Synthesis of highly functionalized pyrrole derivatives via a four-component reaction of two primary amines and diketene in the presence of nitrostyrene

Article abstract of DOI:10.1055/s-2008-1032168

The one-pot synthesis of highly functionalized pyrrole derivatives from the reaction of an enaminone, which can be derived from the reaction between two primary amines and diketene, in the presence of nitrostyrene is described. The reaction occurred under neutral conditions and in excellent yields. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1032168

PAPER
725
Synthesis of Highly Functionalized Pyrrole Derivatives via a Four-Component
Reaction of Two Primary Amines and Diketene in the Presence of Nitrostyrene
Synthesis of
Highl
b
y Functional
d
ized
P
yrrole
o
D
erivatives lali Alizadeh,* Atieh Rezvanian, Hamid R. Bijanzadeh
Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran 18716, Iran
Fax +98(21)88006544; E-mail: abdol_alizad@yahoo.com; E-mail: aalizadeh@modares.ac.ir
Received 7 November 2007; revised 2 December 2007
In the context of our ongoing studies on heterocyclic con-
Abstract: The one-pot synthesis of highly functionalized pyrrole
derivatives from the reaction of an enaminone, which can be de-
rived from the reaction between two primary amines and diketene,
in the presence of nitrostyrene is described. The reaction occurred
under neutral conditions and in excellent yields.
struction mediated by the enaminone intermediate,23,24 the
possibility of trapping the intermediate formed between
two primary amines and diketene with nitrostyrene, ap-
peared attractive from the viewpoint of devising a novel
multicomponent reaction (MCR).
Key words: amine, diketene, enaminones, nitrostyrene, pyrrole,
multicomponent reaction
In the present work, we wish to report a novel one-pot,
four-component reaction between an enaminone, derived
from the addition of various primary amines to diketene,
and nitrostyrene, leading to highly functionalized 1H-pyr-
role-3-carboxamide derivatives 4.
N-Heterocycles receive considerable attention in the liter-
ature as a consequence of their exciting biological proper-
ties and their role as pharmacophores.1 Of these
heterocycles, the pyrrole ring is one of the most funda-
mental.2 Pyrrole and its derivatives are ubiquitous among
naturally occurring organic compounds.3 They can take
part in several stereoselective transformations, such as
conjugate additions,4 cycloadditions,5 acyliminium ion
chemistry,6 and allylic substitutions.7 The synthesis, reac-
tions and biological activities of pyrroles stand as an area
of research in heteroaromatic chemistry and this structural
motif appears in a large number of pharmaceutical agents
and natural products.8,9
The reaction of N-alkyl-3-oxobutanamide 5, which was
derived from the addition of a primary amine 1 to
diketene, with primary amine 2 in dichloromethane at am-
bient temperature, leads to enaminocarbonyl compound 6
(Scheme 1). Subsequently, reaction of these in situ pre-
pared enaminones 6 with nitrostyrene leads to pyrrole de-
rivatives 4 in 80–90% yields. (Table 1).
The structures of compounds 4a–g were deduced from
1
their elemental analysis, IR, and high-field H and 13C
NMR spectra. No products other than 4 could be detected.
The mass spectrum of 4a displayed the molecular ion
peak at m/z = 298, which is consistent with the 2,5-di-
methyl-4-phenyl-N3,1-dipropyl-1H-pyrrole-3-carboxamide
structure.
Pyrrole and several pyrrole derivatives, especially the
methyl homologues, are found in coal-tar and bone oil.
