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Synthesis of Polyhydroquinoline Derivatives under Solvent Free Conditions
method. Furthermore, high thermal stability, easy han-
dling, reusability and non-toxicity of the catalyst make
the present protocol as an eco-friendly and economi-
cally acceptable method for synthesis of these heterocy-
cles.
4H), 2.38 (s, 3H), 4.05 (q, J=7.0 Hz, 2H), 5.05 (s, 1H),
5.78 (s, 1H), 7.07—7.32 (m, 5H); IR (KBr) ν: 3290,
-
1
1698, 1612 cm . Anal. calcd for C21H25NO3: C 74.31,
H 7.42, N 4.13; found C 74.42, H 7.39, N 4.10.
Catalyst recovery and reuse
To a mixture of dimedone (10 mmol), benzaldehyde
(10 mmol), ethyl acetoacetate (10 mmol) and ammo-
nium acetate (10 mmol) in a round bottom flask was
added MgO (10 mol%) and heated for 4 min at 70 ℃.
The reaction progress was monitored by TLC. After
completion of the reaction, the mixture was cooled to
room temperature and diluted with CH2Cl2 (10 mL).
The catalyst was separated via centrifugation and
washed with CH2Cl2 (10 mL). The catalyst was dried at
100 ℃, and then reused in the next run. The solvent
was evaporated and the residue was purified by recrys-
talization in n-hexane or by column chromatography.
Experimental
All materials were commercial reagent grade and
were obtained from Merck or Alderich. 1H NMR spectra
were recorded on a Bruker-Arance AQS 300 MHz. A
multiwave ultrasonic generator (Bandlin Sonopuls Ger-
ate-Typ: UW 3200, Germany) equipped with a con-
verter/transducer and titanium oscillator (horn), 12.5
mm in diameter, operating at 30 kHz with a maximum
power output of 780 W, was used for the ultrasonic irra-
diation. The ultrasonic generator automatically adjusted
the power level. The wave amplitude in each experiment
was adjusted as needed. X-ray powder diffraction (XRD)
measurements were performed using a Philips diffrac-
tometer of X’pert Company with mono chromatized Cu
Kα radiation. The crystallite sizes of selected samples
were estimated using the sherrer method. nanoparticles
were characterized with a scanning electron microscope
(SEM) (Philips XL 30) with gold coating. IR spectra
were recorded on a SHIMADZU-IR460 spectrometer in
a KBr matrix. All melting points were obtained by Stu-
art Scientific apparatus. TLC monitored all reactions
and all yields refer to isolated ones.
Acknowledgment
The support of this work by Vali-e-Asr University
(Grant No. 2747) is gratefully acknowledged.
References
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General procedure for the synthesis of polyhydro-
quinoline
A mixture of dimedone (1 mmol), aldehyde (1
mmol), ethyl acetoacetate (1 mmol), ammonium acetate
(1 mmol) and MgO nanoparticles (5 mol%) was placed
in a round bottom flask and heated for appropriate time
(Table 2) at 70 ℃. After completion of the reaction, as
indicated by TLC, the mixture was cooled to room tem-
perature and diluted with CH2Cl2 (10 mL). The catalyst
was separated via centrifugation and washed with
CH2Cl2 (10 mL). The solvent was evaporated and the
residue was purified by recrystalization or by column
chromatography. Experimental data for 5a: m.p. 200—
1
201℃; H NMR (CDCl3, 500 MHz,) δ 0.94 (s, 3H),
20 Heravi, M. M.; Bakhtiari, K.; Javadi, M. N.; Bamoharram, F.
1.08 (s, 3H), 1.19 (t, J=7.0 Hz, 3H), 2.14—2.33 (m,
Chin. J. Chem. 2011, 29, 1624— 1628
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