Microwave-assisted conjugate addition of pyrrole on electron-deficient nitro-olefins

Article abstract of DOI:10.1080/00397910903458025

Michael addition of pyrrole to-nitrovinyl compounds were carried out using microwave methodology. Monosubstituted pyrroles were obtained selectively in a major amount. Formation of novel product obtained during one of the reactions was explained by the double addition to nitrostyrene.

Full text of DOI:10.1080/00397910903458025

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Microwave-Assisted Conjugate Addition
of Pyrrole on Electron-Deficient Nitro-
Olefins
Radhika S. Kusurkar a & Nabil A. H. Alkobati a
a Department of Chemistry , University of Pune , Pune, India
Published online: 06 Jan 2010.
To cite this article: Radhika S. Kusurkar & Nabil A. H. Alkobati (2010) Microwave-Assisted
Conjugate Addition of Pyrrole on Electron-Deficient Nitro-Olefins, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 40:3, 320-327, DOI:
10.1080/00397910903458025
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Synthetic Communications1, 40: 320–327, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903458025
MICROWAVE-ASSISTED CONJUGATE ADDITION OF
PYRROLE ON ELECTRON-DEFICIENT NITRO-OLEFINS
Radhika S. Kusurkar and Nabil A. H. Alkobati
Department of Chemistry, University of Pune, Pune, India
Michael addition of pyrrole to b-nitrovinyl compounds were carried out using microwave
methodology. Monosubstituted pyrroles were obtained selectively in a major amount.
Formation of novel product obtained during one of the reactions was explained by the
double addition to nitrostyrene.
Keywords: Conjugate additions; microwave; nitro-olefins; pyrrole; silica gel
INTRODUCTION
The pyrrole skeleton is a common unit in many naturally occurring com-
pounds, such as vitamin B12, haemin, and chlorophyll, which have pharmacological
and biological properties.[1] Pyrrole acts as a nucleophile from C-2 in reactions like
Michael addition, where protic acids or Lewis acids are used as catalysts.[2] The main
disadvantages of the reactions using acids are side reactions such as dimerization or
polymerization, long reaction time, and toxic reagents. Catalysts such as indium tri-
chloride, bismuth trichloride, iodine and sulfamic acid, heteropoly acids, aluminium
dodecyl sulfate trihydrate, and trifluoroacetic acid (TFA) are also used[3] for Michael
addition reactions.
Recently, microwave methodology has been used[4] extensively; the advantages
are very short reaction time, good yield and selectivity, and no catalysts. This
technique involves green chemistry, where the reactions are ecofriendly. In con-
tinuation of our earlier work using this technique,[5] we report here the micro-
wave-assisted addition reactions of pyrrole to several b-nitrovinyl compounds,
such as b-nitrostyrenes.
RESULTS AND DISCUSSION
The Michael reaction between pyrrole and b-nitrostyrene 4a was carried out by
loading both of these compounds on silica gel and irradiating them in a microwave
oven at 800 W. Two products were isolated from this reaction. Addition took place
at the 2-position, giving monosubstituted pyrrole 5a as a major product, and at
Received August 26, 2008.
Address correspondence to Radhika S. Kusurkar, Department of Chemistry, University of Pune,
Pune 411 007, India. E-mail: rsk@chem.unipune.ernet.in
320

MICROWAVE-ASSISTED CONJUGATE ADDITIONS
321
Scheme 1. Reaction of pyrrole with nitro olefins.
2- and 5-positions, giving disubstituted pyrrole 6a as a minor product (Scheme 1). By
adding pyrrole in double amounts, the percentage of monosubstituted product 5a
increased (Table 1).