The biological importance of pyrrole and its derivatives
cannot be overemphasized because several natural pig-
ments, such as heme, chlorophyll and bile pigments, or
enzymes like the various cytochromes, include the pyrrole
nucleus. Many alkaloids and at least two amino acids,
namely, proline and hydroxyproline, also contain the re-
duced pyrrole ring (pyrrolidine).10
1
The H NMR spectrum of 4a exhibited nine signals that
were readily recognized as arising from four methyl
3
groups (d = 0.63 ppm, t, JH–H = 7.3 Hz; d = 0.98 ppm, t,
3JH–H = 7.4 Hz; d = 2.08, s and d = 2.58 ppm, s), four
methylenes (d = 1.14–1.22, m; d = 1.66–1.73 ppm, m; d =
3.08 ppm, q, 3JH–H = 5.8 Hz; d = 3.76 ppm, t, 3JH–H = 7.7
Hz) and an NH group (d = 4.96 ppm). The phenyl moiety
gave rise to characteristic signals in the aromatic region of
the spectrum. The 1H decoupled 13C NMR spectrum of 4a
showed 17 distinct resonances that were in agreement
with the 2,5-dimethyl-4-phenyl-N3,1-dipropyl-1H-pyr-
role-3-carboxamide structure. The 1H and 13C NMR spec-
tra of compounds 4b–e were similar to those of 4a, except
for the aromatic moiety, which exhibited characteristic
signals with appropriate chemical shifts for the specific
substitution patterns.
An interesting and versatile pyrrole synthesis involves
enamines and enaminones.11–13 Enaminones are versatile,
readily obtainable reagents and their chemistry has re-
ceived considerable attention in recent years.14–17 The
enaminones are thus an important class of organic syn-
thetic intermediates. They have a very high impact as syn-
thons for the synthesis of various heterocyclic and
biologically active analogues,18 including anticonvul-
sant,19 anti-inflammatory20 and antitumor agents,21
dopamine auto-receptor agonists, acetylcholinesterase in-
hibitors and oxytocin antagonists.22
Although the mechanism of the reaction between nitrosty-
rene 3 and enaminone 6, has not yet been established in an
experimental manner, a possible explanation is proposed
in Scheme 2. On the basis of the well-established chemis-
try of enaminone nucleophiles,25 it is reasonable to as-
SYNTHESIS 2008, No. 5, pp 0725–0728
Advanced online publication: 08.02.2008
DOI: 10.1055/s-2008-1032168; Art ID: Z25407SS
x
x
.
x
x
.2
0
0
8
© Georg Thieme Verlag Stuttgart · New York

726
A. Alizadeh et al.
PAPER
Table 1 Reaction of Amines 1, 2 and Diketene in the Presence of Nitrostyrene 3
R1
H
O
O
Ph
R3
N
NO2
R3
CH2Cl2
r.t.
R1 NH2
+
+
R2 NH2
O
+
Ph
Me
N
R2
4
1
2
3
4
R1
R2
Pr
Pr
Pr
Pr
R3
Me
Me
Me
H
Yield of 4 (%)
a
Pr
90
90
85
90
80
85
90
b
c
t-Bu
i-Bu
allyl
Pr
d
e
allyl
H
f
t-Bu
i-Bu
allyl
H
g
i-Bu
H
sume that 4 results from reaction of the primary amine 2 an interesting alternative to complex multistep approach-
with N-alkyl-3-oxobutanamide 5 (which is derived from es.
the addition of primary amine 1 to diketene) and subse-
quent attack of the resulting reactive enamine 6 on the ni-
Amines and diketene were obtained from Merck (Germany) and
trostyrene, to yield a betaine 7 that rearranges to
intermediate 8. Cyclization of the intermediate 8 and sub-
sequent loss of a nitrite anion leads to intermediate 9. Fi-
nally, intermediate 9 apparently oxidizes26 under the
reaction conditions employed, to produce compound 4
(Scheme 1).
