370
R D SHAH
The IR spectra of 3 showed bands at 3500-3140 cm-1 for amino and 1680-1670 cm-1 for
C=O of ester functionality. Table 2 shows physical constants and 1H NMR spectral data.
Table 2. Physical constants of 3-amino-4-arylthiophene-2-carboxylates (3a-f)
% C
%H
%N
Mol. Formula
(MW)
1H NMR (δ ppm)
Entry
Calcd Calcd Calcd
(Found) (Found) (Found)
3a*
C12H11NO2S
(233.39)
61.80
(61.35)
4.75
(4.59)
6.01 (s, 5H, 7.0) Ar-H; (s, 1H, 6.75);
(5.86) Ar-H at C4, (m, 2H, 5.3) NH2; (s,
3H, 3.6) CH3
3b** C13H13NO2S
(263.31)
59.31
(59.59)
4.98
(4.81)
5.32 (d, 2H, 7.3) Ar-H; (d, 2H, 6.9)
(5.19) Ar-H; (s, 1H, 7.05) Ar-H at C4;
(m, 2H, 5.5) NH2; (s, 3H, 3.95)
OCH3; (s, 3H, 3.8) CH3
3c*
C14H11NO3S
(273.31)
61.56
(61.94)
4.06
(3.91)
5.13 (m, 5H, 7.1-7.6) Ar-H; (s, 1H,
(4.85) 6.7) Ar-H at C4;(m, 2H, 6.1)
NH2, (s, 3H, 3.75) CH3
3d*
C10H9NO2S2
(239.32)
50.21
(49.81)
53.93
3.79
(3.67)
4.90
5.86 (m, 4H, 6.9-7.3) Ar-H; (m, 2H,
(5.69) 5.7) NH2; (s, 3H, 3.75) CH3
5.24 (s, 1H, 6.95) Ar-H at C4, (s, 1H,
(5.11) 6.5) Ar-H; (m, 2H, 5.5) NH2; (s,
3H, 3.75), CH3 of ester; (s, 3H,
2.45) CH3 at C2’; (s, 3H, 2.35)
CH3 at C5’
3e*
C12H13NO2S2
(267.37)
(53.66)
(4.85)
3f*
C13H13NO2S
(247.07)
63.13
(63.01)
5.30
(5.34)
5.66 (s, 5H, 7.1) Ar-H; (s, 1H,6.8) Ar-
(5.53) H at C4; (m, 2H, 5.3) NH2; (q,
2H, 4.3) CH2; (s, 3H, 3.6) CH3;
(t, 3H, 1.29) CH3 of ester
Solvent used for crystallization *ethanol and **benzene:ether mixture (5:5)
Experimental
Melting points were determined by electro thermal method in open capillary tube and are
uncorrected. The IR spectra were recorded (in cm-1 for KBr pellets) on Buck-500
spectrophotometer. The 1H NMR spectra were recorded on Bruker 300 MHz
spectrophotometer in CDCl3 using TMS as internal standard and the chemical shifts are
expressed in δ ppm. MS spectra were recorded on JEOL/ SX-102 mass spectrophotometer
under electron-impact (EI) ionization. Elemental analyses were performed on a Carlo Erba
1108 microanalyzer or Elementar’s Vario EL III microanalyzer. The purity of the compounds
was routinely checked by TLC using silica gel G and spots were exposed in iodine vapour.
General method for Synthesis of methyl or ethyl 3-amino-4-arylthiophene-2-
carboxylates (3a-f)
Method 1
Solid-liquid PTC: A well stirred solution of toluene or MeCN (20 mL), powdered KOH
(840 mg, 15 mmol) and 18-crown-6 (0.132 g, 0.5 mmol) was added with 3-hydroxy-2-
arylacrylonitriles (1, 5 mmol) and thioglycolates (2, 5 mmol) and 2 drops of concentrated
HCl. Thereafter the reaction mixture was stirred for 20 min at room temperature (35-40 0C).
The solvent was distilled under reduced pressure and the reaction mixture was poured onto
Shah
