Synthesis and photochemistry of novel 3,5-diacetyl-1,4-dihydropyridines

Article abstract of DOI:10.1007/s007060200038

Some novel 3,5-diacetyl-1,4-dihydropyridine derivatives were synthesized; their photochemical behaviour was studied under oxygen or argon atmosphere. Irradiation of these compounds resulted in the aromatization of the ring and formation of 3,5-diacetylpyr

Full text of DOI:10.1007/s007060200038

Monatshefte f uÈ r Chemie 133, 661±667 ꢀ2002)
Synthesis and Photochemistry of Novel
3
,5-Diacetyl-1,4-dihydropyridines
1
;Ã
1
1
Hamid R. Memarian , Majid M. Sadeghi , Ahmad R. Momeni ,
2
and Dietrich D oÈ pp
1
University of Isfahan, Faculty of Sciences, Department of Chemistry, 81744 Isfahan, Iran
Institut f u r Chemie, Gerhard Mercator-Universit a t=GH Duisburg, D-47048 Duisburg, Germany
2
Summary. Some novel 3,5-diacetyl-1,4-dihydropyridine derivatives were synthesized; their photo-
chemical behaviour was studied under oxygen or argon atmosphere. Irradiation of these compounds
resulted in the aromatization of the ring and formation of 3,5-diacetylpyridine derivatives. The
presence of oxygen plays an important role in the type, rate, or failure of oxidation. Irradiation of
these compounds with of 2-furyl or 5-methyl-2-furyl substituents in position 4 under argon resulted
in the formation of a pyridine ring with retention of these substituents, whereas loss of these sub-
stituents and ring aromatization was observed upon irradiation under oxygen.
Keywords. 1,4-Dihydropyridines; Heterocycles; Photochemistry; Photooxidation.
Introduction
In the course of our studies on the chemistry of 1,4-dihydropyridine-3,5-diesters,
also known as Hantzsch esters [1], especially their photochemical behaviour, we
were interested to investigate the effect of an acetyl group instead of an ester group
in positions 3 and 5 on the rate and type of oxidation.
Recent results have indicated that not only the type and nature of the 4-sub-
stituent plays an important role in the photooxidation, but also the presence or
absence of oxygen has an effect on the rate or failure of the reaction [2, 3]. Berson
and Brown [4] have shown that upon irradiation of dihydropyridine 1 dispropor-
tionation with loss of a molecule of water and formation of 2 occurs.
à Corresponding author. E-mail: memarian@sci.ui.ac.ir

6
62
H. R. Memarian et al.
Further investigations [5] on the photoreactivity of 3,5-diacetyl-1,4-dihydro-
pyridines 3a±c ꢀt-butanol, medium pressure mercury lamp, N atmosphere) have
2
shown that only in the case of 3a the product 4 has been obtained; in all other
cases, irradiation resulted in the recovery of unchanged starting material. Chromic
acid oxidation of the photoproduct led to the known diacetyl pyridine 5 [6].
In continuation of our work, we synthesized the novel 3,5-diacetyl-1,4-dihydro-
pyridines 6a±e and investigated their photochemical behaviour under oxygen or
argon atmosphere.
Results and Discussion
À3
A 15 Â 10 M solution of 3a or 6a±e in CHCl was irradiated under oxygen and
3
argon atmosphere until all starting material had disappeared. The results are sum-
marized in Table 1.
It is interesting to compare the results of the reactions under oxygen or argon
atmosphere in the following aspects:
i) Whereas in the presence of oxygen the irradiation time, can be shortened, oxi-
dation of 6d does not occur in the absence of oxygen.
ii) Whereas irradiation of 6a and 6e under both atmospheres yields 7a and 7e with
retention of the substituent in position 4, loss of this substituent and formation
of 5 were observed only upon irradiation of 6b and 6c under oxygen.
