mL). The combined organic layer was dried over anhydrous sodium sulfate,
evaporated under reduced pressure, and purified by silica-gel column chromato-
graphy to afford the pure product.
General Procedure for Preparation of b-Nitrostyrenes (2a–i)[6]
The title compound was prepared by mixing nitromethane (0.2 mol) and the
corresponding aromatic aldehyde (0.2 mol) in methanol (50 mL) at 0 ꢂC. An aqueous
solution of sodium hydroxide (0.225 mol) was added to the stirring solution over a
period of 30 min. The stirring was continued for another half hour in the tempera-
ture range of 0–5 ꢂC. The mixture was diluted with ice water (100 mL) and poured
over crushed ice containing 32 mL of concentrated HCl. The solid, which pre-
cipitated out, was filtered, dried in a vacuum desiccator, and recrystallized from
hot EtOH.
Spectral Data of the Products 3a–i
3-(2-Nitro-1-phenylethyl)-1H-indole (3a).[7] 1H NMR (600 MHz, CDCl3):
d 8.09 (bs, 1H), 7.44 (d, J ¼ 7.99 Hz, 1H), 7.35–7.24 (m, 6H), 7.19 (t, J ¼ 7.52 Hz,
1H), 7.07 (t, J ¼ 7.59 Hz, 1H), 7.01 (s, 1H), 5.18 (t, J ¼ 7.98 Hz, 1H), 5.05 (dd,
J ¼ 12.54, 7.71 Hz, 1H), 4.93 (dd, J ¼ 12.54, 8.37 Hz, 1H); 13C NMR (150 MHz,
CDCl3): d 138.15, 135.40, 127.86, 126.71, 126.51, 125.02, 121.60, 120.59, 118.87,

376
X. JI, H. TONG, AND Y. YUAN
117.84, 113.23, 110.38, 78.47, 40.48; EIMS: Mþ1, m=z 266; IR (KBr): 3420, 1550,
1456, 1377, 912, 743, 702 cmꢁ1
.
3-(1-(4-Fluorophenyl)-2-nitroethyl)-1H-indole (3b).[8] 1H NMR (600 MHz,
CDCl3): d 8.12 (bs, 1H), 7.39 (d, J ¼ 7.93 Hz, 1H), 7.36 (d, J ¼ 8.14 Hz, 1H),
7.30–7.28 (m, 2H), 7.20 (t, J ¼ 7.35 Hz, 1H), 7.08 (t, J ¼ 7.46 Hz, 1H), 7.02–6.99
(m, 3H), 5.17 (t, J ¼ 7.80 Hz, 1H), 5.05 (dd, J ¼ 12.50, 7.43 Hz, 1H), 4.89 (dd,
J ¼ 12.47, 8.65 Hz, 1H); 13C NMR (150 MHz, CDCl3): d 160.18, 135.44, 133.92,
128.35, 128.29, 124.87, 121.73, 120.44, 118.95, 117.77, 114.82, 114.68, 113.05,
110.45, 78.47, 39.80; EIMS: Mþ1, m=z 284; IR (KBr): 3414, 1604, 1551, 1458,
1378, 1223, 1101, 912, 744 cmꢁ1
.
3-(1-(4-Chlorophenyl)-2-nitroethyl)-1H-indole (3c).[7] 1H NMR (600 MHz,
CDCl3): d 8.11 (bs, 1H), 7.39 (d, J ¼ 8.00 Hz, 1H), 7.36 (d, J ¼ 8.18 Hz, 1H), 7.27
(m, 4H), 7.20 (t, J ¼ 7.67 Hz, 1H), 7.08 (t, J ¼ 7.67 Hz, 1H), 7.01 (d, J ¼ 2.27 Hz,
1H), 5.16 (t, J ¼ 7.97 Hz, 1H), 5.04 (dd, J ¼ 12.61, 7.39 Hz, 1H), 4.89 (dd,
J ¼ 12.59, 8.62 Hz, 1H); 13C NMR (150 MHz, CDCl3): d 136.70, 135.42, 132.31,
128.09, 128.03, 124.82, 121.77, 120.50, 119.00, 117.72, 112.74, 110.47, 78.22,
39.88; EIMS: Mþ1, m=z 300; IR (KBr): 3413, 1550, 1490, 1377, 1091, 1014, 906,
741 cmꢁ1
.
