Silica-assisted reactions of pyrroles with 1-acyl-2-bromoacetylenes

Article abstract of DOI:10.1055/s-2004-831244

Pyrroles react with 1-acyl-2-bromoacetylenes at room temperature on silica to give 2-acyl-1,1-di(pyrrol-2-yl)ethenes as major products in yields of up to 60%. Under reaction conditions employed, the intermediates (E)-2-(2-acyl-1- bromoethenyl)pyrroles (3-

Full text of DOI:10.1055/s-2004-831244

2736
PAPER
Silica-Assisted Reactions of Pyrroles with 1-Acyl-2-bromoacetylenes
S
ilica-Assisted
i
Reactio
n
ns of Pyrrole
a
s
w
ith1-A
i
cyl-2-
b
d
romacetylen
a
e
s
V. Stepanova, Lubov’ N. Sobenina,* Al’bina I. Mikhaleva, Igor’ A. Ushakov, Nina N. Chipanina,
Valentina N. Elokhina, Vladimir K. Voronov, Boris A. Trofimov
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, 1 Favorsky Str., Irkutsk 664033, Russia
Fax +7(3952)419346; E-mail: sobenina@irioch.irk.ru
Received 28 June 2004; revised 19 July 2004
In the present work, we have for the first time undertaken
Abstract: Pyrroles react with 1-acyl-2-bromoacetylenes at room
a study of the reaction of pyrroles 1a–c with 1-acyl-2-bro-
moacetylenes 2a,b.
temperature on silica to give 2-acyl-1,1-di(pyrrol-2-yl)ethenes as
major products in yields of up to 60%. Under reaction conditions
employed, the intermediates (E)-2-(2-acyl-1-bromoethenyl)pyr-
roles (3–11% isolated yields) either readily exchange the bromine
atom for the pyrrole molecule or eliminate HBr to afford 2-(2-acyl-
ethynyl)pyrroles, which can be isolated in 9–22% yields by chroma-
tography of the reaction mixture on Al2O3.
Under solvent-free conditions, the process is accompa-
nied by strong exothermic effect (sometimes up to explo-
sion) and resinification, whereas in solvents it slows down
drastically. For example, in Et2O, the reactants 1a and 2b
did not show any reaction at room temperature for 24
hours.
Key words: pyrroles, 1-acyl-2-bromoacetylenes, 2-(2-acyl-1-bro-
moethenyl)pyrroles, 2-acyl-1,1-di(pyrrol-2-yl)ethenes, 2-(2-acyl-
ethynyl)pyrroles, silica
A successful application of silica as a reaction medium for
the C-ethenylation of pyrroles with acylacetylenes7,8
prompted us to employ this methodology for the addition
of pyrroles to 1-acyl-2-bromoacetylenes.
Silica plays an important role in organic synthesis and is
widely used both in industrial processes and preparative
organic reactions. Such reactions often proceed under
mild conditions with high chemo-, regio-, and stereoselec-
tivity and allow for simpler product isolation procedures
as compared to analogous reactions in solution.1–3 Syn-
thetic application of solid supports and chromatographic
sorbents, including their modified forms, are steadily
growing.4–6
According to Scheme 1, pyrroles 1a–c reacted with acyl-
bromoacetylenes 2a,b on silica under mild conditions
(room temperature, moderate self-heating, 15 to 30 min-
utes) to form unexpectedly 2-acyl-1,1-di(pyrrol-2-
yl)ethenes 4a–f as major products (in yields of up to 60%,
based on a starting pyrrole).
The expected primary adducts, 2-(2-acyl-1-bromoethe-
nyl)pyrroles 3a–f, could be isolated (by chromatography
on Al2O3) in 3–11% yields only.
The use of silica as a solid support in the C-ethenylation
of pyrroles with acylacetylenes proved to be advanta-
geous; it allowed one to achieve significant reaction accel-
eration, improved regio- and stereoselectivity, and
increased yields of adducts.7,8
Monitoring of the reaction of pyrrole (1a) with acetylene
1
2b by H NMR (CDCl3 extracts of probes) confirmed
(Figure 1) the primary adduct to be 2-(1-bromo-2-
thenoylethenyl)pyrrole (3d), the content of which in-
creased over the time studied (one hour). During the first
five minutes, 1,1-di(pyrrol-2-yl)-2-thenoylethene (4d)
(the 3d/4d ratio, 2:1) and trace amounts of 2-(2-thenoyl-
ethynyl)pyrrole (5d) were detected in the reaction mix-
ture. The content of the latter remained constant for one
hour, whereas the 3d/4d ratio had changed to 3:1 by the
time the starting pyrrole (1a) (45 min) had disappeared
completely. Additionally, the reaction mixture contained
discernable (Z)-1,2-dibromo-2-thenoylethene (6), origi-
nating from HBr addition to the bromo-thenoylacetylene
2b (HBr can be formed in the addition-elimination reac-
tion of 3d with 1a). The final reaction mixture consisted
of 3d, 4d, and 6 in a ratio of 7:2:4, thus indicating that the
adduct 3d remained a major component of the reaction
mixture before work up.
Acyl-haloacetylenes have not yet been studied in the reac-
tion with pyrroles, although this would not only contribute
to understanding the reactivity of both pyrroles and acyl-
haloacetylenes, but also provide a route to novel function-
alized vinylpyrroles, potent building blocks for design of
drugs9 and advanced materials.10
Generally, the interaction of haloacetylenes with nucleo-
philes can proceed via halogen substitution or addition to
the triple bond.11,12 Introduction of strong electron-with-
drawing substituents into haloacetylenes not only enhanc-
es their reactivity, but also makes the halogen substitution
a major pathway of their reactions with nucleophiles.