Several other nitrovinyl compounds (4b–e and 4g–j) were used for the Michael
addition with pyrrole. b-Nitrovinyl compounds (4c, 4h, 4i, 4j) furnished exclusively
Table 1. Reactions of pyrrole with nitro-olefins
Total yield
of 5 and 6
(using 1:4
as 2:1) %
Ratio of 5:6
(using 1:4
as 1.2:1)
Ratio of 5:6
(using 1:4 as 2:1)
Electrophile
Time (min)
1
90
51:30
49:25
82:8
82a
67:15
—
5
75
Only mono
1
1
86
85
62:15
62:15
81:5
75:10
1
(Continued )

322
R. S. KUSURKAR AND N. A. H. ALKOBATI
Table 1. Continued
Total yield
of 5 and 6
(using 1:4
as 2:1) %
Ratio of 5:6
(using 1:4
as 1.2:1)
Ratio of 5:6
(using 1:4 as 2:1)
Electrophile
Time (min)
5
84a
74a
87a
83
59:26
74:10
—
Only mono
Only mono
Only mono
5
5
5
—
—
aYield calculated according to the recovered starting material.
mono-substituted products, whereas in all other cases, monosubstituted products
were in major amounts along with disubstituted products (Table 1). During the reac-
tion with 4b, the disubstituted product obtained was shown to be R, S isomer (6b),
because the four carbons of the pyrrole ring were resonating at different d values in
13C NMR, which was confirmed by a distortionless enhancement by polarization
transfer (DEPT) experiment. The methoxyls and pyrrole ring protons were also reso-
1
nating at different d values in H NMR.
Typically, the b-nitrovinyl compounds (4h–j) with b-methyl substituent gave an
inseparable mixture of diastereomers of the mono-substituted pyrrole as the exclus-
ive product (5h–j, Table 1). These reactions were not going to completion, because
some amount of starting material was recovered. Most of the Michael adducts
obtained were unreported and were characterized using spectral data such as
1H NMR, 13C NMR, infrared (IR), gas chromatography mass spectrometry
(GCMS), and elemental analysis. All the microwave reactions were very clean,
and no polymerization was observed, in contrast to the similar, previously reported
reactions using different catalysts.
To check the effect of substituents at pyrrole nitrogen on the reactivity, N-
methyl (2) and N-benzoyl pyrroles (3) were used for Michael addition reaction using
b-nitrostyrene 4a. In the case of N-methyl pyrrole, monosubstituted product 5f was
1
obtained in 65% yield along with a new compound in 15% yield. From H NMR,
13C NMR, and DEPT data, it was shown to be 7f and not 2,5-disubstituted pyrrole.
The formation of this product could be explained by the addition of pyrrole to two
molecules of nitrostyrene 4a as shown in Scheme 2.

MICROWAVE-ASSISTED CONJUGATE ADDITIONS
323
Scheme 2. Probable mechanism for the formation of 7f.
In the case of N-benzoyl pyrrole, no reaction was observed by irradiation for a
longer time or even by using more reactive 1-nitro-4-(b-nitrovinyl)benzene 4c. This
can be attributed to decreased reactivity of pyrrole as a result of electron-
withdrawing N-benzoyl substituent.
CONCLUSION
Michael additions of pyrrole to b-nitrovinyl compounds were successfully
achieved using microwave methodology. Monosubstituted products were obtained
exclusively in most of the cases. Compound 7f was obtained as a novel observation,
formation of which was explained by a double addition of pyrrole to nitrostyrene 4a.
EXPERIMENTAL
Thin-layer chromatographic analysis (TLC) was performed using silica gel on
glass plates and was detected under ultraviolet (UV) light. All recorded melting
1
points are uncorrected. The H and 13C NMR spectra were recorded as @ values
in CDCl3 with reference to tetramethylsilane (TMS) as internal standard on a Varian
1
Mercury instrument (300 MHz for H and 75 MHz for 13C). Fourier transform–
infrared (FT-IR) spectra were recorded on Perkin-Elmer 1600. Mass spectra were
recorded on Shimadzu QP 5050. Elemental analyses were recorded on Flash
EA1112 Thermo instrument. A Daewoo 616T domestic microwave oven was used
to carry out Michael additions.