3-(1-(4-Bromophenyl)-2-nitroethyl)-1H-indole (3d).[8] 1H NMR (600 MHz,
CDCl3): d 8.11 (bs, 1H), 7.43 (d, J ¼ 8.39 Hz, 2H), 7.39 (d, J ¼ 7.99 Hz, 1H), 7.35
(d, J ¼ 8.17 Hz, 1H), 7.22–7.19 (m, 3H), 7.08 (t, J ¼ 7.37 Hz, 1H), 7.00 (d,
J ¼ 2.30 Hz, 1H), 5.14 (t, J ¼ 7.92 Hz, 1H), 5.04 (dd, J ¼ 12.56, 7.83 Hz, 1H), 4.89
(dd, J ¼ 12.58, 8.61 Hz, 1H); 13C NMR (150 MHz, CDCl3): d 137.22, 135.41,
130.99, 128.45, 124.80, 121.78, 120.52, 120.43, 119.01, 117.71, 112.64, 110.48,
78.12, 39.94; EIMS: Mþ1, m=z 344; IR (KBr): 3421, 1550, 1488, 1457, 1421, 1377,
1073, 1010, 912, 743 cmꢁ1
.
3-(2-Nitro-1-p-tolylethyl)-1H-indole (3e).[7] 1H NMR (600 MHz, CDCl3):
d 8.05 (bs, 1H), 7.44 (d, J ¼ 8.00 Hz, 1H), 7.33 (d, J ¼ 8.16 Hz, 1H), 7.21–7.17 (m,
3H), 7.11 (d, J ¼ 7.90 Hz, 2H), 7.06 (t, J ¼ 7.66 Hz, 1H), 7.00 (d, J ¼ 2.30 Hz, 1H),
5.14 (t, J ¼ 7.97 Hz, 1H), 5.03 (dd, J ¼ 12.44, 7.68 Hz, 1H), 4.90 (dd, J ¼ 12.44,
8.44 Hz, 1H), 2.30 (s, 3H); 13C NMR (150 MHz, CDCl3): d 136.14, 135.41,
135.11, 128.53, 126.56, 125.03, 121.54, 120.52, 118.81, 117.86, 113.41, 110.36,
78.58, 40.14, 19.98; EIMS: Mþ1, m=z 280; IR (KBr): 3420, 1550, 1457, 1378, 913,
744 cmꢁ1
.
3-(1-(3-Methoxyphenyl)-2-nitroethyl)-1H-indole (3f).[9] 1H NMR (600 MHz,
CDCl3): d 8.10 (bs, 1H), 7.46 (d, J ¼ 8.00 Hz, 1H), 7.34 (d, J ¼ 8.15 Hz, 1H), 7.22 (d,
J ¼ 7.97 Hz, 1H), 7.19 (t, J ¼ 7.45 Hz, 1H), 7.07 (t, J ¼ 7.59 Hz, 1H), 7.02 (d,
J ¼ 2.37 Hz, 1H), 6.92 (d, J ¼ 7.65 Hz, 1H), 6.86 (m, 1H), 6.78 (dd, J ¼ 8.22,
2.35 Hz, 1H), 5.15 (t, J ¼ 7.98 Hz, 1H), 5.03 (dd, J ¼ 12.56, 7.18 Hz, 1H), 4.92 (dd,
J ¼ 12.59, 8.30 Hz, 1H), 3.75 (s, 3H); 13C NMR (150 MHz, CDCl3): d 158.86,
139.84, 135.40, 128.88, 125.04, 121.58, 120.59, 118.99, 118.85, 117.80, 113.08,
112.98, 111.44, 110.39, 78.40, 54.15, 40.46; EIMS: Mþ1, m=z 296; IR (KBr): 3419,
1598, 1548, 1487, 1455, 1376, 1261, 911, 742, 702 cmꢁ1
.

