2-arylazo-1-vinylpyrroles: A novel promising family of reactive dyes

Article abstract of DOI:10.1002/ejoc.200600357

New reactive dyes, 2-arylazo-1-vinylpyrroles, have been synthesized in 52-94 % yield by a modified azo coupling of readily accessible 1-vinylpyrroles with arenediazonium hydrocarbonates in aqueous ethanol (∥3:1) at 0°C. The λ_max values for the

Full text of DOI:10.1002/ejoc.200600357

FULL PAPER
DOI: 10.1002/ejoc.200600357
2-Arylazo-1-vinylpyrroles: A Novel Promising Family of Reactive Dyes
Boris A. Trofimov,*[a] Elena Yu. Schmidt,[a] Al’bina I. Mikhaleva,[a]
Alexander M. Vasil’tsov,[a] Alexey B. Zaitsev,[b] Natalia S. Smolyanina,[a]
Elena Yu. Senotrusova,[a] Andrey V. Afonin,[a] Igor’ A. Ushakov,[a]
Konstantin B. Petrushenko,[a] Olga N. Kazheva,[c] Oleg A. Dyachenko,[c]
Vladimir V. Smirnov,[d] Alexander F. Schmidt,[d] Marina V. Markova,[a] and
Ludmila V. Morozova[a]
Keywords: 2-Arylazo-1-vinylpyrroles / Azo coupling / Conformation / Copolymerization / 1-Vinylpyrroles / Dyes
New reactive dyes, 2-arylazo-1-vinylpyrroles, have been
synthesized in 52–94% yield by a modified azo coupling of
readily accessible 1-vinylpyrroles with arenediazonium hy-
drocarbonates in aqueous ethanol (Ϸ3:1) at 0 °C. The λmax
values for the UV/Vis absorption of the dyes ranges from
377.8–480.6 nm with logε = 4.11–4.99, and this strongly de-
pends on the substituent structure both in the pyrrole and
the benzene ring, and is indicative of highly polarizable and
tunable chromophores. X-ray, 1H NMR spectroscopic and
quantum chemical studies [B3LYP/6-311 (d,p)] show the
E,anti,anti isomer of the dyes to be the most stable under
normal conditions. The dyes are reversibly protonated and
complex to BF3 with a color change. Their copolymerization
across the vinyl group affords intrinsically colored copoly-
mers. They have also been shown to act as good ligands in
the Pd-catalyzed Heck alkene arylation. Thus, the properties
of the novel dyes are promising for creating new molecular
switches, memory and recording devices, acid-base and
metal sensors, as well as transition-metal complex catalysts.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
1 eV when compared to polypyrrole).[1,2,4,9] This material
has one of the narrowest bandgaps among the neutral pyr-
role-based conducting polymers.[9] The E/Z-isomerizable
N=N double bond within a conducting chain can work as
a molecular switcher, making the aryl- or hetarylazopyrrolic
systems promising candidates for molecular devices.[9] 4-(1-
n-Octadecylpyrrol-2-ylazo) benzoic acid, a representative of
arylazopyrroles, affords Langmuir-Blodgett films with elec-
trically conducting and non-linear optical (NLO) proper-
ties.[3]
Introduction
Aryl- and hetarylazopyrrole dyes have been attracting
much attention over the past decade because of their
rapidly increasing role in the design of advanced materials
and devices.[1–12] The insertion of an azo group between di-
pyrrole moieties by anodic coupling of 2,2Ј-azopyrrole re-
sults in polyazopyrrole, the first reported narrow-bandgap
polyconjugated pyrrole-based polymer, which exhibits a
dramatic drop in the energy gap (from 2.5–2.8 eV to about
Diverse aryl- and hetarylazopyrroles,[5,6] and related
metal chelates[7,8] have extensively been patented as thermal
transfer printing dyes[5,6] and optical recording materi-
als.[7,8] The latter can be recorded and read by light with a
wavelength of 600–720 nm at good light speeds and is also
stable enough for storage on DVD R systems using semi-
conductor laser beams with a shorter wavelength.
Chromonophores (reagents changing color in the pres-
ence of ions) with 2,5- or 2,3-bis(azo) pyrrole entities in
crown ether macrocycles make the membrane electrodes po-
tassium-selective.[10]
The pyrrolylazo entity, when combined with a suitable
heteroarene acceptor, exhibits a donor capacity in the de-
sign of chromophoric self-assembled thin films with NLO
properties, which have the potential to be applied as pho-
tonic and electrooptic materials.[11] For this purpose, highly
polarizable push–pull systems with large intramolecular
[a] A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch
of the Russian Academy of Sciences,
1 Favorsky St., Irkutsk 664033, Russian Federation
Fax: +7-3952-419346
E-mail: boris_trofimov@irioch.irk.ru
[b] Department of Organic Chemistry, the Arrhenius Laboratory,
Stockholm University,
10691 Stockholm, Sweden
Fax: +46-8-154908
E-mail: zaitsev@organ.su.se
[c] Institute of Problems of Chemical Physics of the Russian Acad-
emy of Sciences,
1 Semenov’s Av., Chernogolovka, Moscow District 142432,
Russian Federation
Fax: +7-096-5155420
E-mail: koh@icp.ac.ru
[d] Irkutsk State University,126 Lermontov St., Irkutsk, 664033,
Russian Federation,
Fax: +7-3952-426856
E-mail: aschmidt@chem.isu.ru
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B. A. Trofimov et al.
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charge-transfer excitation, such as 5-(1-methylpyrrol-2-yl-
azo)quinoline and particularly, its N-methyl triflate, have
been employed.[11] Imperative for active second-order NLO
chromophores is a noncentrosymmetric charge distribution
as it is in the above hetarylazopyrroles.
A recent DFT study[12] has revealed significantly lower
excitation energies for N=N spaced pyrroles with aromatic
or heteroaromatic rings relative to those of similar but di-
rectly linked π-systems. This offers an additional opportu-
nity in the search for materials with improved electronic
and optical properties.
Results and Discussion
Synthesis
As mentioned above, first, we have studied the direct vi-
nylation of 2-arylazopyrroles 1 with acetylene using 2-phen-
ylazopyrrole (R1 = R2 = R3 = H) as an example (Scheme 1,
a). To this end, the superbasic catalytic system KOH/
DMSO has been employed under conditions (110 °C, at
room temperature initial acetylene pressure = 14 atm, 2 h)
that have proved optimal for vinylation of diverse pyr-
roles.[17] However, the expected 2-phenylazo-1-vinylpyrrole
(3) is not discernible in the reaction mixture. In the analysis
In spite of all these spectacular recent strides in the
chemistry and applications of azopyrrolic dyes, little is
known about their vinyl congeners. Meanwhile, the vinyl
substituent could multiply the potential of these com-
pounds, which imparts upon them diverse multi-faceted ex-
tra reactivity including polymerizability. A limited, though
important family[13–16] of such compounds are the long-
known azo coupled bile pigments (bilirubin and related spe-
cies). The bilirubin serum and its conjugates are commonly
measured in clinics by an azo coupling method.[16] The syn-
thesis of bilirubin-based C-vinyl arylazopyrroles helped to
elucidate the mechanism of anti-oxidation by bilirubin and
its metabolites as well as their important role as anti-oxi-
dants to control various oxidative stresses in humans.[16]
Apart from this quite specific class of arylazo vinylpyrroles,
to the best of our knowledge, no similar dyes with vinyl
substituents in the pyrrole ring, especially at the nitrogen
atom, are reported to date.
To meet a challenge and introduce such a promising fam-
ily of dyes to chemistry, material science, and medicine, we
have explored two possible general approaches to the syn-
thesis of 2-arylazo-1-vinylpyrroles 3–22: (a) direct vinyla-
tion of (arylazo)pyrroles 1 by acetylene and (b) azo coup-
ling of 1-vinylpyrroles 2 with arenediazonium salts. Con-
trary to expectation, the former approach, on first glance,
appeared to be the most obvious and straightforward, but
in actuality turned out to be a failure, while the latter
proved to be both facile and universal (Scheme 1).
1
of the H NMR spectrum of the crude product, signals for
the N-vinyl group are not observed. Instead, along with sig-
nals of starting 2-phenylazopyrrole 1 [δ = 9.23 (br. s, 1 H,
NH), 7.76 (d, 2 H, Ho), 7.43 (m, 2 H, Hm), 7.36 (t, 1 H,
Hp), 6.99 (m, 1 H, 5-H), 6.90 (m, 1 H, 3-H), 6.99 (m, 1 H,
4-H) ppm], two unassignable multiplets (δ = 3.4 and
3.8 ppm) and a quartet (δ = 4.7 ppm) with intensities close
to those of the starting pyrrole 1 are present.
1
The H NMR spectrum of a crude product obtained at
a higher temperature (130 °C) contains no signals represent-
ing the starting 2-phenylazopyrrole (in the region of 1.0–
7.5 ppm, broad multiplets and singlets at δ = 1.5, 2.5, 3.4,
5.0, 5.8, 5.6 ppm were observed), indicating its complete de-
composition.
The results may be rationalized in terms of a strong che-
lation between the potassium cation and the azopyrrole salt
23 (Scheme 2) similar to that claimed in the patents.[7,8]
Scheme 2. Tentative chelating of potassium cation by 2-phenylazo-
pyrrole.
In this paper we discuss the main features of the synthe-
Obviously, such an interaction should greatly decrease
sis of 2-arylazo-1-vinylpyrroles 3–22, peculiarities of their the nucleophilicity of the pyrrole anion and hence suppress
structure, and some fundamental properties. its vinylation.
Scheme 1. Synthesis of 2-aryazo-1-vinylpyrroles (for R1, R2 and R3 see Table 1).