Thus, the first step of interaction of 1-acyl-2-bromoacety-
lenes with nucleophiles is the exclusive formation of ethy-
nylketones.13
However, in this case we failed to isolate the adduct 3d in
pure form. During chromatography on alumina, it partial-
ly underwent HBr elimination to form the acetylene 5d in
12% yield, while the major part of 3d polymerized.
SYNTHESIS 2004, No. 16, pp 2736–2742
Advanced online publication: 22.09.2004
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DOI: 10.1055/s-2004-831244; Art ID: Z12904SS
© Georg Thieme Verlag Stuttgart · New York

PAPER
Silica-Assisted Reactions of Pyrroles with 1-Acyl-2-bromoacetylenes
2737
Scheme 1
1
Still, 2-(2-acyl-1-bromoethenyl)pyrroles 3b,c,f were sta- According to H NMR, 2-(2-acyl-1-bromoethenyl)pyr-
ble enough to be isolated by chromatography on alumina roles 3a–f are (E)-isomers with s-cis-conformation by dis-
in 3–11% yield.
position of the carbonyl group and pyrrole ring.
The isolated yields of 2-acyl-1,1-di(pyrrol-2-yl)ethenes Thus, 2D NOESY spectrum of the 2-(2-benzoyl-1-bromo-
4a–f were also sensitive towards the nature of substituents ethenyl)-5-phenylpyrrole (3c) shows the following char-
in the pyrrole ring.
acteristic nuclear Overhauser effects (NOE): the Ha atom
only has a resonance with the benzoyl Hortho atom. For
Hortho atoms in the 5-phenyl substituent, there are NOEs
with the NH and the H-4 pyrrole atoms. Such a conforma-
tion implies a strong intramolecular hydrogen bond be-
tween the NH and the carbonyl group, which causes a
considerable down-field shift of the NH signal to the re-
gion of d = 13.5–14.5 ppm.14 Indeed, in the case of pyrrole
3c (Figure 2), a broadened singlet of the NH atom is ob-
served at d = 14.50 ppm.
Thus, from the equimolar mixtures of pyrroles 1b,c and
acetylene 2b, after their short contact (15 min) with silica,
the adducts 4e,f were prepared in 57% and 60% yields, re-
spectively. Meanwhile, in order to attain a preparatively
acceptable yield (31%) of the dipyrrolylethene 4d, it was
necessary to use a two-fold molar excess of the pyrrole
(1a) and increase the reaction time to 30 minutes. Howev-
er, further prolonging the process resulted in resinification
of the products.
The existence of such an interaction is supported by the
absence of NH stretching vibrations at n = 3100–3400
cm–1 in the IR spectrum of 3c, as well as in the IR spectra
of compounds 4b and 5c, all recorded in KBr pellets.
Likewise, in IR spectra of 2-(2-acyl-1-phenylethenyl)-5-
phenylpyrroles (c = 10–3–10–4 mol /L solutions in CCl4),
having a similar strong intramolecular H-bond, the NH
band was also anomalously shifted to the n = 3000–3100
cm–1 region at low temperatures.15 In the IR spectra of
pyrroles 3a–f the C=O stretches are correspondingly shift-
ed to a very low frequency region, at n = 1633–1620
cm–1. The source of such spectral anomalies is assumed to
be a contribution of the zwitterionic structure 3¢c
(Scheme 2).
In the above-mentioned cases, acetylenes 5e and 5f were
also formed in low yields (3% and 2%, respectively). The
yields of these products increased to 20–22% after chro-
matographic treatment of reaction mixtures on alumina,
again supporting the HBr elimination from the primary
adducts 3 to be the source of acetylenes 5.
Correspondingly, 2-acyl-1,1-di(pyrrol-2-yl)ethenes 4a–f
are mainly formed as a result of the exchange of bromine
atom in 2-(2-acyl-1-bromoethenyl)pyrroles 3a–f for a
second molecule of the pyrrole 1 (presumably, through an
addition-elimination two-step process). Another probable
route to 4a–f is the addition of the pyrrole 1 to acetylenes
5a–f. It is also possible that both of these routes are fol-
lowed.
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Z. V. Stepanova et al.
PAPER
Figure 1 1H NMR monitoring of the reaction of the pyrrole (1a) with 2-bromo-1-thenoylacetylene (2b) on silica (the ratio 1a/2b, 1:1). The
ratio of the reaction products was determined by the integral intensity of atoms Ha (3d, 4d, 6). *: CDCl3
Scheme 2
Figure 2
Synthesis 2004, No. 16, 2736–2742 © Thieme Stuttgart · New York

PAPER
Silica-Assisted Reactions of Pyrroles with 1-Acyl-2-bromoacetylenes
2739
mortar with a 10-fold exess of SiO2 at r.t. over 1–2 min. The reac-
tion paste self–heated (5–8 °C) and instantly acquired a bright co-
lour, which then turned to yellow and further to orange-brown in ca.
10 min. The paste was allowed to stay for 15–30 min, then the prod-
ucts were successively extracted with n-hexane, n-hexane–Et2O
mixture (from 2:1–1:2) and Et2O. The extracts were chromato-
graphed on Al2O3 (column or TLC). Crystalline products were re-
crystallised from n-hexane–Et2O mixture (1:1).
