Tricyanovinylation of 2-aryl-1-vinylpyrroles: solvent- and substituent controlled chemo- and regioselectivity

Article abstract of DOI:10.1016/j.tet.2009.03.094

2-Aryl-1-vinylpyrroles in acetone, THF and benzene react with tetracyanoethene chemo- and regiospecifically across the vinyl group to give 3-(2-arylpyrrol-1-yl)-1,1,2,2-cyclobutanetetracarbonitriles in 88-94% yield. The latter, upon recrystallization from

Full text of DOI:10.1016/j.tet.2009.03.094

Tetrahedron 65 (2009) 4326–4331
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Tetrahedron
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Tricyanovinylation of 2-aryl-1-vinylpyrroles: solvent- and substituent controlled
chemo- and regioselectivity
*
Boris A. Trofimov , Lyubov’ N. Sobenina, Vladislav N. Drichkov, Igor’ A. Ushakov, Al’bina I. Mikhaleva
A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences, 1 Favorsky Str., 664033 Irkutsk, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
2-Aryl-1-vinylpyrroles in acetone, THF and benzene react with tetracyanoethene chemo- and re-
giospecifically across the vinyl group to give 3-(2-arylpyrrol-1-yl)-1,1,2,2-cyclobutanetetracarbonitriles in
88–94% yield. The latter, upon recrystallization from EtOH, eliminates HCN and entirely rearranges to
afford stereospecifically trans-(3E)-4-(2-arylpyrrol-1-yl)-1,3-butadiene-1,1,2-tricarbonitriles. In DMSO,
along with the above [2þ2]-cycloaddition, tricyanovinylation of the pyrrole ring occurs to form the
corresponding 3- and 5-tricyanovinylpyrroles, the product ratio being dependent on the substituents in
the pyrrole ring and the reaction conditions.
Received 12 December 2008
Received in revised form 10 March 2009
Accepted 26 March 2009
Available online 2 April 2009
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
charge-transfer ability in the electronic ground state and as
promising organic conductors. Due to their strong solvatochromic
Tricyanovinylation of NH-pyrroles with tetracyanoethene
(TCNE) is known to proceed selectively at the annular
-position.1
When both -positions are substituted, the pyrroles are tricyano-
vinylated onto the free
-position.1c In the case of N-substituted
-tricyanovinylation has been reported to
properties, which mainly originate from their donor-acceptor
substitution, they can be utilized as dyes with strong NLO
characteristics.2
Replacing the NH group of the pyrrole ring with another sub-
stituent prevents the formation of intra- and intermolecular hy-
drogen bonding, which influences the macroscopic structures and
NLO properties. Some of these molecules, e.g., 3-, 4- or 5-tricya-
novinyl-1-(alkyl)aryl-2-(20-thienyl)pyrroles, have proven to be
prospective monomers for manufacture of semi-conductors or
materials with the pronounced NLO properties.2
a
a
b
pyrroles, both
take place.2–4
a- and b
With 1-vinylpyrroles, the [2þ2]-cycloaddition of TCNE to the
exocyclic double bond is also possible. Indeed, such a cycloaddition
was observed as the only example in the pyrrole series for 1-vinyl-
4,5,6,7-tetrahydroindole, which gave the corresponding 3-(4,5,6,7-
tetrahydroindol-1-yl)-1,1,2,2-cyclobutanetetracarbonitrile.5
In contrast, 1-vinyl- and 1-isopropenyl-2-methyl-4,5,6,7-tetra-
The alternative products of the tricyanovinylation of 1-vinyl-
pyrroles, the corresponding [2þ2]-cycloadducts at the vinyl group,
are also intriguing compounds (intermediates, monomers, and
charge-transfer molecules).
hydroindoles reacted with TCNE exclusively at the free b-position
to deliver the corresponding 3-tricyanovinyl derivatives with the
vinyl (isopropenyl) group intact.1c The attempted [2þ2]-cycload-
dition of TCNE to 1-vinyl-4,5,6,7-tetrahydro-4,5,7-trime-
thylpyrrolo[3,2-c]pyridine led only to tricyanovinylation of the
azine ring.6
Meanwhile, vinylpyrroles bearing the double bond conjugated
to the pyrrole ring represent an important heterocyclic class. They
are building blocks for the construction of indoles via Diels–Alder
reaction,7 as well as active bifunctional monomers for the design of
conducting and NLO materials.8
2. Results and discussion
In this work, we have studied the direct tricyanovinylation of 1-
vinyl-2-arylpyrroles 1a–e with TCNE to gain a better understanding
of both chemo- and regioselectivity of the reaction and to develop
expedient syntheses of new building blocks and monomers of the
pyrrole series.
As shown by the experiments in acetone, THF, and benzene, 1-
vinylpyrroles 1a–e reacted with TCNE (rt, 1 h) chemoselectively to
form only the [2þ2]-cycloadducts 2a–e. We have failed to detect any
side products (1H NMR). The cycloadducts 2a–e upon refluxing from
EtOH (78 ꢀC, 15 min) eliminated HCN and entirely stereospecifically
rearranged to afford butadiene derivatives, trans-(3E)-4-(2-arylpyr-
rol-1-yl)-1,3-butadiene-1,1,2-tricarbonitriles 3a–e (Table 1). In
Introduction of the tricyanovinyl substituent in the pyrrole ring
provides compounds of interest both as molecules possessing high
* Corresponding author. Tel.: þ7 3952 461411/511431; fax: þ7 3952 419346.