MICHAEL ADDITION OF INDOLE
377
3-(1-(4-Methoxyphenyl)-2-nitroethyl)-1H-indole(3g).[9] 1HNMR(600 MHz,
CDCl3): d 8.07 (bs, 1H), 7.42 (d, J ¼ 7.99 Hz, 1H), 7.34 (d, J ¼ 8.16 Hz, 1H), 7.24
(d, J ¼ 9.06 Hz, 2H), 7.19 (t, J ¼ 7.52 Hz, 1H), 7.07 (t, J ¼ 7.57 Hz, 1H), 7.01 (d,
J ¼ 1.74 Hz, 1H), 6.84 (d, J ¼ 8.55 Hz, 2H), 5.13 (t, J ¼ 7.95 Hz, 1H), 5.03 (dd,
J ¼ 12.37, 7.59 Hz, 1H), 4.88 (dd, J ¼ 12.35, 8.46 Hz, 1H), 3.76 (s, 3H); 13C NMR
(150 MHz, DMSO): d 158.08, 136.18, 132.52, 128.84, 125.95, 122.04, 121.30,
118.59, 118.41, 113.77, 111.47, 79.38, 54.93, 39.99; EIMS: Mþ1, m=z 296; IR
(KBr): 3420, 1550, 1510, 1249, 912, 744 cmꢁ1
.
3-(1-(Benzo[d][1,3]dioxol-5-yl)-2-nitroethyl)-1H-indole (3h).[7] 1H NMR
(600 MHz, CDCl3): d 8.09 (bs, 1H), 7.43 (d, J ¼ 7.95 Hz, 1H), 7.35 (d, J ¼ 8.15 Hz,
1H), 7.20 (t, J ¼ 7.61 Hz, 1H), 7.08 (t, J ¼ 7.64 Hz, 1H), 7.04 (d, J ¼ 2.33 Hz, 1H),
6.82 (dd, J ¼ 7.94, 1.71 Hz, 1H), 6.76–6.74 (m, 2H), 5.91 (dd, J ¼ 10.22, 1.25 Hz,
2H), 5.10 (t, J ¼ 7.93 Hz, 1H), 5.02 (dd, J ¼ 12.34, 7.52 Hz, 1H), 4.86 (dd,
J ¼ 12.35, 8.42 Hz, 1H); 13C NMR (150 MHz, DMSO): d 147.09, 145.85, 135.94,
134.37, 125.77, 121.85, 121.15, 120.87, 118.45, 118.24, 113.44, 111.28, 107.95,
107.81, 100.87, 79.01, 40.20; EIMS: Mþ1, m=z 310; IR (KBr): 3420, 1550, 1490,
1442, 1375, 1244, 1038, 911, 743 cmꢁ1
.
3-(1-(Furan-2-yl)-2-nitroethyl)-1H-indole (3i).[7] 1H NMR (600 MHz,
CDCl3): d 8.13 (bs, 1H), 7.55 (d, J ¼ 7.97 Hz, 1H), 7.38–7.37 (m, 2H), 7.22 (t,
J ¼ 7.44 Hz, 1H), 7.15–7.12 (m, 2H), 6.31 (t, J ¼ 2.55 Hz, 1H), 6.16 (d, J ¼ 3.17 Hz,
1H), 5.25 (t, J ¼ 7.76 Hz, 1H), 5.05 (dd, J ¼ 12.58, 8.19 Hz, 1H), 4.92 (dd,
J ¼ 12.58, 7.35 Hz, 1H); 13C NMR (150 MHz, CDCl3): d 151.15, 141.21, 135.25,
124.82, 121.73, 121.56, 118.99, 117.63, 110.54, 110.42, 109.44, 106.33, 76.84, 34.66;
EIMS: Mþ1, m=z 256; IR (KBr): 3412, 1551, 1458, 1423, 1377, 1114, 1099, 1012,
913, 743 cmꢁ1
.
ACKNOWLEDGMENTS
We are grateful for support from the National Natural Science Foundation of
China (20702043), the Jiangsu Provincial Natural Science Foundation (BK2006549),
and the Program for New Century Excellent Talents in Yangzhou University.