The observed fast reaction under oxygen atmosphere indicates the involvement
of the singlet state of 3a and 6a±e in the reaction, since it could not be quenched by

Photochemistry of Dihydropyridine Derivatives
663
Table 1. Irradiation of dihydropyridines 3a and 6a±e under O and Ar
2
O2
Ar
a
b
a
b
Product ꢀ%)
Time ꢀh)
Product ꢀ%)
Time ꢀh)
3
6
6
6
6
6
a
a
b
c
5 ꢀ85)
7a ꢀ81)
5 ꢀ85)
4
12.5
7
5 ꢀ81)
7a ꢀ77)
7b ꢀ75)
7c ꢀ79)
6d ꢀ±)
9.5
19
22
5 ꢀ88)
7d ꢀ80)
7e ꢀ78)
6
19.5
12
d
e
11.5
14
7e ꢀ80)
17
a
b
Isolated yield; Irradiation times refer to disappearance of the starting material
triplet oxygen ꢀoxygen in its ground state). This suggestion is also supported by the
fact that in the case of 6d the photooxidation did not occur under argon. Another
possibility that singlet oxygen formed by energy transfer from excited 3a and 6a±e
to oxygen in the ground state is involved in the reaction can be ruled out since
dihydropyridines are not suitable triplet sensitizers for the formation of singlet
oxygen. Recently, we have reported on the photosensitized oxidation of Hantzsch
esters using rose bengal, methylene blue, and tetraphenylporphine under oxygen
[
7]. The results indicated that photooxidation in the presence of these triplet sen-
sitizers is faster in comparison to the reaction in their absence. Additional studies
have shown that photooxidation of 3a and 6a±e proceeds fast in the presence of
these sensitizers [8].
The loss of the substituent in position 4 has been observed earlier in photo-
chemical reactions of Hantzsch esters only in the cases of carboxy groups [9], some
heterocyclic groups [3], and secondary alkyl and benzyl groups [3]. Thermal
oxidation of Hantzsch esters with expulsion of benzylicand se co ndary substituents
in position 4 by various oxidants such as pyridinium chlorochromate ꢀPCC) [10],
ceric ammonium nitrate ꢀCAN) [11], bismuth nitrate pentahydrate [12], manga-
neseꢀIII) acetate [13], tetrakis-pyridine cobaltꢀII) dichromate ꢀTPCD) [14], 3-car-
boxypyridinium chlorochromate ꢀCPCC) [15], nicotinium dichromate ꢀNDC) [16],
sodium nitrite=oxalica icd [17], sodium nitrite =sodium hydrogen sulfate [18],
sodium nitrite=magnesium hydrogen sulfate [19], sodium nitrate in the presence
of wet SiO [20], barium manganate [21], and potassium peroxodisulfate [22] has
2
been reported.
1
IR, H NMR ꢀTable 2), and UV data gave useful information on the structural
assignment of the photoproducts 5 and 7a±e. A comparison of the IR spectra
showed the disappearance of the NH band and a shift of the CO vibration to higher
frequency due to oxidation and aromatization of the ring, which cause a decrease in
the conjugation of the CO groups with the C±C double bonds. Comparison of the
1
H NMR spectra indicated the loss of the NH signal and of characteristic peaks of
the substituent in position 4 in the case of 5 because of the expulsion of the
substituent upon photooxidation of 6b and 6c. In this case, H±C appears in the
4
1
aromaticregion at 8.25 ppm. In the H NMR spectra of photoproducts containing
the 4-substitunt, the loss of NH and H±C resonances was observed. Owing to
4
conjugation of the C±C double bond of dihydropyridine with the carbonyl double

6
64
H. R. Memarian et al.
1
Table 2. Comparison of the IR and H NMR spectra of 3a, 6a±e with those of 5, 7a±e
À1
1
À1
1
IR ꢀꢃ=cm
NH CO
)
H NMR ꢀꢂ=ppm)
IR ꢀꢃ=cm
CO
)
H NMR ꢀꢂ=ppm)
2,6-CH3 3,5-COCH3 4-H NH
2,6-CH3 3,5-COCH3 4-H
3
6
6
6
6
6
a
a
b
c
3400 1670 2.18
3260 1665 2.24
3250 1665 2.32
3280 1668 2.32
3200 1655 2.25
3320 1670 2.33
2.23
2.28
2.36
2.37
2.32
2.34
3.43 5.26
5
1680
2.64
1.90
2.15
2.19
2.08
2.03
2.77
2.40
2.51
2.49
2.56
2.51
8.25
5.29 6.15 7a 1683, 1700
5.15 6.71 7b 1690, 1700
5.07 6.83 7c 1690
5.31 8.09 7d 1700
5.38 6.72 7e 1690
±
±
±
±
±
d
e
bond, the methyl groups in positions 2 and 6 are shifted down®eld and the protons
of the acetyl groups are shifted up®eld in comparison with these resonances in the
photoproduct ꢀpyridine ring). Also, the UV spectra did not show any strong ab-
sorption above 300 nm, which is characteristic for the pyridine ring.