E-mail address: boris_trofimov@irioch.irk.ru (B.A. Trofimov).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.03.094

B.A. Trofimov et al. / Tetrahedron 65 (2009) 4326–4331
4327
Table 1
Table 2
Reaction of 2-aryl-1-vinylpyrroles 1a–e with TCNE in acetonea
Reaction of 2-aryl-1-vinylpyrroles 1a–c with TCNE in DMSOa
R
R
TCNE
R
+
+
Ar
Ar
N
Ar
N
TCNE
EtOH
78 °C
N
Ar
CN
CN
CN
CN
Ar
N
Ar
N
N
r.t., 1 h
CN
CN
CN
CN
2a-e
CN
CN
1a-c
2a-c
NC
CN
CN
NC
NC
Ar
3a-c
NC
3a-e
1a-e
CN
CN
CN
+
+
Ar
Entry 2-Aryl-1-vinylpyrrole 1
Product 2 (yield, %)
Product 3 (yield, %)
N
N
NC
Ph
N
5a-c
4a-c
Ph
N
Ph
N
NC
1
NC
CN
Pyrrole
Ar
T, ꢀC
Composition of reaction mixture, %
NC
NC
1
2
3
4
5
CN
3a (95%)
CN
2a (89%)b,c
1a
1a
1b
1c
Ph
20
45
20
45
20
45
14
9
20
19
13
0
43
35
48
33
15
0
1
18
1
15
0
9
22
22
16
18
46
63
20
16
15
15
26
29
4-BrC6H4
4-MeOC6H4
4-BrC6H4
NC
N
4-BrC6H4
N
a
4-BrC6H4
The reactions time was 1 h.
N
NC
2
CN
NC
NC
CN
3b (92%)
CN
1b
2b (92%)
3-anisyl-cyclobutane-1,1,2,2-tetracarbonitrile in methanol, but un-
der heating in dioxane, acetonitrile, or benzene solution, the reaction
does not occur.11
4-MeOC6H4
NC
N
In DMSO, the chemo- and regioselectivity of the reaction was
breached. As well as the [2þ2]-cycloaddition products, cyclo-
butanes 2a–e, and butadienes 3a–e, the tricyanovinylation of the
4-MeOC6H4
N
4-MeOC6H4
N
NC
NC
NC
3
CN
pyrrole ring on both a- and b-position occurred to give pyrroles 5a–
CN
d and 4a–c (Tables 2 and 3). In the case of 2-aryl-1-vinylpyrroles
1a–c, 3- and 5-tricyanovinyl-1-vinylpyrroles 4a–c and 5a–c were
simultaneously formed, the product ratio was determined by the
substituents’ (Ar) structure and the reaction conditions (Table 2).
[2þ2]-Cycloaddition at the vinyl group in tricyanovinylpyrroles 4
and 5 is not observed due to a very strong deactivating effect of the
tricyanovinyl group.
As seen from Table 2, at room temperature pyrrole 1a and
pyrrole 1b gave all four products in a close ratio; at 45 ꢀC the
content of butadienes 3a,b increased (from 1% to 15–18%) due to
the above cyclobutanes 2a,b rearrangement. In the case of 2-(4-
methoxyphenyl)-1-vinylpyrrole 1c, tricyanovinylation of the 3-
annular position turned out to be a major reaction (the content of
1c
CN
3c (89%)
2c (94%)
Pr
Pr
Ph
Ph
Pr
N
N
NC
Ph
4
N
NC
CN
NC
NC
CN
CN
1d
2d (88%)
3d (78%)
C7H15
C7H15
Ph
C7H15
Ph
Ph
N
N
Table 3
NC
Reaction of 2-aryl-1-vinylpyrroles 1d,e with TCNE in DMSOa
5
N
NC
NC
R
R
CN
2e (88%)
R
NC
R
CN
1e
TCNE
CN
CN
CN
+
Ph
+
Ph
N
Ph
N
Ph
3e (71%)
N
N
CN
CN
CN
CN
a
All reactions were performed at rt for 1 h.
NC
b Yield of 2a in THF is 85%.
CN
CN
1d,e
NC
3d,e
2d,e
5d
c Yield of 2a in benzene is 42%.
Pyrrole
R
T, ꢀC
Composition of reaction
mixture, %
contrast, recrystallization from CHCl3 allowed the cyclobutanes 2a–e
to be recovered unchanged. Alcohols as proton donors seem to be
essential for the ring cleavage reaction. This is also supported by the
literature data. For example, the cyclobutane ring opening in 3-
(indol-1-yl)9 and 3-(isopropylpyrazol-4-yl)10-cyclobutane-1,1,2,2-
tetracarbonitriles proceeds only in methanol9,10 or aqueous
acetonitrile.9 4-Anisyl-1,1,2-tricyano-1,3-butadiene is formed from
1
2
3
5
1d
n-Pr
20
45
20
2
0
0
76
26
2
19
62
98
4
12
0
1e
n-C7H15
a
The reactions time was 1 h.

4328
B.A. Trofimov et al. / Tetrahedron 65 (2009) 4326–4331
3-tricyanovinylated product 4c increased up to 46% at rt and 63% at
45 ꢀC) and the tricyanovinylation position 5 became almost two
times faster (the content of 5c increased from 16 to 26%), conse-
quently the content of the corresponding cyclobutane 2c and bu-
tadiene 3c dropped (Table 2).
NC
NC
NC
Ar
-
CN
CN
CN
-
.
NC
NC
CN
CN
NC
Ar
.
