LETTER
Synthesis of Pyrrolo[3,2-f]- and Pyrrolo[2,3-h]quinoline Derivatives
721
f]quinoline and pyrrolo[2,3-h]quinoline derivatives ex-
ploiting a one-pot process using easily accessible starting
materials such as indoloamines, benzaldehydes, and phe-
nylacetylenes. To our best knowledge, this is the first re-
port to make these two pyrroloquinolines in one step. We
have also observed an interesting and unexpected mecha-
nistic pathway in this reaction.
References and Notes
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A Typical Procedure for the Preparation of 4a and 5a
In a round-bottom flask equipped with a magnetic stirring bar, to a
mixture of 1,2,3-trimethyl-1H-indol-5-ylamine (1a, 1.0 mmol),
benzaldehyde (2a, 1.0 mmol), and phenylacetylene (3a, 1.0 mmol)
in ionic liquid [Bmim][BF4] (5 mL) as solvent was added of
La(OTf)3 (10 mol%). The reaction mixture was stirred at 90–95 °C
for 4 h. After completion of the reaction as indicated by the TLC,
H2O (20 mL) was added to the crude reaction mass. Then aqueous
layer was extracted with CH2Cl2 (3 × 20 mL). The combined organ-
ic layers were dried over Na2SO4, filtered, and concentrated under
the reduced pressure. The product was purified by column chroma-
tography on silica gel (eluent: hexanes–EtOAc). Compounds 4a and
5a were afforded in 46% and 27% yield, respectively. Rf (4a) = 0.36
and Rf (5a) = 0.78 (10% of EtOAc in hexanes).
1,2,3-Trimethyl-7,9-diphenyl-3H-pyrrolo[3,2-f] Quinoline (4a)
Mp 138–140 °C. IR (KBr): 3055, 1556, 1026, 688 cm–1. 1H NMR
(400 MHz, CDCl3, TMS): d = 8.20 (2 H, d, J = 8.0 Hz), 7.94 (1 H,
d, J = 8.0 Hz), 7.72 (1 H, s), 7.67 (1 H, d, J = 8.0 Hz), 7.52–7.54 (2
H, m), 7.46–7.50 (2 H, m), 7.38 (4 H, m), 3.60 (3 H, s), 2.19 (3 H,
s), 1.20 (3 H, s). 13C NMR (100 MHz, CDCl3, TMS): d = 152.7,
147.4, 147.1, 144.2, 139.9, 134.1, 132.8, 130.1, 129.3, 128.8, 128.3,
127.6, 127.4, 121.0, 120.7, 120.0, 114.5, 111.2 (arom. C); 30.1,
12.0, 10.5 (aliph. C). MS (positive mode): m/z = 363 [M + H]. Anal.
Calcd (%) for C26H22N2: C, 86.15; H, 6.12; N, 7.73. Found: C,
86.21; H, 6.18; N, 7.65.
7,8,9-Trimethyl-2,4-diphenyl-7H-pyrrolo[2,3-h]quinoline (5a)
1
Mp 200–202 °C. IR (KBr): 3042, 1558, 767, 692 cm–1. H NMR
(400 MHz, CDCl3, TMS): d = 8.38 (2 H, d, J = 7.6 Hz), 7.78 (1 H,
s), 7.59–7.61 (3 H, m), 7.50–7.56 (5 H, m), 7.40–7.46 (2 H, m), 3.78
(3 H, s), 2.9 (3 H, s), 2.48 (3 H, s). 13C NMR (100 MHz, CDCl3,
TMS): d = 153.8, 148.9, 145.7, 140.5, 140.3, 135.2, 131.8, 129.8,
128.8, 128.7, 128.4, 127.9, 127.3, 122.4, 120.9, 117.8, 115.5, 111.2,
111.1 (arom. C); 29.4, 12.4, 10.1 (aliph. C). MS (positive mode):
m/z = 363 [M + H]. Anal. Calcd (%) for C26H22N2: C, 86.15; H,
6.12; N, 7.73. Found: C, 86.05; H, 6.18; N, 7.68.
(c) Yamashl, S. A.; Kucherenko, N. Y.; Yurovskaya, M. A.
Chem. Heterocycl. Compd. 1997, 33, 823. (d) Ferlin, M. G.;
Marzano, C.; Via, L. D.; Chilin, A.; Zagotto, G.; Guiotto, A.;
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(e) Chetverikov, V. P.; Yamashkin, S. A.; Kost, A. N.;
Yudin, L. G. Khim. Geterotsikl. Soedin. 1979, 8, 1087.
(f) Yamashkin, S. A.; Trushkov, I. V.; Tomilin, O. B.;
Terekhin, I. I.; Yurovskaya, M. A. Chem. Heterocycl.
Compd. 1998, 34, 1050. (g) Yamashkin, S. A.; Oreshkina,
E. A.; Zhukova, N. V. Chem. Heterocycl. Compd. 2007, 43,
1044.
Supporting Information for this article is available online at
Acknowledgment
We gratefully acknowledge DST for financial assistance (Project
Number: SR/S1/OC–70/2008) and for providing the single-crystal
X-ray diffractometer facility in our school. SR thanks CSIR for Se-
nior Research Fellowship. We thank the editor for suggestions re-
garding the mechanism.
(6) Review: Yamashkin, S. A.; Yurovskaya, M. A. Chem.
Heterocycl. Compd. 2001, 37, 1439.
© Thieme Stuttgart · New York
Synlett 2012, 23, 717–722