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Jemin R Avalani et al.
Scheme 1. General synthetic pathway for the synthesis of 1,4-dihydropyridines (1,4-DHPs).
2. Experimental
stretching of amine), 2949 (-CH stretching), 1696,
1645 (respectively due to C=O and C=C stretching of
conjugate ester), 1487, 1342, 1215;1H NMR (400 MHz,
CDCl3): δ 2.37 (s, 6H,-CH3), 3.66 (s, 6H,-OCH3), 5.12
(s, 1H,aryl –CH of C4), 5.86 (s, 1H,-NH), 7.45 (d,
J =8.8 Hz, 2H, Ar-H), 8.10 (d, J =8.8 Hz, 2H, Ar-H);
13C NMR (100 MHz, CDCl3): δ 19.63 (-CH3), 39.87,
51.14, 103.02, 123.45, 128.60, 144.91, 146.43, 154.75,
167.47 (C=O). ESI-MS: m/z: 346.9(M+H)+
2.1 General
All chemicals were of research grade and were used
as obtained. The reactions were carried out by using
700 Watt CATA-R scientific microwave system. Melt-
ing points were measured in open capillaries and are
uncorrected. TLC was performed on Silica Gel 60 F254
pre-coated plates (Merck). IR spectra were recorded on
a FT IR Perkin Elmer Spectrum 100 spectrometer, mass
spectra on a Shimadzu LCMS 2010 spectrometer, and
elemental analysis on Perkin Elmer PE 2400 elemental
analyzer. 1H NMR and 13C NMR spectra were recorded
on Bruker Avance 400 MHz instrument with TMS as
an internal standard. The IL [Hmim]Tfa was prepared
according to the procedure reported in literature.27
2.3b Diethyl
4-(furan-2-yl)-2,6-dimethyl-1,4-dihy-
dropyridine-3,5-dicarboxylate (4k): Anal.Calcd. For
C17H21NO5: C, 63.94; H, 6.63; N, 4.39. Found: C,
63.72; H, 7.01; N, 4.11. IR (KBr) cm−1: 3348 (-NH
stretching of amine), 2985 (-CH stretching), 1692,
1649 (respectively due to C=O and C=C stretching
of conjugate ester), 1486, 1209.1H NMR (400 MHz,
CDCl3): δ 1.28 (t, J=7.2 Hz, 6H, -CH2CH3), 2.34 (s,
6H, -CH3), 4.18 (m, 4H, -CH2CH3), 5.22 (s, 1H, aryl –
CH of C4), 5.84 (s, 1H, -NH), 5.95 (d, J =3.2 Hz, 1H,
Ar-H), 6.23 (dd, J = 2.8, 2 Hz, 1H, Ar-H), 7.23 (s, 1H,
Ar-H); 13C NMR (100 MHz, CDCl3): δ 14.32, 19.51,
33.43, 59.80, 100.78, 104.43, 109.98, 140.84, 145.02,
158.70, 167.46 (C=O). ESI-MS: m/z: 319.8(M+H)+
2.2 Procedure for the synthesis of 1,4-DHPs
A
mixture of aldehyde
1
(1 mmol), 1,3-
dicarbonylcompound 2 (2.1 mmol), ammonium acetate
3 (3 mmol), ethanol (1 ml) and [Hmim]Tfa (20 mol%)
were taken in a round bottom flask containing a
teflon-coated magnetic stirrer bar. It was subjected to
microwave irradiation at power level 7 (455 watt) for
an appropriate time shown in table 3. The completion
of reaction was monitored by TLC. The reaction mix-
ture was treated with cold water, extracted with diethyl
ether and dried over anhydrous Na2SO4. It was then
concentrated under reduced pressure to leave the crude
product which was crystallized in ethanol. The com-
pounds have been identified by comparison of spectral
data and mp with those reported elsewhere.
2.3c Diisopropyl 4-(furan-2-yl)-2,6-dimethyl-1,4-di-
hydropyridine-3,5-dicarboxylate
(4l): Anal.Calcd.
For C19H25NO5: C, 65.69; H, 7.25; N, 4.03. Found: C,
65.86; H, 7.57; N, 3.79. IR (KBr) cm−1: 3347 (-NH
stretching of amine), 2978 (-CH stretching), 1696,
1649 (respectively due to C=O and C=C stretching
1
of conjugate ester), 1483, 1208. H NMR (400 MHz,
CDCl3): δ 1.22 (dd, J=6,0.8 Hz, 6H, -CH3), 1.28 (dd,
J=6.4,1.2 Hz, 6H), 2.33 (s,6H), 5.05 (m, 2H), 5.2 (s,
1H), 5.76 (s,1H), 5.95 (s,1H), 6.22 (m,1H), 7.22(s,1H);
13C NMR (100 MHz,CDCl3): δ 19.52, 22.07, 33.59,
67.02, 101.15, 104.47, 109.92, 140.67, 144.54, 158.92,
167.01 C=O. ESI-MS: m/z: 347.9 (M+H)+
2.3 Spectral data for selected compounds
2.3a Dimethyl
2,6-dimethyl-4-(4-nitrophenyl)-1,4-
dihydropyridine-3,5-dicarboxylate (4d): Anal.Calcd.
For C17H18N2O6: C,58.96; H,5.24; N,8.09. Found: C,
59.30; H, 5.10; N, 7.84. IR (KBr) cm−1: 3304 (-NH