+
+
N
Ar
- HCN
N
N
Even more dramatic was the effect of alkyl substituents in the 3-
position of the pyrrole ring. 2-Phenyl-3-propyl-1-vinylpyrrole 1d at
4
rt was tricyanovinylated almost negligibly to afford just 4% of a-
Scheme 3.
tricyanovinylated product 5d; at 45 ꢀC its content increased to 12%
(Table 3). The main reaction in this case became [2þ2]-cycloaddi-
tion delivering cyclobutane 2d (76% at rt and 26% at 45 ꢀC) together
with its rearrangement product 3d (19% at rt and 62% at 45 ꢀC),
Table 3.
Amazingly, in the case of 3-heptyl-2-phenyl-1-vinylpyrrole 1e
no products of tricyanovinylation of the pyrrole ring at rt were
observed and the major product was almost exclusively butadiene
3e (98%), Table 3.
Thus, tricyanovinylation of 3-alkyl-2-aryl-1-vinylpyrroles was
strongly controlled by the solvent and the substituent nature. To
rationalize these phenomena, let us consider the primary in-
termediate of the reaction, the ion–radical pair 6 formed by the
charge-transfer from the pyrrole moiety to TCNE (such a mecha-
nism for the tricyanovinylation of the pyrrole ring has been
established by the ESR spectroscopic study)1a (Scheme 1). For the
[2þ2]-cycloaddition of TCNE to the vinyl group, the above single
electron transfer is less probable since a double bond is not as
1c (the positive charge transfer onto the methoxy group). This
approach explained why in DMSO tricyanovinylation of the
pyrrole nucleus occurred and why the reaction was not chemo-
and regioselective. When an alkyl substituent was located at the
position 3, the coplanarity of the benzene and pyrrole rings was
distorted and hence the stabilization of the pyrrole radical–cat-
ion was minimized. Consequently, the pyrrole ring lost its nu-
cleophilicity and therefore the [2þ2]-cycloaddition across the
vinyl group remained more favorable reaction. The higher pref-
erence of the [2þ2]-cycloaddition for R¼C7H15 having the greater
steric hindrance than C3H7 was in agreement with this
rationalization.
3. Conclusions
The reaction of 2-aryl- and 2-aryl-3-alkyl-1-vinylpyrroles with
TCNE allows 3- and 5-tricyanovinyl-1-vinylpyrroles, pyrrol-1-yl-
cyclobutanetetracarbonitriles, and pyrrol-1-ylbutadienetricarbo-
nitriles to be synthesized. The latter two series can be prepared
chemo-, regio-, and stereospecifically – (E-isomers for butadiene)
in high yields. The chemo- and regioselectivity of the reaction
(tricyanovinylation of pyrrole ring vs [2þ2]-cycloaddition to the
vinyl group) depends strongly on the solvent and the pyrrole sub-
stituents’ nature and can be controlled by their variation. The novel
series of functionalized pyrroles are promising precursors for de-
sign of conducting and NLO materials.
strong p-donor as a pyrrole moiety.
R
R
NC
NC
CN
CN
TCNE
Ar
Ar
N
N
6
Scheme 1.
4. Experimental section
4.1. General information
In DMSO, the pyrrole radical–cation is more stabilized than in
less polar solvents such as acetone, THF, and benzene, and hence
tricyanovinylation of the pyrrole ring in this solvent should be more
feasible (as observed in experiment). Consequently thermody-
namically favored tricyanovinylation of the pyrrole ring results
from the solvent stabilization of the intermediate 6. Conversely, the
[2þ2]-cycloaddition with the vinyl group is the kinetically pre-
ferred route in acetone.
The positive charge of the pyrrole radical–cation was distributed
between positions 2 and 5. The 2-position was preferable owing to
the aryl substituents’ participation in the positive charge distribu-
tion (a benzyl type cation), Scheme 2.
IR spectra were obtained in KBr pellets. 1H and 13C NMR
spectra were recorded at 400.13 MHz and 101.6 MHz, respectively.
The concerted application of 1H–1H 2D homonuclear experiments
COSY and NOESY and also 1H–13C 2D heteronuclear experiments
HSQC and HMBC were used for the distinction of the carbon and
proton resonances in all cases. The reaction was monitored by TLC
on ‘Silufol UV254’ plates (hexane/diethyl ether, 2:1) and by 1H
NMR (CDCl3). Fractionation of reaction mixtures was performed
by column chromatography (silica, hexane/diethyl ether, 1:1 and
2:1).
Alk
Alk
Alk
Ar
Alk
.
2-Aryl-1-vinylpyrroles 1a–e were prepared from oximes and
.
+
.
.
acetylene by Trofimov reaction.12
+
+
+
Ar
Ar
Ar
N
N
N
N
4.2. Reaction of 2-aryl-1-vinylpyrroles 1a–e with TCNE in
acetone (general procedure)
Scheme 2.
TCNE (128 mg,1 mmol) was added to a solution of pyrroles 1a–e
(1.1 mmol) in acetone (5 mL) at room temperature. Instantly the
solution turned blue and in 10 min it became red. The reaction
mixture was stirred for 1 h, and then acetone was removed in
vacuum. Grayish or light-beige powder, which was left after re-
moving acetone, was washed with hexane to delete unreacted
pyrroles 1a–e and to give 3-(2-arylpyrrol-1-yl)-1,1,2,2-cyclobuta-
netetracarbonitriles 2a–e.
Consequently, positions 3 and 5, where a larger spin density was
concentrated, were most favorable for the attack by the radical
center of TCNE radical–anion, e.g., as is depicted in Scheme 3 for
position 3 (Scheme 3).