In 2-acyl-1,1-di(pyrrol-2-yl)ethenes 4a–f a similar in-
tramolecular hydrogen bond of the NH group in one of the
pyrrole rings with the carbonyl group causes the same
very strong down-field shift of the NH signal (d = 13.80–
14.96 ppm), while the signal of the second NH group (a
free one) appeared in the region of d = 8.16–8.86 ppm. For
these compounds, the spin systems of both pyrrole rings
are reliably separated in 2D COSY spectra by cross-peaks
between the NH and ring H atom signals. The major inter-
actions observed are shown below by example of com-
pound 4e (Figure 3).
2-(2-Benzoyl-1-bromoethenyl)-4,5,6,7-tetrahydroindole (3b)
Red-orange solid; mp 127–128 °C.
IR (KBr): 3065, 3004, 2924, 2852, 1633, 1614, 1596, 1575, 1556,
1540, 1483, 1434, 1394, 1346, 1302, 1285, 1233, 1177, 1139, 1052,
1022, 973, 954, 906, 811, 780, 719, 698, 668 cm–1.
1H NMR: d = 13.63 (br s, 1 H, NH), 7.97 (m, 2 H, HorthoPh), 7.55
(m, 1 H, HparaPh), 7.47 (m, 2 H, HmetaPh), 7.13 (s, 1 H, H-a), 6.84 (d,
4J = 1.8 Hz, 1 H, H-3), 2.76 (m, 2 H, CH2-7), 2.59 (m, 2 H, CH2-4),
1.80 (m, 4 H, CH2-5,6).
Anal. Calcd for C17H16BrNO: C, 61.83; H, 4.88; N, 4.24; Br, 24.19.
Found: C, 61.51; H, 4.35; N, 3.99.
2-(2-Benzoyl-1-bromoethenyl)-5-phenylpyrrole (3c)
Red crystals; mp 124–125 °C.
IR (KBr): 3115, 3067, 3006, 2927, 2861, 1624, 1594, 1574, 1536,
1502, 1472, 1453, 1361, 1319, 1212, 1177, 1075, 1039, 1023, 1001,
967, 922, 896, 866, 814, 794, 760, 738, 691, 780, 668, 651, 602, 533
cm–1.
Figure 3
1H NMR: d = 14.50 (br s, 1 H, NH), 8.00 (m, 2 H, HorthoCOPh), 7.78
IR spectra of solutions of compounds 4c and 4f in CCl4
(c = 10–3–10–4 mol/L) show absorption bands of the free
NH group stretches at n = 3460 cm–1 and 3440 cm–1, re-
spectively. The bands related to the second NH group par-
ticipating in the intramolecular H-bond are supposed to be
shifted to the low frequency region and do not show up in
this solvent at room temperature, similar to compounds
with the same type of H-bond.14
(m, 2 H, HorthoPh-5), 7.56 (m, 1 H, HparaCOPh), 7.51 (m, 2 H,
H
metaCOPh), 7.47 (m, 2 H, Ph-5), 7.32 (m, 1 H, HparaPh-5), 7.28
(s, 1 H, H-a), 7.11 (dd, 3J = 4.1 Hz, 4J = 2.2 Hz, 1 H, H-3), 6.76 (dd,
3J = 4.1 Hz, 4J = 2.4 Hz, 1 H, H-4).
Anal. Calcd for C19H14BrNO: C, 64.79; H, 4.01; N, 3.98; Br, 22.68.
Found: C, 65.15; H, 4.11; N, 3.86; Br, 22.21.
2-(1-Bromo-2-thenoylethenyl)-4,5,6,7-tetrahydroindole (3e)
1H NMR: d = 13.47 (br s, 1 H, NH), 7.73 (dd, 3J = 3.9 Hz, 4J = 1.2
Hz, 1 H, H-3 of thenoyl), 7.61 (dd, 3J = 4.8 Hz, 4J = 1.2 Hz, 1 H, -5
of thenoyl), 7.13 (dd, 3J = 4.8 Hz, 3J = 3.9 Hz, 1 H, H-4 of thenoyl),
IR spectra (4000–400 cm–1) were taken with KBr pellets or in solu-
tions (CCl4) using a Bruker IFS-25 spectrometer. 1H and 13C NMR
4
7.02 (s, 1 H, H-a), 6.81 (d, J = 2.0 Hz, 1 H, H-3), 2.71 (m, 2 H,
1
CH2-7), 2.55 (m, 2 H, CH2-4), 1.89 (m, 2 H, CH2-6), 1.74 (m, 2 H,
CH2-5).
spectra were recorded on a Bruker DPX 250 [250.13 MHz for H
and 62.9 MHz for 13C, respectively] instrument in trichlorometh-
anol solutions with HMDS as an internal standard. Assignment of
signals in 1H NMR spectra was done using 2D COSY and NOESY
homonuclear correlation techniques.16 Resonance signals of carbon
atoms in 13C NMR spectra were assigned on the basis of analysis of
2D HSQC and HMBC spectra.17
2-(1-Bromo-2-thenoylethenyl)-5-phenylpyrrole (3f)
Red-orange crystals; mp 160–161 °C.
IR (KBr): 3099, 2918, 2856, 1620, 1602, 1579, 1537, 1504, 1474,
1452, 1409, 1375, 1348, 1314, 1303, 1283, 1263, 1242, 1214, 1187,
1077, 1060, 1042, 1028, 1017, 968, 921, 906, 886, 858, 841, 810,
753, 728, 705, 685, 656, 592, 578 cm–1.
Analysis of reaction mixtures and purity control of compounds ob-
tained were performed by TLC using Silufol plates; eluent: n-hex-
ane–Et2O (2:1).