REFERENCES
1. (a) Trost, B. M. On inventing reactions for atom economy. Acc. Chem. Res. 2002, 35, 695;
(b) Trost, B. M. The atom economy—A search for efficiency. Science 1991, 254, 1471.
2. Sundberg, R. J. The Chemistry of Indoles; Academic Press: New York, 1996; p. 113.
3. (a) Hiemstra, H.; Wiberg, H. Addition of aromatic thiols to conjugated cycloalkenones,
catalyzed by chiral b-hydroxy amines: A mechanistic study of homogeneous catalytic
asymmetric synthesis. J. Am. Chem. Soc. 1981, 103, 417; (b) Suzuki, K.; Ikekawa, A.;
Mukaiyama, T. The enantioselective Michael addition of thiols to cycloalkenones by using
(2S,4S)-2-anilinomethy-l-ethyl-4-hydroxypyrrolidine as chiral catalyst. Bull. Soc. Chem.
Jpn. 1982, 55, 3277; (c) Yamashata, H.; Mukaiyama, T. Asymmetric Michael addition of
thiophenol to maleic acid esters. Chem. Lett. 1985, 363; (d) Zhu, S.; Chohen, T. The prep-
aration of synthetically useful carbonyl-protected a- and b-lithio ketones via reductive
lithiation. Tetrahedron 1997, 53, 17607; (e) Emori, E.; Arai T.; Sasai, H.; Shibasaki, M.
Catalytic Michael addition of thiols to b-unsaturated carbonyl compounds: Asymmetric

378
X. JI, H. TONG, AND Y. YUAN
Michael additions and asymmetric protonations. J. Am. Chem. Soc. 1998, 120, 4043; (f) An,
L. T.; Zou, J. P.; Zhang, L. L.; Zhang, Y. Sulfamic acid–catalyzed Michael addition of
indoles and pyrrole to electron-deficient nitroolefins under solvent-free condition. Tetra-
hedron Lett. 2007, 48, 4297; (g) Yadav, J. S.; Subba Reddy, B. V.; Raju, A.; Ravindar,
K.; Baishya, G. 1-(Chloromethyl)-4-fluoro-1,4-diazoniabicyclo-[2,2,2]octane bis(tetrafluor-
oborate) as novel and efficient reagent for the conjugate addition of indoles to a,b-unsatu-
rated ketones. Chem. Lett. 2007, 36, 1056; (h) Sri Hari, G.; Nagaraju, M.; Marthanda
Murthy, M. Silica sulfuric acid–catalyzed Friedel–Crafts alkylation of indoles with nitroo-
lefins. Synth. Commun. 2008, 38, 100.
4. Olah, G. A.; Krishnamurty, R.; Prakash, G. K. S. Friedel–Crafts Alkylation. in Comprehen-
sive Organic Synthesis, 1st ed.; B. M. Trost, I. Fleming (Eds.); Pergamon: Oxford, 1991;
vol. III, p. 293.
5. For some examples of Lewis-catalyzed Michael reaction, see (a) Harrington, P. E.; Kerr,
M. A. Reaction of indoles with electron-deficient olefins catalyzed by Yb(OTf)3 ꢀ 3H2O.
Synlett. 1996, 1047; (b) Yadav, J. S.; Abraham, S.; Reddy, B. V. S.; Sabitha, G. InCl3-cat-
alysed conjugate addition of indoles with electron-deficient olefins. Synthesis 2001, 2165; (c)
Bandini, M.; Melchiorre, P.; Melloni, A.; Umani-Ronchi, A. A practical indium tribro-
mide–catalysed addition of indoles to nitroalkenes in aqueous media. Synthesis 2002,
1110; (d) Zhou, J.; Tang, Y. Sidearm effect: Improvement of the enantiomeric excess in
the asymmetric Michael addition of indoles to alkylidene malonates. J. Am. Chem. Soc.