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2-Arylazo-1-vinylpyrroles: A Novel Promising Family of Reactive Dyes
FULL PAPER
Although the azo coupling of NH-pyrroles with arenedi- (84–94%, Table 1). Also high (76–81%) are the yields for
azonium cations can be successful within a broad pH the cases of other acceptor substituents in the arenediazon-
range,[11,13,14,16] in the case of 1-vinylpyrroles 2 the reaction ium cations (R3 = Br, PhN2). At the same time, introduc-
must be carried out in neutral or basic media (pH Ն 7) and tion of acceptor substituents (Ph, 4-MeOC6H4, 2-furyl, 2-
at a temperature around 0 °C, otherwise in the presence of thienyl) into the pyrrole moiety leads to an adverse yield
acids, hydrolysis or dimerization and oligomerization in- trend (53–57%).
volving the N-vinyl group occur.[17a,17b] Therefore, to keep
As exemplified by the coupling of 1-vinyl-4,5,6,7-tetra-
the N-vinyl group intact, the azo coupling of 1-vinylpyrroles hydroindole 2 [R1–R2 = (CH2)4] with the benzenediazon-
2 with arenediazonium cations (Scheme 1 b, Table 1) was ium cation, with short reaction times (1 h) the conversion
conducted in an aqueous ethanolic (Ϸ3:1) solution of of pyrrole 2 decreases (75%) and the yield of the corre-
NaHCO3 (pH Ϸ 7) at 0 °C for 2 h. Under these uniform sponding coupling product 11 drops from 87 to 72%. At
(not optimized for each couple) conditions, the yields of the a higher temperature (50–60 °C) the yield of the coupling
coupling products 3–22 ranged within 52–94%.
product 11 becomes negligible (Ϸ2%) because of the rapid
decomposition of the arenediazonium salt.
Because of the electron-withdrawing effect of the vinyl
group and the noticeable competition for the p-π-conjuga-
tion with the nitrogen atom,[18a] which persists even in 1-
vinylpyrrolium cations,[18] the reaction is strictly regiospec-
ific. In neither case are the coupling products at the pyrrole
β-position identified in the reaction mixture.
Table 1. Yields of 2-arylazo-1-vinylpyrroles 3–22 and their UV/Vis
spectral characteristics in MeCN.
Azopyrrole
R1
R2
R3
Yield λmax [nm] log ε
[%]
3
4
H
H
H
H
H
EtO
80
52
383.1
377.8
4.32
4.91
393.0 (sh) 4.85
428.5 (sh) 4.71
5
6
7
8
9
10
11
12
H
H
H
H
H
H
H
NO2
H
EtO
NO2
Br
PhN2
H
EtO
84
80
76
85
76
79
87
80
413.4
397.5
402.0
439.8
405.8
445.1
408.8
410.3
4.85
4.62
4.93
4.54
4.69
4.72
4.84
4.41
Also, despite the high nucleophilicity of the N-vinyl
group, under the selected conditions it remains essentially
unreactive towards the arenediazonium cations.
An advantage of the developed synthetic approach, apart
from its generality and efficiency, is that it is based on avail-
able starting materials, 1-vinylpyrroles, which are com-
monly prepared in a one-pot procedure by the Trofimov
reaction from ketoximes and acetylene[17a,17b,19] or by its
newer version[20] directly from ketones and acetylene.
Me
Me
Me
Me
Me
(CH2)4
(CH2)4
451.1 (sh) 4.43
470.8
416.4
13
14
(CH2)4
(CH2)4
NO2
Br
94
82
4.77
4.82
449.6 (sh) 4.74
15
16
17
18
19
20
21
22
(CH2)4
Ph
Ph
PhN2
H
NO2
H
NO2
H
H
81
53
56
57
56
53
53
79
476.8
407.3
454.2
414.9
477.6
–
4.68
4.81
4.89
4.64
4.99
–
H
H
H
H
H
H
H
4-MeOC6H4
4-MeOC6H4
2-furyl
2-thienyl
2-thienyl
UV/Vis and 13C NMR Spectra
418.6
480.6
4.48
4.11
Table 1 presents UV/Vis optical spectroscopic data (λmax
,
NO2
logε) for 2-arylazo-1-vinylpyrroles 3–22 in acetonitrile.
Analysis of the structure effects on the λmax and logε values
reveals a noticeable push–pull character of the synthesized
The azo coupling thus realized represents a typical aro- dyes. Indeed, both donor substituents in the pyrrole ring
matic electrophilic substitution, hence electron-releasing [Me, (CH2)4] and acceptor substituents in the areneazo
substituents on the pyrrole ring (R1, R2) and electron-with- counterpart (NO2, PhN2) promote a sizeable (up to about
drawing ones in the arenediazonium cation should facilitate 100 nm) bathochromic shift (∆λ) relative to that of parent
the reaction, which is in agreement with the yield trend seen compound 3 (∆λ = λimax –λ3max), which in most cases is
from Table 1. Indeed, when a π-donor (EtO) is introduced accompanied by an increase in the absorption intensity, the
on the benzenediazonium cation, the yield considerably ∆logε value reaches 0.67 (∆logε = logεi –logε3). Substitu-
drops (from 80 to 52%, cf. pyrroles 3 and 4, Table 1), ents such as MeO, EtO and Br, which are simultaneous π-
whereas for 4-nitrobenzene diazonium cation with unsubsti- donors and σ-acceptors by nature, display the complex re-
tuted (R1 = R2 = H) and donor-substituted [R1 = Me, R2 sponse that is manifested both in appearance of the shorter
= H; R1–R2 = (CH2)4] 1-vinyl pyrroles, it is always high wavelength absorption maxima and the longer wavelength
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B. A. Trofimov et al.
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shoulders (for 3 Ǟ 4: λmax = 383.1Ǟ 377.8, 393.0 sh, which have recently been successfully employed as building
428.5 nm sh; for 11 Ǟ 12: λmax = 408.8 Ǟ 410.3, 451.1 nm blocks for NLO materials.[11] Indeed, such dyes with nonce-
sh). The multiplet nature of the absorption is likely a result ntrosymmetric charge distribution are of key value in for
of the different orientation (conformation) of the EtO the design of efficient second-order NLO-phores.[11]
group with respect to the benzene ring (syn or anti; planar
The 13C NMR spectra confirm a significant charge
or non-planar). The bathochromic shift and absorption in- transfer from the vinylpyrrole moiety to the arylazo group
tensity are also expectedly increased with the extension of and a high polarizability of the whole dye molecules. This
the chromophore π-core. For phenyl and 2-thienyl substitu- is manifested by a strong downfield shift of the C-4 and C-
ents on the pyrrole ring this effect successfully competes 5 signals (2–3 ppm and 2–7 ppm, respectively) and an up-
with their σ-acceptor adverse contributions (cf. spectra of field shift of the C-3 signals (7–10 ppm) compared to the
3, 16, 18, and 21, Scheme 3).
corresponding values of the same pyrroles without arylazo
Especially strong bathochromic shifts and an increase in substituents[21] (Scheme 5). Correspondingly, the vinyl
the absorption intensity are observed when all these effects group is considerably depolarized: for the 5-unsubstituted
are in one direction (a donor in the pyrrole ring, an ac- dyes, the Cα signals are shifted upfield (1–3 ppm), while the
ceptor in the areneazo moiety, and general extension of π- Cβ signals display a downfield shift (4–11 ppm) relative to
conjugation) like those in dyes 13, 15, 19, 22 (Scheme 4).
the corresponding values of the unsubstituted N-vinylpyr-
The remarkable optical response to the structure effects role[21] (Scheme 5). The substituents at the C-5 atom, which
in the synthesized dyes is indicative of their highly polariz- force the vinyl group to deviate out of the pyrrole plane
able π-electron core and suggests that these new chromo- even more, decrease the p-π-conjugation of the double bond
phores possess hyperpolarizability comparable to, or higher with the nitrogen atom (cf. 1-vinylpyrrole, 2-methyl-1-vinyl-
than, that of the azinium-(N=N bridge)-pyrrole systems, pyrrole,[22] the pyrroles 3 and 6, Scheme 5).
Scheme 3. Effects of the extended π-systems on the UV/Vis spectral characteristics of 2-arylazo-1-vinylpyrroles.
Scheme 4. Combined structure effects on the UV/Vis spectral characteristics of 2-arylazo-1-vinylpyrroles.
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2-Arylazo-1-vinylpyrroles: A Novel Promising Family of Reactive Dyes
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Table 2. Crystallographic data and structure refinement for 2-phen-
ylazo-1-vinylpyrrole (3).
Empirical formula
C12H11N3
197.24
monoclinic
P21/n
6.702(1)
11.869(2)
13.252(3)
92.91(2)
1052.8(3)
4
Molecular mass
Crystal system
Space group
a [Å]
b [Å]
c [Å]
β [°]
V [Å3]
Z
λ [Å]
0.7107 (Mo)
1.24
0.077
Calculated density [Mg·m–3]
µ [mm–1]
Scheme 5. The charge redistribution in the N-vinylpyrrole moiety
under the influence of arenylazo substituents as evidenced from 13
chemical shifts (ppm).
C
Reflections collected
Independent reflections
Reflections for [Fo Ͼ 4σ(Fo)]
Number of parameters
(2θ)max [°]
Interval for h
Interval for k
Interval for l
R – factor [Fo Ͼ 4σ(Fo)]
1943
1784
1420
181
Since the 13C chemical shifts of the corresponding car-
bon atoms and atomic charges are roughly inversely related,
all the changes observed in the 13C NMR spectra of 2-aryl-
azo-1-vinylpyrroles relative to those of 1-vinylpyrroles do
reflect a remarkable electron density displacement towards
the azo group.
49.94
0 Յ h Յ 7
0 Յ k Յ 14
–15 Յ l Յ 15
0.037
The distant NO2 substituent in the benzene ring renders
a noticeable charge displacement not only from the most
remote C-5 and C-4 atoms of the pyrrole ring, but from the
vinyl group as well (cf. pyrroles 3 and 5, Scheme 5), thus
again demonstrating the easy electron communication
within the whole dye molecules.
Table 3. Selected X-ray bond lengths [Å] and bond angles [°] for 2-
phenylazo-1-vinylpyrrole (3).
Bonds
N(1)–C(5)
N(1)–C(2)
N(1)–C(6)
N(2)–N(3)
N(2)–C(2)
N(3)–C(8)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(6)–C(7)
1.359(2)
1.390(2)
1.409(2)
1.271(1)
1.376(2)
1.424(2)
1.375(2)
1.396(2)
1.349(2)
1.288(2)
X-ray Structure
Dyes 3–22 are deeply colored (green, orange, red, crim-
son) crystals or powders melting in the range of 52–180 °C
(mostly 60–120 °C).