The largest yield of the 3-tricyanovinylated 4c (46–63%, Table
2) was due to the stronger stabilization of the positive charge in
the 2-position of the radical–cation originated from the pyrrole

B.A. Trofimov et al. / Tetrahedron 65 (2009) 4326–4331
4329
4.2.1. 3-(2-Phenyl-1H-pyrrol-1-yl)-1,1,2,2-
2H, CH2), 1.46 (m, 2H, CH2), 1.19 (m, 8H, CH2), 0.84 (t, J¼6.6 Hz, 3H,
CH3); dC (101.6 MHz, CDCl3) 132.0 (C2), 131.4 (C1 Ph), 131.1 (C3,5 Ph),
129.9 (C4 Ph), 129.4 (C2,6 Ph), 126.3 (C3), 117.1 (C5), 112.6 (C4), 110.1
(CN), 109.7 (CN), 108.5 (CN), 107.9 (CN), 55.3 [CH], 46.9 [CHC(CN)2],
38.8 [CH2C(CN)2], 31.8 (CH2), 30.8 [CH2C(CN)2], 29.3, 29.1, 25.9, 22.7
(CH2), 14.1 (CH3).
cyclobutanetetracarbonitrile, 2a
Yield 264 mg (89%) as light-beige solid, mp¼159–160 ꢀC (chlo-
roform). [Found: C, 72.58; H, 3.64; N, 23.21. C18H11N5 requires C,
72.72; H, 3.73; N, 23.56%.] nmax (KBr) 2257 cmꢁ1
; dH (400.13 MHz,
CDCl3) 7.50 (m, 1H, CH4 Ph), 7.48 (m, 2H, CH3,5 Ph), 7.34 (m, 2H,
CH2,6 Ph), 7.06 (dd, J¼3.3, 1.5 Hz, 1H, H5), 6.43 (dd, J¼3.8, 3.3 Hz, 1H,
H4), 6.34 (dd, J¼3.8, 1.5 Hz, 1H, H3), 5.48 (dd, J¼11.1, 8.6 Hz, 1H, CH),
3.70 (dd, J¼13.1, 11.1 Hz, 1H, CH2), 3.48 (dd, J¼13.1, 8.6 Hz, 1H, CH2);
dC (101.6 MHz, CDCl3) 135.8 (C2), 130.4 (C1 Ph), 129.9 (C2,6 Ph), 129.5
(C3,5 Ph), 129.4 (C4 Ph), 118.4 (C5), 112.4 (C4), 112.2 (C3), 110.0 (CN),
109.5 (CN), 108.5 (CN), 107.8 (CN), 54.9 (CH), 47.0 [CHC(CN)2], 39.3
(CH2), 31.0 [CH2C(CN)2].
4.3. Synthesis of (3E)-4-(2-aryl-1H-pyrrol-1-yl)-1,3-
butadiene-1,1,2-tricarbonitriles 3a–e
3-(2-Arylpyrrol-1-yl)-1,1,2,2-cyclobutanetetracarbonitriles 2a–e
(150 mg) were refluxed in ethanol (10 mL) for 15 min. After cooling
to room temperature pyrroles 3a–e were filtered off.
4.2.2. 3-(2-(4-Bromophenyl)-1H-pyrrol-1-yl)-1,1,2,2-
cyclobutanetetracarbonitrile, 2b
4.3.1. (3E)-4-(2-Phenyl-1H-pyrrol-1-yl)-1,3-butadiene-1,1,2-
tricarbonitrile, 3a
Yield 345 mg (92%) as beige crystals, mp¼179–180 ꢀC (chloro-
form). [Found: C, 57.11; H, 2.38; Br, 20.84; N, 18.26. C18H10BrN5
requires C, 57.47; H, 2.68; Br, 21.24; N, 18.62%.] nmax (KBr)
2258 cmꢁ1 (CN); dH (400.13 MHz, CDCl3) 7.49 (d, J¼8.2 Hz, 2H, CH3,5
Ar), 7.34 (d, J¼8.2 Hz, 2H, CH2,6 Ar), 7.06 (dd, J¼3.3, 1.5 Hz, 1H, H5),
6.43 (dd, J¼3.8, 3.3 Hz, 1H, H4), 6.33 (dd, J¼3.8, 1.5 Hz, 1H, H3), 5.48
(dd, J¼11.1, 7.2 Hz, 1H, CH), 3.70 (dd, J¼13.1, 11.1 Hz, 1H, CH2), 3.48
(dd, J¼13.1, 7.2 Hz, 1H, CH2); dC (101.6 MHz, CDCl3) 133.3 (C2), 132.4
(C2,6 Ar), 131.9 (C3,5 Ar), 130.9 (C1 Ar), 122.3 (C4 Ar), 121.8 (C5), 112.7
(C3), 112.4 (CN), 112.2 (CN), 110.7 (C4), 110.6 (CN), 109.4 (CN), 55.2
(CH), 46.3 [CHC(CN)2], 37.1 (CH2), 32.4 [CH2C(CN)2].
Yield 129 mg (95%) as bright-yellow crystals, mp¼236 ꢀC.
[Found: C, 75.37; H, 3.73; N, 20.56. C17H10N4 requires C, 75.54;
H, 3.73; N, 20.73%.] nmax (KBr) 2218, 2231 cmꢁ1 (CN); dH
(400.13 MHz, CDCl3) 7.98 (d, J¼13.4 Hz, 1H, NCH]CH–), 7.50 (m,
3H, CH3,4,5 Ph), 7.33 (m, 2H, CH2,6 Ph), 7.25 (dd, J¼3.3, 1.5 Hz, 1H,
H5), 6.72 (d, J¼13.4 Hz, 1H, NCH]CH–), 6.56 (dd, J¼3.8, 3.3 Hz, 1H,
H4), 6.44 (dd, J¼3.8, 1.5 Hz, 1H, H3); dC NMR (101.6 MHz, DMSO-d6)
143.5 (NCH]), 139.8 [(CN)C]], 136.3 (C2), 129.6 (C1 Ph), 129.5
(C2,6 Ph), 128.9 (C3,5 Ph), 128.6 (C4 Ph), 121.2 (C5), 115.4 (C3), 114.5
(C4), 112.7 (CN), 112.2 (CN), 111.0 (CN), 106.8 (NCH]CH), 84.2
[C(CN)2].