Fluka (Switzerland) and were used without further purification. Ni-
trostyrene was prepared according to the literature procedure.27,28
Elemental analyses (CHN) were performed using a Heraeus
CHN-O-Rapid analyzer. Mass spectra were recorded on a FINNI-
GAN MATT 8430 mass spectrometer, operating at an ionization
1
potential of 70 eV. H and 13C NMR spectra were measured in
CDCl3 with a Bruker DRX-500 Avance spectrometer at 500.1 and
In conclusion, we have demonstrated a simple and novel 125.8 MHz, respectively. IR spectra were recorded on a Shimadzu
IR-460 spectrometer. Chromatography columns were prepared
from Merck silica gel 230–240 mesh.
synthesis of pyrrole derivatives in a one-pot operation
from primary amines, diketene and nitrostyrene. The
present method carries the advantage that, not only is the
reaction performed under neutral conditions, but also the
substances can be mixed without any activation or modi-
fication. The simplicity of the present procedure makes it
Synthesis of 2,5-Dimethyl-4-phenyl-N3,1-dipropyl-1H-pyrrole-
3-carboxamide (4a); Typical Procedure
To a magnetically stirred solution of n-propylamine (0.059 g, 1
mmol) and diketene (0.084 g, 1 mmol) in anhyd CH2Cl2 (5 mL) was
added, after ten minutes, n-propylamine (0.059 g, 1 mmol) via a sy-
ringe and the mixture was stirred at r.t. for 2 h. A solution of ni-
trostyrene (0.163 g, 1 mmol) in anhyd CH2Cl2 (5 mL) was added at
r. t. over 10 min and the reaction mixture was allowed to stir for 3
h. On completion of the reaction, the solvent was removed under re-
duced pressure and the residue was separated by column chroma-
tography (silica gel; hexane–EtOAc, 5:1) to give the product.
O
O
O
O
2
R1HN
Me
R2
+
O
1
5
Yield: 0.27 g (90%); yellow oil.
IR (KBr): 3235 (NH), 1620 (CONH), 1530, 1454 (Ar) cm–1.
H
N
H
R2
O
N
R1HN
Me
1H NMR (500 MHz, CDCl3): d = 0.63 (t, 3J = 7.3 Hz, 3 H,
CH3CH2CH2N), 0.98 (t, 3J = 7.4 Hz, 3 H, CH3CH2CH2NH), 1.14–
1.22 (m, 2 H, CH3CH2CH2N), 1.66–1.73 (m, 2 H, CH2CH2NH),
3
R1HN
R1HN
Me
NO2
Ph
R3
3
6
7
2.08 (s, 3 H, CH3), 2.58 (s, 3 H, CH3), 3.08 (q, J = 5.8 Hz, 2 H,
CH2NH), 3.76 (t, 3J = 7.7 Hz, 2 H, CH2N), 5.11 (s, 1 H, NH), 7.27–
O
O
Me
R3
Me
7.39 (m, 5 H, Ph).
R1HN
[O]
NHR2
NO2
13C NMR (125 MHz, CDCl3): d = 10.30 (CH3CH2CH2NH), 11.16
(CH3CH2CHN), 11.22 (CH3), 11.28 (CH3), 22.50 (CH2CH2NH),
23.91 (CH2CH2N), 40.74 (CH2NH), 45.27 (CH2N), 113.75 (C-3 of
pyrrole ring), 119.34 (C-4 of pyrrole ring), 124.76 (C-5 of pyrrole
ring), 126.76 (CH of Ph), 128.44 (2 × CH of Ph), 130.81 (2 × CH of
4
N
R2
– HNO2
Ph
Ph
R3
8
9
Scheme 1
Synthesis 2008, No. 5, 725–728 © Thieme Stuttgart · New York

PAPER
Synthesis of Highly Functionalized Pyrrole Derivatives
727
Ph), 132.25 (Cipso of Ph), 136.25 (C-2 of pyrrole ring), 166.18
(CONH).
MS (EI, 70 eV): m/z (%) = 298 (79) [M+], 283 (15), 269 (4), 256
(21), 240 (100), 212 (19), 197 (19), 128 (16.4), 115 (6), 77 (4), 43
(11).
pyrrole ring), 115.67 (C-5 of pyrrole ring), 118.92 (CH=CH2),
122.63 (C-4 of pyrrole ring), 126.72 (CH of Ph), 128.49 (2 × CH of
Ph), 129.17 (2 × CH of Ph), 133.64 (Cipso of Ph), 134.39 (CH=CH2),
135.30 (C-2 of pyrrole ring), 166.20 (CONH).