The main crystallographic data and the parameters of
the X-ray structure refinement of 2-phenylazo-1-vinylpyr-
role (3), a parent compound of the family, are given in
Table 2. Selected bond lengths and angles are listed in
Table 3. According to these parameters, the pyrrole ring of
3 is distorted, in agreement with the expected charge trans-
fer. In Scheme 6, some of the most pronounced changes in
the bond lengths and angles in comparison with those of
unsubstituted pyrrole[14] (in brackets) are shown.
Indeed, the bonds N(1)–C(5), C(3)–C(4), and N(2)–C(2)
are considerably shortened, while the bonds C(2)–C(3),
C(4)–C(5), and N(2)–N(3) are lengthened compared to the
normal bond length in pyrroles[14] and standard C–N and
N=N bond lengths from the reference.[23] Correspondingly,
the angles C(5)–N(1)–C(2) and C(3)–C(2)–N(1) are
changed in opposite directions (Scheme 6). These structural
distortions are explicable by a contribution of the quinoid
resonance structure B to the basic structure A (Scheme 6)
and confirm the intramolecular charge-transfer from the
pyrrole moiety to the phenylazo counterpart.
Angles
C(5)–N(1)–C(2)
C(5)–N(1)–C(6)
C(2)–N(1)–C(6)
N(3)–N(2)–C(2)
N(2)–N(3)–C(8)
C(3)–C(2)–N(2)
C(3)–C(2)–N(1)
N(2)–C(2)–N(1)
C(2)–C(3)–C(4)
C(5)–C(4)–C(3)
C(4)–C(5)–N(1)
C(7)–C(6)–N(1)
C(9)–C(8)–N(3)
C(13)–C(8)–N(3)
107.5(1)
127.8(1)
124.7(1)
113.7(1)
113.4(1)
134.8(1)
107.9(1)
117.3(1)
107.0(1)
108.1(1)
109.4(1)
125.3(2)
125.2(1)
115.5(1)
Crystals of pyrrole 3 are built from crystallographically
independent molecules C12H11N3 (Figure 1) and have a par-
quet structure (Figure 2). The molecules are paired by a
Scheme 6. The structure distortion in 2-phenylazo-1-vinylpyrrole
symmetry center in a “head to tail” manner (Figure 3). (3) versus standard bond lengths and angles.
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B. A. Trofimov et al.
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Molecules in the pairs are parallel, and the distance be-
tween the planes formed by the pyrrole, the benzene rings,
and the azo group is 3.62 Å. The dihedral angle between
the planes of different molecular pairs is 74.4°.
Figure 3. Molecular pairing of 2-phenylazo-1-vinylpyrrole 3.
whole molecule of 2-phenylazo-1-vinylpyrrole 3 is essen-
tially planar securing the maximal possible conjugation and
intramolecular charge transfer through the four interacting
π-systems.
Figure 1. ORTEP diagram for 2-phenylazo-1-vinylpyrrole 3.
It is noteworthy that the distance between the N(2) atom
The azo group of pyrrole 3 has the E configuration with and the α-H atom of the vinyl group (2.50 Å) is shorter
anti orientation of the N(1) and N(3) atoms and lies in the than the van der Waals radii of these atoms (2.75 Å).[24]
plane of the pyrrole and benzene rings (the dihedral angles Such close contacts are often explained[24–27] by weak hy-
are 0° and 3.5°, respectively). The dihedral angle between drogen bonding, here C–H···N.[28] In spite of the fact that
the vinyl group plane and the pyrrole ring is also small the contact is not close enough,[29] the conclusion is sup-
(–7.1°) with anti orientation to the azo group. Thus, the ported by NMR spectroscopy (see below).
Figure 2. Parquet structure of 2-phenylazo-1-vinylpyrrole 3.
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2-Arylazo-1-vinylpyrroles: A Novel Promising Family of Reactive Dyes
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NMR and Quantum Chemical Study of the Isomerism
E,anti,anti isomer are certainly much less preferred under
normal conditions (Scheme 8).
Discerning the most stable configuration and conforma-
tion and their energy differences of the synthesized dyes is
necessary for further investigations of the reversible config-
urational and/or conformational interconversions of their
molecules under electromagnetic, chemical, or heat stimuli,
which are the most important aspects in the design of novel
molecular switches, memory, and recording devices.
From the optimized geometry it follows that the most
energetically preferred E,anti,anti isomer of dye 3 is com-
pletely planar with the C–HX···N(2) distance equal to
2.40 Å (the X-ray experimental distance in the crystal form
is 2.50 Å). Thus, the calculated structure corresponds well
to that derived from the X-ray analysis of the crystal.
1
The major feature of the H NMR spectrum of azopyr-
role 3 is that the signal of its vinyl α-hydrogen HX is un-
usually far downfield (δ = 7.87 ppm), while for 2-substi-
tuted 1-vinylpyrroles, the chemical shift of this hydrogen is
commonly in the range of 6.6–6.9 ppm, depending weakly
on the substituent effect.[28] This strong downfield shift of
the HX signal agrees with the above X-ray evidence of a
weak intramolecular C–HX···N(2) bond (Scheme 7).
Reactivity
Protonation
Unlike alkyl- or aryl-substituted 1-vinylpyrroles,[18] the
N-vinyl group in 2-arylazo-1-vinylpyrroles 3–22 remains in-
tact in the presence of excess strong acids at ambient tem-
perature for several hours. Meanwhile, upon addition of tri-
fluoromethanesulfonic or trifluoroacetic acids to azopyr-
roles 9 or 12 in benzene or CHCl3, the orange solution
color turns instantly deep red thus demonstrating the ca-
pacity of the dyes to serve as pH indicators or as acidity
function sensors.
The protonated center is assumed to be the N(2) atom
of the azo moiety (Scheme 9), since it is the atom that par-
ticipates in the intramolecular hydrogen bonding C–
HX···N(2) and its computed [B3LYP/6-311(d,p)] Mulliken
atomic charge exceeds that of the N(3) atom (–0.23 and
–0.22, respectively). Other evidence in favor of this assump-
tion are the following: a downfield shift of signal for the
hydrogen atom at the pyrrole position 3-H (the closest to
the N(2) atom), is very large (for azopyrrole 9, ∆δ =
+1.12 ppm) and the signal for the β-vinyl hydrogens HA and
HB are also strongly shifted downfield (for the same pyrrole
9 ∆δ = +0.66 and 0.28 ppm, respectively), while the α-vinyl
hydrogen HX resonates upfield (∆δ = –0.31 ppm). All these
changes are indicative of a remarkable decrease in the p-π-
conjugation in the N-vinyl group[18] because of the strong
electron-withdrawing effect of the N(2)-protonated azo
group and the breaking of the HX···N(2) hydrogen bond
(Scheme 9).
Scheme 7. The C–HX···N hydrogen bonding in 2-phenylazo-1-vi-
nylpyrrole (3).
In the 2D NOESY spectrum of azopyrrole 3 the HB–5-
H cross-peak (Scheme 7) indicates that the anti orientation
of the double bond to the azo group, observed in the crystal
state, persists also in solution, evidently due to the C–
HX···N(2) bonding.
Quantum chemical calculations [B3LYP/6-311(d,p)] for
azopyrrole 3 has shown that the global energy minimum
does correspond to the E configuration of the azo group
with both the anti orientation of the N(1) and N(3) atoms
and the anti orientation of the double bond relative to the
azo group (E,anti,anti isomer), Scheme 7. The isomer with
syn configuration of the double bond to the azo group
(E,anti,syn form) is 2.3 kcalmol–1 less energetically favor-
able. The conformations having a syn disposition of the
N(1) and N(3) atoms (E,syn,anti and E,syn,syn isomers)
with their energy 17 kcalmol–1 higher than that of
Scheme 9. Reversible protonation of 2-(4-bromophenylazo)-5-
methyl-1-vinylpyrrole (9).
Neutralization of the acidic solution of the dyes com-
1
pletely restores their initial color and H NMR spectra.
Complexation with BF3
Upon treatment of dye 12 with BF3·OEt2 in benzene or
CHCl3, a violet solution (λmax = 537.8 nm, logε = 4.60, in
benzene) of complex 24 is formed. From the 1H NMR
Scheme 8. Computed [B3LYP/6-311(d,p)] energy differences for
conformations of 2-phenylazo-1-vinylpyrrole 3.
Eur. J. Org. Chem. 2006, 4021–4033
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4027

B. A. Trofimov et al.
FULL PAPER
spectrum it may be assumed that the coordination, like the content of dye 12 in the monomer mixture (1 mol%), a col-
protonation, occurs at the N(2) site of the azo group ored (bright yellow in solution) water-soluble copolymer is
(Scheme 10), since it is accompanied by similar shifts of the formed in 17% yield.
hydrogen signals [∆δ = +0.91 (3-H), +0.42 (HA), +0.20
(HB), –0.32 (HX) ppm].
The ability of the synthesized dyes to be copolymerized
with common monomers opens an opportunity for the fab-
rication of intrinsically colored materials, which, when
cross-linked, will not fade under the action of solvents or
washing. Additionally, the water-solubility of polymer chro-
mogenic azo reagents is known[30] to be important for spec-
troscopic determination of trace metals in water.
Ligands for Pd Complex Catalysis
Scheme 10. Complexation of 2-(4-ethoxyphenylazo)-1-vinyl-
4,5,6,7-tetrahydroindole 12 with BF3·OEt2.
Inspired by the work[31] where polymer-tethered azo dyes
were used in the design of recoverable Pd catalysts for the
Heck reaction, we decided to evaluate the ability of 2-aryl-
azo-1-vinylpyrroles 3–22 to serve the same purpose. The
presence of the polymerizable N-vinyl group (see above) as
well as the intrinsically electron-rich pyrrole ring in these
molecules, makes cyclopalladation possible and may open
up additional possibilities for the development of recovera-
ble polymer-supported transition-metal catalysts based on
these molecules. In our preliminary studies we assayed the
activity of a Pd complex generated in situ from PdCl2 and
2-methyl-5-phenylazo-1-vinylpyrrole (6) in catalysis of the
Heck reaction. The reactants (arylbromides and styrene)
were treated in the presence of PdCl2 and phenylazopyrrole
A few hours later, the signal of 3-H disappears and those
of the vinyl group broaden, which indicates further trans-
formations that involve the pyrrole ring without the ex-
pected polymerization across the double bond.
