S. Santra et al. / Tetrahedron Letters 52 (2011) 3825–3827
3827
A.; Alvarez, E.; Rodriguez, F. Eur. J. Org. Chem. 2010, 7027; (d) Das, S.; Rahman,
M.; Kundu, D.; Majee, A.; Hajra, A. Can. J. Chem. 2010, 88, 150. and references
cited therein.
was reused for six times without noticeable decrease in catalytic
activity (80% for entry 1, Table 2).
In conclusion, a method for direct alkenylation of indoles at the
3-position with 1,3-dicarbonyl compounds under Brønsted acidic
ionic liquid catalysis has been developed. The advantages of this
procedure are: (a) simple operation; (b) excellent yields; (c) fast
reaction; (d) general applicability; (e) reusability of catalyst and
(f) above all, metal-free synthesis avoiding toxic reagents and
solvents. Further studies to broaden the scope of this methodology
toward the synthesis of biologically important compounds are
under investigation.
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J. H., Jr. J. Am. Chem. Soc. 2002, 124, 5962; (b) Fang, D.; Zhou, X.-L.; Ye, Z.-W.; Liu,
Z.-L. Ind. Eng. Chem. Res. 2006, 45, 7982; (c) Leng, Y.; Wang, J.; Zhu, D.; Ren, X.;
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Acknowledgments
6. (a) Ranu, B. C.; Dey, S. S.; Hajra, A. Tetrahedron 2003, 59, 2417; (b) Kundu, D.;
Debnath, R. K.; Majee, A.; Hajra, A. Tetrahedron Lett. 2009, 50, 6998; (c) Kundu,
D.; Majee, A.; Hajra, A. Catal. Commun. 2010, 11, 1157; (d) Rahman, M.; Majee,
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A.H. is pleased to acknowledge the financial support from DST,
Govt. of India (Grant No. SR/S5/GC-05/2010). A.M. acknowledges
financial support from CSIR (Grant No. 01(2251)/08/EMR-II).
7. Synthesis of methyl 3-(2-methyl-1H-3-indolyl)-2-butenoate (Table 2, entry 10):
Supplementary data
A
mixture of 2-methylindole (262 mg, 2 mmol) and methyl acetoacetate
l
(237 L, 2.2 mmol) was stirred in presence of acidic ionic liquid (74 mg,
10 mol %) at room temperature for 1.5 h (TLC). After completion, the reaction
mixture was extracted with diethyl ether (10 mL Â 3). Evaporation of solvent
furnished the crude product which was subjected to column chromatography to
obtain the analytically pure product as a brown solid (422 mg, 92%). Mp 132–
Supplementary data (spectral data) associated with this article
133 °C. IR (KBr) 3330, 2950, 1677, 1600, 1423 cmÀ1 1H NMR (300 MHz, CDCl3):
.
d 8.17 (br 1H), 7.66 (dd, J = 6.7, 2.7 Hz, 1H), 7.31–7.27 (m, 1H), 7.18–7.14 (m,
2H), 5.98 (d, J = 1.0 Hz, 1H), 3.77 (s, 3H), 2.70 (d, J = 1.0 Hz, 3H), 2.51 (s, 3H); 13
C
References and notes
NMR (75 MHz, CDCl3): d 167.9, 152.7, 135.2, 133.2, 127.0, 121.8, 120.4, 119.6,
116.7, 116.6, 110.6, 51.0, 20.5, 13.5. Anal. Calcd for C14H15NO2: C, 73.34; H, 6.59;
N, 6.11. Found: C, 73.21; H, 6.42; N, 6.01%. The catalyst, left in the reaction vessel
was dried under vacuum and was reused for subsequent reactions. Small
amount of methanol (0.5 mL) was added to the reaction mixture when both
indoles and 1,3-dicarbonyl compounds are solids. The spectral and analytical
data of another new compound is given below.
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Miguel, D.; Martinez, A.; Gohain, M.; Garcia-Garcia, P.; Fernandez-Rodriguez, M.
Ethyl 3-(2-methyl-1H-3-indolyl)-2-butenoate (Table 2, entry 11): Pale yellow
solid, mp 114–116 °C. IR (KBr) 3411, 2933, 1718, 1625, 1454 cmÀ1 1H NMR
.
(300 MHz, CDCl3): d 8.27 (br 1H), 7.66 (dd, J = 8.5, 2.5 Hz, 1H), 7.29–7.25 (m, 1H),
7.16–7.12 (m, 2H), 5.96 (d, J = 1.1 Hz, 1H), 4.24 (q, J = 7.1 Hz, 2H), 2.68 (d,
J = 1.1 Hz, 3H), 2.49 (s, 3H), 1.34 (t, J = 7.1 Hz, 3H); 13C NMR (75 MHz, CDCl3): d
167.6, 152.4, 135.3, 133.2, 127.1, 121.8, 120.4, 119.6, 117.1, 116.8, 110.6, 59.7,
20.6, 14.5, 13.6. Anal. Calcd for C15H17NO2: C, 74.05; H, 7.04; N, 5.76. Found: C,
73.91; H, 7.01; N, 5.62.