146 JOURNAL OF CHEMICAL RESEARCH 2015
temperature for 30 min. Then enaminone or enaminoester derivative
(1 mmol) was added in small portions. The solution was stirred at
room temperature for 10 h. The resulting precipitate was filtered off
and washed with diethyl ether (20 mL) to afford the pure product.
Diethylꢀꢀ1,1′′-dibenzyl-5,5′′-dimethyl-2,2′′-diphenyl-3,2′:5′,3′′-
terpyrrole-4,4′′-dicarboxylate (4a): Brown powder; yield 0.62 g (87%);
m.p. 170–173 °C; IR: NH 3378, C=O 1687 cm–1; 1H NMR: δ 1.17 (t, 6H,
2 CH3, J=7.4 Hz), 2.37 (s, 6H, 2 CH3), 4.14 (q, 4H, 2 OCH2, J=7.4 Hz),
4.99 (s, 4H, 2 NCH2), 5.04 (d, 2H, 2 CH of pyrrole, J=2.4 Hz),
6.83–7.31 (20 H, aromatic), 11.18 ppm (s, 1 H, NH). 13C NMR: δ 12.0
(2 CH3), 14.0 (2 CH3), 47.0 (2 NCH2), 59.4 (2 OCH2), 107.6, 109.9,
115.0, 123.5, 125.4, 127.1, 128.1, 128.3, 128.6, 131.0, 131.2, 132.2,
135.2, 137.5 ppm (aromatic carbons), 165.8 ppm (2 C=O). Anal. calcd
for C46H43N3O4: C, 78.72; H, 6.18; N, 5.99; found: C, 78.61; H, 6.07; N,
5.90%.
protons related to ethoxy groups were observed as a triplet and a
quartet (3JHH =7 Hz) respectively at 1.17 at 4.14 ppm. Protons of
two methyl groups were observed as a single signal at 2.37 ppm
and the two NCH2 groups were observed at 4.99 pp as a singlet.
The aromatic protons resonated between 6.83 and 7.31 ppm.
13C NMR spectrum of 4a shows 19 distinct signals in consistent
with the proposed structure, the carbonyl carbons resonating at
165.8 ppm. The structure of compound 4a was also confirmed
by its IR spectrum, which exhibited an absorption band at
3378 cm–1 for NH and an absorption band at 1687 cm–1 for the
carbonyl group.
A
suggested mechanism for formation of terpyrrole
derivatives 4a–g by reaction between pyrrole, arylglyoxal
monohydrates and enaminones is shown in Scheme 2.
Reaction between pyrrole and arylglyoxal derivative in the
presence of FeBr3 afforded 2,5-bis[aroyl(hydroxyl)methyl]
pyrrole intermediate 5. FeBr3 also promoted the formation
of intermediate 6 by elimination of a molecule of water from
intermediate 5. The addition of enaminone 3 to intermediate 6
afforded intermediate 7 which cyclises and dehydrated to form
bipyrrole intermediate 9. Similar sequences of reaction steps
between bipyrrole 9 and another molecule of enaminone lead to
terpyrrole product 4.
Dimethylꢀꢀ1,1′′-dibenzyl-5,5′′-dimethyl-2,2′′-diphenyl-3,2′:5′,3′′-
terpyrrole-4,4′′-dicarboxylate (4b): Pink powder; yield 0.65 g (91%);
1
m.p. 140–142 °C; IR: NH 3343, C=O 1691 cm–1; H NMR: δ 2.37 (s,
6H, 2 CH3), 3.67 (s, 6H, 2 OCH3), 5.00 (s, 4H, 2 NCH2), 5.04 (d, 2H,
2 CH of pyrrole, J=2.3 Hz), 6.83–7.39 (20 H, aromatic), 11.21 ppm
(s, 1H, NH); 13C NMR: δ 12.0 (2 CH3), 47.1 (2 NCH2), 50.8 (2 OCH3),
107.6, 109.8, 115.1, 123.6, 125.4, 127.1, 128.1, 128.3, 128.6, 131.1, 131.2,
132.2, 135.3, 137.5 (aromatic carbons), 166.2 ppm (2 C=O). Anal. calcd
for C44H39N3O4: C, 78.43; H, 5.83; N, 6.24; found: C, 78.40; H, 5.36; N,
6.20%.
Conclusion
4,4′-Diacetyl-1,1′′-diphenyl-5,5′′-dimethyl-2,2′′-bis(2-naphthyl)-
3,2′:5′,3′′-terpyrrole (4c): Dark blue powder; yield 0.63 g (88%); m.p.