Unlike this result, dye 9 in the presence of BF3·OEt2 un-
dergoes polymerization, probably because of the weaker do-
nating power of the 5-methyl substituent (compared to that
of the 4,5-fused cyclohexane moiety) that decreases the pyr-
role ring reactivity with respect to the vinyl group, hence
vinyl polymerization becomes possible.
Free Radical Copolymerization
As preliminary tests showed, the homopolymerization of 6 in DMF (AcONa, HCOONa, Me4NBr, 140 °C, 1 h,
dyes 9 and 12 with a radical initiator such as azobisisobu- Scheme 12). In the reaction mixture, apart from the major
tyronitrile (AIBN) appeared to be inhibited. However, un- products, E-stilbenes 26, their minor regioisomers, 1,1-diar-
der the same conditions (2% AIBN, benzene, 70 °C, 30 h), ylethenes 27 (yields up to 5%), have been detected (GLC).
copolymer 25 of dye 12 with 1-vinylpyrrolidone (VP)
(monomer molar ratio 12:VP = 1:9) was obtained in 10% allows for a nearly quantitative conversion (90–100%) of
yield (Scheme 11). arylbromides, including those which are commonly less re-
As can be seen from Table 4, the PdCl2/6 catalytic system
According to the elemental composition, copolymer 25 active in the Heck reaction (R = Me, OMe), and high yield
consists of 3 mol-% of dye 12. It forms bright yellow solu- of the resulting stilbenes 26 (85–95%) can be obtained,
tions in acetone, ethanol, and chloroform, while solutions whereas without ligand 6 the conversions and yields are
in dioxane, DMSO, and acetonitrile are red. At a lower about four times less. Unlike organic tertiary phosphanes
Scheme 11. Copolymerization of dye 12 with 1-vinylpyrrolidone.
Scheme 12. Arylation of styrene with the PdCl2/6 catalyst (R and corresponding yields are given in Table 4.).
4028
www.eurjoc.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 4021–4033

2-Arylazo-1-vinylpyrroles: A Novel Promising Family of Reactive Dyes
FULL PAPER
Geometrical optimizations were performed with GAMESS code,[32]
at the DFT-B3LYP level; Becke’s three-parameter hybrid func-
tional[33] where non local correlation is provided by Lee, Yang, and
Parr correlation functional[34] with the 6-311G* basis set of Pople
and coworkers.[35] In all calculations no symmetry constraints were
applied as the C1 symmetry point group was assumed throughout.
commonly employed as ligands for Pd-based catalysts, the
arylazopyrroles are stable in air, allowing for arylations
without an inert atmosphere. Furthermore, the presence of
the polymerizable N-vinyl group may appear useful in the
design of recoverable catalysts for such processes.
The X-ray diffraction data were collected with an Enraf–Nonius
CAD-4 diffractometer with graphite-monochromatized Mo-Kα ra-
diation at room temperature (ω/2θ scanning). The crystalline struc-
ture was solved by direct methods and Fourier synthesis
(SHELXL-97).[36] Non-hydrogen atoms were refined anisotropi-
cally by full-matrix procedure on F2 with the SHELXL-97 pack-
age.[36] Hydrogen atoms were found experimentally and refined iso-
tropically.
Table 4. Arylation of styrene with arylbromides in the presence of
the PdCl2/6 catalytic system.
R
Conversion of 4-RC6H4Br [%]
Yield of 26 [%]
H
H
Me
OMe
Ac
25[a,b]
100
90
90
100
23[b]
95
85
85
90
CCDC-270103 (3) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
[a] GLC-based yields. [b] Without ligand 6.
The starting 1-vinylpyrroles 2 were prepared by the Trofimov reac-
tion, aromatic amines were of commercial grade.
Conclusions
In conclusion, a general efficient approach to the synthe-
sis of a novel promising family of reactive azo dyes, namely
2-arylazo-1-vinylpyrroles, has been developed. The ap-
proach is based on the low temperature azo coupling of 1-
vinylpyrroles, readily available from ketones and acetylene
by the Trofimov reaction,[19] with arenediazonium salts in a
neutral medium.
Because of the push–pull character and the high polariz-
ability with noncentrosymmetric charge distribution of the
synthesized dyes, their UV/Vis spectra are highly responsive
to the substituent effects. These results indicate that the
dyes can act as tunable chromophores and serve as prospec-
tive building blocks for second-order NLO materials.
The potential multifacet isomerism of the dyes (the pos-
sible EhZ configuration transition of the azo group along
with the synhanti conformational reversible interconver-
sions of the π-conjugated structural units) may appear use-
ful in the design of novel molecular switches, and memory
and recording devices.
Strong chromogenic response of the dyes to protonation
and complexing secures the potential for the development
of new acid-base and metal sensors.
The polymerizability of the dyes paves the way to intrin-
sically colored polymer materials capable of a reversible
color change under the action of light, heat, or chemicals.
Finally, the 2-arylazo-vinylpyrroles synthesized demon-
strate the ability to act as robust active ligands in Pd-cata-
lyzed cross-coupling reactions.
General Procedure for the Synthesis of 2-Arylazo-1-vinylpyrroles 3–
22: A 0 °C solution of the aromatic amine (10 mmol) and aqueous
HCl (3 mL) in water 15 (mL) was treated with a 0 °C solution of
NaNO2 (0.69 g, 10 mmol) in water (10 mL), and the mixture was
stirred at 0 °C for 0.5 h. The resulting diazonium salt solution was
neutralized (pH Ϸ 7) with dry NaHCO3 (3.0 g, 36 mmol). After
stirring for 10 min the solution obtained was poured into a 0 °C
solution of 1-vinylpyrrole (10 mmol) in ethanol (10 mL). The mix-
ture was stirred at 0 °C for 2 h. The precipitate was filtered off and
dried in vacuo. When no precipitate was formed the reaction mix-
ture was extracted with Et2O (15×3 mL). The extract was dried
with K2CO3 and distilled off. The products were purified by col-
umn chromatography (Al2O3, eluent n-hexane) or recrystallization
from n-hexane.
Upon storage of the azo coupling products 3–22 at ambient tem-
perature for several months neither change in their UV/Vis spectra
nor appearance of foreign signals in their 1H NMR spectra were
observed, which provides evidence of their stability.
2-Phenylazo-1-vinylpyrrole 3: Yield: 1.58 g (80%), crimson crystals,
m.p. 72–74 °C. 1H NMR (400 MHz, CDCl3): δ = 7.88 (m, 2 H,
3
Ho), 7.87 (dd, 3JB–X = 16.0 Hz, JA–X = 8.8 Hz, 1 H, HX), 7.52 (m,
2 H, Hm), 7.43 (m, 1 H, Hp), 7.36 (m, 1 H, 5-H), 6.79 (m, 1 H, 3-
H), 6.45 (m, 1 H, 4-H), 5.38 (d, 1 H, HB), 4.97 (d, 1 H, HA) ppm.
13C NMR (100 MHz, CDCl3): δ = 153.46 (Ci), 145.73 (C-2), 129.97
(Cp), 129.84 (Cα), 129.07 (Cm), 122.33 (Co), 120.73 (C-5), 112.14
(C-4), 100.03 (C-3), 99.66 (C ) ppm. IR (KBr): ν = 3165–3105,
˜
β
1630, 1535, 1501, 1475, 1450, 1410, 1360, 1345, 1305, 1280, 1230,
1180, 1125, 1045, 1005, 955, 905, 880, 800, 765, 710, 675, 650, 580,
550, 500, 450 cm–1. C12H11N3 (197.23): calcd. C 73.07, H 5.62, N
21.30; found C 73.24, H 5.70, N 21.17.
2-(4-Ethoxyphenylazo)-1-vinylpyrrole 4: Yield: 1.25 g (52%), dark-
red crystals, m.p. 72–76 °C. 1H NMR (400 MHz, CDCl3): δ = 7.83
Experimental Section
3
3
3
(d, Jo–m = 8.8 Hz, 2 H, Hm), 7.83 (dd, JB–X = 16.1 Hz, JA–X
=
1
General: H- and 13C NMR spectra were recorded with a Bruker
8.8 Hz, 1 H, HX), 7.29 (m, 1 H, 5-H), 7.00 (m, 2 H, Ho), 6.70 (m,
DPX 400 spectrometer, HMDS as an internal standard. In order
to attribute 1H and 13C peaks 2D homonuclear COSY and NOESY
routines, as well as 2D heteronuclear HSQC and HMBC tech-
niques were used. IR spectra were recorded with a Bruker IFS 25
spectrometer in KBr pellets. Spectrophotometric measurements
1 H, 3-H), 6.41 (m, 1 H, 4-H), 5.33 (d, 1 H, HB), 4.91 (d, 1 H, HA),
3
4.14 (q,
2
H, CH2Me, JCH –Me
=
6.9 Hz), 1.48 (t,
3
H,
2
CH2Me) ppm. 13C NMR (100 MHz, CDCl3): δ = 160.72 (Cp),
147.69 (Ci), 145.72 (C-2), 129.94 (Cα), 124.02 (Co), 119.78 (C-5),
114.72 (Cm), 111.86 (C-4), 99.14 (C-3), 99.08 (Cβ), 63.82 (CH2Me),
were carried out with
Lambda 35.
a
Perkin–Elmer UV/Vis spectrometer
14.86 (CH Me) ppm. IR (KBr), ν = 2975, 2930, 1640, 1590, 1580,
1595, 1475, 1405, 1350, 1310, 1290, 1250, 1130, 1100, 1060, 1030,
˜
2
Eur. J. Org. Chem. 2006, 4021–4033
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4029

B. A. Trofimov et al.
FULL PAPER
955, 905, 875, 820, 800, 710, 660, 625, 575, 550, 545, 515, 475 cm–1.
C14H15N3O (241.29): calcd. C 69.69, H 6.27, N 17.41; found C
70.01, H 6.38, N 17.57.