4.2.3. 3-[2-(4-Methoxyphenyl)-1H-pyrrol-1-yl]-1,1,2,2-
cyclobutanetetracarbonitrile, 2c
4.3.2. (3E)-4-[2-(4-Bromophenyl)-1H-pyrrol-1-yl]-1,3-butadiene-
1,1,2-tricarbonitrile, 3b
Yield 307 mg (94%) as beige crystals, mp¼144–145 ꢀC (chloro-
form). [Found: C, 70.03; H, 3.79; N, 21.56. C19H13N5O requires C,
69.71; H, 4.00; Br, 21.24; N, 18.62%.] nmax (KBr) 2255 cmꢁ1 (CN); dH
(400.13 MHz, acetone-d6) 7.50 (dd, J¼3.3, 1.5 Hz, 1H, H5), 7.41 (d,
J¼8.4 Hz, 2H, CH2,6 Ar), 7.07 (d, J¼8.4 Hz, 2H, CH3,5 Ar), 6.37 (dd,
J¼3.8, 3.3 Hz, 1H, H4), 6.27 (dd, J¼3.8, 1.5 Hz, 1H, H3), 5.96
(dd, J¼10.8, 9.3 Hz, 1H, CH), 4.33 (dd, J¼13.7, 10.8 Hz, 1H, CH2), 4.03
(dd, J¼13.7, 9.3 Hz, 1H, CH2), 3.88 (s, 3H, MeO); dC NMR (101.6 MHz,
acetone-d6) 161.1 (C4 Ar), 135.7 (C2), 132.1 (C2,6 Ar), 124.4 (C1 Ar),
120.2 (C5), 115.2 (C3,5 Ar), 112.3 (CN), 112.1 (CN, C4), 111.3 (C3), 110.7
(CN), 109.7 (CN), 56.2 (MeO), 55.7 (CH), 47.4 [CHC(CN)2], 38.9 (CH2),
32.8 [CH2C(CN)2].
Yield 128 mg (92%) as bright-yellow crystals, mp¼252 ꢀC.
[Found C, 58.37; H, 2.54; Br, 22.48; N, 16.36. C17H9BrN4 requires C,
58.47; H, 2.60; Br, 22.88; N, 16.05%.] nmax (KBr) 2218, 2231 cmꢁ1
(CN); dH (400.13 MHz, CDCl3) 7.90 (d, J¼13.4 Hz, 1H, NCH]CH–),
7.62 (d, J¼8.0 Hz, 2H, CH3,5 Ar), 7.25 (dd, J¼3.3, 1.5 Hz, 1H, H5), 7.19
(d, J¼8.0 Hz, 2H, CH2,6 Ar), 6.73 (d, J¼13.4 Hz, 1H, NCH]CH–), 6.54
(dd, J¼3.8, 3.3 Hz, 1H, H4), 6.43 (dd, J¼3.8, 1.5 Hz, 1H, H3); dC
(101.6 MHz, CDCl3) 144.0 (NCH]), 140.3 [(CN)C]], 135.6 (C2), 132.4
(C3,5 Ar), 131.9 (C2,6 Ar), 129.6 (C1 Ar), 122.6 (C4 Ar), 122.3 (C5), 115.9
(C3), 115.6 (C4), 113.3 (CN), 112.8 (CN), 111.6 (CN), 107.6 (NCH]CH),
85.1 [C(CN)2].
4.2.4. 3-(2-Phenyl-3-propyl-1H-pyrrol-1-yl)-1,1,2,2-
4.3.3. (3E)-4-[2-(4-Methoxyphenyl)-1H-pyrrol-1-yl]-1,3-
cyclobutanetetracarbonitrile, 2d
butadiene-1,1,2-tricarbonitrile, 3c
Yield 299 mg (88%) as beige solid, mp¼131–132 ꢀC. [Found: C,
74.60; H, 5.30; N, 21.56. C21H17N5 requires C, 74.32; H, 5.05; N,
20.63%.] nmax (KBr) 2256 cmꢁ1 (CN); dH (400.13 MHz, CDCl3) 7.51
(m, 2H, CH3,5 Ph), 7.52 (m, 1H, CH4 Ph), 7.27 (m, 2H, CH2,6 Ph), 6.94
(d, J¼3.1 Hz, 1H, H5), 6.32 (d, J¼3.1 Hz, 1H, H4), 5.28 (dd, J¼11.7,
9.0 Hz, 1H, CH), 3.68 (dd, J¼13.3, 11.7 Hz, 1H, CH2), 3.42 (dd, J¼13.3,
9.0 Hz, 1H, CH2), 2.30 (m, 2H, CH2Et), 1.51 (m, 2H, CH2CH3), 0.84 (t,
J¼6.6 Hz, 3H, CH3); dC (101.6 MHz, CDCl3) 131.7 (C2), 131.1 (C1, C3,5
Ph), 130.0 (C4 Ph), 129.4 (C2,6 Ph), 126.1 (C3), 117.2 (C5), 112.6 (C4),
110.3 (CN), 109.7 (CN), 108.6 (CN), 108.0 (CN), 55.4 [CH], 47.0
[CHC(CN)2], 38.8 [CH2], 31.0 [CH2C(CN)2], 28.1 (EtCH2), 24.0
(CH3CH2), 14.0 (CH3).
