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A.R. Khosropour et al. / C. R. Chimie 14 (2011) 441–445
Table 3
Tandem synthesis of 2,4,5-triarylpyridines from benzyl alcohols and 1-arylethanols promoted by [HMIm]NO3-[BMIm]BF4.
Entry
Ar
Ar’
Y
Time (s)
Yield (%)a
1
C6H5
C6H5
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
CH(OH)CH3
490
480
420
450
270
550
510
420
510
210
310
450
300
510
270
95
89
97
96
92
96
93
94
98
96
92
96
91
95
90
2
2-CH3C6H4
4-BrC6H4
2-naphtyl
2-thiophenyl
C6H5
C6H5
3
C6H5
4
C6H5
5
C6H5
6
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
7
2-CH3C6H4
4-BrC6H4
2-naphtyl
2-thiophenyl
C6H5
8
9
10
11
12
13
14
15
2-CH3C6H4
4-BrC6H4
2-naphtyl
2-thiophenyl
a
Yields refer to isolated pure products characterized by NMR, IR and Mass spectroscopy [17–29].
3.2. Typical procedure for the synthesis of 2,4,6-
167, 149, 57. 4-(naphthalen-2-yl)-2,6-di-4-tolylpyridine
(Table 2, entry 18). Mpt 124 8C. IR (KBr, cmÀ1
3100, 3050, 2900, 2870, 1610, 1590, 1500, 810, 740.
1HNMR (500 MHz, CDCl3)
H: 8.22 (s, 1H), 8.15 (d, J = 8.05,
triphenylpyridine from benzyl alcohol and acetophenone
) nmax:
A mixture of benzyl alcohol (1 mmol), [HMIm]NO3
(1 mmol) and [BMIm]BF4 (1 mmol) was stirred under
microwave irradiation (96 8C, 200 watt in Micro-SYNTH)
for 200 s. Once conversion to benzaldehyde was completed
(TLC), acetophenone (2 mmol) and ammonium acetate
(3 mmol) were added and the reaction allowed to stir
under microwave at the same temperature until the
completion of the reaction. When the reaction was
completed, quenched with ice-water (10 ml) and extracted
with ethyl acetate (3 Â 5 ml). The organic layer was dried
(Na2SO4), concentrated under vacuum and recrystallized
by 25% ethyl acetate/n-hexane to give 2,4,6-triphenylpyr-
idine in 98% yield.
d
4H), 8.01–7.97 (m, 4H), 7.92 (t, J = 6.4, 1H), 7.88–7.86 (m,
1H), 7.58–7.55 (m, 2H), 7.34 (d, J = 8, 4H), 2.46 (s, 6H). EIMS
m/z 385, 91, 77, 67, 57, 55. 2,6-bis(4-chlorophenyl)-4-(4-
(phenoxymethyl)phenyl)pyridine (Table 2, entry 27): mpt
154 8C. IR (KBr, cmÀ1
810, 770. 1HNMR (500 MHz, CDCl3)
)
n
max: 3120, 2900, 2800, 1580, 1340,
d
H: 8.12 (d, J = 8.25 Hz,
4H), 7.82 (s, 2H), 7.69 (d, J = 8.35 Hz, 2H), 7.44–7.26 (m,
9H), 7.13 (d, J = 8.32, 2H), 5.16 (s, 2H). EMIS m/z 481, 188,
91, 77, 67, 65, 55, 51. 2,6-bis(4-chlorophenyl)-4-(5-
methylthiphen-2-yl) pyridine (Table 2, entry 29): mpt
184 8C. IR (KBr, cmÀ1
1490, 1400, 1070, 805, 770. 1HNMR (500 MHz, CDCl3) dH
) nmax: 3118, 2912, 2803, 1595,
:
8.09 (d. J = 8.35, 4H), 7.75 (s, 2H), 7.48 (d, J = 8.35, 4H), 7.49
(d. J = 3.35, 1H), 6.84 (d, J = 2.53, 1H), 2.57 (s, 3H). EMIS m/z
396 (M++1), 395, 70,69,54,55.
3.3. Typical procedure for the synthesis of 2,4,6-
triphenylpyridine from benzyl alcohol and 1-phenylethanol
To a mixture of benzyl alcohol (1 mmol) and 1-
phenylethanol (2 mmol) in [BMIm]BF4 (1 mmol),
[HMIm]NO3 (2.5 mmol) was added. The reaction mixture
was stirred in a microwave oven (MicroSYNTH) at 96 8C
(200 watt). When conversion to the benzaldehyde and
acetophenone were completed, as indicated by TLC,
ammonium acetate (3 mmol) was added and the reaction
allowed to irradiate under microwave condition. After
completion of the reaction (490 s), the reaction mixture was
poured into 10 ml ice-water and extracted with ethyl
acetate for three times. The combined organic layer was
washed with water and dried over Na2SO4. The solvent was
evaporated and the pure 2,4,6-triphenylpyridine in 95% was
obtained by recrystallization with 25% ethyl acetate/n-
hexane.
4. Conclusion
This work demonstrates a novel, simple, efficient and
green protocol by a microwave-promoted tandem process
for the synthesis of 2,4,6-triarylpyridines using
[HMIm]NO3-[BMIm]BF4 as a binary task specific ionic
liquid. Moreover fast, clean and easy work-up of the
expected products could be considered as other advan-
tages of this method. To the best of our knowledge, this is
the first example of tandem process for the synthesis of
these pyridine derivatives under microwave irradiations.
The use of [HMIm]NO3-[BMIm]BF4 makes this method a
versatile alternative procedure for the synthesis of
Kro¨hnke pyridines. Further studies to delineate of the
mechanism and limitations of the present methodology
are underway.
3.4. Spectral data for selected compounds
2,6-diphenyl-4-(thiophen-2-yl)pyridine (Table 2, entry
9): mpt 154 8C. IR (KBr, cmÀ1
)
n
max: 3050, 1595, 1400, 760,
Acknowledgments
690. 1HNMR (500 MHz, CDCl3)
d
H: 8.21 (d, J = 13.7, 4H),
7.89 (s, 2H), 7.63 (d, J = 3.4, 1H), 7.54 (t, J = 7.35, 4H), 7.50–
7.45 (m, 3H), 7.19 (t, J = 4, 1H). EIMS m/z 315, 314, 313, 312,
The authors are grateful to the Center of Excellence of
Chemistry of University of Isfahan (CECUI) and also the