Enaminones in a multicomponent synthesis of 4-aryldihydropyridines for potential applications in photoinduced intramolecular electron-transfer systems

Article abstract of DOI:10.3762/bjoc.8.50

An efficient three component reaction with enaminones, primary amines and aldehydes resulted in easy access to 1,4-dihydropyridines with different substituents at the 1-, 3-, 4- and 5-positions. Microwaves improved the reaction yield, reducing also considerably the reaction time and the amount of solvent used. Chiral primary amines gave chiral 1-substituted-1,4-dihydropyridines. The 4-(1-naphthyl) and 4-(phenanthren-9-yl)dihydropyridine derivatives exhibited an interesting photoluminescence behavior, which suggests their potential application as suitable photoinduced intramolecular electron-transfer systems.

Full text of DOI:10.3762/bjoc.8.50

Supporting Information
for
Enaminones in a multicomponent synthesis of
4-aryldihydropyridines for potential applications in
photoinduced intramolecular electron-transfer systems
Nouria A. Al-Awadi*, Maher R. Ibrahim, Mohamed H. Elnagdi, Elizabeth John
and Yehia A. Ibrahim
Address: Chemistry Department, Faculty of Science, Kuwait University, P.O. Box 5969,
Safat 13060, Kuwait
Email: Nouria A. Al-Awadi - n.alawadi@ku.edu.kw
*Corresponding author
Experimental procedures and characterization of compounds, including
copies of 1H and 13C NMR spectra.
Contents
Experimental details, analytical and spectral data of products ……………….S2–S14
1H NMR and 13C NMR of all products ………………………………………...S15–S49
S1

Synthesis
Synthesis of dihydropyridines 2, 4, 10, 12 and 14: General procedure
Method A: A mixture of the appropriate enaminones 1 (2.2 mmol) [1,2], aromatic
aldehyde (1 mmol) and ammonium acetate (0.228 g, 1.5 mmol), or aromatic amine
(1 mmol) in glacial acetic acid (20 mL) was heated under reflux for 1–3 h. The mixture
was then poured into ice water (ca. 50 g) and the precipitate was collected by filtration
and crystallized from the proper solvent to yield compounds 2a–o (Table 1), 4a,b, 10a,b,
12 and 14.
Method B: A mixture of the starting material in few drops of acetic acid (0.5 mL) was
irradiated in a microwave oven for 2 min at 160 °C, and after cooling, ice water (5 mL)
was added. The precipitated product was collected and crystallized from the proper
solvent to give 2, (Table 1) 4a,b and 10b.
Method C: A mixture of the appropriate enaminones 1 (2.2 mmol) and the appropriate
Schiff’s base 3 (1.0 mmol) in acetic acid (20 mL) was heated under reflux for 2 h. After
cooling, ice water (50 mL) was added and the yellow precipitate formed was collected
and crystallized from ethanol to give 2 (Table 1).
3,5-Dibenzoyl-4-phenyl-1,4-dihydropyridine (2a). Yellow needles from ethyl acetate; mp
245–246 °C (lit. [3] mp 246–248 °C). MS: m/z = 365 (M+, 80%), 288 (100%). LCMS:
m/z = 366 (M + 1); IR: 3412, 3241, 3031, 2963, 1633, 1614, 1571, 1490, 1371, 1220,
1115, 1080, 968; 1H NMR (400 MHz, DMSO-d6):  9.28 (t, 1H, NH, J = 5.6), 7.54–7.50
(m, 2H), 7.44 (m, 8H), 7.35 (d, 2H, J = 7.4), 7.27 (t, 2H, J = 7.6), 7.17–7.13 (m, 1H),
13
7.13 (d, 2H, J = 5.6), 5.41 (s, 1H); C NMR (100 MHz, 100 MHz, DMSO-d6):  193.6,
146.8, 139.29, 139.27, 130.7, 128.3, 128.1, 128.0, 127.6, 126.0, 116.3, 35.7. Anal. calc.
for C25H19NO2 (365.4): C 82.17; H 5.24; N 3.83. Found: C 82.08; H 5.18; N 3.77.
4-p-Chlorophenyl-3,5-dibenzoyl-1,4-dihydropyridine (2b). Yellow needles from ethyl
acetate, mp 232–234 °C. LCMS = 400 (M + 1); MS: m/z = 401 (M + 2, 32%), 399 (M+,
100%), 288 (80%), 105 (25%); IR: 3417, 3236, 3160, 3044, 1655, 1621, 1566, 1481,
1
1369, 1224, 1176, 1084, 970, 727; H NMR (400 MHz, CDCl3):  7.45–7.41 (m, 6H),
7.38–7.33 (m, 6H), 7.18 (d, 2H, J = 8.4), 6.93 (d, 2H, J = 8.4), 6.76 (t, 1H, J = 4.8), 5.56
S2