General Procedure for Michael Addition
A mixture of pyrrole (1.39 ml, 0.02 mol) and nitro-olefin (0.01 mol) was loaded
on silica gel (60–120 mesh) and was irradiated in the microwave oven. Completion of
reaction was confirmed by TLC. The same silica gel was loaded on a silica-gel
column, and further chromatographic separation using hexane–ethyl acetate
furnished the products.
Spectroscopic Data
Compound 5a. Mp 73–75ꢀC (lit.[3a] mp 77–77.5ꢀC); yield 82%; IR (KBr)
1
3425, 1377, 1553 cmꢁ1; H NMR 4.72 (dd, J ¼ 6.87 and 11.0 Hz, 1H), 4.78–4.95
(m, 2H), 6.03 (bs, 1H), 6.12 (dd, J ¼ 2.75 and 5.5 Hz, 1H), 6.6 (bs, 2H), 7.1–7.2

324
R. S. KUSURKAR AND N. A. H. ALKOBATI
(bd, J ¼ 7.7 Hz, 1H), 7.21–7.35 (m, 3H), 7.8 (bs, 1H, exchangeable with D2O);
13C NMR 42.83, 79.04, 105.58, 108.41, 118.06, 127.7, 127.9, 128.69, 128.98,
137.79; MS m=z 216 Mþ, 186, 168, 156, 115, 139.
Compound 6a. Mixture of diastereomers; oily liquid; yield 8%; IR (KBr)
1
3429, 1545, 1367 cmꢁ1; H NMR 4.62–4.8 (m, 4H), 4.8–4.92 (m, 2H), 5.92–6.04
(m, 2H), 7.06–7.2 (m, 4H), 7.2–7.4 (m, 6H), 7.61 (2 ꢂ bs, 1H, exchangeable with
D2O); MS 365 (Mþ ꢁ HNO2), 271 (Mþ ꢁ 2HNO2), 258 (Mþ ꢁ HNO2ꢁCH2NO2),
246 (Mþ ꢁ C18 H16 N), 246, 128, 105, 91, 77, 69.
Compound 5b. Mp 145–148ꢀC; yield 67%; IR (KBr) 3356, 1512, 1375 cmꢁ1
;
1H NMR 3.82 (s, 3H), 3.86 (s, 3H), 4.72–4.9 (m, 2H), 4.97 (dd, J ¼ 10.7, 6.1 Hz, 1H),
6.08 (bs, 1H), 6.16 (dd, J ¼ 6.1, 2.8 Hz, 1H), 6.68 (t, J ¼ 1.7, 5.5 Hz, 2H), 6.72–6.86
(m, 2H), 7.85 (bs, exchangeable with D2O, 1H); 13C NMR 42.63, 55.91, 79.32,
105.49, 108.55, 110.89, 111.38, 118.0, 119.89, 128.94, 130.1, 148.63, 149.24; MS
m=z 276 Mþ, 242, 229 (100%), 216, 198, 184, 172, 151, 92, 77, 65. Anal. calcd. for
C14H16N2O4: C, 60.68; H, 5.84. Found: C, 60.50; H, 5.81.
Compound 6b. Mp 95ꢀC; yield 15%; IR (KBr) 3348, 1552, 1375 cmꢁ1
;
1H NMR 3.75 (s, 3H), 3.78 (s, 3H), 3.83 (two overlap singlets, 6H), 4.64–4.78
(m, 4H), 4.8–4.94 (m, 2H), 6.0 (2 ꢂ d, J ¼ 2.70 Hz, 2H), 6.58 (t, J ¼ 2.75 Hz, 2H),
6.65–6.72 (m, 2H), 6.74–6.82 (m, 2H), 7.99 (bs, 1H, exchangeable with D2O);
13C NMR 42.45, 55.68, 79.14, 105.56, 105.94, 110.68, 111.18, 119.66, 119.76,
129.42, 130.110, 148.38, 148.97; DEPT protonated carbons nine, six CH groups,
one CH2 and two CH3 groups; MS m=z 485 Mþ, 483, 425, 408, 392, 378 (100%),
276, 228, 216, 198, 164, 151, 136, 91, 77, 65.
