Photoinduced Aromatization of Unsymmetrically Substituted 1,4 ...

138 J. Chin. Chem. Soc., Vol. 54, No. 1, 2007 Memarian et al.
8.06 Hz, 2-H and 6-H); MS m/z (rel. int. %): 311 [M + ]
(65), 296 [M + -CH3] (25), 282 [M + -CH2CH3] (11), 268
[M + - COCH3] (16), 250 [M + -CH3CH2OH-CH3] (100),
238 [M + -CO2CH2CH3] (6), 224 [M + - COCH3 -CH3CHO]
(20), 43 [CH3CO + ] (49); Anal. Calcd. for C19H21NO3
(311.38): C, 73.29; H, 6.80; N, 4.50; O, 15.41. Found: C,
73.22; H, 6.81; N, 4.46.
Ethyl 5-acetyl-2,6-dimethyl-4-(3-pyridyl)pyridine-3carboxylate
(3i)
PLC (petroleum ether/ethyl acetate, 3:2). m.p. 57-59
C. UV (MeOH) max [nm] (log ): 266 (3.75), 209 (3.97).
IR max: 1724 (CO2C2H5), 1705 (COCH3)cm -1 ; 1 H NMR :
1.09 (t, 3H, J = 7.13 Hz, CO2CH2CH3), 2.04 (s, 3H, 6-CH3),
2.58 (s, 3H, 2-CH3), 2.67 (s, 3H, COCH3), 4.09 (q, 2H, J =
7.05 Hz, CO2CH2CH3), 7.40 (dd, 1H, J = 7.58 Hz and 4.90
Hz, 5-H), 7.63 (d, 1H, J = 7.87 Hz, 4-H), 8.56 (s, 1H, 6-
H), 8.71 ppm (br s, 1H, 2-H); MS m/z (rel. int. %): 298
[M + ] (21), 283 [M + -CH3] (100), 269 [M + -CH2CH3] (7),
256 [M + - COCH2] (27), 255 [M + - COCH3] (24), 237 [M + -
CH3CH2OH-CH3] (13), 227 [M + - COCH3 -C2H4] (17),
182 [M + -CO2CH2CH3 - COCH3] (4), 43 [CH3CO + ] (39);
Anal. Calcd. for C17H18N2O3 (298.34): C, 68.44; H, 6.08;
N, 9.39; O, 16.09. Found: C, 67.96; H, 6.17; N, 8.73.
Ethyl 5-acetyl-2,6-dimethyl-4-(4-pyridyl)pyridine-3carboxylate
(3j)
PLC (petroleum ether/ethyl acetate, 3:2). m.p. 92-94
C. UV (MeOH) max [nm] (log ): 268 (3.67), 212 (4.20);
IR max: 1737 (CO2C2H5), 1722 (COCH3)cm -1 ; 1 H NMR :
0.98 (t, 3H, J = 7.10 Hz, CO2CH2CH3), 2.05 (s, 3H, 6-CH3),
2.58 (s, 3H, 2-CH3), 2.67 (s, 3H, COCH3), 4.07 (q, 2H, J =
7.07 Hz, CO2CH2CH3), 7.26 (d, 2H, J = 5.41 Hz, 3-H and
5-H), 8.72 ppm (d, 2H, J =4.03Hz,2-H and 6-H); MS
m/z (rel. int. %): 298 [M + ] (37), 283 [M + -CH3] (100), 270
[M + -C2H4] (5), 269 [M + -CH2CH3] (5), 255 [M + - COCH3]
(23), 237 [M + -CH3 -CH3CH2OH] (16), 227 [M + - COCH3
-C2H4] (12), 182 [M + -COCH3 -CO2CH2CH3] (5), 43
[CH3CO + ] (38); Anal. Calcd. for C17H18N2O3 (298.34): C,
68.44; H, 6.08; N, 9.39; O, 16.09. Found: C, 68.71; H, 6.18;
N, 8.65.
CONCLUSIONS
Photo-induced electron transfer oxidation of unsymmetrically
substituted 1,4-dihydropyridines in chloroform
solution resulted in the oxidation of ring and the formation
of the corresponding pyridine derivatives. The effect of
4-substituent has influenced the rate of reaction under oxygen
or argon atmosphere, and it explained the extent of the
light sensitivity of these compounds depending on the type
and nature of 4-substituent. Because of the completion of
the reaction, the products can be isolated by simple chromatography
methods.
ACKNOWLEDGEMENTS
We thank the Office of Graduate Studies of the University
of Isfahan for financial support.
Received April 28, 2006.
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