13
(s, 1H); C NMR (100 MHz, CDCl3):  194.6, 144.7, 139.1, 137.4, 132.1, 131.0, 129.5,
128.4, 128.33, 128.26, 118.4, 36.2; Anal. calc. for C25H18ClNO2 (399.9): C 75.09; H
4.54; N 3.50. Found: C 75.10; H 4.39; N 3.47.
3,5-Dibenzoyl-4-p-tolyl-1,4-dihydropyridine (2c). Yellow needles from ethanol, mp 228–
230 °C. MS: m/z = 379 (M+, 85%), 288 (100%), 105 (80%); IR: 3430, 3240, 3151, 3031,
2995, 1629, 1560, 1474, 1369, 1223, 1176, 1116, 969, 762; 1H NMR (400 MHz, CDCl3):
 7.45–7.39 (m, 6H), 7.34 (d, 2H, J = 8.0), 7.30–7.26 (m, 4H), 7.01 (d, 2H, J = 8.0), 6.89
13
(d, 2H, J = 5.2), 6.75 (t, 1H, J = 5.2), 5.54 (s, 1H), 2.23 (s, 3H); C NMR (100 MHz,
DMSO-d6):  194.3, 144.5, 139.8, 139.6, 135.4, 131.2, 129.2, 128.8, 128.5, 128.1, 116.9,
35.8, 21.1. Anal. calc. for C26H21NO2 (379.5): C 82.30; H 5.58; N 3.69. Found: C 82.18;
H 5.39; N 3.67.
3,5-Bis(2-thiophenecarbonyl)-4-phenyl-1,4-dihydropyridine (2d). Yellow needles from
ethanol, mp 315–317 °C. MS: m/z = 377 (M+, 90%), 300 (100%), 111 (35%); IR: 3413,
1
3100, 3022, 1661, 1591, 1468, 1412, 1365, 1290, 1199, 1086, 742, 719; H NMR (400
MHz, DMSO-d6):  9.41 (br, 1H, NH), 7.85 (dd, 2H, J = 4.8, 1.2), 7.58 (dd, 2H, J = 3.6,
1.2), 7.55 (br, 2H), 7.28 (dd, 2H, J = 7.6, 1.2), 7.21 (t, 2H, J = 7.6), 7.15 (dd, 2H, J = 4.8,
3.6), 7.08 (t, 1H, J = 7.8), 5.36 (s, 1H); 13C NMR (100 MHz, DMSO-d6):  184.4, 146.6,
143.4, 137.5, 132.2, 131.3, 128.0, 127.9, 127.8, 126.1, 115.9, 36.7. Anal. calc. for
C21H15NO2S2 (377.5): C 66.82; H 4.01; N 3.71; S 16.99. Found: C 66.78; H 4.08; N 3.70;
S 16.98.
3,5-Bis(2-furoyl)-4-phenyl-1,4-dihydropyridine (2e). Yellow crystals from ethanol, mp
238–240 °C. MS: m/z = 345 (M+, 75%), 224 (100%), 168 (25%); IR: 3327, 3106, 2946,
1698, 1664, 1598, 1404, 1318, 1206, 1118, 819; 1H NMR (400 MHz, DMSO-d6):  9.56
(t, 1H, J = 5.4), 7.89 (d, 2H, J = 0.6), 7.85 (d, 2H, J = 5.4), 7.25 (d, 2H, J = 8.4), 7.19 (t,
2H, J = 8.0), 7.11 (d, 2H, J = 3.0), 7.07 (t, 1H, J = 7.8), 6.63 (dd, 2H, J = 3.0, 0.6), 5.34
13
(s, 1H); C NMR (100 MHz, DMSO-d6):  178.8, 152.3, 146.7, 146.1, 137.6, 128.0,
127.7, 126.0, 116.9, 115.6, 111.9, 35.4. Anal. calc. for C21H15NO4 (345.4): C 73.04; H
4.38; N 4.06. Found: C 73.00; H 4.28; N 4.00.
S3