MS (EI, 70 eV): m/z (%) = 284 (23) [M+ + 1], 269 (4), 256 (8), 240
(100), 226 (12), 184 (14), 129 (46), 105 (19), 77 (19), 69 (23), 43
(34).
Anal. Calcd for C19H26N2O: C, 76.47; H, 8.78; N, 9.39. Found: C,
76.42; H, 8.73; N, 9.41.
Anal. Calcd for C18H22N2O: C, 76.56; H, 7.85; N, 9.92. Found: C,
76.49; H, 7.81; N, 9.94.
N3-(tert-Butyl)-2,5-dimethyl-4-phenyl-1-propyl-1H-pyrrole-3-
carboxamide (4b)
Yield: 0.28 g (90%); yellow oil.
1-Allyl-2-methyl-4-phenyl-N3-propyl-1H-pyrrole-3-carbox-
amide (4e)
Yield: 0.25 g (90%); yellow oil.
IR (KBr): 3410 (NH), 1639 (CONH), 1526, 1442 (Ar) cm–1.
1H NMR (500 MHz, CDCl3): d = 0.98 (t, 3J = 7.3 Hz, 3 H,
CH3CH2), 1.07 (s, 9 H, t-C4H9), 1.67–1.72 (m, 2 H, CH3CH2), 2.09
(s, 3 H, CH3), 2.56 (s, 3 H, CH3), 3.76 (t, 3J = 7.7 Hz, 2 H, CH2N),
4.96 (s, 1 H, NH), 7.27–7.40 (m, 5 H, Ph).
13C NMR (125 MHz, CDCl3): d = 10.29 (CH3CH2), 11.07 (CH3),
11.29 (CH3), 23.93 (CH3CH2), 28.57 [C(CH3)3], 45.24 [C(CH3)3],
50.35 (CH2N), 114.89 (C-3 of pyrrole ring), 119.40 (C-4 of pyrrole
ring), 124.46 (C-5 of pyrrole ring), 126.69 (CH of Ph), 128.37 (2 ×
CH of Ph), 131.03 (2 × CH of Ph), 131.86 (Cipso of Ph), 136.24 (C-
2 of pyrrole ring), 165.68 (CONH).
IR (KBr): 3295 (NH), 1651 (CONH), 1539, 1440 (Ar) cm–1.
1H NMR (500 MHz, CDCl3): d = 0.69 (t, 3J = 7.3 Hz, 3 H,
CH3CH2), 1.21–1.30 (m, 2 H, CH3CH2), 2.47 (s, 3 H, CH3), 3.11–
3
3.18 (m, 2 H, CH2NH), 4.41–4.42 (d, J = 5.07 Hz, 2 H, CH2N),
3
3
5.02 (d, J = 17.0 Hz, 1 H, CH=CH2), 5.20 (d, J = 10.3 Hz, 1 H,
CH=CH2), 5.29 (br, 1 H, NH), 5.86–5.94 (m, 1 H, CH=CH2), 6.50
(s, 1 H, CH-5), 7.18–7.37 (m, 5 H, Ph).
13C NMR (125 MHz, CDCl3): d = 10.72 (CH3CH2), 11.30 (CH3),
22.55 (CH3CH2), 41.11 (CH2NH), 49.00 (CH2N), 114.56 (C-3 of
pyrrole ring), 117.39 (C-5 of pyrrole ring), 118.88 (CH=CH2),
122.85 (C-4 of pyrrole ring), 126.76 (CH of Ph), 128.46 (2 × CH of
Ph), 129.19 (2 × CH of Ph), 133.27 (CH=CH2), 133.70 (Cipso of Ph),
135.28 (C-2 of pyrrole ring), 166.22 (CONH).
MS (EI, 70 eV): m/z (%) = 312 (86) [M+], 297 (8), 284 (3), 270 (3),
256 (30), 240 (100), 212 (20), 197 (19), 168 (9), 128 (15), 115 (7),
77 (6), 57 (20), 42 (35).