5.16 (d, 1 H, HA), 2.41 (s, 3 H, Me) ppm. 13C NMR (100 MHz,
CDCl3): δ = 152.57 (Ci), 147.01 (C-2), 135.53 (C-5), 132.16 (Cm),
129.55 (Cα), 123.58 (Co), 123.01 (Cp), 112.09 (C-4), 108.17 (Cβ),
100.93 (C-3), 14.55 (Me) ppm. IR (KBr): ν = 3127, 3055, 2911,
˜
2-(4-Nitrophenylazo)-1-vinylpyrrole 5: Yield: 2.03 g (84%), orange
crystals, m.p. 176–180 °C. H NMR (400 MHz, CDCl3): δ = 8.38
1643, 1582, 1567, 1535, 1474, 1433, 1416, 1388, 1344, 1303, 1293,
1206, 1182, 1150, 1062, 1026, 1004, 960, 886, 831, 812, 783, 774,
762, 706, 510, 492, 458 cm–1. C13H12BrN3 (290.16): calcd. C 53.81,
H 4.17, Br 27.54, N 14.48; found C 53.97, H 4.09, Br 27.51, N
14.33.
1
3
3
(d, Jo–m = 8.9 Hz, 2 H, Hm), 7.95 (m, 2 H, Ho), 7.80 (dd, JB–X
=
3
16.1 Hz, JA–X = 8.7 Hz, 1 H, HX), 7.48 (m, 1 H, 5-H), 6.90 (m, 1
H, 5 H), 6.51 (m, 1 H, 4-H), 5.45 (d, 1 H, HB), 5.06 (d, 1 H,
HA) ppm. 13C NMR (100 MHz, CDCl3): δ = 157.09 (Ci), 147.74
(Cp), 146.23 (C-2), 129.54 (Cα), 124.84 (Cm), 123.35 (C-5), 122.70
5-Methyl-2-(4-phenylazophenylazo)-1-vinylpyrrole 10: Yield: 2.48 g
(79%), vinous crystals, m.p. 120–122 °C. 1H NMR (400 MHz,
(C ), 113.19 (C-4), 102.55 (C-3), 101.08 (C ) ppm. IR (KBr) ν =
˜
o
β
3
3
3110, 3090, 1640, 1600, 1575, 1505, 1460, 1370, 1350, 1325, 1255,
1180, 1130, 1100, 1065, 1110, 960, 870, 845, 750, 745, 685, 650,
605, 590, 500, 455 cm–1. C12H10N4O2 (242.24): calcd. C 59.50, H
4.16, N 23.13; found C 59.52, H 4.24, N 22.87.
CDCl3): δ = 8.01 (d, Jo–m = 8.3 Hz, 2 H, Ho), 7.92 (d, JoЈ–mЈ
=
7.6 Hz, 2 H, HoЈ), 7.89 (d, 2 H, Hm), 7.50 (m, 2 H, HmЈ), 7.47 (m,
3
3
2 H, HpЈ), 7.35 (dd, JB–X = 16.2 Hz, JA–X = 9.3 Hz, 1 H, HX),
6.77 (d, 3J3–4 = 3.4 Hz, 1 H, 3-H), 6.16 (d, 1 H, 4-H), 5.45 (d, 1 H,
HB), 5.22 (d, 1 H, HA), 2.43 (s, 3 H, Me) ppm. 13C NMR
(100 MHz, CDCl3): δ = 155.33 (Ci), 152.90 (CiЈ), 152.53 (Cp),
147.59 (C-2), 136.13 (C-5), 131.12 (CpЈ), 129.56 (Cα), 129.18 (CmЈ),
123.91 (Co), 123.00 (CoЈ), 122.90 (Cm), 112.43 (C-4), 108.35 (Cβ),
5-Methyl-2-phenylazo-1-vinylpyrrole 6: Yield: 1.69 g (80%), brick-
red crystals, m.p. 52–54 °C. 1H NMR (400 MHz, CDCl3): δ = 7.76
3
3
(d, Jo–m = 7.5 Hz, 2 H, Ho), 7.42 (m, 2 H, Hm), 7.34 (dd, JB–X
=
3
16.2 Hz, JA–X = 8.8 Hz, 1 H, HX), 7.32 (m, 1 H, Hp), 6.71 (d,
3J3–4 = 4.1 Hz, 1 H, 3-H), 6.12 (d, 1 H, 4-H), 5.43 (d, 1 H, HB),
5.17 (d, 1 H, HA), 2.42 (s, 3 H, Me) ppm. 13C NMR (100 MHz,
CDCl3): δ = 153.78 (Ci), 147.11 (C-2), 134.79 (C-5), 129.22 (Cp),
129.22 (Cα), 128.99 (Cm), 122.15 (Co), 111.66 (C-4), 107.72 (Cβ),
100.93 (C-3), 14.61 (Me) ppm. IR (KBr): ν = 3095, 3031, 2939,
˜
1640, 1474, 1430, 1411, 1388, 1364, 1343, 1291, 1224, 1179, 1126,
1080, 1071, 1031, 972, 880, 859, 786, 771, 689, 628, 553, 529,
452 cm–1. C19H17N5 (315.37): calcd. C 72.36, H 5.43, N 22.21;
found C 72.25, H 5.43, N 21.28.
99.87 (C-3), 14.47 (Me) ppm. IR (KBr) ν = 3056, 2981, 2975, 2955,
˜
2920, 2910, 1638, 1538, 1480, 1452, 1433, 1411, 1384, 1348, 1331,
1291, 1186, 1150, 1082, 1072, 1030, 1017, 993, 978, 919, 906, 884,
862, 840, 772, 692, 675, 636, 613, 577, 556, 514 cm–1. C13H13N3
(211.26): calcd. C 73.91, H 6.20, N 19.89; found C 73.66, H 6.34,
N 19.46.
2-Phenylazo-1-vinyl-4,5,6,7-tetrahydroindole 11: Yield: 2.19 g
(87%), brick-red crystals, m.p. 62–66 °C. 1H NMR (400 MHz,
3
3
CDCl3): δ = 7.74 (d, Jo–m = 8.0, Hz 2 H, Ho), 7.47 (dd, JB–X
16.1 Hz, JA–X 9.3 =Hz, 1 H, HX), 7.42 (m, 2 H, Hm), 7.31 (m, 1
=
3
H, Hp), 6.57 (s, 1 H, 3 H), 5.31 (d, 1 H, HB), 5.00 (d, 1 H, HA),
3
3
2.78 (t, J6–7 = 6.1 Hz, 2 H, 7-H), 2.56 (t, J4–5 = 6.1 Hz, 2 H, 4-
H), 1.85 (m, 2 H, 6-H), 1.75 (m, 2 H, 5-H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 153.91 (Ci), 146.14 (C-2), 134.71 (C-8),
129.43 (Cα), 129.01 (Cm), 129.01 (Cp), 122.66 (C-9), 122.09 (Co),
104.54 (Cβ), 98.97 (C-3), 24.60 (C-7), 23.20 (C-4), 23.20 (C-6),
2-(4-Ethoxyphenylazo)-5-methyl-1-vinylpyrrole 7: Yield: 1.94 g
(76%), brick-red powder, m.p. 74–76 °C. 1H NMR (400 MHz,
3
3
CDCl3): δ = 7.73 (d, Jo–m = 8.8 Hz, 2 H, Ho), 7.33 (dd, JB–X
=
3
16.1 Hz, JA–X = 9.3 Hz, 1 H, HX), 6.92 (d, 2 H, Hm), 6.62 (d,
3J3–4 = 3.9 Hz, 1 H, 3-H), 6.07 (d, 1 H, 4-H), 5.40 (d, 1 H, HB),
3
22.86 (C-5) ppm. IR (KBr): ν = 2937, 2835, 1640, 1473, 1447, 1432,
˜
5.12 (d, 1 H, HA), 4.07 (q, J
= 6.9 Hz, 2 H, CH2Me), 2.40
CH2–Me
(s, 3 H, MePy), 1.42 (t, 3 H, CH2Me) ppm. 13C NMR (400 MHz,
CDCl3): δ = 160.19 (Cp), 147.64 (Ci), 146.06 (C-2), 133.77 (C-5),
129.78 (Cα), 123.74 (Co), 114.71 (Cm), 111.30 (C-4), 107.06 (Cβ),
98.80 (C-3), 63.78 (CH2Me), 14.88 (CH2Me), 14.53 (MePy) ppm.
1412, 1360, 1338, 1323, 1291, 1261, 1242, 1199, 1137, 1094, 1069,
971, 952, 911, 868, 830, 807, 765, 719, 690, 633, 558, 514 486,
454 cm–1. C16H17N3 (251.33): calcd. C 76.46, H 6.82, N 16.72;
found C 76.38, H 6.87, N 16.35.
IR (KBr): ν = 3122, 3076, 2974, 2938, 1642, 1598, 1578, 1499, 1474,
˜
2-(4-Ethoxyphenylazo)-1-vinyl-4,5,6,7-tetrahydroindole 12: Yield:
2.36 g (80%), red crystals, m.p. 112–114 °C. H NMR (400 MHz,
1428, 1409, 1393, 1371, 1352, 1326, 1299, 1252, 1187, 1149, 1114,
1081, 1042, 1024, 967, 921, 879, 840, 803, 773, 669, 635, 576, 556,
531, 462 cm–1. C15H17N3O (255.31): calcd. C 70.56, H 6.71, N
16.46; found C 71.01, H 6.80, N 16.46.