1H NMR: d = 14.41 (br s, 1 H, NH), 7.84 (dd, 3J = 3.8 Hz, 4J = 1.0
Hz, 1 H, H-3 of thenoyl), 7.79 (m, 2 H, HorthoPh-5), 7.69 (dd, 3J =
4.7 Hz, 4J = 1.0 Hz, 1 H, H-5 of thenoyl), 7.48 (m, 2 H, HmetaPh-5),
Preparative separation of compounds was carried out by chroma-
tography (on column or in non-fixed thin layer) on Al2O3. Pyrrole
(1a) was a commercial product (Aldrich). 4,5,6,7-Tetrahydroindole
(1b) and 2-phenylpyrrole (1c) were prepared correspondingly from
cyclohexanonoxime and acetophenonoxime by the Trofimov reac-
tion.18 Silica (silica gel, L 100/160 m, pH 4.5–5, Chemapol) was
washed with distilled water and EtOH and dried in an oven (180 °C)
until a constant weight.
3
7.35 (m, 1 H, HparaPh-5), 7.21 (s, 1 H, H-a), 7.18 (dd, J = 4.7 Hz,
3J = 3.8 Hz, 1 H, H-4 of thenoyl), 7.11 (dd, 3J = 3.9 Hz, 4J = 2.0 Hz,
1 H, H-3), 6.76 (dd, 3J = 3.9 Hz, 4J = 2.6 Hz, 1 H, H-4).
13C NMR: d = 179.60 (C=O), 146.37 (C-2 of thenoyl), 139.07 (C-5
of pyrrole), 134.17 (C-5 of thenoyl), 133.95 (Cb), 131.86 (C-3 of
thenoyl), 131.15 (Cipso), 130.92 (C-2 of pyrrole), 129.21 (Cmeta),
128.61 (C-4 of thenoyl), 128.31 (Cpara), 125.00 (Cortho), 124.65 (C-3
of pyrrole), 116.17 (Ca), 110.31 (C-4 of pyrrole).
Reaction of Pyrroles with 1-Acyl-2-bromoacetylenes; General
Procedure
Equimolar amounts of pyrrole 1a–c (2 mmol) and 1-acyl-2-bro-
moacetylene 2a,b (2 mmol) were vigorously rubbed up in a china
Anal. Calcd for C17H12BrNOS: C, 56.99; H, 3.37; N, 3.91; S, 8.95;
Br, 22.30. Found: C, 57.15; H, 3.49; N, 3.96; Br, 21.98.
Synthesis 2004, No. 16, 2736–2742 © Thieme Stuttgart · New York

2740
Z. V. Stepanova et al.
PAPER
1,1¢-Di(pyrrol-2-yl)-2-benzoylethene (4a)
IR (KBr): 3295, 3096, 2922, 1643, 1605, 1551, 1512, 1499, 1407,
1350, 1265, 1243, 1189, 1140, 1080, 1061, 1043, 995, 965, 885,
856, 815, 746, 722, 653, 589 cm–1.
1H NMR: d = 13.85 (br s, 1 H, NH), 8.65 (br s, 1 H, NH¢), 7.77 (dd,
3J = 3.7 Hz, 4J = 1.2 Hz, 1 H, H-3 of thenoyl), 7.58 (dd, 3J = 4.9 Hz,
4J = 1.2 Hz, 1 H, H-5 of thenoyl), 7.12 (dd, 3J = 4.9 Hz, 3J = 3.7 Hz,
1 H, H-4 of thenoyl), 7.09 (m, 1 H, H-5), 6.96 (m, 1 H, H-5¢), 6.75
(s, 1 H, H-a), 6.70 (m, 2 H, H-3, H-3¢), 6.35 (m, 2 H, H-4, H-4¢).
Red-orange oil.
IR (KBr): 3311, 3101, 3058, 1617, 1595, 1574, 1547, 1522, 1499,
1487, 1451, 1429, 1402, 1383, 1353, 1316, 1241, 1227, 1176, 1139,
1103, 1041, 1021, 1002, 973, 938, 899, 881, 843, 777, 763, 741,
698, 600 cm–1.
1H NMR: d = 13.99 (br s, 1 H, NH), 8.67 (br s, 1 H, NH¢), 7.98 (m,
2 H, HorthoCOPh), 7.52 (m, 1 H, HparaCOPh), 7.47 (m, 2 H, Hmeta
-
COPh), 7.15 (m, 1 H, H-5), 6.95 (m, 1 H, H-5¢), 6.84 (s, 1 H, H-a),
13C NMR: d = 181.84 (C=O), 147.93 (C-2 of thenoyl), 140.80 (Cb),
133.00 (C-2¢ of pyrrole), 132.97 (C-5 of thenoyl), 130.93 (C-3 of
thenoyl), 129.88 (C-2 of pyrrole), 128.43 (C-4 of thenoyl), 123.71
(C-5 of pyrrole), 120.56 (C-5¢ of pyrrole), 118.99 (C-3 of pyrrole),
112.60 (C-3¢ of pyrrole), 111.58 (C-4 of pyrrole), 111.12 (Ca),
110.28 (C-4¢ of pyrrole).
6.73 (m, 2 H, H-3, H-3¢), 6.38 (m, 1 H, H-4), 6.33 (m, 1 H, H-4¢).
13C NMR: d = 189.82 (C=O), 140.75 (Cb), 140.75 (CipsoCOPh),
133.06 (C-2¢), 132.11 (CparaCOPh), 129.89 (C-2 of pyrrole), 128.57
(CmetaCOPh), 128.20 (CorthoCOPh), 123.48 (C-5 of pyrrole), 120.69
(C-5¢ of pyrrole), 118.90 (C-3 of pyrrole), 112.60 (C-3¢ of pyrrole),
111.81 (Ca), 111.49 (C-4 of pyrrole), 110.23 (C-4¢ of pyrrole).