Experimental
All melting points were determined with a Stuart Scienti®c SMP2 and are uncorrected. IR: Shimadzu
1
IR-435; UV: Shimadzu UV-160; H NMR: Bruker AW80 ꢀ80 MHz), Bruker WM 300 ꢀ300 MHz);
mass spectra: AMD 604; EI mode ꢀ70 eV): temperature of inlet system given; FD mode: high voltage
applied given, no additional heating of the emitter ®lament. Elemental analyses: Carlo Erba 1106
CHN-analyzer; the results agreed favourably with the calculated values. Preparative thin layer chro-
2
matography ꢀPLC) was carried out on 20 Â 20 cm plates coated with a 1 mm layer of Merk silica gel
PF prepared by applying the silica as a slurry and drying in air.
254
All irradiations were performed using a 400 W high-pressure Hg-vapour lamp from NARVA with
cooling of samples in Duran glass ꢀꢀ ꢀ 280 nm) by running cold water. Argon ꢀ99.99%) or oxygen
ꢀ99.99%) was bubbled through the solutions during irradiation.
General procedure for the preparation of compound 3a, 6a±e
3
A mixture of 0.02 mol of appropriated aldehyde and 0.04 mol of acetylacetone in 20 cm EtOH was
3
saturated with NH gas ꢀ3a) or treated with 3 cm of NH solution ꢀ6a±e) and re¯uxed for the time
3
3
given. The solvent was evaporated, and the residue was cooled in refrigerator. The solid material was
puri®ed by recrystallization.
3
,5-Diacetyl-2,6-dimethyl-1,4-dihydropyridine ꢀ3a; C H NO )
11 15 2
ꢁ ꢁ
h re¯uxed, recrystallized from ethanol=petroleum ether ꢀ5 : 1); m.p.: 197 C ꢀRef. [6]: 198 C); IR
8
À1
1
ꢀ
KBr): ꢁ ˆ 3400 ꢀNH), 1670 ꢀCO) cm ; H NMR ꢀCDCl ): ꢂ ˆ 2.18 ꢀs, 6H, 2- and 6-CH ), 2.23 ꢀs,
3
3
ꢁ
6
H, 3- and 5-COCH ), 3.43 ꢀs, 2H, 4-H), 5.26 ꢀs, 1H, NH) ppm; EI-MS ꢀ170 C): m=z ꢀ%) ˆ 193
‡ ‡ ‡ ‡ ‡
3
[
M ] ꢀ93), 192 [M -H] ꢀ100), 178 [M -CH ] ꢀ81), 150 [M -COCH ] ꢀ37), 107 [M -2 Â
3
3
COCH ] ꢀ10); UV ꢀCHCl ): ꢀ
3
ꢀlg ") ˆ 393 ꢀ3.92), 275 ꢀ3.90), 249 ꢀ3.97) nm; UV ꢀCH OH): ꢀ
3
max
3
max
ꢀ
lg ") ˆ 408 ꢀ3.63), 276 ꢀ3.62), 251 ꢀ3.88) nm.
0 0
,5-Diacetyl-4-'2 ,5 -dimethoxyphenyl)-2,6-dimethyl-1,4-dihydropyridine ꢀ6a; C H NO )
19 23 4
3
ꢁ
À1
6
1
h re¯uxed, recrystallized from EtOH; m.p.: 192 C; IR ꢀKBr): ꢁ ˆ 3260 ꢀNH), 1665 ꢀCO) cm
;
H NMR ꢀCDCl ): ꢂ ˆ 2.24 ꢀs, 6H, 2- and 6-CH ), 2.28 ꢀs, 6H, 3- and 5-COCH ), 3,69 ꢀs, 3H,
3
3
3

Photochemistry of Dihydropyridine Derivatives
665
0
0
0
5
-OCH ), 3.77 ꢀs, 3H, 2 -OCH ), 5.29 ꢀs, 1H, 4-H), 6.15 ꢀs, 1H, NH), 6.61 ꢀd, J ˆ 2.98 Hz, 1H, 6 -
3
3
0
0
H), 6.65 ꢀdd, J ˆ 8.73 Hz and 3.04 Hz, 1H, 4 -H), 6.74 ꢀd, J ˆ 8.73 Hz, 1H, 3 -H) ppm; EI-MS
ꢁ
‡
‡
‡
‡
ꢀ
160 C): m=z ꢀ%) ˆ 329 [M ] ꢀ13), 298 [M -OCH ] ꢀ78), 283 [M -OCH , -CH ] ꢀ11), 192 [M -
3
3
3
4
-substituent] ꢀ100), 150 ꢀ21); UV ꢀCHCl ): ꢀ
3
ꢀlg ") ˆ 367 ꢀ3.62), 341 ꢀ3.7), 298 ꢀ3.5), 258
max
ꢀ
3.5) nm; UV ꢀCH OH): ꢀ
3
ꢀlg ") ˆ 373 ꢀ3.65), 240 ꢀ3.55) nm.