1
3
3
CDCl3): δ = 7.70 (d, Jo–m = 8.2 Hz, 2 H, Hm), 7.47 (dd, JB–X
=
16.3 Hz, 3JA–X 9.2 Hz, 1 H, HX), 6.93 (d, 2 H, Ho), 6.49 (s, 1 H, 3-
H), 5.30 (d, 1 H, HB), 4.97 (d, 1 H, HA), 4.08 (q, 3JCH –Me = 6.7 Hz,
2
3
3
2 H, CH2Me), 2.78 (t, J6–7 = 5.7 Hz, 2 H, 7-H), 2.55 (t, J4–5
=
5-Methyl-2-(4-nitrophenylazo)-1-vinylpyrrole 8: Yield: 2.18 g (85%),
red crystals, m.p. 138–140 °C. 1H NMR (400 MHz, CDCl3): δ =
5.7 Hz, 2 H, 4-H), 1.85 (m, 2 H, 6-H), 1.75 (m, 2 H, 5-H), 1.43 (t,
3 H, CH2Me) ppm. 13C NMR (100 MHz, CDCl3): δ = 160.02 (Cp),
148.11 (Ci), 146.04 (C-2), 133.48 (C-8), 129.55 (Cα), 123.64 (Co),
122.20 (C-9), 114.71 (Cm), 103.87 (Cβ), 98.02 (C-3), 63.79
(CH2Me), 24.56 (C-7), 23.27 (C-4), 23.17 (C-6), 22.91 (C-5), 14.90
3
8.27 (d, Jo–m = 9.0 Hz, 2 H, Hm), 7.81 (d, 2 H, Ho), 7.29 (dd,
3JB–X = 15.9 Hz, 3JA–X = 9.3 Hz, 1 H, HX), 6.84 (d, 3J3–4 = 4.2 Hz,
1 H, 3-H), 6.21 (d, 1 H, 4-H), 5.44 (d, 1 H, HB), 5.29 (d, 1 H, HA),
2.45 (s, 3 H, Me) ppm. 13C NMR (100 MHz, CDCl3): δ = 157.58
(Ci), 147.64 (C-2), 147.06 (Cp), 138.21 (C-5), 129.27 (Cα), 124.78
(Cm), 122.34 (Co), 113.33 (C-4), 109.54 (Cβ), 102.70 (C-3), 14.60
(CH Me) ppm. IR (KBr): ν = 2975, 2932, 2857, 1642, 1598, 1578,
˜
2
1556, 1496, 1468, 1422, 1406, 1390, 1366, 1329, 1310, 1297, 1243,
1164, 1141, 1126, 1096, 1076, 1045, 1020, 956, 921, 887, 840, 824,
807, 790, 687, 633, 573, 563, 533 cm–1. C18H21N3O (295.38): calcd.
C 73.19, H 7.17, N 14.23; found C 73.15, H 7.47, N 14.06.
(Me) ppm. IR (KBr): ν = 3122, 3095, 2995, 2958, 2913, 1643, 1603,
˜
1585, 1517, 1472, 1432, 1391, 1367, 1335, 1297, 1179, 1149, 1104,
1076, 1035, 997, 894, 781, 753, 691, 620, 507, 458 cm–1.
C13H12N4O2 (256.26): calcd. C 60.93, H 4.72, N 21.86; found C
60.56, H 4.54, N 21.68.
2-(4-Nitrophenylazo)-1-vinyl-4,5,6,7-tetrahydroindole 13: Yield:
2.78 g (94%), vinous crystals, m.p. 150–152 °C. 1H NMR
3
2-(4-Bromophenylazo)-5-methyl-1-vinylpyrrole 9: Yield: 2.21 g
(400 MHz, CDCl3): δ = 8.26 (d, Jo–m = 8.6 Hz, 2 H, Hm), 7.80 (d,
(76%), orange needles, m.p. 72–74 °C. 1H NMR (400 MHz, 2 H, Ho), 7.41 (dd, JB–X = 16.1 Hz, JA–X = 9.0 Hz, 1 H, HX),
3
3
3
CDCl3): δ = 7.62 (d, Jo–m = 8.8 Hz, 2 H, Ho), 7.53 (d, 2 H, Hm),
6.70 (s, 1 H, 3-H), 5.36 (d, 1 H, HB), 5.13 (d, 1 H, HA), 2.81 (m, 2
H, 7-H), 2.58 (m, 2 H, 4-H), 1.88 (m, 2 H, 6-H), 1.78 (m, 2-H, 5-
3
3
7.31 (dd, JB–X = 16.1 Hz, JA–X = 9.3 Hz, 1 H, HX), 6.71 (d,
3J3–4 = 3.9 Hz, 1 H, 3-H), 6.13 (d, 1 H, 4-H), 5.40 (d, 1 H, HB), H) ppm. 13C NMR (100 MHz, CDCl3): δ = 157.86 (Ci), 146.84
4030
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 4021–4033

2-Arylazo-1-vinylpyrroles: A Novel Promising Family of Reactive Dyes
FULL PAPER
(Cp), 146.84 (C-2), 138.58 (C-8), 128.98 (Cα), 124.82 (Cm), 124.51 1450, 1410, 1380, 1310, 1305, 1295, 1180, 1145, 1095, 1035, 1000,
(C-9), 122.22 (Co), 106.43 (Cβ), 101.56 (C-3), 24.77 (C-7), 23.10 (C- 905, 895, 855, 840, 875, 750, 710, 700, 690, 650, 530, 490 cm–1.
4), 22.95 (C-6), 22.68 (C-5) ppm. IR (KBr): ν = 3104, 2937, 2857,
C18H14N4O2 (318.33): calcd. C 67.92, H 4.43, N 17.60; found C
67.92, H 4.48, N 17.37.
˜
1639, 1603, 1585, 1511, 1466, 1410, 1326, 1312, 1294, 1283, 1220,
1197, 1133, 1104, 1073, 1016, 884, 851, 752, 687, 668, 613, 542,
498 cm–1. C16H16N4O2 (296.32): calcd. C 64.85, H 5.44, N 18.91;
found C 65.04, H 5.85, N 18.68.
5-(4-Methoxyphenyl)-2-phenylazo-1-vinylpyrrole 18: Yield: 1.73 g
1
(57%), red crystals, m.p. 76–78 °C. H NMR (400 MHz, CDCl3):
3
δ = 7.85 (d, Jo–m = 8.7 Hz, 2 H, Ho), 7.50 (m, 2 H, Hm), 7.48 (d,
3
2-(4-Bromophenylazo)-1-vinyl-4,5,6,7-tetrahydroindole 14: Yield:
3JoЈ–mЈ = 8.7 Hz, 2 H, HmЈ), 7.40 (m, 1 H, Hp), 7.22 (dd, JB–X
=
2.71 g (82%), brick-red crystals, m.p. 78–79 °C. 1H NMR
15.9 Hz, JA–X = 9.0 Hz, 1 H, HX), 7.01 (m, 2 H, HoЈ), 6.94 (d,
3
3
(400 MHz, CDCl3): δ = 7.61 (d, Jo–m = 8.6 Hz, 2 H, Ho), 7.52 (d, 3J3–4 = 4.0 Hz, 1 H, 3-H), 6.42 (d, 1 H, 4-H), 5.46 (d, 1 H, HB),
3
3
2 H, Hm), 7.42 (dd, JB–X = 16.1 Hz, JA–X = 9.3 Hz, 1 H, HX),
6.58 (s, 1 H, 3-H), 5.30 (d, 1 H, HB), 5.02 (d, 1 H, HA), 2.77 (t, CDCl3): δ = 159.61 (CpЈ), 153.76 (Ci), 148.12 (C-2), 138.60 (C-5),
5.21 (d, 1 H, HA), 3.90 (s, 3 H, Me) ppm. 13C NMR (100 MHz,
3
3J6–7 = 5.9 Hz, 2 H, 7-H), 2.55 (t, J4–5 = 6.1 Hz, 2 H, 4-H), 1.86
130.52 (CoЈ), 129.97 (Cα), 129.47 (Cp), 129.08 (Cm), 124.58 (CiЈ),
(m, 2 H, 6-H), 1.75 (m, 2 H, 5-H) ppm. 13C NMR (100 MHz, 122.31 (Co), 114.07 (CmЈ), 112.23 (C-4), 110.09 (Cβ), 100.54 (C-3),
CDCl3): δ = 152.70 (Ci), 146.06 (C-2), 135.47 (C-8), 132.08 (Cm), 55.44 (Me) ppm. IR (KBr): ν = 2996, 2967, 2934, 2836, 1643, 1608,
˜
129.24 (Cα), 123.78 (Co), 123.04 (C-9), 122.64 (Cp), 104.89 (Cβ), 1573, 1537, 1503, 1464, 1448, 1436,1406, 1390, 1356, 1316, 1298,
99.59 (C-3), 24.59 (C-7), 23.10 (C-4), 23.10 (C-6), 22.77 (C-5) ppm.
1247, 1213, 1178, 1149, 1109, 1069, 1035, 1023, 959, 892, 835, 782,
771, 714, 684, 629, 613, 593, 559, 525, 499, 471 cm–1. C19H17N3O
(303.36): calcd. C 75.23, H 5.65, N 13.85; found C 74.96, H 5.48,
IR (KBr): ν = 2924, 2855, 1642, 1468, 1412, 1363, 1337, 1323, 1288,
˜
1197, 1136, 1095, 1064, 1000, 959, 889, 834, 739, 705, 629, 601,
587, 511, 484, 460 cm–1. C16H16BrN3 (330.23): calcd. C 58.20, H N 13.74.
4.88, Br 24.20, N 12.72; found C 58.18, H 4.87, Br 24.31, N 12.74.