Anal. Calcd for C15H12N2OS: C, 67.14; H, 4.51; N, 10.44; S, 11.95.
Found: C, 66.74; H, 4.14; N, 10.02; S, 11.80.
Anal. Calcd for C17H14N2O: C, 77.84; H, 5.38; N, 10.68. Found: C,
77.46; H, 5.49; N, 10.32.
1,1¢-Di(4,5,6,7-tetrahydroindol-2-yl)-2-thenoylethene (4e)
Dark red crystals; mp 210–211 °C.
1,1¢-Di(4,5,6,7-tetrahydroindol-2-yl)-2-benzoylethene (4b)
Red crystals; mp 186–187 °C.
IR (KBr): 3225, 3162, 3100, 3072, 2926, 2851, 1613, 1575, 1558,
1535, 1513, 1483, 1456, 1409, 1334, 1295, 1233, 1142, 1089, 1056,
995, 952, 928, 843, 809, 745, 725, 676, 622 cm–1.
1H NMR: d = 13.80 (br s, 1 H, NH), 8.16 (br s, 1 H, NH¢), 7.71 (dd,
3J = 3.7 Hz, 4J = 1.2 Hz, 1 H, H-3 of thenoyl), 7.51 (dd, 3J = 4.9 Hz,
4J = 1.2 Hz, 1 H, H-5 of thenoyl), 7.08 (dd, 3J = 4.9 Hz, 3J = 3.7 Hz,
1 H, H-4 of thenoyl), 6.57 (d, 4J = 2.2 Hz, 1 H, H-3), 6.56 (s, 1 H,
H-a), 6.44 (d, 4J = 2.4 Hz, 1 H, H-3¢), 2.75 (m, 2 H, CH2-7), 2.64
(m, 2 H, CH2-7¢), 2.54 (m, 4 H, CH2-4, CH2-4¢), 1.80 (m, 8 H, CH2-
5,6, CH2-5¢,6¢).
13C NMR: d = 180.07 (C=O), 148.75 (C-2 of thenoyl), 140.81 (Cb),
135.85 (C-5 of pyrrole), 131.78 (C-5 of thenoyl), 131.32 (C-2 of
pyrrole), 131.20 (C- 5¢ of pyrrole), 129.71 (C-3 thenoyl), 128.61 (C-
2¢ of pyrrole), 128.18 (C-4 thenoyl), 122.19 (C-4 of pyrrole), 119.36
(C-4¢ of pyrrole), 118.56 (C-3 of pyrrole), 112.41 (C-3¢ of pyrrole),
107.30 (Ca), 23.78 (CH2-7), 23.70 (CH2-5,5¢), 23.26 (CH2-6,6¢),
23.16 (CH2-7¢), 22.92 (CH2-4,4¢).
IR (KBr): 3309, 3065, 2927, 2851, 1592, 1570, 1541, 1517, 1500,
1479, 1446, 1429, 1336, 1319, 1286, 1267, 1235, 1176, 1140, 1073,
1052, 1035, 1021, 955, 925, 900, 822, 810, 780, 720, 701, 639, 604,
577 cm–1.
1H NMR: d = 14.00 (br s, 1 H, NH), 8.25 (br s, 1 H, NH¢), 7.97 (m,
2 H, HorthoPh), 7.50 (m, 1 H, HparaPh), 7.48 (m, 2 H, HmetaPh), 6.65
(s, 1 H, H-a), 6.62 (d, 4J = 2.0 Hz, 1 H, H-3), 6.50 (d, 4J = 2.2 Hz, 1
H, H-3¢), 2.81 (m, 2 H, CH2-7), 2.68 (m, 2 H, CH2-7¢), 2.60 (m, 2 H,
CH2-4), 2.58 (m, 2 H, CH2-4¢), 1.84 (m, 8 H, CH2-5,6, CH2-5,6¢).
13C NMR: d = 188.34 (C=O), 141.86 (Cb), 141.15 (CipsoCOPh),
135.45 (C-5 of pyrrole), 131.48 (C-2 of pyrrole), 131.33 (Cpara
-
COPh), 131.18 (C-5¢ of pyrrole), 128.69 (C-2¢ of pyrrole), 128.42
(CmetaCOPh), 127.93 (CorthoCOPh), 122.26 (C-4 of pyrrole), 119.65
(C-4¢ of pyrrole), 118.48 (C-3 of pyrrole), 112.48 (C-3¢ of pyrrole),
108.24 (Ca), 23.76 (CH2-7,7¢), 23.22 (CH2-5,5¢), 23.18 (CH2-6,6¢),
22.94 (CH2-4,4¢).
Anal. Calcd for C23H24N2OS: C, 73.37; H, 6.42; N, 7.44; S, 8.52.
Found: C, 72.95; H, 6.64; N, 7.58; S, 8.86.
Anal. Calcd for C25H26N2O: C, 81.05; H, 7.07; N, 7.56. Found: C,
81.38; H, 7.50; N, 7.30.
1,1¢-Di(5-phenylpyrrol-2-yl)-2-thenoylethene (4f)
Dark red crystals; mp 195–198 °C.
1,1¢-Di(5-phenylpyrrol-2-yl)-2-benzoylethene (4c)
Red crystals; mp 203–205 °C.
IR (KBr): 3294, 3094, 2922, 2850, 1619, 1602, 1581, 1536, 1503,
1476, 1452, 1405, 1376, 1348, 1313, 1264, 1241, 1076, 1060, 1045,
1021, 968, 922, 907, 885, 856, 810, 789, 755, 728, 706, 684, 592
cm–1.
