Journal of the Iranian Chemical Society
multicomponent reaction of ethyl acetoacetate, hydrazine,
remarkable achievements, biocompatible synthesis of these
potent pyridines using an inexpensive, easily available and
metal-free catalyst is still in demand. This work focuses on
the developing triethanolamine–sodium acetate (TEA:SA)
as a new deep eutectic solvent and application of it in the
synthesis of dipyrazolopyridines.
Some selected spectroscopic data
3,5‑Dimethyl‑4‑(4‑bromophenyl)‑1,4,7,8‑tetr
ahydrodipyrazolo [3,4‑b; 4′,3′‑e] Pyridine (5e)
Cream solid, m.p. 221–224 °C. FT-IR (ATR), ῡ (cm−1):
3333, 3272, 1596, 1518, 1474, 833, 663. 1H NMR
(400 MHz, DMSO-d6), δ (ppm), 2.06 (s, 6H, 2CH3), 4.78
(s, 1H, CH),7.03 (d, J=8 Hz, 2 H, ArH), 7.39 (d, J=8 Hz,
2H, ArH), 11.50 (s, 3H, 3NH) ppm; 13C NMR (100 MHz,
DMSO-d6), δ (ppm): 10.23, 32.43, 104.45, 118.30, 129.62,
130.34, 131.85, 142.66, 157.00.
3,5‑Dimethyl‑4(3‑hydroxyphenyl)‑1,4,7,8‑ tetrahydrodipyra‑
zolo [3,4‑b; 4′,3′‑e]Pyridine (5d)
Experimental
Pink solid, m.p. 225–228 °C. FT-IR (ATR) ῡ (cm−1): 3464,
1
General
3336, 1607, 1449, 1395, 1262, 875, 832, 686. H NMR
(400 MHz, DMSO-d6) /δ ppm: 11.32 (s, NH, 3H), 9.11 (s,
OH, 1H), 6.99 (t, J = 7.6 Hz, 1H), 6.57 (s, 1H), 6.53 (d,
J=8.8 Hz, 1H), 6.51 (d, J=8.4 Hz, 1H), 4.74 (s, 1H), 2.07
(s, 6H). 13C NMR (100 MHz, DMSO-d6) /δ ppm: 161.58,
157.41, 145.32, 140.29, 128.98, 118.71, 115.05, 112.84,
104.73, 33.04, 10.86.
All chemicals were purchased from Merck, Fluka and were
used without further purifcation. A conventional cell was
used for studying the electrochemical behavior of DES. Plat-
inum electrode was used as working electrode, Ag/AgCl,
KCl (3 M) as reference electrodes and platinum as coun-
ter electrode. A computer-controlled potentiostat [Sama,
IRAN] was used for electrochemical experiment. Thermo-
gravimetric analysis (TGA/DTA) was done with “STA 504”
instrument. Diferential scanning calorimeter (DSC-60, Shi-
madzu Japan) was used for the study of phase transition of
TEA:SA (0.88:0.12 mol) mixture. The pH and conductivity
of DES were measured by Metrohm pH meter model 691
and Metrohm 912 conductometer. The viscosity of DES was
measured Brookfeld DV-E viscometer (spindle, 2 RV and
rotating speed 50 RPM). Fourier transform infrared (FT-IR,
ATR) spectra were run on a Bruker, Equinox 55 spectrom-
eter. A Bruker (DRX-400 Avance) nuclear magnetic reso-
nance (NMR) instrument was used to record the 1H-NMR
spectra. Melting points were determined by a Buchi melting-
point B-540 B.V.CHI apparatus.
3,5‑Dimethyl‑4(3,4‑dihydroxy phenyl)‑1,4,7,8‑ tetrahy‑
drodipyrazolo [3,4‑b; 4′,3′‑e] Pyridine (5 l).
Cream solid, m.p. 204–207 °C, FT-IR (ATR), ῡ (cm−1):
3343, 3297, 1600, 1511, 1439, 1172, 1075, 834, 787, 737.
1H NMR (400 MHz, DMSO-d6), δ (ppm) 11.30 (s, NH, 3H),
8.63 (s, OH, 1H), 8.52 (s, OH, 1H), 6.56 (d, J=8 Hz, 1H),
6.55(s, 1H), 6.35 (d, J=8 Hz, 1H), 4.67 (s, 1H), 2.06 (s, 6H).
13C NMR (100 MHz, DMSO-d6), δ (ppm): 161.59, 144.97,
143.43, 140.21, 134.55, 118.56, 115.61, 115.32, 105.18,
32.36, 10.86.
Results and discussion
General procedure for the synthesis of dipyrazo-
lopyridines
The eutectic temperature of triethanolamine (TEA), as
hydrogen bond donor, and sodium acetate trihydrate (SA),
as hydrogen bond acceptor, initially, was determined by
freezing and defreezing of various mole fractions of them.
The melting point of every mole fraction of TEA and SA
was determined by digital thermometer (−50–150 °C). The
obtained data are shown in Fig. 1. The eutectic point of
this system was obtained as 4 °C in 0.91 mol fraction of
triethanolamine.
A mixture of hydrazine hydrate (0.5 mmol), ethyl acetoac-
etate (0.5 mmol), aldehyde (0.25 mmol), ammonium acetate
(1 mmol) and TEA:SA (0.88:0.12), (0.01 g) was charged
in the microwave Tefon vessel and allowed to react under
microwave irradiation. The progress of the reaction was
monitored by thin-layer chromatography (n-hexane:EtOAc,
50:50). After completion of the reaction, the reaction mix-
ture was cooled to room temperature. Then, the solid product
was obtained by adding water to reaction mixture. The prod-
uct was fltered and dried at room temperature.
For the determination of eutectic point of TEA:SA, the
0.88:0.12) from −100 to+250 °C were obtained (Fig. 2a–b).
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