max
0
3
,5-Diacetyl-4-'2 -furyl)-2,6-dimethyl-1,4-dihydropyridine ꢀ6b; C H NO )
1
5
17
3
ꢁ
8
h re¯uxed, recrystallized from ethanol=petroleum ether ꢀ5 : 1); m.p.: 167 C; IR ꢀKBr): ꢁ ˆ 3250
À1 1
ꢀ
NH), 1665 ꢀCO) cm ; H NMR ꢀCDCl ): ꢂ ˆ 2.32 ꢀs, 6H, 2- and 6-CH ), 2.36 ꢀs, 6H, 3- and 5-
3
3
0
COCH ), 5.15 ꢀs, 1H, 4-H), 5.89 ꢀdd, J ˆ 3.18 Hz and 0.63 Hz, 1H, 3 -H), 6.21 ꢀdd, J ˆ 3.18 Hz and
3
0
0
1
.87 Hz, 1H, 4 -H), 6.71 ꢀs, 1H, NH), 7.24 ꢀdd, J ˆ 1.60 Hz and 0.66 Hz, 1H, 5 -H) ppm; EI-MS
ꢁ
‡
‡
‡
‡
ꢀ
ꢀ
ꢀ
130 C): m=z ꢀ%) ˆ 259 [M ] ꢀ51), 244 [M -CH ] ꢀ10), 216 [M -COCH ] ꢀ100), 192 [M -furyl]
3
3
‡
25), 174 ꢀ47), 149 [M -furyl, -COCH ] ꢀ8); UV ꢀCHCl ): ꢀ
max
ꢀlg ") ˆ 368 ꢀ3.77), 343 ꢀ3.79), 255
3
3
3.60) nm; UV ꢀCH OH): ꢀ
3
ꢀlg ") ˆ 391 ꢀ3.68), 342 ꢀ3.66), 238 ꢀ3.48) nm.
max
0
0
3
,5-Diacetyl-2,6-dimethyl-4-'5 -methyl-2 -furyl)-1,4-dihydropyridine ꢀ6c; C H NO )
1
6
19
3
ꢁ
7
1
6
h re¯uxed, recrystallized from ethanol=cyclohexane ꢀ4 : 1); m.p.: 175 C; IR ꢀKBr): ꢁ ˆ 3280 ꢀNH),
À1 1
0
668 ꢀCO) cm ; H NMR ꢀCDCl ): ꢂ ˆ 2.19 ꢀs, 3H, 5 -CH ), 2.32 ꢀs, 6H, 2- and 6-CH ), 2.37 ꢀs,
3
3
3
0
H, 3- and 5-COCH ), 5.07 ꢀs, 1H, 4-H), 5.73 ꢀd, J ˆ 3.01 Hz, 1H, 3 -H), 5.77 ꢀdd, J ˆ 3.04 Hz
3
0
ꢁ
‡
and 0.88 Hz, 4 -H), 6.83 ꢀs, 1H, NH) ppm; EI-MS ꢀ60 C): m=z ꢀ%) 192 [M -4-substituent];
‡
‡
FD-MS ꢀ0.005V): m=z ꢀ%) ˆ 273 [M ] ꢀ31), 192 [M -4-substituent] ꢀ100), 134 ꢀ17); UV ꢀCHCl ):
3
ꢀ
ꢀlg ") ˆ 347 ꢀ3.97), 249 ꢀ4.07) nm; UV ꢀCH OH): ꢀ
ꢀlg ") ˆ 362 ꢀ3.81), 252 ꢀ3.99), 222
max
3
max
ꢀ3.92) nm.