IR (KBr): 3270, 3066, 3039, 1600, 1573, 1562, 1539, 1517, 1484,
1474, 1454, 1413, 1384, 1375, 1314, 1288, 1271, 1252, 1236, 1203,
1179, 1158, 1101, 1074, 1051, 1022, 999, 961, 924, 815, 776, 762,
752, 717, 685, 670, 651, 603, 575, 499 cm–1.
1H NMR: d = 14.71 (br s, 1 H, NH), 8.84 (br s, 1 H, NH¢), 7.82 (dd,
3J = 3.8 Hz, 4J = 1.0 Hz, 1 H, H-5 of thenoyl), 7.80 (m, 2 H, HorthoPh-
5), 7.59 (dd, 3J = 4.7 Hz, 4J = 1.0 Hz, 1 H, H-3 of thenoyl), 7.55 (m,
2 H, HorthoPh-5¢), 7.44 (m, 2 H, HmetaPh-5), 7.41 (m, 2 H, HmetaPh-
5¢), 7.29 (m, 1 H, HparaPh-5), 7.26 (m, 1 H, HparaPh-5¢), 7.13 (dd,
3J = 4.7 Hz, 3J = 3.8 Hz, 1 H, H-4 of thenoyl), 6.87 (dd, 3J = 3.7 Hz,
4J = 2.4 Hz, 1 H, H-3 of pyrrole), 6.79 (s, 1 H, H-a), 6.77 (dd, 3J =
3.1 Hz, J = 2.2 Hz, 1 H, H-3¢ of pyrrole), 6.72 (dd, J = 3.7 Hz,
4J = 2.0 Hz, 1 H, H-4 of pyrrole), 6.63 (dd, 3J = 3.1 Hz, 4J = 2.4 Hz,
1 H, H-4¢ of pyrrole).
13C NMR: d = 180.87 (C=O), 147.97 (C-2 of thenoyl), 139.86 (Cb),
137.78 (C-5 of pyrrole), 134.99 (C-5¢ of pyrrole), 134.15 (C-5 of
thenoyl), 133.77 (C-2¢ of pyrrole), 131.97 (CipsoPh-5), 131.54
(CipsoPh-5¢), 130.97 (C-2 of pyrrole), 130.71 (C-3 of thenoyl),
129.20 (CmetaPh-5,5¢), 128.38 (C-4 of thenoyl), 127.82 (CparaPh-5),
127.21 (CparaPh-5¢), 124.88 (CorthoPh-5), 124.31 (CorthoPh-5¢),
120.99 (C-3 of pyrrole), 114.56 (C-3¢ of pyrrole), 110.07 (Ca),
109.82 (C-4 of pyrrole), 108.08 (C-4¢ of pyrrole).
1H NMR: d = 14.96 (br s, 1 H, NH), 8.86 (br s, 1 H, NH¢), 8.06 (m,
2 H, HorthoCOPh), 7.87–7.31 (m, 5 H, Ph-5), 7.57–7.29 (m, 5 H, Ph-
5¢), 7.53 (m, 1 H, HparaCOPh), 7.48 (m, 2 H, HmetaCOPh), 6.95 (d, 1
H, H-3), 6.89 (s, 1 H, H-a), 6.83 (d, 1 H, H-3¢), 6.81 (d, 1 H, H-4),
6.67 (d, 1 H, H-4¢).
13C NMR: d = 189.28 (C=O), 141.21 (CipsoCOPh), 140.25 (Cb),
137.39 (C-5 of pyrrole), 135.05 (C-5¢ of pyrrole), 133.97 (C-2¢ of
pyrrole), 131.90 (CipsoCOPh), 131.85 (CparaCOPh), 131.58 (CipsoPh-
5¢), 131.04 (C-2 of pyrrole), 129.17 (CmetaPh-5, Ph-5¢), 128.57
(CmetaCOPh), 128.20 (CorthoCOPh), 127.83 (CparaPh-5), 127.22
(CparaPh-5¢), 124.84 (CorthoPh-5), 124.33 (CorthoPh-5¢), 120.98 (C-3
of pyrrole), 114.65 (C-3¢ of pyrrole), 110.82 (Ca), 109.89 (C-4 of
pyrrole), 108.12 (C-4¢ of pyrrole).
4
3
Anal. Calcd for C29H22N2O: C, 84.03; H, 5.35; N, 6.76. Found: C,
83.78; H, 5.67; N, 6.60.
1,1¢-Di(pyrrol-2-yl)-2-thenoylethene (4d)
Orange-red oil.
Synthesis 2004, No. 16, 2736–2742 © Thieme Stuttgart · New York

PAPER
Silica-Assisted Reactions of Pyrroles with 1-Acyl-2-bromoacetylenes
2741
3
4
Anal. Calcd For C27H20N2OS: C, 77.12; H, 4.79; N, 6.66; S, 7.62.
Found: C, 76.79; H, 5.09; N, 7.02; S, 7.67.
5 of thenoyl), 7.14 (dd, J = 4.9 Hz, J = 3.9 Hz, 1 H, H-4 of
thenoyl), 6.96 (m, 1 H, H-5), 6.83 (m, 1 H, H-3), 6.28 (m, 1 H, H-4).
13C NMR: d = 169.71 (C=O), 144.82 (C-2 of thenoyl), 134.84 (C-5
of thenoyl), 134.66 (C-3 of thenoyl), 128.36 (C-4 of thenoyl),
123.68 (C-5 of pyrrole), 120.77 (C-3 of pyrrole), 110.78 (C-4 of
pyrrole), 110.03 (C-2 of pyrrole), 91.34 (Ca), 87.05 (Cb).