3,5-Dibenzoyl-1,4-diphenyl-1,4-dihydropyridine (2f). Yellow needles from ethanol, mp
296–298 °C. MS: m/z = 441 (M+, 80%), 364 (100%), 105 (50%); IR: 3058, 3024, 2894,
1
1657, 1624, 1592, 1568, 1491, 1448, 1344, 1285, 1236, 1144, 1071, 978, 695; H NMR
(400 MHz, CDCl3):  7.59–7.55 (m, 4H), 7.52–746 (m, 4H), 7.44–7.39 (m, 6H), 7.32 (s,
2H), 7.29 (m, 3H), 7.17 (m, 3H), 5.72 (s, 1H); 13C NMR (100 MHz, DMSO-d6):  193.9,
145.5, 142.9, 139.6, 138.6, 131.4, 130.0, 128.5, 128.34, 128.28, 128.0, 126.8, 126.4,
121.3, 118.8, 36.3. Anal. calc. for C31H23NO2 (441.5): C 84.33; H 5.25 ; N 3.17. Found:
C 84.25; H 5.21 ; N 3.12.
3,5-Dibenzoyl-1-(p-hydroxyphenyl)-4-phenyl-1,4-dihydropyridine (2g). Yellow needles
from ethanol, mp 330–332 °C. MS: m/z = 457 (M+, 80%), 380 (100%), 105 (50%); IR:
3257, 3057, 3030, 2971, 1656, 1626, 1552, 1512, 1448, 1337, 1281, 1236, 1147, 1115,
980, 719; 1H NMR (400 MHz, DMSO-d6):  9.72 (s, 1H, OH), 7.53 (dt, 6H, J = 8.4, 1.2),
7.43 (dt, 6H, J = 8.4, 1.2), 7.30 (t, 2H, J = 8.0), 7.24 (d, 2H, J = 8.4), 7.17 (s, 2H), 7.14 (t,
13
1H, J = 7.8), 6.76 (d, 2H, J = 8.4), 5.46 (s, 1H); C NMR (150 MHz, DMSO-d6): 
193.8, 156.5, 145.8, 140.6, 138.7, 134.9, 131.3, 128.5, 128.3, 128.2, 128.0, 126.4, 123.6,
118.1, 116.2, 36.0. Anal. calc. for C31H23NO3 (457.5): C 81.38; H 5.07; N 3.06. Found: C
81.25; H 5.01 ; N 3.10.
3,5-Bis(2-furoyl)-1,4-diphenyl-1,4-dihydropyridine (2h). Yellow needles from ethanol,
mp 229–230 °C. MS: m/z = 421 (M+, 80%), 364 (100%), 105 (50%); IR: 3090, 3022,
2914, 1662, 1618, 1598, 1563, 1491, 1463, 1348, 1299, 1245, 1168, 1117, 1074, 740;
1H NMR (400 MHz, DMSO-d6):  8.06 (s, 2H), 7.93 (dd, 2H, J = 1.8, 0.8), 7.66 (d, 2H, J
= 7.6), 7.54 (t, 2H, J = 7.8), 7.38 (t, 1H, J = 8.0), 7.35 (d, 2H, J = 8.8), 7.28 (dd, 2H, J =
1.6, 0.8), 7.23 (t, 2H, J = 7.8), 7.11 (t, 1H, J = 7.6), 6.64 (dd, 2H, J = 3.6, 1.6), 5.41 (s,
1H); 13C NMR (100 MHz, DMSO-d6):  179.0, 151.9, 146.8, 145.4, 143.1, 138.1, 130.1,
128.2, 128.0, 126.7, 126.4, 121.4, 118.2, 118.0, 112.1, 35.9. Anal. calc. for C27H19NO4
(421.5): C 76.95; H 4.54; N 3.32. Found: C 76.90; H 4.51; N 3.22.
S4

3,5-Bis(2-furoyl)-1-(p-methoxyphenyl)-4-phenyl-1,4-dihydropyridine (2i). Yellow needles
from ethanol, mp 220–222 °C. MS: m/z = 451 (M+, 90%), 374 (100%), 331 (25%); IR:
3122, 3012, 2928, 1657, 1610, 1560, 1512, 1337, 1292, 1246, 1170, 1115, 1077, 746;
1H NMR (400 MHz, DMSO-d6):  7.96 (s, 2H), 7.92 (dd, 2H, J = 1.6, 0.8), 7.60 (dd, 2H,
J = 8.0. 1.6), 7.36 (dd, 2H, J = 8.0, 1.2), 7.26 (dd, 2H, J = 3.6, 0.8), 7.23 (t, 2H, J = 8.0),
7.11 (t, 1H, J = 7.4), 7.08 (dd, 2H, J = 8.0, 1.6), 6.65 (dd, 2H, J = 3.6, 1.6), 5.40 (s, 1H),
13
3.81 (s, 3H, OCH3); C NMR (100 MHz, DMSO-d6):  178.9, 158.1, 151.9, 146.7,
145.6, 138.9, 136.5, 128.2, 128.0, 126.3, 123.5, 117.8, 117.6, 115.1, 112.1, 55.5, 35.6.
Anal. calc. for C28H21NO5 (451.5): C 74.49; H 4.69; N 3.10. Found: C 74.40; H 4.51; N
3.02.
3,5-Bis(p-chlorobenzoyl)-1-(p-methoxyphenyl)-4-phenyl-1,4-dihydropyridine
(2j).
Yellow needles from ethanol, mp 196–198 °C. MS: m/z = 543 (M + 4, 8%), 541 (M + 2,
50%), 539 (M+, 94%), 462 (100%), 400 (20%); IR: 3061, 3024, 2958, 1626, 1590, 1508,
1476, 1457, 1289, 1237, 1085, 826, 747, 692; 1H NMR (400 MHz, DMSO-d6):  7.58 (d,
4H, J = 8.4), 7.50 (d, 4H, J = 8.4), 7.43 (t, 2H, J = 7.4), 7.40 (d, 2H, J = 8.8), 7.30 (t, 2H,
J = 7.8 ), 7.27 (s, 2H), 7.16 (t, 1H, J = 7.4), 6.97 (d, 2H, J = 8.8), 5.44 (s, 1H), 3.75 (s,
3H); 13C NMR (100 MHz, DMSO-d6):  192.6, 158.0, 145.5, 140.6, 137.3, 136.1, 136.0,
130.2, 128.5, 128.3, 128.0, 126.4, 123.4, 118.1, 114.9, 55.5, 36.0. Anal. calc. for
C32H23Cl2NO3 (540.5): C 71.12; H 4.29; N 2.59. Found: C 71.05; H 4.21; N 2.52.
3,5-Bis(2-thiophenecarbonyl)-1-(p-methoxyphenyl)-4-phenyl-1,4-dihydropyridine (2k).
Yellow needles from ethanol, mp 228–230 °C. MS: m/z = 483 (M+, 90%), 406 (100%),
111 (60%); IR: 3100, 3024, 2914, 1661, 1610, 1569, 1510, 1415, 1338, 1285, 1226,
1
1122, 1073, 1024, 822, 738; H NMR (400 MHz, DMSO-d6):  7.90 (dd, 2H, J = 4.8,
0.8), 7.76 (dd, 2H, J = 3.6, 0.8), 7.65 (s, 2H), 7.57 (d, 2H, J = 8.8), 7.40 (d, 2H, J = 8.0),
7.26 (t, 2H, J = 7.6), 7.16 (dd, 2H, J = 4.8, 3.6), 7.12 (t, 1H, J = 7.8), 7.03 (d, 2H, J =
13
8.8), 5.43 (s, 1H), 3.79 (s, 3H); C NMR (100 MHz, DMSO-d6):  184.8, 157.9, 145.5,
143.2, 138.6, 136.5, 133.0, 132.3, 128.22, 128.15, 128.06, 126.4, 123.4, 118.0, 114.9,
55.5, 37.1. Anal. calc. for C28H21NO3S2 (483.6): C 69.54; H 4.38; N 2.90; S 13.26.
Found: C 69.45; H 4.31; N 2.82; S 13.21.
S5