0
,5-Diacetyl-2,6-dimethyl-4-'2 -pyridyl)-1,4-dihydropyridine ꢀ6d; C H N O )
16 18 2 2
3
ꢁ
1
0 h re¯uxed, recrystallized from ethanol=petroleum ether ꢀ5 : 1); m.p.: 178 C. IR ꢀKBr): ꢁ ˆ 3200
À1 1
ꢀ
NH), 1655 ꢀCO) cm ; H NMR ꢀCDCl ): ꢂ ˆ 2.25 ꢀs, 6H, 2- and 6-CH ), 2.32 ꢀs, 6H, 3- and 5-
3
3
0
COCH ), 5.31 ꢀs, 1H, 4-H), 7.12 ꢀddd, J
3
0
0
ˆ 6 Hz, J
0
0
ˆ 4.9 Hz, J
0 0
5 ,3
ˆ 1.1 Hz, 1H, 5 -H), 7.34
5 ,4
5 ,6
0
0
ꢀdd, J3
0
0
ˆ 7.8 Hz, J
0
0
ˆ 0.9 Hz, 1H, 3 -H), 7.60 ꢀddd, J
0
0
or J
0
0
ˆ 7.8 Hz, J
0 0
4 ,6
ˆ 1.8 Hz, 1H, 4 -
,4
3 ,5
4 ,3
4 ,5
0
H), 8.09 ꢀs, 1H, NH), 8.45 ꢀddd, J
0
0
ˆ 4.8 Hz, J
0
0
ˆ 1.8 Hz, J
0 0
ˆ 0.9 Hz, 1H, 6 -H) ppm; EI-MS
6
,5
6 ,4
6 ,3
ꢁ
‡
‡
‡
ꢀ
ꢀ
145 C): m=z ꢀ%) ˆ 270 [M ] ꢀ5), 192 [M -pyridyl] ꢀ100); FD-MS ꢀ0.01 V): m=z ˆ ꢀ%) 270 [M ]
‡
100), 227 [M -COCH ] ꢀ13); UV ꢀCHCl ): ꢀ
3
ꢀlg ") ˆ 371 ꢀ3.74), 255 ꢀ4.0) nm; UV ꢀCH OH):
3
max
3
ꢀmax ꢀlg ") ˆ 386 ꢀ3.74), 250 ꢀ4.25), 210 ꢀ3.8) nm.
0
3
,5-Diacetyl-2,6-dimethyl-4-'2 -thienyl)-1,4-dihydropyridine ꢀ6e; C H NO S)
1
5
17
2
ꢁ
À1
;
8
h re¯uxed, recrystallized from ethanol; m.p.: 171 C; IR ꢀKBr): ꢁ ˆ 3320 ꢀNH), 1670 ꢀCO) cm
1
H NMR ꢀCDCl ): ꢂ ˆ 2.33 ꢀs, 6H, 2- and 6-CH ), 2.34 ꢀs, 6H, 3- and 5-COCH ), 5.38 ꢀs, 1H, 4-H),
3
3
3
0
0
6
.72 ꢀs, 1H, NH), 6.76 and 6.77 ꢀ2 bt, 1H, 3 -H), 6.84 ꢀdd, J ˆ 5.1 Hz and 3.5 Hz, 1H, 4 -H), 7.07 ꢀdd,
‡ ‡
0
ꢁ
J ˆ 5.1 Hz and 1.19 Hz, 1H, 5 -H) ppm; EI-MS ꢀ145 C): m=z ꢀ%) ˆ 275 [M ] ꢀ70), 260 [M -CH ]
3
‡
‡
ꢀ
17), 232 [M -COCH ] ꢀ100), 192 [M -thienyl] ꢀ72); UV ꢀCHCl ): ꢀ
3
ꢀlg ") ˆ 365 ꢀ4.02), 248
3
max
ꢀ4.1) nm; UV ꢀCH OH): ꢀ
3
ꢀlg ") ˆ 377 ꢀ3.86), 241 ꢀ4.17) nm.
max
General procedure for the irradiation of dihydropyridines
3
A solution of 0.3 mmol 3a or 6a±e in 20 cm CHCl under Ar or O was irradiated until all starting
3
2
material had disappeared ꢀTLC; the corresponding times are given in Table 1). When the reaction
was complete, the solvent was evaporated and the product was isolated by PLC.