Compound 5c. Mp 124–126ꢀC; yield 75%; IR (KBr) 3404, 1551, 1358 cmꢁ1
;
1H NMR 4.85 (dd, J ¼ 10.71 and 15.1 Hz, 1H), 4.95–5.08 (m, 2H), 6.08 (bs, 1H), 6.19
(dd, J ¼ 3.02, 6.0 Hz, 1H), 6.72 (dd, J ¼ 1.37 and 2.75 Hz, 1H), 7.4 (d, J ¼ 8.8 Hz,
2H), 7.95 (bs, 1H, exchangeable with D2O), 8.18 (d, J ¼ 8.8 Hz, 2H); 13C NMR
42.58, 78.43, 106.38, 108.84, 118.89, 124.26, 127.01, 128.77, 145.38, 147.33; MS
m=z 261 Mþ, 214 (100), 201, 167, 139, 115, 93. Anal. calcd. for C12 H11N3O4: C,
55.17; H, 4.24. Found: C, 55.19; H, 4.26.
Compound 5d. Oily liquid; yield 81%; IR (KBr) 3462, 1556, 1377 cmꢁ1
;
1H NMR 4.7–4.89 (m, 2H), 4.95 (t, J ¼ 7.7 Hz, 1H), 6.0 (bs, 1H), 6.1 (m, 2H),
6.26 (m, 1H), 6.65 (d, J ¼ 1.37 Hz, 1H), 7.32 (bs, 1H), 8.15 (bs, 1H, exchangeable
with D2O); 13C NMR 37.35, 78.11, 106.95, 108.11, 109.11, 110.86, 118.55, 126.43,
142.97, 150.84.
Compound 6d. Oily liquid; yield 5%; IR (KBr) 3450, 1555, 1379 cmꢁ1
;
1H NMR 4.7–4.86 (m, 4H), 4.94 (dd, J ¼ 7.42 and 14.85 Hz, 2H), 6.0 (d, J ¼ 2.75 Hz,
2H), 6.15 (d, J ¼ 3.02 Hz, 2H), 6.32 (bs, 2H), 7.38 (bs, 2H), 8.25 (bs, 1H, exchange-
able with D2O).
Compound 5e. Mp above 250ꢀC; yield 75%; IR (KBr) 3402, 1551, 1379 cmꢁ1
;
1H NMR 4.82 (dd, J ¼ 8.25 and 12.92 Hz, 1H), 4.92 (dd, J ¼ 8.25 and 12.92 Hz, 1H),
5.2 (t, J ¼ 7.7 Hz, 1H), 6.0–6.24 (m, 2H), 6.7 (t, J ¼ 2.2 Hz, 1H), 6.84–7.04 (m, 2H),
7.16–7.32 (m, 1H), 8.04 (bs, 1H, exchangeable with D2O); 13C NMR 38.23, 79.63,

MICROWAVE-ASSISTED CONJUGATE ADDITIONS
325
105.83, 108.73, 118.18, 125.47, 125.77, 127.07, 128.17, 140.84; MS m=z 224 (Mþ þ 2),
222 Mþ, 175, 162, 143, 130, 109, 65. Anal. calcd. for C10 H10N2O2S: C, 54.04; H,
4.53. Found: C, 54.19; H, 4.70.
Compound 6e. Oily liquid; yield 10%; IR (KBr) 3414, 1558, 1458 cmꢁ1
;
1H NMR 4.72–4.92 (m, 4H), 5.06–5.16 (dt, J¼ 2.2 and 7.0 Hz, 2H), 6.02 (d,
J ¼ 2.75 Hz, 2H), 6.84–6.89 (m, 2H), 6.89–6.96 (m, 2H), 7.18–7.26 (m, 2H), 7.93 (bs,
1H, exchangeable with D2O); MS 330 (Mþ ꢁ HNO2), 283, 270, 190, 174, 89, 77, 64.