Anal. Calcd for C20H28N2O: C, 76.88; H, 9.03; N, 8.97. Found: C,
76.69; H, 9.10; N, 8.83.
MS (EI, 70 eV): m/z (%) = 282 (13) [M+], 257 (20), 224 (100), 183
(30), 129 (43), 105 (34), 56 (83), 43 (96).
N3-Isobutyl-2,5-dimethyl-4-phenyl-1H-pyrrole-3-carboxamide
(4c)
Anal. Calcd for C18H22N2O: C, 76.56; H, 7.85; N, 9.92. Found: C,
76.52; H, 7.79; N, 9.87.
Yield: 0.28 g (90%); yellow oil.
IR (KBr): 3415 (NH), 1636 (CONH), 1530, 1453 (Ar) cm–1.
1-Allyl-N3-(tert-butyl)-2-methyl-4-phenyl-1H-pyrrole-3-carb-
oxamide (4f)
Yield: 0.25 g (85%); yellow oil.
1H NMR (500 MHz, CDCl3): d = 0.62 (d, 3J = 6.7 Hz, 6 H, i-C3H7),
0.99 (t, 3J = 7.3 Hz, 3 H, CH3CH2), 1.39–1.44 (m, 1 H, CH), 1.68–
1.73 (m, 2 H, CH3CH2), 2.07 (s, 3 H, CH3), 2.59 (s, 3 H, CH3), 2.96
(t, 3J = 5.8 Hz, 2 H, CH2NH), 3.79 (t, 3J = 4.8 Hz, 2 H, CH2N), 5.20
(s, 1 H, NH), 7.28–7.40 (m, 5 H, Ph).
13C NMR (125 MHz, CDCl3): d = 10.28 (CH3CH2), 11.16
(CH3CH2CHN), 11.22 (CH3), 11.29 (CH3), 19.95 [CH(CH3)2],
23.91 (CH3CH2), 28.20 [CH(CH3)2], 45.28 (CH2NH), 46.53
(CH2N), 113.71 (C-3 of pyrrole ring), 119.32 (C-4 of pyrrole ring),
124.79 (C-5 of pyrrole ring), 126.87 (CH of Ph), 128.55 (2 × CH of
Ph), 130.85 (2 × CH of Ph), 132.33 (Cipso of Ph), 136.38 (C-2 of pyr-
role ring), 166.25 (CONH).
IR (KBr): 3315 (NH), 1651 (CONH), 1521, 1439 (Ar) cm–1.
1H NMR (500 MHz, CDCl3): d = 1.18 (s, 9 H, t-C4H9), 2.51 (s, 3 H,
3
2
CH3), 4.44–4.46 (m, 2 H, CH2N), 5.06 (dd, J = 17.0 Hz, J = 1.0
3
Hz, 1 H, CH=CH2), 5.13 (s, 1 H, NH), 5.23 (dd, J = 10.3 Hz,
2J = 1.1 Hz, 1 H, CH=CH2), 5.90–5.97 (m, 1 H, CH=CH2), 6.52 (s,
1 H, CH-5), 7.25–7.40 (m, 5 H, Ph).
13C NMR (125 MHz, CDCl3): d = 10.64 (CH3), 28.64 [C(CH3)],
48.96 (CH2N), 50.71 [C(CH3)], 115.77 (C-3 of pyrrole ring), 117.35
(C-5 of pyrrole ring), 118.49 (CH=CH2), 122.89 (C-4 of pyrrole
ring), 126.73 (CH of Ph), 128.33 (2 × CH of Ph), 129.53 (2 × CH of
Ph), 133.35 (CH=CH2), 135.30 (Cipso of Ph), 141.00 (C-2 of pyrrole
ring), 165.53 (CONH).
MS (EI, 70 eV): m/z (%) = 296 (59) [M+], 257 (42), 240 (55), 224
(100), 213 (30), 196 (15), 183 (20), 129 (26), 105 (19), 57 (31), 41
(53).