3,5-Bis(2-thiophenecarbonyl)-1,4-diphenyl-1,4-dihydropyridine (2l). Yellow needles
from ethanol, mp 298–300 °C. MS: m/z = 453 (M+, 90%), 376 (100%), 342 (20%); IR:
3092, 3023, 2920, 1659, 1595, 1569, 1491, 1415, 1342, 1286, 1232, 1122, 1070, 852,
740; 1H NMR (400 MHz, DMSO-d6):  7.91 (dd, 2H, J = 4.8, 1.2), 7.79 (dd, 2H, J = 3.6,
1.2), 7.75 (s, 2H), 7.63 (d, 2H, J = 7.8), 7.51 (t, 2H, J = 8.0), 7.40 (d, 2H, J = 7.6), 7.36 (t,
1H, J = 7.4), 7.25 (t, 2H, J = 7.8), 7.16 (dd, 2H, J = 4.8, 3.6), 7.12 (t, 1H, J = 7.8), 5.44
13
(s, 1H); C NMR (100 MHz, DMSO-d6):  184.9, 145.2, 143.1, 143.0, 137.8, 133.1,
132.4, 129.9, 128.21, 128.19, 128.0, 126.5, 126.4, 121.3, 118.5, 37.2. Anal. calc. for
C27H19NO2S2 (453.6): C 71.50; H 4.22; N 3.09; S 14.14. Found: C 71.45; H 4.17 ; N
3.02; S 14.11.
3,5-Dibenzoyl-1-(o-cyanophenyl)-4-phenyl-1,4-dihydropyridine (2m). Yellow needles
from ethanol, mp 225–227 °C. MS: m/z = 466 (M+, 100%), 389 (100%), 105 (20%); IR:
1
3063, 3024, 2971, 2223, 1638, 1571, 1489, 1333, 1275, 1229, 1089, 787, 754; H NMR
(600 MHz, DMSO-d6):  7.93 (d, 1H, J = 8.8), 7.74 (t, 1H, J = 7.6), 7.62 (d, 1H, J = 8.0),
7.58 (d, 4H, J = 7.8), 7.53–7.49 (m, 5H), 7.42 (t, 4H, J = 7.8), 7.29 (t, 2H, J = 7.6), 7.27
13
(s, 2H), 7.17 (t, 1H, J = 7.8), 5.54 (s, 1H); C NMR (100 MHz, DMSO-d6):  193.9,
145.4, 145.3, 140.1, 138.3, 135.0, 134.2, 131.6, 128.5, 128.4, 128.3, 128.21, 128.18,
126.6, 125.7, 118.7, 116.6, 108.0, 36.3. Anal. calc. for C32H22N2O2 (466.5): C 82.38; H
4.75; N 6.00. Found: C 82.25; H 4.71 ; N 6.02.
3,5-dibenzoyl-4-phenyl-1-tert-butyl-1,4-dihydropyridine (2n). Yellow needles from
ethanol, mp 218–220 °C. MS: m/z = 421 (M+, 90%), 364 (80%), 288 (100%); IR: 3082,
3033, 2913, 1671, 1593, 1556, 1443, 1410, 1352, 1256, 1212, 1024, 1070, 864, 737;
1H NMR (400 MHz, DMSO-d6):  7.56–7.52 (m, 2H), 7.50–7.44 (m, 8H), 7.31 (d, 2H, J
= 7.6), 7.25 (s, 2H), 7.23 (t, 2H, J = 7.8), 7.13 (t, 1H, J = 7.8), 5.38 (s, 1H), 1.30 (s, 9H);
13C NMR (100 MHz, CDCl3):  194.5, 146.1, 139.6, 138.0, 130.8, 128.5, 128.3, 128.2,
127.9, 126.3, 119.2, 57.9 36.7, 29.2. Anal. calc. for C29H27NO2 (421.5): C 82.63; H 6.46;
N 3.32. Found: C 82.55; H 6.41; N 3.30.
S6