1
Compound 5f. Mp 65ꢀC; yield 68%; IR (KBr) 1553, 1377 cmꢁ1; H NMR
3.34 (s, 3H), 4.73 (dd, J ¼ 6.9 and 14.6 Hz, 1H), 4.8–5.0 (m, 2H), 6.1 (d, J ¼ 1.92 Hz,
2H), 6.56 (d, J ¼ 1.92 Hz, 1H), 7.14 (d, J ¼ 6.6 Hz, 2H), 7.2–7.34 (m, 3H); 13C NMR
34.22, 42.12, 79.76, 106.15, 107.12, 123.21, 128.08, 128.13, 129.34, 129.52, 138.22;
MS m=z 230 Mþ, 196, 183, 170, 167, 106, 91, 77, 65.
Compound 7f. Mp 146–148ꢀC; yield 15%; IR (KBr) 1551, 1371 cmꢁ1
;
1H NMR 3.16 (s, 3H), 4.08 (d, J ¼ 11.55 Hz, 1H), 4.55–4.7 (m, 2H), 4.75–4.9
(m, 1H), 5.56 (bd, 1H), 6.2 (d, J ¼ 2.75 Hz, 1H), 6.39 (d, J ¼ 1.92 Hz, 1H), 6.55
(bs, 1H), 6.71 (d, J ¼ 7.15 Hz, 2H), 7.08–7.26 (m, 4H), 7.26–7.41 (m, 4H); 13C
NMR 33.63, 43.62, 44.08, 75.64, 92.15, 106.34, 107.73, 122.23, 127.58, 128.38,
128.43, 128.63, 128.69, 129.09, 132.31, 137.11; DEPT one CH3 group, one CH2
group; MS m=z 379 Mþ, 283, 205, 183, 170 (100%), 167, 149, 128, 115, 105, 91, 77, 58.
Compound 5g. Mixture of two diastereomers in the ratio of 3.5:1. Mp
65–67ꢀC; yield 74%; IR (KBr) 3375, 1551, 1358 cmꢁ1; 1H NMR 1.43 (d, J ¼ 6.60 Hz,
3H), 4.55 (d, J ¼ 10.45 Hz, 1H), 5.1–5.22 (m, 1H), 6.12 (t, J ¼ 1.92 Hz, 2H), 6.65 (d,
J ¼ 3.0 Hz, 1H), 7.18–7.4 (m, 5H), 7.87 (bs, 1H, exchangeable with D2O); 13C NMR
18.81, 49.13, 86.65, 105.65, 108.27, 117.75, 127.39, 127.66, 128.24, 128.91, 137.57.
1
Small signals of other diastereomer were also seen in H NMR and 13C NMR.
MS 163 (Mþ ꢁ C4H5N), 115 (100%), 105, 91, 77.
Compound 6g. Mixture of diastereomers, oily liquid; yield 10%; IR (KBr)
1
3422, 1549, 1358 cmꢁ1; H NMR 1.3–1.42 (m, 3H), 1.5–1.58 (m, 3H), 1.63 (bs,
1H, exchangeable with D2O), 4.28–4.45 (m, 2H), 5.0–5.14 (m, 2H), 5.9–6.04 (m,
2H), 7.01–7.07 (m, 10H); MS m=z 393 Mþ, 365, 332, 318, 271, 258, 148, 103, 91,
72, 65.
Compound 5h. Mixture of two diastereomers in ꢁt1he ratio of 2.5:1. Mp
;
1H NMR 1.44 (d,
162–164ꢀC; yield 74%; IR (KBr) 3360, 1550, 1387 cm
J ¼ 6.6 Hz, 3H), 1.66 (d, J ¼ 6.6 Hz, 3H), 3.84 (m four singlets overlapping, 12H),
4.41 (d, J ¼ 10.17 Hz, 1H), 4.48 (d, J ¼ 10.17 Hz, 1H), 5.04–5.2 (m, 2H), 6.1 (bs,
2H), 6.15 (bs, 2H), 6.6–6.9 (m, 8H), 7.9 (bs, 2H, exchangeable with D2O);
13C NMR 18.86, 19.11, 48.79, 49.23, 55.78, 55.81, 55.87, 86.77, 86.94, 105.64,
106.5, 108.41, 108.75, 111.04, 111.15, 111.29, 117.71, 119.26, 120.48, 128.33,
129.48, 129.95, 130.67, 148.27, 148.41, 148.91, 149.12; MS m=z 290 Mþ 243, 228,
216 (100%), 200, 154, 142, 130, 77.