5-(4-Methoxyphenyl)-2-(4-nitrophenylazo)-1-vinylpyrrole 19: Yield:
2-(4-Phenylazophenylazo)-1-vinyl-4,5,6,7-tetrahydroindole 15: Yield:
1.95 g (56%), vinous crystals, m.p. 122–124 °C. 1H NMR
1
3
2.88 g (81%), green powder, m.p. 98–100 °C. H NMR (400 MHz,
(400 MHz, CDCl3): δ = 8.34 (d, Jo–m = 9.0 Hz, 2 H, Hm), 7.80 (d,
3
3
3
3
CDCl3): δ = 7.99 (d, Jo–m = 8.8 Hz, 2 H, Ho), 7.92 (d, JoЈ–mЈ
=
2 H, Ho), 7.52 (d, JoЈ–mЈ = 8.8 Hz, 2 H, HmЈ), 7.17 (dd, JB–X =
3
7.1 Hz, 2 H, HoЈ), 7.87 (d, 2 H, Hm), 7.51 (m, 2 H, HmЈ), 7.48 (dd, 15.9 Hz, JA–X = 9.1 Hz, 1 H, HX), 7.06 (d, 2 H, HoЈ), 7.03 (d,
3
3JB–X = 16.2 Hz, JA–X = 9.5 Hz, 1 H, HX), 7.46 (m, 1 H, HpЈ),
3J3–4 = 4.3 Hz, 1 H, 3-H), 6.52 (d, 1 H, 4-H), 5.53 (d, 1 H, HB),
6.65 (s, 1 H, 3-H), 5.34 (d, 1 H, HB), 5.07 (d, 1 H, HA), 2.80 (t, 5.37 (d, 1 H, HA), 3.87 (s, 3 H, Me) ppm. 13C NMR (100 MHz,
3
3J6–7 = 5.9 Hz, 2 H, 7-H), 2.57 (t, J4–5 = 6.1 Hz, 2 H, 4-H), 1.86
CDCl3): δ = 160.04 (CpЈ), 157.55 (Ci), 148.68 (C-2), 147.15 (Cp),
(m, 2 H, 6-H), 1.77 (m, 2 H, 5-H) ppm. 13C NMR (100 MHz, 141.44 (C-5), 130.55 (CmЈ), 129.69 (Cα), 124.89 (Cm), 123.76 (CiЈ),
CDCl3): δ = 155.33 (Ci), 152.93 (CiЈ), 152.35 (Cp), 146.70 (C-2), 122.49 (Co), 114.22 (CoЈ), 113.57 (C-4), 111.75 (Cβ), 103.06 (C-3),
136.19 (C-8), 131.02 (CpЈ), 129.27 (Cα), 129.14 (CmЈ), 123.91 (Co),
55.40 (Me) ppm. IR (KBr): ν = 3114, 2934, 2832, 1642, 160,8 1583,
˜
123.43 (C-9), 122.77 (CoЈ), 122.96 (Cm), 105.17 (Cβ), 99.97 (C-3), 1535, 151, 1458, 1437, 1417, 1381, 1333, 1286, 1254, 1239, 1188,
24.67 (C-7), 23.12 (C-4), 23.09 (C-6), 22.77 (C-5) ppm. IR (KBr):
1151, 1147, 1105, 1080, 1043, 1024, 970, 916, 899, 832, 810, 783,
753, 718, 691, 656, 627, 518, 528, 507, 467 cm–1. C19H16N4O3
(348.36): calcd. C 65.51, H 4.63, N 16.08; found C 65.67, H 5.00,
N 15.85.
ν = 3058, 2932, 2853, 1640, 1597, 1504, 1471, 1436, 1408, 1362,
˜
1333, 1323, 1311, 1287, 1222, 1200, 1138, 1124, 1093, 1073, 1058,
1019, 854, 834, 813, 764, 684, 627, 550, 527 cm–1. C22H21N5
(355.44): calcd. C 74.34, H 5.96, N 19.70; found C 74.80 H 6.03,
N 19.31.
5-Furyl-2-phenylazo-1-vinylpyrrole 20: Yield: 1.40 g (53%), orange
1
crystals, m.p. 86–88 °C. H NMR (400 MHz, CDCl3): δ = 7.80 (d,
5-Phenyl-2-phenylazo-1-vinylpyrrole 16: Yield: 1.45 g (53%), red
3Jo–m = 7.8 Hz, 2 H, Ho), 7.49 (m, 1 H, 5Ј-H), 7.45 (m, 2 H, Hm),
1
3
3
3
crystals, m.p. 72–74 °C. H NMR (400 MHz, CDCl3): δ = 7.85 (d,
7.37 (t, Jp–m = 7.1 Hz, 1 H, Hp), 7.26 (dd, JB–X = 15.8 Hz, JA–X
3
3
3Jo–m = 8.1 Hz, 2 H, Ho), 7.53 (d, JoЈ–mЈ = 7.7 Hz, 2 H, HoЈ), 7.45 = 8.8 Hz, 1 H, HX), 6.87 (br. s, 1 H, 3-H), 6.62 (d, J3–4 = 4.3 Hz,
(m, 2 H, Hm), 7.45 (m, 2 H, HmЈ), 7.39 (m, 1 H, Hp), 7.39 (m, 1 H, 1 H, 4-H), 6.58 (m, 1 H, 4Ј-H), 6.49 (m, 1 H, 3Ј-H), 5.57 (d, 1 H,
3
HpЈ), 7.22 (dd, 3JB–X = 16.0 Hz, JA–X = 9.2 Hz, 1 H, HX), 6.92 (d,
HB), 5.36 (d, 1 H, HA) ppm. 13C NMR (100 MHz, CDCl3): δ =
3J3–4 = 4.2 Hz, 1 H, 3-H), 6.44 (d, 1 H, 4-H), 5.42 (d, 1 H, HB), 153.67 (Ci), 148.18 (C-2), 146.27 (C-2Ј), 142.64 (C-5Ј), 129.74 (Cα),
5.19 (d, 1 H, HA) ppm. 13C NMR (100 MHz, CDCl3): δ = 153.78 129.74 (Cp), 129.09 (Cm), 128.72 (C-5), 122.40 (Co), 112.16 (Cβ),
(Ci), 148.33 (C-2), 138.41 (C-5), 132.10 (CiЈ), 129.87 (Cα), 129.64 111.69 (C-4), 111.59 (C-4Ј), 109.07 (C-3Ј), 100.73 (C-3) ppm. IR
(Cp), 129.14 (CoЈ), 129.08 (Cm), 128.44 (CmЈ), 128.00 (CpЈ), 122.38 (KBr): ν = 3143, 3123, 3062, 3026, 2926, 1639, 1486, 1479, 1453,
˜
(C ), 112.68 (C-4), 110.36 (C ), 100.38 (C-3) ppm. IR (KBr): ν = 1427, 1390, 1374, 1344, 1327, 1298, 1236, 1217, 1148, 1070, 1057,
˜
o
β
3111, 3061, 3027, 2860, 1641, 1600, 1533, 1496, 1465, 1449, 1418,
1392, 1351, 1298, 1278, 1234, 1154, 1072, 1040, 999, 962, 895, 760,
690, 658, 561, 512 cm–1. C18H15N3 (273.34): calcd. C 79.10, H 5.53,
N 17.37; found C 79.38, H 5.87, N 17.14.
1041, 1016, 959, 924, 886, 876, 779, 763, 695, 687, 604, 552, 522,
496 cm–1. C16H13N3O (263.30): calcd. C 72.99, H 4.98, N 15.96;
found C 73.16, H 5.06, N 16.11.
2-Phenylazo-5-thienyl-1-vinylpyrrole 21: Yield: 1.48 g (53%), orange
1
2-(4-Nitrophenylazo)-5-phenyl-1-vinylpyrrole 17: Yield: 1.78 g
(56%), orange crystals, m.p. 140–144 °C. 1H NMR (400 MHz,
crystals, m.p. 74–76 °C. H NMR (400 MHz, CDCl3): δ = 7.84 (d,
3Jo–m = 7.8 Hz, 2 H, Ho), 7.50 (m, 2 H, Hm), 7.41 (m, 1 H, Hp),
3
3
3
CDCl3): δ = 8.35 (d, Jo–m = 9.0 Hz, 2 H, Hm), 7.92 (d, 2 H, Ho),
7.40 (m, 1 H, 5Ј-H), 7.26 (dd, JB–X = 15.9 Hz, JA–X = 8.9 Hz, 1
3
7.58 (m, 2 H, HoЈ), 7.48 (m, 2 H, HmЈ), 7.39 (m, 1 H, HpЈ), 7.24 H, HX), 7.26 (m, 1 H, 3Ј-H), 7.14 (m, 1 H, 4Ј-H), 6.90 (d, J3–4
=
3
3
(dd, JB–X = 15.9 Hz, JA–X = 9.0 Hz, 1 H, HX), 7.05 (d, 1 H, 3- 4.2 Hz, 1 H, 3-H), 6.55 (d, 1 H, 4-H), 5.62 (d, 1-H, HB), 5.37 (d, 1
H), 6.55 (d, 1 H, 4-H), 5.45 (d, 1 H, HB), 5.30 (d, 1 H, HA) ppm.
H, HA) ppm. 13C NMR (100 MHz, CDCl3): δ = 153.10 (Ci), 147.89
(C-2), 133.05 (C-5), 131.12 (C-2Ј), 129.23 (Cp), 129.08 (Cα), 128.62
13C NMR (100 MHz, CDCl3): δ = 157.48 (Ci), 148.88 (C-2), 147.36
(Cp), 141.11 (C-5), 132.48 (CiЈ), 129.63 (Cα), 129.36 (CoЈ), 128.74 (Cm), 127.23 (C-4Ј), 126.79 (C-3Ј), 125.95 (C-5Ј), 121.89 (Co),
(CmЈ), 128.66 (CpЈ), 124.87 (Cm), 122.62 (Co), 113.89 (C-4), 111.84 112.60 (C-4), 111.70 (C ), 100.17 (C-3) ppm. IR (KBr): ν = 3122,
˜
β
(C ), 102.88 (C-3) ppm. IR (KBr): ν = 1625, 1600, 1575, 1500, 3063, 3031, 1634, 1466, 1450, 1435, 1422, 1388, 1344, 1321, 1213,
˜
β
Eur. J. Org. Chem. 2006, 4021–4033
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4031

B. A. Trofimov et al.
FULL PAPER
1193, 1147, 1070, 1057, 1040, 1013, 959, 928, 843, 778, 762, 700,
686, 600, 543, 522, 498 cm–1. C16H13N3S (279.36): calcd. C 68.79,
H 4.69, N 15.04, S 11.48; found: C 69.06, H 4.50, N 15.24, S 11.71.
Acknowledgments
This work was supported by the Russian Science Support Founda-
tion, President grant (MK-1707.2005.3) and the Presidium of the
Russian Academy of Sciences (grant No. 10002-251/P-25/155-305/
200404-072).
2-(4-Nitrophenylazo)-5-thienyl-1-vinylpyrrole 22: Yield: 2.56 g
(79%), vinous crystals, m.p. 136–140 °C. 1H NMR (400 MHz,
3
CDCl3): 8.39 δ = (d, Jo–m = 9.0 Hz, 2 H, Hm), 7.81 (d, 2 H, Ho),
3
3
7.50 (d, J4Ј–5Ј = 4.4 Hz, 1 H, H5Ј), 7.39 (d, J3Ј–4Ј = 3.5 Hz, 1 H,
H3Ј), 7.26 (dd, 3JB–X = 15.7 Hz, 3JA–X = 8.8 Hz, 1 H, HX), 7.14 (m,
1 H, 4Ј-H), 7.07 (d, J3–4 = 4.3 Hz, 1 H, 3-H), 6.68 (d, 1 H, 4-H),
3
[1] N. Yokomichi, K. Seki, S. Tada, T. Yamabe, Synth. Met. 1995,
69, 577–578.