Yield 122 mg (89%) as bright-yellow crystals, mp¼238–239 ꢀC.
[Found: C, 71.67; H, 3.87; N, 18.44. C18H12N4O requires C, 71.99; H,
4.03; N, 18.66%.] nmax (KBr) 2233, 2211 cmꢁ1 (CN); dH NMR
(400.13 MHz, CDCl3) 7.94 (d, J¼13.7 Hz, 1H, NCH]CH–), 7.23 (m,
3H, CH2,6 Ar, H5), 7.01 (d, J¼8.4 Hz, 2H, CH3,5 Ar), 6.71 (d, J¼13.7 Hz,
1H, NCH]CH–), 6.52 (dd, J¼3.8, 3.3 Hz, 1H, H4), 6.36 (dd, J¼3.8,
1.5 Hz, 1H, H3), 3.85 (s, 3H, MeO). The 13C NMR spectra of 3c were
failed to be recorded due to low solubility of the compound in
CDCl3 and acetone. In DMSO-d6 compound 3c was decomposed.
4.3.4. (3E)-4-(2-Phenyl-3-propyl-1H-pyrrol-1-yl)-1,3-butadiene-
1,1,2-tricarbonitrile, 3d
Yield 107 mg (78%) as bright-red crystals, mp¼137 ꢀC. [Found: C,
76.58; H, 5.30; N, 17.56. C20H16N4 requires C, 76.90; H, 5.16; N,
17.94%.] nmax (KBr) 2228, 2220 cmꢁ1 (CN); dH (400.13 MHz, CDCl3)
7.94 (d, J¼2.9 Hz, 1H, H5), 7.70 (d, J¼13.6 Hz, 1H, NCH]CH–), 7.53
(m, 3H, CH3,4,5 Ph), 7.36 (m, 2H, CH2,6 Ph), 6.98 (d, J¼13.6 Hz, 1H,
NCH]CH–), 6.57 (d, J¼2.9 Hz, 1H, H4), 2.31 (m, 2H, CH2Et), 1.50 (m,
2H, CH2CH3), 0.81 (t, J¼6.7 Hz, 3H, CH3); dC (101.6 MHz, CDCl3)
143.2 (NCH]), 139.0 [(CN)C]],131.9 (C2), 130.5 (C2,6 Ph), 128.7 (C3),
128.6 (C4 Ph), 128.4 (C3,5 Ph), 128.1 (C1 Ph), 118.4 (C5), 117.2 (C4),
4.2.5. 3-(2-Phenyl-3-heptyl-1H-pyrrol-1-yl)-1,1,2,2-
cyclobutanetetracarbonitrile, 2e
Yield 348 mg (88%) as beige solids, mp¼119–120 ꢀC. [Found: C,
75.70; H, 6.30; N, 17.54. C25H25N5 requires C, 75.92; H, 6.37; N,
17.71%.] nmax (KBr) 2261 cmꢁ1 (CN); dH (400.13 MHz, CDCl3) 7.49 (m,
3H, CH3,4,5 Ph), 7.26 (m, 2H, CH2,6 Ph), 6.96 (d, J¼3.0 Hz,1H, H5), 6.31
(d, J¼3.0 Hz, 1H, H4), 5.30 (dd, J¼11.5, 8.8 Hz, 1H, CH), 3.71 (dd,
J¼12.8, 11.5 Hz, 1H, CH2), 3.46 (dd, J¼12.8, 8.8 Hz, 1H, CH2), 2.32 (m,

4330
B.A. Trofimov et al. / Tetrahedron 65 (2009) 4326–4331
112.9 (CN), 112.2 (CN), 111.3 (CN), 105.0 (NCH]CH), 81.8 [C(CN)2],
27.5, 22.7 (CH2), 13.7 (CH3).
4.4.3. 2-[2-(4-Bromophenyl)-1-vinyl-1H-pyrrol-3-yl]-1,1,2-
ethylentricarbonitrile, 4b
Yield 49 mg (7%) as yellow crystals, mp¼175 ꢀC. [Found: C,
58.74; H, 2.81; Br, 22.53; N, 15.65. C17H9BrN4 requires C, 58.47; H,
2.60; Br, 22.88; N, 16.05%.] nmax (KBr) 2217 cmꢁ1 (CN); dH
(400.13 MHz, CDCl3) 7.67 (d, J¼8.4 Hz, 2H, CH3,5 Ar), 7.23 (m, 2H, H4,5),
7.19 (d, J¼8.4 Hz, 2H, CH2,6 Ar), 6.58 (dd, JHx, HA¼15.6 Hz, JHx, HB¼9.0 Hz,
1H, Hx), 5.38 (dd, JHx, HA¼15.6 Hz, JHA, HB¼2.0 Hz, 1H, HA), 4.97 (dd,
4.3.5. (3E)-4-(2-Phenyl-3-heptyl-1H-pyrrol-1-yl)-1,3-butadiene-
1,1,2-tricarbonitrile, 3e
Yield 99 mg (71%) as bright-red crystals, mp¼137 ꢀC. [Found:
C, 78.29; H, 6.53; N, 15.04. C24H24N4 requires C, 78.23; H, 6.57; N,
15.21%.] nmax (KBr) 2226 cmꢁ1 (CN); dH (400.13 MHz, CDCl3) 7.73
(d, J¼13.6 Hz, 1H, NCH]CH–), 7.49 (m, 2H, CH2,6 Ph), 7.20 (m, 3H,
CH3,4,5 Ph), 7.16 (d, J¼3.5 Hz, 1H, H5), 6.60 (d, J¼13.6 Hz, 1H,
NCH]CH–), 6.47 (d, J¼3.5 Hz, 1H, H4), 2.36 (m, 2H, CH2), 1.49 (m,
2H, CH2), 1.20 (m, 8H, CH2), 0.84 (t, J¼6.6 Hz, 3H, CH3); dC
(101.6 MHz, CDCl3) 143.5 (NCH]), 139.5 [(CN)C]], 132.8 (C2),
131.1 (C2,6 Ph), 129.8 (C3), 129.5 (C4 Ph), 129.2 (C3,5 Ph), 128.7 (C1
Ph), 118.1 (C5, C4), 111.8 (CN), 111.4 (CN), 111.1 (CN), 105.3
(NCH]CH), 83.1 [C(CN)2], 31.8 (CH2), 30.2, 29.2, 29.0, 26.0, 22.7
(CH2), 14.1 (CH3).