Compound 5i. Mixture of two diastereomers inꢁ1the ratio of 4.7:1;
;
1H NMR 1.47 (d,
mp 155–157ꢀC; yield 87%; IR (KBr) 3393, 1524, 1348 cm
J ¼ 6.6 Hz, 3H), 1.69 (d, J ¼ 6.6 Hz, 3H), 4.56 (d, J ¼ 10.45 Hz, 1H), 4.69 (d,

326
R. S. KUSURKAR AND N. A. H. ALKOBATI
J ¼ 9.9 Hz, 1H), 5.21 (m, 2H), 6.14 (bs, 2H), 6.19 (bs, 2H), 6.68 (bs, 2H), 7.38–7.46
(m, 4H), 8.0 (bs, 2H, exchangeable with D2O), 8.14 (d, J ¼ 8.25 Hz, 2H), 8.2 (d,
J ¼ 8 Hz, 2H); 13C NMR 18.83, 19.10, 48.87, 49.48, 86.01, 86.57, 106.75, 107.04,
108.89, 109.39, 118.45, 118.61, 124.09, 124.23, 128.49, 129.26, 144.99, 145.57.
Compound 5j. Mixture of two diastereomers. Oily liquid; yield 83%; IR
(CHCl3) 3431, 1551, 1360 cmꢁ1 1H NMR 1.4 (two overlapping doublet, 6H),
;
4.7 (d, J ¼ 9.35 Hz, 2H), 5.0–5.18 (m, 2H), 6.0–6.4 (m, 8H), 6.76 (bd, J ¼ 1.65 Hz,
2H), 7.42 (d, J ¼ 0.55 Hz, 2H), 8.15 (bs, 2H, exchangeable with D2O); 13C NMR
17.77, 17.93, 42.94, 43.04, 85.7, 86.31, 107.45, 107.82, 108.44, 108.49, 108.61,
108.65, 110.40, 110.52, 118.11, 118.37, 124.95, 126.12, 142.43, 142.57, 150.21,
150.76; MS m=z 220, 202, 188, 173, 159, 146, 130, 117, 104, 91, 77, 65.
ACKNOWLEDGMENTS
We are grateful to Prof. M. S. Wadia for helpful discussions, Mr. A. P. Gadgil
for IR spectra and elemental analysis, Mrs. J. P. Chaudhari for NMR spectra, and
Mr. Shishupal for GC-MS.
REFERENCES
1. (a) Thomas, L. G. Heterocyclic Chemistry; 3rd ed.; Longman: England, 1997; vol. 11,
parts 1, 2 and 5; (b) Sundberg, R. D. Pyrroles and their benzo derivatives: Synthesis and
applications; In Comprehensive Heterocyclic Chemistry; A. R. Katrizky, C. W. Ress
(Eds.); Pergamon: Oxford, 1984; vol. 4, pp. 313–376; (c) Saxton, J. E. Recent progress in
the chemistry of the monoterpenoid indole alkaloids. Nat. Product Rep. 1997, 14, 559;
(d) Toyota, M.; Ihara, N. Recent progress in the chemistry; of non-monoterpenoid indole
alkaloids. Nat. Product Rep. 1998, 15, 327; (e) Leonid, I.; Belen, K. Relative stabilities of
hetarenium ions: Factors controlling positional selectivities of electrophilic substitution
and acid-induced transformations of pyrrole, furan, and thiophene derivatives. Hetero-
cycles 1994, 37, 2029.