6
66
H. R. Memarian et al.
3
,5-Diacetyl-2,6-dimethylpyridine ꢀ5; C H NO )
1
1
13
2
ꢁ
PLC, ethyl acetate=cyclohexane ꢀ3 : 2), R ˆ 0.50, recrystallized from n-hexane; m.p.: 66 C; IR
f
À1
1
ꢀ
KBr): ꢁ ˆ 1680 ꢀCO) cm ; H NMR ꢀCDCl ): ꢂ ˆ 2.64 ꢀs, 6H, 2- and 6-CH ), 2.77 ꢀs, 6H, 3- and
3
3
ꢁ
‡
‡
5
1
ꢀ
-COCH ), 8.25 ꢀs, 1H, 4-H) ppm; EI-MS ꢀ45 C): m=z ꢀ%) ˆ 191 [M ] ꢀ3), 176 [M -CH ] ꢀ52),
3
‡
3
‡
‡
48 [M -COCH ] ꢀ5), 106 [M -COCH , -H CCO] ꢀ34), 105 [M -2 Â COCH ] ꢀ5); UV ꢀCHCl ):
3
3
2
3
3
ꢀlg ") ˆ 256 ꢀ4.20) nm; UV ꢀCH OH): ꢀ
ꢀlg ") ˆ 277 ꢀ3.88), 245 ꢀ4.12) nm.
max
3
max
0 0
,5-Diacetyl-4-'2 ,5 -dimethoxyphenyl)-2,6-dimethylpyridine ꢀ7a; C H NO )
19 21 4
3
ꢁ
PLC, ethyl acetate=cyclohexane ꢀ3 : 2), R ˆ 0.67, recrystallized from n-hexane; m.p. 106 C; IR
f
À1
1
ꢀ
KBr): ꢁ ˆ 1700, 1683 ꢀCO) cm ; H NMR ꢀCDCl ): ꢂ ˆ 1.9 ꢀs, 6H, 2- and 6-CH ), 2.4 ꢀs, 6H,
3
3
0 0 0 0 0
- and 5-COCH ), 3.7 ꢀs, 6H, 2 - and 5 -OCH ), 6.6 ꢀs, 1H, 6 -H), 6.9 ꢀs, 2H, 3 - and 4 -H) ppm; EI-
3 3
3
ꢁ
‡
‡
‡
‡
MS ꢀ100 C): m=z ꢀ%) ˆ 327 [M ] ꢀ89), 312 [M -CH ] ꢀ6), 297 [M -2  CH ] ꢀ21), 296 [M -
3
3
‡
OCH ] ꢀ100), 253 [M -OCH , -COCH ] ꢀ4), 226 ꢀ10), 127 ꢀ9), 115 ꢀ9), 43 [COCH ] ꢀ65); UV
3
3
3
3
ꢀ
CHCl ): ꢀ
3
ꢀlg ") ˆ 258 ꢀ3.40) nm; UV ꢀCH OH): ꢀ
ꢀlg ") ˆ 241 ꢀ3.40) nm.
max
3
max
0
3
,5-Diacetyl-4-'2 -furyl)-2,6-dimethylpyridine ꢀ7b; C H NO )
15
1
5
3
ꢁ
PLC, ethyl acetate=cyclohexane ꢀ1 : 2), R ˆ 0.61, recrystallized from n-hexane; m.p.: 86 C; IR
f
À1
1
ꢀ
KBr): ꢁ ˆ 1700 ꢀsh), 1690 ꢀCO) cm ; H NMR ꢀCDCl ): ꢂ ˆ 2.15 ꢀs, 6H, 2- and 6-CH ), 2.51 ꢀs,
3
3
0
6
1
2
H, 3- and 5-COCH ), 6.54 ꢀdd, J ˆ 1.7 Hz and 3.4 Hz, 1H, 4 -H), 6.59 ꢀdd, J ˆ 0.7 Hz and 3.5 Hz,
‡
3
0
0
ꢁ
H, 3 -H), 7.58 ꢀdd, J ˆ 0.7 Hz and 1.6 Hz, 5 -H) ppm; EI-MS ꢀ70 C): m=z ꢀ%) ˆ 257 [M ] ꢀ49),
‡
‡
‡
‡
42 [M -CH ] ꢀ3), 214 [M -COCH ] ꢀ63), 200 [M -H CCO, -CH ] ꢀ60), 199 [M -COCH ,
3
3
3
2
3
‡
-
CH ] ꢀ4), 173 [M -2 Â H CCO] ꢀ7), 43 ꢀCOCH ); UV ꢀCHCl ): ꢀ
ꢀlg ") ˆ 260 ꢀ3.70) nm;
3
2
3
3
max
UV ꢀCH OH): ꢀ
3
ꢀlg ") ˆ 237 ꢀ3.80) nm.