(3,5-Dibenzoyl-4-phenyl-4H-pyridin-1-yl)acetic acid (2o). Yellow needles from ethyl
acetate, mp 258–260 °C. MS: m/z = 423 (M+, 90%), 364 (80%), 288 (100%); IR: 3082,
3033, 2913, 1671, 1593, 1556, 1443, 1410, 1352, 1256, 1212, 1024, 1070, 864, 737;
1H NMR (400 MHz, CDCl3):  7.52–7.42 (m, 4H), 7.39 (t, 4H, J = 7.8), 7.31 (t, 4H, J =
7.6), 7.19 (t, 2H, J = 7.8), 7.05 (t, 1H, J = 7.8), 6.76 (s, 2H), 5.52 (s, 1H), 4.06 (s, 2H),
13
2.91 (br, 1H); C NMR (150 MHz, CDCl3):  194.7, 170.3, 145.7, 141.6, 139.0, 131.1,
128.6, 128.34, 128.29, 128.25, 126.4, 119.2, 55.5, 36.5. Anal. calc. for C27H21NO4
(423.5): C 76.58; H 5.00; N 3.31. Found: C 76.55; H 5.01; N 3.30.
3,5-Dibenzoyl-4-phenyl-1-(1-phenylethyl)-1,4-dihydropyridine (4a). Yellow needles from
ethanol, yield 78% (method A), 94% (method B), mp 289–290 °C. MS: m/z = 469 (M+,
80%), 364 (95%), 288 (50%); IR: 3095, 3027, 2983, 1659, 1599, 1563, 1411, 1365, 1287,
1230, 1201, 1090, 939, 734; 1H NMR (400 MHz, DMSO-d6):  7.44–7.38 (m, 11H), 7.32
(t, 4H, J = 7.8), 7.18 (t, 4H, J = 7.8), 7.13 (t, 1H, J = 7.6), 6.97 (dd, 2H, J = 3.6, 1.2), 5.60
13
(s, 1H), 4.71 (q, 1H, J = 7.0), 1.67 (d, 3H, J = 7.0); C NMR (100 MHz, DMSO-d6): 
194.3, 194.1, 146.0, 139.8, 139.5, 139.4, 139.3, 129.2, 130.9, 130.8, 129.2, 128.6, 128.5,
128.3, 128.1, 128.0, 126.6, 126.4, 119.2, 118.9, 62.3, 37.1, 19.6. Anal. calc. for
C33H27NO2 (469.6): C 84.41; H 5.80; N 2.98. Found: C 84.45; H 5.71; N 3.00.
3,5-Bis(2-thiophenecarbonyl)-1-(1-phenylethyl)-4-phenyl-1,4-dihydropyridine
(4b).
Yellow needles from ethanol, yield 78% (method A), 93% (method B), mp 310–312 °C.
MS: m/z = 481 (M+, 100%), 376 (100%), 300 (70%); IR: 3055, 3022, 2938, 1661, 1624,
1
1566, 1450, 1418, 1360, 1275, 1248, 1192, 1113, 972, 786, 756, 727; H NMR
(400 MHz, CDCl3):  7.85 (dd, 2H, J = 3.6, 1.2), 7.54–7.42 (m, 6H), 7.39 (t, 1H, J = 7.8),
7.36 (dd, 1H, J = 3.6, 1.2), 7.30 (dd, 1H, J = 3.6, 1.2), 7.23–7.17 (m, 4H), 7.12–6.98 (m,
13
3H), 5.32 (q, 1H, J = 7.0), 5.27 (s, 1H), 1.75 (d, 3H, J = 7.0); C NMR (100 MHz,
DMSO-d6):  184.3, 184.1, 145.9, 143.4, 143.3, 140.1, 139.0, 138.5, 132.7, 132.6,
131.58, 131.55, 129.0, 128.2, 128.1, 127.9, 127.7, 127.2, 126.3, 116.9, 116.7, 61.0, 37.2,
18.7. Anal. calc. for C29H23NO2S2 (481.6): C 72.32; H 4.81; N 2.91; S 13.31. Found: C
72.25; H 4.74; N 2.82 ; S 13.30.
S7