[2] G. Zotti, S. Zecchin, G. Schiavon, A. Berlin, G. Pagani, A.
Canavesi, G. Casalbore-Miceli, Synth. Met. 1996, 78, 51–57.
[3] A. Chyla, S. Kucharski, J. Sworakowski, M. Bien´kovski, Thin
Solid Films 1996, 284–285, 496–499.
[4] J. D. Nero, D. Laks, Synth. Met. 1999, 101, 440–441.
[5] Y. Ishida, Y. Murata, JP 06145544, 1994 [Chem. Abstr. 1994,
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[6] T. Kawafuoni, N. Yanagihara, Y. Shinjo (Ricoh Co., Ltd., Ja-
pan), JP 2002129049, 2002 [Chem. Abstr. 2002, 136, 18109].
[7] Y. Ueno, T. Sato, T. Tomura, T. Noguchi (Ricoh Co., Ltd.,
Japan), JP 20022883731, 2002 [Chem. Abstr. 2002, 137,
286541].
5.68 (d, 1 H, HB), 5.54 (d, 1 H, HA) ppm. 13C NMR (100 MHz,
CDCl3): δ = 157.44 (Ci), 148.91 (C-2), 147.38 (Cp), 134.44 (C-5),
132.93 (C-2Ј), 129.39 (Cα), 127.99 (C-4Ј), 127.82 (C-3Ј), 127.26 (C-
5Ј), 124.89 (Cm), 122.62 (Co), 114.02 (C-4), 114.02 (Cβ), 103.16 (C-
3) ppm. IR (KBr): ν = 3113, 3077, 2958, 2922, 2852, 1640, 1601,
˜
1584, 1512, 1460, 1379, 1330, 1304, 1196, 1172, 1151, 1101, 1038,
851, 770, 753, 694 cm–1. C16H12N4O2S (324.36): calcd. C 59.25, H
3.73, N 17.27, S 9.88; found C 59.59, H 4.01, N 17.00, S 9.69.
Protonation of Azopyrrole 9: An orange solution of azopyrrole 9
(10 mg, 0.034 mmol) in CDCl3 (1 mL) was added to CF3COOH
(4 mg, 0.035 mmol). The reaction mixture became red-brown. After
recording the spectrum [1H NMR (400 MHz, CDCl3): δ = 7.83 (d,
[8] Y. Ueno (Ricoh Co., Ltd., Japan), JP 20022347348, 2003
3
3J3–4 = 3.9 Hz, 1 H, 3-H), 7.59 (d, Jo–m = 8.8 Hz, 2 H, Ho), 7.47
[Chem. Abstr. 2003, 138, 18109].
3
3
[9] Z. Zhu, Y. Wang, Y. Lu, Macromolecules 2003, 36, 9585–9593.
[10] E. Wagner-Wysiecka, E. Luboch, M. Kowalczyk, J. F. Biernat,
Tetrahedron 2003, 59, 4415–4420.
(d, 2 H, Hm), 7.00 (dd, JB–X = 16.1 Hz JA–X = 9.3 Hz, 1 H, HX),
6.86 (d, 1 H, 4-H), 5.82 (d, 1 H, HA), 5.68 (d, 1 H, HB), 2.61 (s, 3 H,
Me) ppm], the solution was mixed with NaHCO3 (9 mg) at room
temperature and then filtered. The initial color was completely re-
[11] A. Facchetti, A. Abbotti, L. Beverina, M. E. van der Boom, P.
Dutta, G. Evmenenko, T. J. Marks, G. A. Pagani, Chem. Mater.
2002, 14, 4996–5005.
1
stored, and the H NMR, spectrum corresponded to that of initial
compound 9. Protonation of azopyrrole 12 was carried out analo-
gously.
[12] Y. Wang, J. Ma, Y. Jiang, J. Phys. Chem. A 2005, 109, 7197–
7206.
[13] A. Gossauer, Die Chemie der Pyrrole, Springer-Verlag, Berlin,
Heidelberg, New York, 1974, pp. 37–38.
[14] R. A. Jones, G. P. Bean, The Chemistry of Pyrroles, Academic
Press, London, New York, San Francisco, 1977, pp. 188–189.
[15] K. P. M. Heirwegh, G. P. Van Hees, P. Leroy, F. P. Van Roy,
F. H. Jansen, Biochem. J. 1970, 120, 877.
[16] T. Yamaguchi, I. Shhiji, A. Sugimoto, Y. Komoda, H. Naka-
jima, Biochim. Biophys. Acta 1996, 1289, 110–114.
[17] a) B. A. Trofimov, A. I. Mikhaleva, S. E. Korostova, A. N. Vas-
il’ev, L. N. Balabanova, Khim. Geterotsikl. Soedin. 1977, 213–
214; b) A. I. Mikhaleva, B. A. Trofimov, S. E. Korostova, A. N.
Vasil’ev, L. N. Balabanova, Izv. SO AN SSSR, Ser. Khim. Nauk
1979, 107–112; c) B. A. Trofimov, A. I. Mikhaleva, N-Vinylpir-
roly, Nauka, Novosibirsk, 1984, p. 264 (in Russian); d) B. A.
Trofimov in The Chemistry of Heterocyclic Compounds, Part 2,
Vinylpyrroles (Ed.: R. A. Jones), Wiley, New York, 1992, vol.
48, pp. 131–298.
Complexing of Azopyrrole 12 with BF3·OEt2: A solution of azopyr-
role 12 (6 mg, 0.020 mmol) in CDCl3 (1 mL) was added to
BF3·OEt2 (3 mg, 0.021 mmol) whilst stirring at room temperature.
The reaction mixture became red-brown. 1H NMR (400 MHz,
3
CDCl3): δ = 7.63 (d, Jo–m = 8.2 Hz, 2 H, Hm), 7.59 (s, 1 H, 3-H),
3
7.13 (dd, 3JB–X = 16.3 Hz, JA–X = 9.2 Hz, 1 H, HX), 6.89 (d, 2 H,
3
Ho), 5.46 (d, 1 H, HB), 5.38 (d, 1 H, HA), 4.05 (q, JCH –Me
=
2
3
8.2 Hz, 2 H, CH2Me), 2.81 (t, J6–7 = 5.7 Hz, 2 H, 7-H), 2.60 (t,
3J4–5 = 5.7 Hz, 2 H, 4-H), 1.85 (m, 2 H, 6-H), 1.75 (m, 2 H, 5-H),
1.43 (t, 3 H, CH2Me) ppm.
A solution of azopyrrole 12 (6 mg, 0.020 mmol) in benzene (10 mL)
was added to BF3·OEt2 (3 mg, 0.021 mmol) whilst stirring at room
temperature. The violet solution prepared was diluted with benzene
to 2×10–4 molL–1 to record the UV/Vis spectrum.
[18] a) M. V. Sigalov, E. Yu. Schmidt, A. I. Mikhaleva, S. E. Koros-
tova, I. M. Lasarev, B. A. Trofimov, Khim. Geterotsykl. Soed.
1993, 48–57; b) B. A. Trofimov, M. V. Sigalov, Main Group
Chem. News 1998, 6, 30–41.
Copolymerization of the Azopyrrole 12 with 1-Vinylpyrrolidone
(VP): A solution of pyrrole 12 (23 mg, 0.078 mmol), VP (77 mg,
0.694 mmol), and AIBN (2 mg, 2%) in benzene (0.1 mL) was
placed in a glass ampule under argon. The ampule was sealed and
kept at 70 °C for 30 h. The copolymer was purified by reprecipi-
tation from the benzene solution to n-hexane and washed with
[19] a) B. A. Trofimov, “Preparation of Pyrroles from Ketoximes
and Acetylenes” in: Adv. Heterocycl. Chem. (Ed.:A. R. Ka-
tritzky), Acad. Press, San Diego, 1990, 51, pp. 177–301; b) G. P.
Bean, “The Synthesis of 1H-Pyrroles” in: Pyrroles. Part One.
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c) R. J. Tedeschi in Encyclopedia of Physical Science and Tech-
nology, Acad. Press: San Diego, 1992, 1, pp. 27–65; d) A. I.
Mikhaleva, E. Yu. Schmidt, “Two-step Synthesis of Pyrroles
from Ketones and Acetylenes through the Trofimov Reaction”
in: Selected Methods for Synthesis and Modification of Hetero-
cycles (Ed.: V. G. Kartsev), IBS Press, Moscow, 2002, 1, pp.
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Et O to give 10 mg of a brown powder (yield 10%). IR (KBr): ν =
˜
2
2950, 2905, 2860, 1680, 1620, 1590, 1570, 1495, 1470, 1420, 1380,
1280, 1220, 1100, 1020, 960, 910, 820 cm–1. 25: C210H309N35O33
(3851.98): calcd. C 65.45, H 8.10, N 12.72; found C 66.28, H 7.98,
N 12.87.
Arylation of Styrene: A mixture of arylbromide (10.00 mmol), sty-
rene (1040 mg, 10.00 mmol), PdCl2 (28 mg, 0.16 mmol), AcONa
(905 mg, 11.00 mmol), HCOONa (136 mg, 2.00 mmol), NMe4Br
(246 mg, 1.60 mmol), and azopyrrole 6 (68 mg, 0.32 mmol) in dry
DMF (10 mL) was stirred at 140 °C for 1 h, and then analyzed by
GLC.
[20] E. Yu. Schmidt, A. I. Mikhaleva, A. M. Vasil’tsov, A. B. Zait-
sev, N. V. Zorina, Arkivoc 2005, vii, VM-1231J, 11–17.
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Eur. J. Org. Chem. 2006, 4021–4033

2-Arylazo-1-vinylpyrroles: A Novel Promising Family of Reactive Dyes
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Received: April 25, 2006
Published Online: July 10, 2006
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