2. (a) Joule, J. A.; Mills, K.; Smith, G. F. Heterocyclic Chemistry; 3rd ed.; Chapman and Hall:
London, 1995; p. 231; (b) Schofield, K. Hetero-aromatic Nitrogen Compounds: Pyrrole and
Pyridines; Plenum Press: New York, 1967; p. 3.
3. (a) Zhan, Z.-P.; Yu, J.-L.; Yang, W.-Z. Bismuth trichloride–catalyzed C-alkylation of pyr-
roles with electron-deficient olefins. Synth. Commun. 2006, 36, 1373; (b) Azizi, N.;
Arynasab, F.; Saidi, M. R. Efficient Friedel–Crafts alkylation of indoles and pyrrole with
enones and nitroalkene in water. Org. Biomol. Chem. 2006, 4, 4275; (c) 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 aluminum dodecyl sulfate
trihydrate [Al(DS)3]. 3H2O in water. Chem. Commun. 2005, 789; (d) Lin, C.; Hsu, J.; Sastry,
M. N. V.; Fang, H.; Tu, Z.; Liu, J.-T.; Ching-Fa, Y. I2-catalyzed Michael addition of indole
and pyrrole to nitroolefins. Tetrahedron 2005, 61, 11751; (e) Dessole, G.; Herrera, R.-P.;
Ricci, A. H-bonding organocatalysed Friedel–Crafts alkylation of aromatic and heteroaro-
matic systems with nitroolefins. Synlett 2004, 13, 2374; (f) Hong, S.-J.; Lee, M.-H.; Lee,
C.-H. Meso-substituted dipyrromethanes from vinylogous aromatic heterocycles and their
utilization to the synthesis of meso-functionalized porphyrins. Bull. Korean Chem. Soc.
2004, 25, 1545; (g) Yadav, J. S.; Abraham, S.; Reddy, B. V. S.; Sabitha, G. Addition of
pyrroles to electron-deficient olefins employing InCl3. Tetrahedron Lett. 2001, 42, 8063;

MICROWAVE-ASSISTED CONJUGATE ADDITIONS
327
(h) 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. Tetrahedron Lett. 2007, 48, 4297.
4. (a) Zhan, Z.-P.; Yang, W.-Z.; Yang, R.-F. Microwave-assisted addition of pyrroles to
electron-deficient olefins: A rapid entry to C-alkyl pyrroles. Synlett 2005, 16, 2425; (b)
Bengtson, A.; Hallberg, A.; Larhed, M. Fast synthesis of aryl triflates with controlled
microwave heating. Org. Lett. 2002, 1231; (c) Poondra, R. R.; Turner, N. J. Microwave-
assisted sequential amide bond formation and intramolecular amidation: A rapid entry
to functionalized oxindoles. Org. Lett. 2005, 863; (d) Saxena, I.; Borah, D. C.; Sarma, J.
C. Three-component condensations catalyzed by iodine-alumina for the synthesis of
substituted 3,4-dihydropyrimidin-2(1H)-ones under microwave irradiation and solvent-free
conditions. Tetrahedron Lett. 2005, 46, 1159; (e) Kaval, N.; Dehaen, W.; Matyus, P.;
Eycken, E. V. Convenient and rapid microwave-assisted synthesis of pyrido-fused ring sys-
tems applying the tert-amino effect. Green Chem. 2004, 6, 125; (f) Poondra, R. R.; Fischer,
P.; Tumer, M. N. J. Efficient palladium-catalyzed cross-coupling of b-chloroalkylidene=
arylidene malonates using microwave chemistry. J. Org. Chem. 2004, 69, 6920; (g)
Lidsttrom, P.; Tiemey, J.; Wathey, B.; Westman, J. Microwave-assisted organic synthesis:
A review. Tetrahedron 2001, 57, 9225.
5. Kusurkar, R. S.; Alkobati, N. A. H.; Gokule, A. S.; Chaudhari, P. M.; Waghchaure, P. B.
Thermal and microwave-assisted conjugate additions of indole on electron-deficient
nitro-olefins. Synth. Commun. 2006, 36, 1075.