max
0
0
3
,5-Diacetyl-4-'5 -methyl-2 -furyl)-2,6-dimethylpyridine ꢀ7c; C H NO )
1
6
17
3
PLC, ethyl acetate=cyclohexane ꢀ1 : 2), R ˆ 0.56, recrystallized from ethyl acetate=petroleum ether
f
ꢁ
À1
1
ꢀ
2 : 7); m.p.: 91 C; IR ꢀKBr): ꢁ ˆ 1690 ꢀCO) cm ; H NMR ꢀCDCl ): ꢂ ˆ 2.19 ꢀs, 6H, 2- and 6-
3
0
CH ), 2.34 ꢀd, J ˆ 0.47, 3H, 5 -CH ), 2.49 ꢀs, 6H, 3- and 5-COCH ), 6.13 ꢀdd, J ˆ 0.84 Hz
3
3
3
0
0
ꢁ
‡
and 3.48 Hz, 1H, 4 -H), 6.47 ꢀd, J ˆ 3.42 Hz, 1H, 3 -H) ppm; EI-MS ꢀ60 C): m=z ꢀ%) ˆ 271 [M ]
‡ ‡ ‡
55), 256 [M -CH ] ꢀ10), 228 [M -COCH ] ꢀ39), 214 [M -H CCO, -CH ] ꢀ100); UV ꢀCHCl ):
3 3 2 3 3
ꢀ
ꢀmax ꢀlg ") ˆ 252 ꢀ3.10) nm; UV ꢀCH OH): ꢀmax ꢀlg ") ˆ 250 ꢀ3.18) nm.
3
0
3
,5-Diacetyl-4-'2 -pyridyl)-2,6-dimethylpyridine ꢀ7d; C H N O )
16 16 2 2
ꢁ
PLC, ethyl acetate=cyclohexane ꢀ3 : 1), R ˆ 0.42, recrystallized from petroleum ether; m.p.: 112 C;
f
À1
1
IR ꢀKBr): ꢁ ˆ 1700 ꢀCO) cm ; H NMR ꢀCDCl ): ꢂ ˆ 2.08 ꢀs, 6H, 2- and 6-CH ), 2.56 ꢀs, 6H, 3-
3
3
0
0
and 5-COCH ), 7.36 ꢀddd, J ˆ 7.78 Hz, 4.59 Hz and 1.17 Hz, 2H, 3 - and 5 -H), 7.76 ꢀddd, J ˆ
3
0
0
7
.74 Hz and 1.7 Hz, 1H, 4 -H), 8.68 ꢀddd, J ˆ 4.2 Hz, 1.6 Hz and 1.2 Hz, 1H, 6 -H) ppm; EI-MS
‡ ‡ ‡
ꢁ
ꢀ
ꢀ
[
ꢀ
85 C): m=z ˆ ꢀ%) 253 [M -CH ] ꢀ71), 211 [M -H CCO, -CH ] ꢀ29), 210 [M -COCH , -CH ]
‡
3
2
3
3
3
14), 182 [M -2  COCH ] ꢀ7), 134 ꢀ25), 120 ꢀ49), 91 ꢀ100); FD-MS ꢀ0.005 V): m=z ꢀ%) ˆ 268
3
‡
‡
‡
M ] ꢀ11), 253 [M -CH ] ꢀ100), 210 [M -COCH , -CH ] ꢀ10); UV ꢀCHCl ): ꢀ
3
ꢀlg ") ˆ 237
3
3
3
max
3.80) nm; UV ꢀCH OH): ꢀ
3
ꢀlg ") ˆ 241 ꢀ3.40) nm.