JHB Hx
,
¼9.0 Hz, JHB, HA¼2.0 Hz,1H, HB); dC (101.6 MHz, CDCl3) 139.8 (C2),
134.5 [(CN)C]], 132.8 (C3,5 Ar), 132.6 (C2,6 Ar), 129.5 (NCH]CH2), 126.1
(C1,4 Ar), 120.9 (C5), 116.0 (C3), 112.6 (CN), 112.4 (CN), 112.3 (CN), 110.6
(C4), 105.4 (CH2]C), 85.9 []C(CN)2].
4.4.4. 2-[2-(4-Bromophenyl)-1-vinyl-1H-pyrrol-5-yl]-1,1,2-
ethylentricarbonitrile, 5b
Yield 42 mg (6%) as red crystals, mp¼163 ꢀC. [Found: C, 58.62; H,
2.71; Br, 23.09; N, 16.15. C17H9BrN4 requires C, 58.47; H, 2.60; Br,
22.88; N, 16.05%.] nmax (KBr) 2219 cmꢁ1 (CN); dH (400.13 MHz,
CDCl3) 7.58 (d, J¼8.8 Hz, 2H, CH3,5 Ar), 7.54 (d, J¼4.5 Hz,1H, H4), 7.31
(d, J¼8.8 Hz, 2H, CH2,6 Ar), 7.02 (dd, JHx, HA¼15.4 Hz, JHx, HB¼8.1 Hz,
4.4. Reaction of pyrroles 1a–e with TCNE in DMSO
A. A solution of TCNE (12.8 mg, 0.1 mmol) in DMSO-d6 (0.3 mL)
was added to a solution of pyrroles 1a–e (0.1 mmol) in DMSO-d6
(0.2 mL) and the resulting mixture was stirred for 1 h at 20 ꢀC or
45 ꢀC. Then the sample was taken, diluted with CDCl3, and analyzed
by 1H NMR.
1H, Hx), 6.58 (d, J¼4.5 Hz, 1H, H3), 5.58 (dd, JHB,
¼8.1 Hz,
Hx
JHB, HA¼1.2 Hz, 1H, HB), 5.20 (dd, JHA, Hx¼15.4 Hz, JHA, HB¼1.2 Hz, 1H,
HA); dC (101.6 MHz, CDCl3) 146.0 (C2),132.4 (C3,5 Ar),130.8 (NCH]CH2),
130.7 (C2,6 Ar), 128.6 (C1 Ar), 128.5 [(CN)C¼], 126.6 (C5), 124.6 (C4 Ar),
124.3 (C4), 120.3 (CH2]C), 114.7 (C3), 113.01 (CN), 112.98 (CN), 112.4
(CN), 83.4 []C(CN)2].
B. A solution of TCNE (256 mg, 2 mmol) in DMSO (4 mL) was
added to a solution of pyrroles 1a–e (2 mmol) in DMSO (6 mL) at
room temperature. The reaction mixture was stirred at 45 ꢀC for
3 h and diluted with water. The products were isolated from the
reaction mixture using the extraction by CH2Cl2. The extracts
were washed with water and dried over MgSO4. The residue after
removing CH2Cl2 was purified by flash chromatography, eluted
with hexane and then with diethyl ether. The ether extracts were
concentrated and fractionated on column (SiO2, l¼60 cm, hexane/
diethyl ether, 1:1) to isolate consequently pyrroles 5a–d, pyrroles
4a–d and pyrroles 3a–d. Pyrroles 5a–d in pure state were
obtained after second chromatography of the first fraction (SiO2,
l¼30 cm, hexane/diethyl ether, 2:1). Pyrroles 4a–d and 3a–d were
purified additionally by washing with mixture of hexane and
diethyl ether, 1:1.
4.4.5. 2-[2-(4-Methoxyphenyl)-1-vinyl-1H-pyrrol-3-yl]-1,1,2-
ethylentricarbonitrile, 4c
Yield 48 mg (8%) as yellow crystals, mp¼160 ꢀC. [Found: C,
72.18; H, 3.85; N, 18.54. C18H12N4O requires C, 71.99; H, 4.03; N,
18.66%.] nmax (KBr) 2220 cmꢁ1 (CN); dH (400.13 MHz, CDCl3): 7.24–7.19
(m, 4H, CH2,6 Ar, H4,5), 7.01 (m, 2H, CH3,5 Ar), 6.65 (dd, JHx, HA¼15.7 Hz,
JHx, HB¼9.0 Hz, 1H, Hx), 5.35 (dd, JHA, Hx¼15.7 Hz, JHA, HB¼1.8 Hz, 1H,
HA), 4.95 (dd, JHB, Hx¼9.0 Hz, JHB, HA¼1.8 Hz, 1H, HB), 3.86 (s, 3H, MeO);
dC (101.6 MHz, CDCl3) 162.0 (C4 Ar), 141.8 (C2), 135.0 [(CN)C]], 132.9
(C2,6 Ar), 129.9 (NCH]CH2), 120.4 (C5), 119.0 (C1 Ar), 116.2 (C3), 114.8
(C3,5 Ar), 113.0 (CN), 112.6 (CN), 112.5 (CN), 110.4 (C4), 104.4 (CH2]C),
84.9 []C(CN)2], 55.5 (OMe).