Synthesis of pyridine derivatives 5a,b: General Procedure
A mixture of each of the appropriate enaminones 1 (4.2 mmol), benzaldehyde (0.22 g,
2 mmol) and the appropriate aliphatic diamine (1 mmol) was heated under reflux in acetic
acid (20 mL) for 2 h (method A), or irradiated in a microwave oven for 2 min at 160 °C
(method B), and after cooling, ice water was added to the mixture. The yellow solid so
formed was collected and crystallized from ethanol to give 5a,b in excellent yield.
1,2-Bis(3,5-dibenzoyl-4-phenyl-1,4-dihydropyridin-1-yl)ethane (5a). Yellow needles
from ethanol, yield 76% (method A), 92% (method B), mp 279–280 °C. MS: m/z = 756
(M+, 30%), 738 (25%), 365 (50%), 105 (100%); IR: 3055, 2938, 1661, 1624, 1566, 1450,
1
1410, 1366, 1285, 1248, 1192, 1113, 972, 786, 756, 727; H NMR (400 MHz, DMSO-
d6):  7.47 (tt, 4H, J = 7.8, 2.0), 7.40–7.29 (m, 20H), 7.18 (t, 4H, J = 7.8), 7.09 (tt, 2H, J
13
= 7.8, 1.4), 7.04 (s, 4H), 5.28 (s, 2H), 3.78 (s, 4H); C NMR (100 MHz, DMSO-d6): 
193.1, 146.3, 142.0, 138.8, 130.9, 128.3, 128.1, 128.0, 127.8, 126.1, 117.3, 52.8, 35.7.
Anal. calc. for C52H40N2O4 (756.9): C 82.52; H 5.33; N 3.70. Found: C 82.45; H 5.31; N
3.72.
1,3-Bis(3,5-dibenzoyl-4-phenyl-1,4-dihydropyridin-1-yl)propane (5b). Yellow needles
from ethanol, yield 75% (method A), 91% (method B) mp 310–312 °C. MS: m/z = 770
(M+, 20%), 752 (35%), 302 (55%), 105 (100%); IR: 3055, 2938, 1661, 1624, 1566, 1450,
1
1410, 1366, 1285, 1248, 1192, 1113, 972, 786, 756, 727; H NMR (400 MHz, DMSO-
d6):  7.51 (tt, 4H, J = 7.8, 1.2 ), 7.45 (d, 8H, J = 7.8), 7.40 (t, 8H, J = 7.6), 7.30 (d, 4H, J
= 7.6), 7.19 (t, 4H, J = 7.4), 7.10 (t, 2H, J = 7.6), 7.07 (s, 4H), 5.36 (s, 2H), 3.48 (t, 4H, J
13
= 7.0), 1.87 (quin, 2H, J = 7.0); C NMR (100 MHz, CDCl3):  193.3, 146.2, 141.9,
139.0, 131.0, 128.4, 128.3, 128.1, 127.6, 126.2, 117.0, 51.4, 35.6, 30.8. Anal. calc. for
C53H42N2O4 (770.9): C 82.57; H 5.49; N 3.63. Found: C 82.55; H 5.31; N 3.62.
3,5-Dibenzoyl-4-(naphthalen-1-yl)-1,4-dihydropyridine (6a). A mixture of each of 3-N,N-
dimethylamino-1-phenylpropenone (0.39 g, 2.2 mmol), 1-naphthaldehyde (0.156 g,
1 mmol) and ammonium acetate (0.07 g, 1 mmol) in glacial acetic acid (10 mL) was
heated under reflux for 8 h. The solvent was then removed in vacuo and the remaining
S8

residue was purified by column chromatography to give 0.1 g (24%) of 6a as yellow
crystals mp 299–300 °C. MS: m/z = 415 (M+); IR: 3241, 3156, 3043, 2957, 1628, 1597,
1573, 1494, 1469, 1369, 1220, 1116, 968, 778, 732, 715, 697, 645; 1H NMR (400 MHz,
CDCl3): δ 8.91 (d, 1H, J = 8.8), 7.71 (d, 1H, J = 8.4), 7.65 (d, 1H, J = 8.4), 7.61–7.58
(m, 2H), 7.48–7.39 (m, 8H), 7.32 (t, 4H, J = 7.6), 6.94–6.93 (m, 2H), 6.53 (br, 1H), 6.37
13
(s, 1H); C NMR (100 MHz, CDCl3): δ 194.8, 139.0, 136.2, 133.5, 131.4, 131.0, 129.1,
128.5, 128.1, 128.0, 127.9, 127.4, 126.2, 125.6, 125.3, 125.1, 120.1, 32.3. HRMS =
415.1567 (C29H21NO2 requires 415.1566).
Synthesis of dihydropyridines 6b–f and 7a,b: General procedure
A mixture of each of the appropriate enaminones 1 (2.2 mmol), 1-naphthaldehyde or 9-
phenanthrenecarboxaldehyde (1 mmol) and the arylamine (1 mmol) in glacial acetic acid
(10 mL) was heated under reflux for 24 h. The solvent was then removed in vacuo and
the remaining residue was crystallized from ethanol or purified by column
chromatography to give the corresponding products 6b–f and 7a,b.
3,5-Dibenzoyl-4-(naphthalen-1-yl)-1-phenyl-1,4-dihydropyridine (6b). Yellow crystals,
yield 0.17 g (34%), mp 259–260 °C. MS: m/z = 491 (M+); IR: 3055, 3030, 1663, 1644,
1628, 1593, 1573, 1494, 1347, 1310, 1276, 1225, 1173, 1142, 1108, 760, 700, 654;
1H NMR (400 MHz, CDCl3): δ 8.96 (d, 1H, J = 8.8), 7.76 (d, 1H, J = 8.0), 7.61–7.65 (m,
3H), 7.54 (d, 4H, J = 8.4), 7.50–7.43 (m, 6H), 7.38 (s, 2H), 7.36–7.28 (m, 5H), 7.24 (d,
13
2H, J = 8.0), 6.50 (s, 1H); C NMR (100 MHz, CDCl3): δ 194.6, 143.3, 138.8, 138.2,
133.6, 131.4, 131.2, 130.2, 128.6, 128.2, 127.9, 127.6, 127.3, 126.8, 126.4, 125.7, 125.3,
125.0, 122.0, 121.1, 32.5. HRMS = 491.1879 (C35H25NO2 requires 491.1879).
3,5-Dibenzoyl-1-(p-methoxyphenyl)-4-(naphthalen-1-yl)-1,4-dihydropyridine
(6c).
Yellow fibers, yield 0.19 g (36%), mp 134–135 °C. MS: m/z = 521 (M+); IR: 3056, 2971,
2931, 1633, 1561, 1511, 1332, 1278, 1244, 1230, 1147, 1111, 784, 711; 1H NMR (400
MHz, CDCl3): δ 8.94 (d, 1H, J = 8.8), 7.74 (d, 1H, J = 8.0), 7.68–7.2 (m, 3H), 7.50 (d,
4H, J = 7.6), 7.46–7.39 (m, 4H), 7.33 (d, 4H, J = 7.6), 7.25 (s, 2H), 7.17 (d, 2H, J = 8.4),
13
6.93 (d, 2H, J = 8.4), 6.46 (s, 1H), 3.81 (s, 3H); C NMR (100 MHz, CDCl3): δ 194.6,
S9