In summary, we report that the reaction of pyrrole
with arylglyoxal monohydrates and enaminoketones or
enaminoesters in alcoholic media provides a pseudo-five-
component facile and efficient route for synthesis of the
expected terpyrrole derivatives in good yields. The advantages
of the method are readily available starting materials, neutral
reaction conditions, using ethanol as an environmentally green
solvent and simple isolation and purification of products.
1
280–284 °C; IR: NH 3441, C=O 1647 cm–1; H NMR: δ 1.98 (s, 6H,
2 CH3), 2.39 (s, 6H, 2 CH3), 5.93 (d, 2H, J=2.5 Hz, 2 CH pyrrole),
7.00–7.65 (24 H, aromatic), 8.99 ppm (s, 1H, NH); 13C NMR: δ 13.4
(2 CH3), 30.2 (2 CH3), 111.5, 122.7, 124.4, 125.8, 125.9, 127.0, 127.4,
128.0, 128.2, 128.3, 128.6, 129.1, 129.9, 132.0, 132.8, 132.8, 132.9,
136.1, 137.5 (aromatic carbons), 197.7 ppm (2 C=O). Anal. calcd for
C50H39N3O2: C, 84.12; H, 5.51; N, 5.89; found: C, 84.10; H, 5.45; N,
5.88%.
Experimental
Dimethylꢀ 1,1′′-dibenzyl-5,5′′-dimethyl-2,2′′-bis(2-naphthyl)-3,2:5′,3′′-
terpyrrole-4,4′′-dicarboxylate (4d): Brown powder; yield 0.62 g
All the utilised arylglyoxals were prepared by the SeO2-oxidation of
the related aryl methyl ketones on the basis of the reported procedure
and used as their monohydrates.24 All melting points are uncorrected.
Elemental analyses were performed using a Heraeus CHN–O‑
Rapid analyser. IR spectra were recorded on a Shimadzu IR-470
1
(80%); m.p. 219–221 °C; IR: NH 3438, C=O 1685 cm–1; H NMR: δ
2.40 (s, 6H, 2 CH3), 3.66 (s, 6H, 2 OCH3), 4.98 (d, 2H, J=2.4 Hz, 2 CH
of pyrrole) 5.06 (s, 4H, 2 NCH2), 6.83–7.84 (24 H, aromatic), 11.25 ppm
(s, 1 H, NH). 13C NMR: δ 12.0 (2 CH3), 47.2 (2 NCH2), 50.8 (2 OCH3),
107.9, 109.9, 115.5, 123.7, 125.4, 126.2, 126.4, 127.1, 127.4, 127.6,
127.8, 128.6, 128.9, 129.6, 130.1, 132.2, 132.6, 135.5, 137.5 (aromatic
carbons), 166.1 ppm (2 C=O). Anal. calcd for (C52H43N3O4): C, 80.70;
H, 5.60; N, 5.43; found: C, 80.56; H, 5.22; N, 5.60%.
1
spectrometer. H and 13C NMR spectra were recorded on Bruker
DRX‑400 Avance spectrometer at 400 and 100 MHz, respectively.
The chemicals used in this work purchased from Fluka (Buchs,
Switzerland) and were used without further purification.
Diethylꢀꢀ1,1′′-dibenzyl-5,5′′-dimethyl-2,2′′-bis(4-chlorophenyl)-
3,2′:5′,3′′-terpyrrole-4,4′′-dicarboxylate (4e): Pink powder; yield
0.72 g (94%); m.p. 215–217 °C; IR: NH 3358, C=O 1684 cm–1;
Synthesis of compounds 4a–g; general procedure
A solution of pyrrole (0.5 mmol), arylglyoxal monohydrate (1 mmol)
and FeBr3 (0.01 mmol) in ethanol (15 mL) was stirred at room
R1
H
Ar
Ar
Ar
Ar
N
O
Ar
-H2O
FeBr3
OH
O
2
O
O
+
O
R2
O
N
N
H
N
H
OH
Ar
HO
HO
O
FeBr3
6
1
2
5
H
R1
H
Ar
N
O
Ar
Ar
OH
N
Ar
FeBr3
R1
O
O
R1
O
R2
O
-H2O
4
N
N
N
H
N
H
NHR1
-2 H2O
H
HO
HO
HO
O
O
O
9
8
7
R2
R2
R2
Scheme 2 Suggested mechanism for formation of terpyrrole derivatives 4a–g.