2-(2-Benzoylethynyl)pyrrole (5a)
Yellow crystals; mp 141–142 °C.
IR (KBr): 3317, 3059, 3030, 2919, 2172, 1628, 1595, 1577, 1560,
1512, 1502, 1448, 1425, 1351, 1316, 1261, 1223, 1176, 1138, 1088,
1038, 1010, 964, 896, 842, 768, 743, 693, 652, 599 cm–1.
1H NMR: d = 8.89 (br s, 1 H, NH), 8.19 (m, 2 H, HorthoCOPh), 7.63
(m, 1 H, HparaCOPh), 7.51 (m, 2 H, HmetaCOPh), 7.00 (m, 1 H, H-5),
6.90 (m, 1 H, H-3), 6.33 (m, 1 H, H-4).
Anal. Calcd for C11H7NOS: C, 65.65; H, 3.51; N, 6.96; S, 15.93.
Found: C, 65.80; H, 3.31; N, 6.57; S, 15.66.
2-(2-Thenoylethynyl)-4,5,6,7-tetrahydroindole (5e)
Dark yellow crystals; mp 147–148 °C.
13C NMR: d = 177.99 (C=O), 136.81 (CipsoCOPh), 133.97 (Cpara
COPh), 129.43 (CorthoCOPh), 128.63 (CmetaCOPh), 123.91 (C-5 of
pyrrole), 120.91 (C-3 of pyrrole), 110.72 (C-4 of pyrrole), 110.05
(C-2 of pyrrole), 95.15 (Ca), 89.02 (Cb).
-
IR (KBr) 3260, 3102, 2945, 2918, 2842, 2153, 1596, 1569, 1514,
1469, 1432, 1410, 1354, 1316, 1302, 1256, 1228, 1166, 1138, 1081,
1051, 1016, 943, 926, 858, 845, 823, 806, 760, 715, 667, 648, 630,
556 cm–1.
Anal. Calcd for C13H9NO: C, 79.98; H, 4.65; N, 7.17. Found: C,
79.88; H, 4.78; N, 6.99.
1H NMR: d = 8.43 (br s, 1 H, NH), 7.87 (dd, 3J = 3.7 Hz, 4J = 1.2
Hz, 1 H, H-3 thenoyl), 7.63 (dd, 3J = 4.9 Hz, 4J = 1.2 Hz, 1 H, H-5
thenoyl), 7.11 (dd, 3J = 4.9 Hz, 3J = 3.7 Hz, 1 H, H-4 thenoyl), 6.58
(d, 4J = 2.0 Hz, 1 H, H-3), 2.57 (m, 2 H, CH2-7), 2.48 (m, 2 H, CH2-
4), 1.76 (m, 4 H, CH2-5,6).
2-(2-Benzoylethynyl)-4,5,6,7-tetrahydroindole (5b)
Orange-red crystals; mp 167–168 °C.
IR (KBr): 3280, 3065, 2948, 2920, 2839, 2155, 1612, 1596, 1567,
1505, 1468, 1445, 1364, 1316, 1304, 1271, 1250, 1224, 1164, 1138,
1042, 1022, 972, 929, 824, 805, 787, 692, 649, 633, 576 cm–1.
1H NMR: d = 8.24 (br s, 1 H, NH), 8.13 (m, 2 H, HorthoCOPh), 7.56
(m, 1 H, HparaCOPh), 7.46 (m, 2 H, HmetaCOPh), 6.61 (d, 4J = 1.8 Hz,
1 H, H-3), 2.59 (m, 2 H, CH2-7), 2.49 (m, 2 H, CH2-4), 1.79 (m, 2
H, CH2-6), 1.74 (m, 2 H, CH2-5).
13C NMR: d = 169.56 (C=O), 145.09 (C-2 of thenoyl), 134.83 (C-5
of pyrrole), 134.21 (C-5 of thenoyl), 134.21 (C-3 of thenoyl),
128.23 (C-4 of thenoyl), 120.24 (C-3 of pyrrole), 120.17 (C-4 of
pyrrole), 107.60 (C-2 of pyrrole), 92.72 (Ca), 89.82 (Cb), 23.36
(CH2-7), 23.15 (CH2-5), 22.84 (CH2-6), 22.67 (CH2-4).
Anal. Calcd for C15H13NOS: C, 70.56; H, 5.13; N, 5.48; S, 12.56.
Found: C, 70.52; H, 5.48; N, 5.49; S, 12.90.
13C NMR: d = 177.63 (C=O), 137.14 (CipsoCOPh), 134.82 (C-5 of
2-(2-Thenoylethynyl)-5-phenylpyrrole (5f)
Red-orange crystals; mp 183 °C.
pyrrole), 133.62 (CparaCOPh), 129.31 (CorthoCOPh), 128.55 (Cmeta
-
COPh), 120.33 (C-3 of pyrrole), 120.29 (C-4 of pyrrole), 107.83 (C-
2 of pyrrole), 93.62 (Ca), 91.15 (Cb), 23.42 (CH2-7), 23.21 (CH2-5),
22.89 (CH2-6), 22.71 (CH2-4).
IR (KBr): 3298, 3066, 2959, 2922, 2855, 2169, 1597, 1558, 1512,
1462, 1406, 1354, 1315, 1302, 1245, 1225, 1194, 1081, 1057, 1044,
1022, 966, 941, 919, 904, 860, 784, 755, 724, 691, 651, 647, 534,
492 cm–1.
