662 JOURNAL OF CHEMICAL RESEARCH 2017
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Fig. 1 Normalised absorption and emission spectra of compounds 3 and 4 in chloroform (1 × 10–5 mol L–1).
spectrometer. UV-Vis absorption and fluorescence spectra were
recorded on a Hitachi U-3900H spectrometer and on a Hitachi F7000
FL spectrophotometer, respectively.
to this one-pot protocol under the same reaction conditions to
give the desired product 4 in moderate yield. These two novel
products were easily purified by column chromatography on
silica gel and were characterised on the basis of spectroscopic
data and also by comparison with analogues in the literature.9,10
The UV-Vis absorption spectra of the two synthesised 4-aryl-
2,6-dicoumarinylpyridines 3 and 4 in diluted chloroform
solutions are given in Fig. 1. It can be seen that the absorption
spectrum of 3 exhibits two peaks at 399 and 434 nm. The
absorption spectrum of 4 also displays two peaks at 399 and 432
nm, which are very close to that of compound 3. Figure 1 also
shows the fluorescence spectra of 3 and 4 in diluted chloroform
solutions. Compound 3 shows an emission maximum at 487
nm. The emission peak of 4 is located at 484 nm, blue-shifted
by only about 3 nm compared with that of 3. Thus, the spectra
of 3 and 4 in Fig. 1 indicate that the different aryl substituents
attached to the 4-position of the pyridine ring did not result in
notable changes in the absorption and emission pattern of these
molecules. However, it should be noted that 7-(diethylamino)-3-
(pyridin-2-yl)coumarin (DAPC, i.e. a monocoumarinylpyridine
compound) reported in the literature exhibits absorption and
emission maxima at 414 and 462 nm, respectively.15 Compared
with DAPC, compounds 3 and 4 synthesised herein show a
clear bathochromic shift in both the absorption and emission
maxima due to their larger conjugated system.
3-Acetyl-7-(diethylamino)coumarin (2)
4-(Diethylamino)salicylaldehyde (0.58 g, 3.0 mmol), ethyl acetoacetate
(0.39 g, 3.0 mmol) and piperidine (0.3 mL) were successively added to a
mortar. The mixture was ground thoroughly at room temperature with a
pestle for 30 min. Then, the resulting solid was dissolved in ethyl acetate
(50 mL), neutralised with 3 N HCl and extracted with brine (3 × 50 mL).
The organic phase was dried over Na2SO4, filtered and evaporated
under vacuum. The resulting residue was recrystallised in ethanol to
afford compound 2 a yellow solid; yield 90%; m.p. 154–155 °C (lit.16
151–153 °C).
2,6-Bis[7-(diethylamino)coumarin-3-yl]-4-(furan-2-yl)pyridine (3)
Furfural (0.19 g, 2.0 mmol), 3-acetyl-7-(diethylamino)coumarin
(1.04 g, 4.0 mmol) and NH4OAc (0.62 g, 8.0 mmol) were dissolved
in ethanol/acetic acid (30 mL, v/v = 1:1) and then TBAHS (0.17 g,
0.5 mmol) was added. The mixture was stirred under reflux conditions
and monitored by TLC. When the reaction was judged to be complete,
the organic solvent was evaporated under vacuum. Then, the mixture
was dissolved in dichloromethane (50 mL) and extracted with brine
(3 × 50 mL). The organic phase was dried over Na2SO4, filtered
and concentrated under reduced pressure. The resulting residue
was purified by column chromatography using petroleum ether/
dichloromethane (v/v = 2:1) as the eluent to afford compound 3 a
reddish-brown solid; yield 48%; m.p. 267–268 °C; IR (KBr) (cm–1):
2974, 1708, 1604, 1508, 1254, 810, 749; 1H NMR (400 MHz, CDCl3):
δ 8.75 (s, 2H), 8.59 (s, 2H), 7.57 (s, 1H), 7.47 (d, J = 8.8 Hz, 2H), 7.02
(d, J = 3.2 Hz, 1H), 6.64–6.62 (m, 2H), 6.56–6.53 (m, 3H), 3.45 (q,
J = 6.8 Hz, 8H), 1.25 (t, J = 6.8 Hz, 12H); 13C NMR (100 MHz, CDCl3):
δ 161.4, 156.8, 152.2, 151.1, 143.5, 142.8, 138.5, 130.0, 118.1, 116.2,
111.9, 109.2, 109.1, 108.9, 96.9, 44.9, 12.5. HRMS calcd for C35H34N3O5
[M + H]+: 576.2493; found: 576.2484.
In conclusion, the succinct synthesis of two novel 4-aryl-
2,6-dicoumarinylpyridines via a one-pot, multi-component
reaction using TBAHS as catalyst has been described. The
UV-Vis absorption and fluorescence spectra of these two
compounds in diluted chloroform solutions were measured,
which show a remarkable bathochromic shift compared with
the monocoumarinylpyridine reported in the literature. The
applicability of these coumarin-based pyridines is yet to be
established.
2,6-Bis[7-(diethylamino)coumarin-3-yl]-4-(naphthalen-1-yl)
pyridine (4)
Experimental
1-Naphthaldehyde (0.16 g, 1.0 mmol), 3-acetyl-7-(diethylamino)
coumarin (0.52 g, 2.0 mmol) and NH4OAc (0.31 g, 4.0 mmol) and a
method similar to that described for compound 3 were used to prepare
compound 4 a yellowish-brown solid; yield 52%; m.p. 311–312 °C; IR
(KBr) (cm–1): 2970, 1713, 1596, 1507, 1350, 1134, 780, 623; 1H NMR
(400 MHz, CDCl3): δ 8.81 (s, 2H), 8.48 (s, 2H), 8.07–8.05 (m, 1H),
7.92–7.89 (m, 2H), 7.58–7.49 (m, 6H), 6.63 (dd, J = 8.8, 2.4 Hz,
2H), 6.54 (s, 2H), 3.44 (q, J = 6.8 Hz, 8H), 1.24 (t, J = 6.8 Hz, 12H);
13C NMR (100 MHz, CDCl3 ): δ 161.4, 156.9, 151.9, 151.1, 149.5, 143.0,
Reagents and solvents were all from commercial sources and used
without further purification. IR spectra were performed on a Digilab
1
FTS-3000 FTIR spectrophotometer. H NMR and 13C NMR spectra
were recorded on a Mercury Plus 400 MHz spectrometer. Melting
points were measured on a Kofler apparatus and are uncorrected.
Column chromatography purifications were performed on 200–300
mesh silica gel. Analytical thin-layer chromatography (TLC) was
performed on silica gel GF254 plates. High-resolution mass spectra
(HRMS) were determined on a Bruker Daltonics APEX II 47e
Wei, Qiang
