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scavenging activity (Molvi et al., 2007). Based on these ob-
servations, particularly the first, we have now synthesized and
characterized a series of closely related arylamides derived
from 2-amino-3-(2-chlorobenzoyl)-5-ethylthiophene, namely
N-[3-(2-chlorobenzoyl)-5-ethylthiophen-2-yl]benzamide, (I),
N-[3-(2-chlorobenzoyl)-5-ethylthiophen-2-yl]-4-phenylbenz-
amide, (II), 2-bromo-N-[3-(2-chlorobenzoyl)-5-ethylthiophen-
2-yl]benzamide, (III), N-[3-(2-chlorobenzoyl)-5-ethylthio-
phen-2-yl]-2-iodobenzamide, (IV), N-[3-(2-chlorobenzoyl)-5-
ethylthiophen-2-yl]-2-methoxybenzamide, (V), and N-[3-(2-
chlorobenzoyl)-5-ethylthiophen-2-yl]-2,6-difluorobenzamide,
(VI). Compounds (I)–(VI) were all prepared using conden-
sation reactions between 2-amino-3-(2-chlorobenzoyl)-5-
ethylthiophene and a substituted benzoic acid in the presence
of 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide as dehy-
drating agent and 1-hydroxybenzotriazole as the acyl carrier
using 3,4-dimethoxybenzoic acid, but omitting the addition of
2-amino-3-(2-chlorobenzoyl)-5-ethylthiophene, yielded (VII).
¨
(Konig & Geiger, 1970) (see Scheme 1). We have also isolated
and characterized the reaction intermediate benzotriazol-1-yl
3,4-dimethoxybenzoate, (VII), by the straightforward expe-
dient of stopping the reaction sequence before the addition of
the aminothiophene reactant, confirming this aspect of the
proposed mechanism. We report here the molecular and
supramolecular structures of compounds (I)–(VII).
2. Experimental
2.1. Synthesis and crystallization
2-Amino-3-(2-chlorobenzoyl)-5-ethylthiophene was a gift
from RL Fine Chem Pvt Ltd, Bengaluru, India. All other
reagents are available commercially and were used as
received. For the synthesis of compounds (I)–(VI), 1-[3-(di-
methylamino)propyl]-3-ethylcarbodiimide (173 mg, 0.9 mmol),
1-hydroxybenzotriazole (126.32 mg, 0.825 mmol) and tri-
ethylamine (0.5 ml, 3.75 mmol) were added to a solution of the
appropriately substituted benzoic acid (0.75 mmol) (see
Scheme 1) in N,N-dimethylformamide (DMF, 5 ml) [i.e.
benzoic acid for (I), biphenyl-4-carboxylic acid for (II),
2-bromobenzoic acid for (III), 2-iodobenzoic acid for (IV),
2-methoxybenzoic acid for (V) and 2,6-difluorobenzoic acid
for (VI)] at 273 K and the resulting mixtures were stirred for
20 min at 273 K. A solution of 2-amino-3-(2-chlorobenzoyl)-5-
ethylthiophene (200 mg, 0.75 mmol) in DMF (5 ml) was then
added to each of the above mixtures and stirring was
continued overnight at ambient temperature. The reactions
were then judged to be complete using thin-layer chromato-
graphy (TLC). The mixtures were poured into an excess of
water and extracted exhaustively with ethyl acetate. For each,
the organic extract was washed first with aqueous hydrochloric
acid solution (1 mol dmꢃ3) and then with brine, and then dried
over anhydrous sodium sulfate and concentrated under
reduced pressure. The crude products of (I)–(VI) were puri-
fied using silica-gel column chromatography (60:120 mesh)
using ethyl acetate–hexane (1:4 v/v) as eluent and crystals
suitable for single-crystal X-ray diffraction were grown by
slow evaporation, at ambient temperature and in the presence
of air, of solutions in DMF. An entirely similar procedure,
2.1.1. Analytical data. Compound (I): yield 85%, m.p.
1
433 K; H NMR (CDCl3): ꢁ 12.99 (s, NH), 8.11–8.09 (m, 2H,
Ar—H), 7.60–7.37 (m, 7H, Ar—H), 6.42 (s, 1H, thiophene),
2.71 (q, J = 7.4 Hz, 2H, CH2), 1.25 (t, J = 7.4 Hz, 3H, CH3).
Compound (II): yield 85%, m.p. 462–464 K; 1H NMR
(CDCl3): ꢁ 13.04 (s, NH), 8.18 (m, 2H, Ar—H), 7.50–7.38 (m,
11H, Ar—H), 6.43 (s, 1H, thiophene), 2.72 (q, J = 7.6 Hz, 2H,
CH2), 1.27 (t, J = 7.6 Hz, 3H, CH3). Compound (III): yield
86%, m.p. 373 K; 1H NMR (CDCl3): ꢁ 12.11 (s, NH), 7.81–7.75
(m, 2H, Ar—H), 7.59–7.47 (m, 6H, Ar—H), 6.45 (s, 1H,
thiophene), 2.69 (q, J = 7.4 Hz, 2H, CH2), 1.15 (t, J = 7.4 Hz,
1
3H, CH3). Compound (IV): yield 82%, m.p. 403–405 K; H
NMR (CDCl3): ꢁ 12.32 (s, NH), 8.00–7.98 (m, 1H, Ar—H),
7.66–7.64 (m, 1H, Ar—H), 7.49–7.20 (m, 6H, Ar—H), 6.43 (s,
1H, thiophene), 2.73–2.70 (q, J = 7.6 Hz, 2H, CH2), 1.26 (t, J =
7.6 Hz, 3H, CH3). Compound (V): yield 83%, m.p. 430–432 K;
1H NMR (CDCl3): ꢁ 12.64 (s, NH), 7.96–7.93 (m, 2H, Ar—H),
7.61–7.48 (m, 4H, Ar—H), 7.19–7.16 (m, 2H, Ar—H), 6.39 (s,
1H, thiophene), 2.68 (q, J = 7.6 Hz, 2H, CH2), 1.14 (t, J =
7.6 Hz, CH3). Compound (VI): yield 60%, m.p. 410–414 K; 1H
NMR (CDCl3): ꢁ 12.82 (s, NH), 7.89–7.77 (m, 2H, Ar—H),
7.56–6.45 (m, 5H, Ar—H), 6.34 (s, 1H, thiophene), 2.69 (q, J =
7.6 Hz, 2H, CH2), 1.26 (t, J = 7.6 Hz, CH3). Compound (VII):
yield 86%, m.p. 435 K; 1H NMR (CDCl3): ꢁ 8.10–8.08 (m, 1H,
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2 of 9 Sagar et al. Six closely related arylamides
Acta Cryst. (2018). C74