max
0
3
,5-Diacetyl-4-'2 -thienyl)-2,6-dimethylpyridine ꢀ7e; C H NO S)
1
5
15
2
PLC, ethyl acetate=cyclohexane ꢀ3 : 2), R ˆ 0.53, recrystallized from ethyl acetate=n-hexane ꢀ1 : 5);
f
ꢁ
À1
1
m.p. 130 C; IR ꢀKBr): ꢁ ˆ 1690 ꢀCO) cm ; H NMR ꢀCDCl ): ꢂ ˆ 2.03 ꢀs, 6H, 2- and 6-CH ), 2.51
3
3

Photochemistry of Dihydropyridine Derivatives
667
0
ꢀ
s, 6H, 3- and 5-COCH ), 7.03 ꢀdd, J ˆ 3.57 Hz and 1.19 Hz, 1H, 3 -H), 7.11 ꢀdd, J ˆ 5.1 Hz and
3
0
0
ꢁ
3
.57 Hz, 1H, 4 -H), 7.51 ꢀdd, J ˆ 5.03 Hz and 1.19 Hz, 1H, 5 -H) ppm; EI-MS ꢀ85 C): m=z ˆ ꢀ%) 273
‡ ‡ ‡
[
M ] ꢀ58), 258 [M -CH ] ꢀ57), 230 [M -COCH ] ꢀ100), 216 ꢀ37), 198 ꢀ11), 189 ꢀ49); UV ꢀCHCl ):
3 3 3
ꢀmax ꢀlg ") ˆ 281 ꢀ3.90), 249 ꢀ3.97) nm; UV ꢀCH OH): ꢀ
ꢀlg ") ˆ 281 ꢀ3.95), 239 ꢀ4.04) nm.
3
max
Acknowledgements
We are thankful to the Isfahan University Research Council for partial support to this work. H. R.
Memarian is indebted to the German Academic Exchange Service ꢀDAAD) for a Scholorship during
the period July±August 1998.
References
[
[
[
[
[
[
[
[
[
1] Hantzsch A ꢀ1982) Justus Liebigs Ann Chem 215: 1
2] Memarian HR, Sadeghi MM, Aliyan H ꢀ1998) Indian J Chem 37B: 219
3] Memarian HR, Sadeghi MM, Momeni AR ꢀ1999) Indian J Chem 38B: 800
4] Berson JA, Brown E ꢀ1955) J Am Chem Soc 77: 447
5] Eisner U, Williams JR, Mathhews BW, Ziffer H ꢀ1970) Tetrahedron 26: 899
6] Scholts M ꢀ1897) Ber Dtsch Chem Ges 30: 2295
7] Memarian HR, Sadeghi MM, Momeni AR ꢀ2001) Indian J Chem S 40B: 508
8] Memarian HR, Sadeghi MM, Momeni AR ꢀin preparation)
9] Biellmann JF, Callot HJ, Pilgrim WR ꢀ1972) Tetrahedron 28: 5911
[
[
[
[
[
[
[
10] Vanden Eynde JJ, Mayence A, Maquestiau A ꢀ1992) Tetrahedron 48: 463
11] P®ster JR ꢀ1990) Synthesis 689
12] Mashraqui SH, Karnik MA ꢀ1998) Synthesis 713
13] Varma RS, Kumer D ꢀ1990) Tetrahedron Lett 40: 21
14] Wang B, Hu Y, Hu H ꢀ1999) Synth Commun 29: 4193
15] Mohammadpoor-Baltork I, Sadeghi MM, Memarian HR, Pairow R ꢀ2000) J Chem Res ꢀS) 40
16] Sadeghi MM, Mohammadpoor-Baltork I, Memarian HR, Sobhani S ꢀ2000) Synth Commun 30:
1
661
17] Zol®gol MA, Kiani-Borazjani M, Sadeghi MM, Mohammadpoor-Baltork I, Memarian HR
2000) Synth Commun 30: 551
18] Zol®gol MA, Kiani-Borazjani M, Sadeghi MM, Memarian HR, Mohammadpoor-Baltork I
2000) Synth Commun 30: 2945
19] Zol®gol MA, Kiani-Borazjani M, Sadeghi MM, Mohammadpoor-Baltork I, Memarian HR
2000) Synth Commun 30: 3919
20] Zol®gol MA, Kiani-Borazjani M, Sadeghi MM, Memarian HR, Mohammadpoor-Baltork I
2000) J Chem Research ꢀS) 167
[
[
[
[
ꢀ
ꢀ
ꢀ
ꢀ
[21] Memarian HR, Sadeghi MM, Momeni AR ꢀ2001) Synth Commun 31: 2241
[22] Memarian HR, Mohammadpoor-Baltork I, Sadeghi MM, Samani ZS ꢀ2001) Indian J Chem
4
0B: 727
Received September 4, 2001. Accepted September 17, 2001