158.5, 139.0, 138.9, 136.7, 133.6, 131.5, 131.2, 128.7, 128.5, 128.2, 127.9, 127.6, 127.4,
126.4, 125.7, 125.4, 125.1, 123.2, 121.4, 115.2, 55.7, 32.4. HRMS = 521.1985
(C36H27NO3 requires 521.1985).
3,5-Bis(p-methoxybenzoyl)-1-(p-methoxyphenyl)-4-(naphthalen-1-yl)-1,4-dihydropyridine
(6d). Yellow crystals, yield 0.09 g (16%), mp 201–202 °C. MS: m/z = 581 (M+); IR:
2930, 2905, 2835, 1661, 1630, 1598, 1572, 1509, 1460, 1339, 1311, 1260, 1227, 1166,
1145, 1110, 1066, 1023, 776, 603; 1H NMR (400 MHz, CDCl3): δ 8.88 (d, 1H, J = 8.8),
7.71 (d, 1H, J = 8.4), 7.66–7.62 (m, 3H), 7.50 (d, 4H, J = 8.8), 7.46–7.41 (m, 2H), 7.22
(s, 2H), 7.17 (d, 2H, J = 9.2), 6.93 (d, 2H, J = 9.2), 6.80 (d, 4H, J = 8.8), 6.47 (s, 1H),
13
3.80 (s, 3H), 3.78 (s, 6H); C NMR (100 MHz, CDCl3): δ 193.7, 162.1, 158.3, 137.9,
136.9, 133.6, 131.43, 131.4, 130.8, 127.9, 127.4 (two overlapped CH), 126.3, 125.6,
125.3, 125.0, 123.0, 121.1, 115.2, 113.4, 55.6, 55.3, 33.1. HRMS = 581.2196 (C38H31NO5
requires 581.2196). Anal. Calcd for C38H31NO5 (581.7): C 78.47; H 5.37; N 2.41. Found:
C 78.22; H 4.70; N 3.07.
3,5-Bis(p-chlorobenzoyl)-1-(p-methoxyphenyl)-4-(naphthalen-1-yl)-1,4-dihydropyridine
(6e). Yellow crystals, yield 0.06 g (11%), mp 192–193 °C. MS: m/z = 590 (M+); IR:
3053, 2955, 2930, 1633, 1590, 1511, 1282, 1229, 1110, 1090, 908, 836, 788, 733;
1H NMR (400 MHz, CDCl3): δ 8.90 (d, 1H, J = 8.8), 7.77 (d, 1H, J = 8.0), 7.71–7.62 (m,
3H), 7.49 (d, 2H, J = 8.0), 7.45 (d, 4H, J = 8.4), 7.31 (d, 4H, J = 8.4), 7.21 (s, 2H), 7.18
13
(d, 2H, J = 8.8), 6.97 (d, 2H, J = 8.8), 6.42 (s, 1H), 3.84 (s, 3H); C NMR (100 MHz,
CDCl3): δ 193.3, 158.7, 138.9, 137.4, 137.1, 136.4, 133.5, 131.3, 129.9, 128.7, 128.6,
128.5, 128.0, 127.7, 126.4, 125.8, 125.3, 124.8, 123.2, 121.2, 115.3, 55.7, 30.9. HRMS =
589.1206 (C36H25Cl2NO3 requires 589.1206).
3,5-Dibenzoyl-1-(p-chlorophenyl)-4-(naphthalen-1-yl)-1,4-dihydropyridine (6f). Yellow
crystals, yield 0.11 g (21%), mp 278–280 °C. MS: m/z = 525 (M+); IR: 3055, 2970, 1664,
1648, 1627, 1592, 1570, 1492, 1334, 1275, 1246, 1224, 1144, 1109, 779, 765, 702, 654;
1H NMR (400 MHz, CDCl3): δ 8.92 (d, 1H, J = 8.4), 7.75 (d, 1H, J = 8.0), 7.69 (d, 1H, J
= 8.0), 7.66–7.63 (m, 2H), 7.52 (d, 4H, J = 8.0), 7.49–7.34 (m, 10H), 7.30 (s, 2H), 7.17
(d, 2H, J = 8.8), 6.48 (s, 1H); 13C NMR (100 MHz, CDCl3): δ 194.5, 141.8, 138.6, 137.6,
S10