4.4.6. 2-[2-(4-Methoxyphenyl)-1-vinyl-1H-pyrrol-5-yl]-1,1,2-
ethylentricarbonitrile, 5c
4.4.1. 2-(2-Phenyl-1-vinyl-1H-pyrrol-3-yl)-1,1,2-
ethylentricarbonitrile, 4a
Yield 42 mg (7%) as red crystals, mp¼155 ꢀC. [Found: C, 72.18; H,
3.85; N, 18.54. C18H12N4O requires C, 71.99; H, 4.03; N, 18.66%.] nmax
(KBr): 2214 cmꢁ1 (CN); dH (400.13 MHz, CDCl3) 7.58 (d, J¼4.4 Hz,
1H, H4), 7.39 (d, J¼8.8 Hz, 2H, CH2,6 Ar), 7.08 (dd, JHx, HA¼15.2 Hz,
JHx, HB¼7.9 Hz, 1H, Hx), 6.97 (d, J¼8.8 Hz, 2H, CH3,5 Ar), 6.55 (d, 1H,
J¼4.4 Hz, H3), 5.55 (dd, JHB, Hx¼7.9 Hz, JHB, HA¼1.5 Hz, 1H, HB), 5.18
(dd, JHA, Hx¼15.2 Hz, JHA, HB¼1.5 Hz, 1H, HA), 3.85 (s, 3H, MeO); dC
(101.6 MHz, CDCl3) 161.0 (C4 Ar),148.1 (C2), 131.2 (NCH]CH2), 130.7
(C2,6 Ar), 127.7 (C5), 126.6 [(CN)C¼], 124.9 (C4), 121.8 (C1 Ar), 119.8
(CH2]C), 114.6 (C3,5 Ar), 114.5 (C3), 113.4 (CN), 113.2 (CN), 112.8
(CN), 80.8 []C(CN)2], 55.5 (OMe).
Yield 48 mg (9%) as yellow crystals, mp¼132–133 ꢀC. [Found: C,
75.39; H, 3.58; N, 20.81. C17H10N4 requires C, 75.54; H, 3.73; N,
20.73%.] nmax (KBr) 2219 cmꢁ1 (CN); dH (400.13 MHz, CDCl3) 7.58–
7.51 (m, 3H, CH3,4,5 Ph), 7.30 (m, 2H, CH2,6 Ph), 7.22 (m, 2H, H4,5),
6.63 (dd, JHx
,
¼15.9 Hz, JHx,
¼8.8 Hz, 1H, Hx), 5.39 (dd, JHA,
HA
HB
¼15.9 Hz, JHA, ¼1.7 Hz, 1H, HA), 4.96 (dd, JHB, ¼8.8 Hz, JHB
,
Hx
HB
Hx
¼1.7 Hz, 1H, HB); dC NMR (101.6 MHz, CDCl3) 141.5 (C2), 134.8
HA
[(CN)C]], 131.4 (C2,6 Ph), 131.2 (C4 Ph), 129.7 (NCH]CH2), 129.2
(C3,5 Ph), 127.2 (C1 Ph), 120.5 (C5), 116.0 (C3), 112.8 (CN), 112.5 (CN),
112.2 (CN), 110.4 (C4), 104.7 (CH2]C), 85.2 []C(CN)2].
4.4.2. 2-(2-Phenyl-1-vinyl-1H-pyrrol-5-yl)-1,1,2-
ethylentricarbonitrile, 5a
Acknowledgements
Yield: 38 mg (7%) as red crystals, mp¼101 ꢀC. [Found: C, 75.20;
H, 3.64; N, 20.41. C17H10N4 requires C, 75.54; H, 3.73; N, 20.73%.]
nmax (KBr) 2220 cmꢁ1 (CN); dH (400.13 MHz, CDCl3) 7.56 (d, J¼4.4 Hz,
1H, H4), 7.45 (m, 5H, Ph), 7.07 (dd, JHx, HA¼15.3 Hz, JHx, HB¼7.9 Hz,1H,
Hx), 6.59 (d, J¼4.4 Hz, 1H, H3), 5.56 (dd, JHB, Hx 7.9 Hz, JHB, HA¼1.5 Hz,
1H, HB), 5.18 (dd, JHA, Hx¼15.3 Hz, JHA, HB¼1.5 Hz, 1H, HA); dC NMR
(101.6 MHz, CDCl3) 147.7 (C2), 131.0 (NCH]CH2), 130.0 (C4 Ph), 129.6
(C1 Ph), 129.3 (C3,5 Ph), 129.0 (C2,6 Ph), 128.4 [(CN)C]], 126.4 (C5),
124.6 (C4), 119.8 (CH2]C), 114.7 (C3), 113.2 (CN), 113.1 (CN), 112.6
(CN), 82.4 []C(CN)2].
This work was supported by the Innovation Agency of the
Russian Federation (grant no. NSH-263.2008.3).
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