Anal. Calcd for C17H15NO: C, 81.90; H, 6.06; N, 5.62. Found: C,
81.56; H, 6.20; N, 5.78.
1H NMR: d = 9.04 (br s, 1 H, NH), 7.95 (dd, 3J = 3.8 Hz, 4J = 1.3
Hz, 1 H, H-3 of thenoyl), 7.68 (dd, 3J = 4.8 Hz, 4J = 1.3 Hz, 1 H, H-
5 of thenoyl), 7.54 (m, 2 H, HorthoPh), 7.42 (m, 2 H, HmetaPh), 7.30
2-(2-Benzoylethynyl)-5-phenylpyrrole (5c)
Orange crystals; mp 180–181 °C.
3
3
(m, 1 H, HparaPh), 7.17 (dd, J = 4.8 Hz, J = 3.8 Hz, 1 H, H-4 of
IR (KBr): 3309, 3067, 2958, 2855, 2166, 1628, 1595, 1573, 1536,
1518, 1505, 1484, 1470, 1457, 1414, 1383, 1315, 1303, 1289, 1274,
1244, 1217, 1171, 1158, 1075, 1054, 1021, 967, 929, 901, 792, 759,
695, 684, 648, 613, 574, 535, 492 cm–1.
3
4
thenoyl), 6.90 (dd, J = 4.0 Hz, J = 2.2 Hz, 1 H, H-3), 6.57 (dd,
3J = 4.0 Hz, 4J = 2.5 Hz, 1 H, H-4).
13C NMR: d = 169.51 (C=O), 144.90 (C-2 of thenoyl), 137.55 (C-5
of pyrrole), 134.79 (C-5 of thenoyl), 134.58 (C-3 of thenoyl),
130.98 (CipsoPh), 129.28 (CmetaPh), 128.37 (C-4 of thenoyl), 128.09
(CparaPh), 124.71 (CorthoPh), 122.53 (C-3 of pyrrole), 110.74 (C-2 of
pyrrole), 108.38 (C-4 of pyrrole), 92.59 (Ca), 87.40 (Cb).
1H NMR: d = 9.04 (br s, 1 H, NH), 8.22 (m, 2 H, HorthoCOPh), 7.65
(m, 1 H, HparaPh-5), 7.59 (m, 2 H, HmetaCOPh), 7.56 (m, 2 H, Hortho
-
Ph-5), 7.46 (m, 2 H, HmetaCOPh), 7.35 (m, 1 H, HparaPh-5), 6.97 (dd,
3J = 3.6 Hz, 4J = 2.5 Hz, 1 H, H-3), 6.62 (dd, 3J = 3.6 Hz, 4J = 2.8
Hz, 1 H, H-4).
13C NMR: d = 177.62 (C=O), 137.50 (C-5 of pyrrole), 136.75
(CipsoCOPh), 133.80 (CparaCOPh), 130.85 (CipsoPh-5), 129.32
(CorthoCOPh), 129.07 (CmetaPh-5), 128.50 (CmetaCOPh), 127.88
(CparaPh-5), 124.62 (CorthoPh-5), 122.54 (C-3 of pyrrole), 110.72 (C-
2 of pyrrole), 108.24 (C-4 of pyrrole), 93.25 (Ca), 89.12 (Cb).
Anal. Calcd for C17H11NOS: C, 73.62; H, 4.00; N, 5.05; S, 11.56.
Found: C, 73.51; H, 4.26; N, 5.16; S, 11.70.
1,2-Dibromo-2-thenoylethene (6)
1H NMR: d = 7.18 (dd, 3J = 4.9 Hz, 3J = 3.8 Hz, 1 H, H-4), 7.73 (dd,
3J = 4.9 Hz, 4J = 1.2 Hz, 1 H, H-5), 7.75 (dd, 3J = 3.8 Hz, 4J = 1.2
Hz, 1 H, H-3), 7.84 (s, 1 H, =CH).
Anal. Calcd for: C19H13NO: C, 84.11; H, 4.83; N, 5.16. Found: C,
83.75; H, 5.09; N, 5.61.
13
NMR: d = 179.34 (C=O), 144.26 (C-2), 135.28 (C-5), 133.84
(=CBr), 132.61 (C-3), 131.32 (=CHBr), 128.50 (C-4).
2-(2-Thenoylethynyl)pyrrole (5d)
MS: m/z [M] calcd for C7H4Br2OS: 295.98; found [M]+: 296.
Yellow crystals; mp 143–144 °C.
IR (KBr): 3167, 3096, 3071, 3004, 2954, 2174, 1581, 1555, 1512,
1433, 1409, 1353, 1320, 1266, 1249, 1231, 1140, 1099, 1079, 1061,
1039, 996, 930, 883, 858, 820, 749, 728, 720, 703, 655, 599, 552
cm–1.
1H NMR: d = 8.93 (br s, 1 H, NH), 7.92 (dd, 3J = 3.9 Hz, 4J = 1.2
Hz, 1 H, H-3 of thenoyl), 7.67 (dd, J = 4.9 Hz, J = 1.2 Hz, 1 H, H-
Acknowledgment
Financial support from the Ministry of Industry, Science and Tech-
nologies of Russian Federation (Grant No. NSH-2241.2003.3) and
the Russian Foundation for Basic Research (Grant No. 02-03-
33017a) is gratefully acknowledged.
Synthesis 2004, No. 16, 2736–2742 © Thieme Stuttgart · New York

2742
Z. V. Stepanova et al.
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Synthesis 2004, No. 16, 2736–2742 © Thieme Stuttgart · New York