2002, 124, 9030; (e) Komoto, I.; Kobayashi, S. Lewis acid catalysis in supercritical carbon
dioxide: Use of poly (ethylene glycol) derivatives and perfluoroalkylbenzenes adsurfactant
molecules which enable efficient catalysis in ScCO2. J. Org. Chem. 2004, 69, 680; (f) Zhan,
Z. P.; Yang, R. F.; Lang, K. Samarium triiodide–catalyzed conjugate addition of indoles
with electron-deficient olefins. Tetrahedron Lett. 2005, 46, 3859; (g) Bartoli, G.; Bosco,
M.; Giuli, S.; Giuliani, A.; Lucarelli, L.; Marcantoni, E.; Sambri, S.; Torregiani, E.
Efficient preparation of 2-indoly-1-nitroalkane derivatives employing nitroalkenes as
versatile Michael acceptors: New practical linear approach to alky 9H-b-carboline-4-
carboxylate. J. Org. Chem. 2005, 70, 1941; (h) Firouzabadi, H.; Iranpoor, N.; Nowrouzi,
F. The facile and efficient Michael addition of indoles and pyrrole to a,b-unsaturated
electron-deficient compounds catalyzed by aluminium dodecyl sulfate trihydrate
Al(DS)3 ꢀ 3H2O in water. Chem. Commun. 2005, 6, 789; (i) Jia, Y. X.; Zhu, S. F.; Yang,
Y.; Zhou, Q. L. Asymmetric Friedel–Crafts alkylations of indoles with nitroalkenes cata-
lyzed by Zn(II)–bisoxazoline complexes. J. Org. Chem. 2006, 71, 75; (j) Umani-Ronchi,
A. Catalytic enantioselective addition of indoles to arylnitroalkenes: An effective route
to enantiomerically enriched tryptamine precursors. Chirality 2005, 17, 522; (k) Zhan, Z.
P.; Lang, K. Microwave-accelerated samarium triiodide–catalyzed conjugate addition of
indoles with electron-deficient olefins. Synlett 2005, 1551; (l) Mohammadpoor-Baltork,
I.; Memarian, H. R.; Khosropour, A. R. Efficient Michael addition of infoles using
bismuthyl perchlorate as catalyst. Heterocycles 2006, 68, 1837; (m) Khodaei, M. M.;
Mohammadpoor-Baltork, I.; Memarian, H. R.; Khosropour, A. R.; Nikoofar, K.;
Ghanbary, P. Synthesis of 3-substituted indoles promoted by pulverization-activation
method catalyzed by Bi(NO3)3 ꢀ 5H2O. J. Heterocycl. Chem. 2008, 45, 377; (n) Giuseppe,
B.; Giustino, D. A.; Sandra, G.; Enrico, M.; Mauro, M.; Melissa, P. The CeCl3 ꢀ 7H2O=
NaI=SiO2 system as an efficient promoter for the Friedel–Crafts reaction of indoles to
nitroalkenes under solvent-free conditions. Synthesis 2008, 2, 320; (o) Tu, Z.; Raju, B.
R.; Liou, T. R.; Kavala, V.; Kuo, C. W.; Jang, Y.; Shih, Y. H.; Wang, C. C.; Yao, C. F.
An efficient method for the synthesis of a-arylated nitroalkanes and a-arylated hydroxi-
moyl chlorides mediated by AlCl3. Tetrahedron 2009, 65, 2436.
6. Worrall, D. E. Nitrostyrene. Org. Synth. Coll. 1941, 1, 413.

MICHAEL ADDITION OF INDOLE
379
7. Habib, P. M.; Kavala, V.; Kuo, C. W.; Yao, C. F. Catalyst-free aqueous-
mediated conjugative addition of indoles to b-nitrostyrenes. Tetrahedron Lett. 2008, 49,
7005.
8. Lin, S. Z.; You, T. P. Synthesis of 9,90-biphenanthryl-10,100-bis(oxazoline)s and their
preliminary evaluations in the Friedel–Crafts alkylations of indoles with nitroalkenes.
Tetrahedron 2009, 65, 1010.
9. Kusurkar, R. S.; Alkobati, N. A. H.; Gokule, A. S.; Puranik, V. G. Use of the Pictet–
Spengler reaction for the synthesis of 1,4-disubstituted-1,2,3,4-tetrahydro-b-carbolines
and 1,4-disubstituted-b-catbolines: Formation of c-carbolines. Tetrahedron 2008, 64,
1654.