MS (EI, 70 eV): m/z (%) = 312 (55) [M+], 298 (76), 283 (14), 256
(47), 240 (100), 212 (28), 197 (28), 128 (24), 77 (9), 43 (34).
Anal. Calcd for C20H28N2O: C, 76.88; H, 9.03; N, 8.97. Found: C,
76.81; H, 9.06; N, 8.93.
N3-Allyl-2-methyl-4-phenyl-1-propyl-1H-pyrrole-3-carbox-
amide (4d)
Anal. Calcd for C19H24N2O: C, 76.99; H, 7.16; N, 9.45. Found: C,
76.95; H, 7.11; N, 9.38.
Yield: 0.25 g (85%); yellow oil.
IR (KBr): 3290 (NH), 1652 (CONH), 1540, 1438 (Ar) cm–1.
N3,1-Diisobutyl-2-methyl-4-phenyl-1H-pyrrole-3-carboxamide
(4g)
Yield: 0.28 g (90%); yellow oil.
IR (KBr): 3295 (NH), 1629 (CONH), 1534, 1454 (Ar) cm–1.
1H NMR (500 MHz, CDCl3): d = 0.96 (t, 3J = 7.3 Hz, 3 H,
CH3CH2), 1.73–1.81 (m, 2 H, CH3CH2), 2.52 (s, 3 H, CH3), 3.79 (t,
3J = 7.2 Hz, 2 H, CH2N), 3.84 (t, J = 4.3 Hz, 2 H, CH2NH), 4.92
3
(dd, 3J = 17.15 Hz, 2J = 1.46 Hz, 1 H, CH=CH2), 4.96 (dd,
1H NMR (500 MHz, CDCl3): d = 0.68 [d, 3J = 6.6 Hz, 6 H,
2
3
3J = 10.35 Hz, J = 1.26 Hz, 1 H, CH=CH2), 5.40 (s, 1 H, NH),
(CH3)2CHCH2NH], 0.92 [d, J = 6.6 Hz, 6 H, (CH3)2CHCH2NH],
5.68–5.73 (m, 1 H, CH=CH2), 6.53 (s, 1 H, CH-5), 7.33–7.39 (m,
5 H, Ph).
13C NMR (125 MHz, CDCl3): d = 10.90 (CH3CH2), 11.23 (CH3),
24.15 (CH3CH2), 41.73 (CH2NH), 48.25 (CH2N), 113.97 (C-3 of
1.49–1.54 (m, 1 H, Me2CHCH2NH), 1.98–2.03 (m, 1 H,
Me2CHCH2N), 2.50 (s, 3 H, CH3), 3.01 (t, 3J = 6.1 Hz, 2 H,
CH2NH), 3.60 (d, 3J = 7.4 Hz, 2 H, CH2N), 5.31 (s, 1 H, NH), 6.46
(s, 1 H, CH-5), 7.21–7.37 (m, 5 H, Ph).
Synthesis 2008, No. 5, 725–728 © Thieme Stuttgart · New York

728
A. Alizadeh et al.
PAPER
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Chem. Int. Ed. 1999, 19, 38.
(12) Yavari, I.; Anary-Abbasinejad, M.; Nasiri, F.; Djahaniani,
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13C NMR (125 MHz, CDCl3): d = 11.11 (CH3), 20.06 [2 ×
(CH3)2CH], 28.29 [(CH3)2CHCH2NH], 29.87 [(CH3)2CHCH2N],
46.72 (CH2NH), 54.14 (CH2N), 114.30 (C-3 of pyrrole ring),
119.52 (CH-5 of pyrrole ring), 122.40 (C-4 of pyrrole ring), 126.74
(CH of Ph), 128.49 (2 × CH of Ph), 129.33 (2 × CH of Ph), 133.60
(Cipso of Ph), 135.58 (C-2 of pyrrole ring), 166.33 (CONH).
MS (EI, 70 eV): m/z (%) = 329 (34), 272 (67), 256 (70), 229 (14),
199 (30), 149 (12), 105 (100), 77 (30), 48 (30).
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76.83; H, 9.06; N, 8.91.
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