133.6, 132.4, 131.42, 130.3, 128.7, 128.5, 128.4, 128.3, 128.0, 127.7, 127.3, 126.5, 125.5,
125.3, 125.0, 122.4, 122.3, 32.5. HRMS = 525.1490 (C35H24ClNO2 requires 525.1490).
3,5-Dibenzoyl-1-(p-methoxyphenyl)-4-(phenanthren-9-yl)-1,4-dihydropyridine
(7a).
Yellow crystals, yield 0.09 g (15%), mp 245–247 °C. MS: m/z = 571 (M+); IR: 2972,
2932, 2884, 1660, 1637, 1597, 1574, 1513, 1465, 1442, 1379, 1312, 1280, 1247, 1228,
1163, 1143, 1108, 953, 723; 1H NMR (400 MHz, CDCl3): δ 9.06 (d, 1H, J = 8.0), 8.65 (t,
2H, J = 9.2), 7.85 (s, 1H), 7.84 (d, 1H, J = 7.2), 7.78 (t, 1H, J = 7.2), 7.65 (t, 1H, J =
8.4), 7.59–7.54 (m, 2H), 7.49 (d, 4H, J = 6.8), 7.40 (t, 2H, J = 7.6), 7.31 (s, 2H), 7.30 (t,
4H, J = 6.8), 7.20 (d, 2H, J = 9.2), 6.95 (d, 2H, J = 8.8), 6.47 (s, 1H), 3.82 (s, 3H);
13C NMR (100 MHz, CDCl3): δ 194.6, 158.6, 139.2, 138.8, 136.7, 132.0, 131.2, 130.7,
130.2, 128.7, 128.2, 128.1, 126.9, 126.4, 126.3, 126.2, 125.8, 123.2, 122.6, 122.5, 121.5,
115.3, 55.7, 32.2. HRMS = 571.2141 (C40H29NO3 requires 571.2141).
3,5-Bis(p-methoxybenzoyl)-1-(p-methoxyphenyl)-4-(phenanthren-9-yl)-1,4-
dihydropyridine (7b). Yellow crystals, yield 0.08 g (13%), mp 138–140 °C. MS: m/z =
631 (M+); IR: 1H NMR (400 MHz, CDCl3): δ 9.02 (d, 1H, J = 8.8), 8.65 (t, 2H, J = 8.8),
7.88 (s, 1H), 7.86 (d, 1H, J = 7.2), 7.77 (t, 1H, J = 8.8), 7.64 (t, 1H, J = 7.6), 7.62–7.57
(m, 2H), 7.53 (d, 4H, J = 8.8), 7.30 (s, 2H), 7.24 (d, 2H, J = 8.8), 6.99 (d, 2H, J = 8.8),
13
6.82 (d, 4H, J = 8.8), 6.50 (s, 1H), 3.85 (s, 3H), 3.79 (s, 6H); C NMR (100 MHz,
CDCl3): δ 193.7, 162.2, 158.4, 138.2, 136.9, 132.0, 131.4, 130.9, 130.7, 130.1, 128.1,
126.9, 126.3, 126.2, 126.1, 125.7, 123.0, 122.6, 122.5, 121.2, 115.2, 113.5, 55.7, 55.3,
31.9. HRMS = 631.2352 (C42H33NO5 requires 631.2353).
4-Phenyl-1,4-dihydropyridine-3,5-dicarboxaldehyde (10a). Yellow needles from ethanol,
yield 73% (method A), mp 244–246 °C. MS: m/z = 213 (M+, 50%), 136 (100%) ; IR:
1
3088, 3029, 2965, 1657, 1597, 1463, 1387, 1265, 1151, 1078, 941, 702 ; H NMR
(400 MHz, DMSO-d6):  10.08 (s, 1H), 9.25 (s, 2H), 7.45 (s, 2H), 7.21 (t, 2H, J = 7.8),
7.14 (d, 2H, J = 7.8), 7.10 (t, 1H, J = 7.6), 4.75 (s, 1H); 13C NMR (100 MHz, DMSO-d6):
 189.3, 145.7, 144.3, 127.9, 127.6, 126.1, 119.9, 32.9. Anal. calc. for C13H11NO2
(213.2): C 73.23; H 5.20; N 6.57. Found: C 73.15; H 5.21; N 6.50.
S11

1,4-Diphenyl-1,4-dihydropyridine-3,5-dicarboxaldehyde (10b). Yellow needles from
ethanol, yield 72% (method A), 86% (method B), mp 176–178 °C. MS: m/z = 289 (M+,
30%), 212 (100%), 154 (10%); IR: 3067, 3027, 2954, 1662, 1577, 1494, 1349, 1201,
1143, 1067, 761, 704; 1H NMR (400 MHz, DMSO-d6):  9.41 (s, 2H), 8.06 (s, 2H), 7.65
(d, 2H, J = 7.6), 7.57 (t, 2H, J = 8.0), 7.41 (t, 1H, J = 7.8), 7.24 (m, 4H), 7.14 (m, 1H),
4.80 (s, 1H); 13C NMR (100 MHz, DMSO-d6):  189.9, 145.2, 144.5, 142.0, 129.8, 128.1,
127.8, 126.8, 126.4, 122.4, 120.8, 32.7. Anal. calc. for C19H15NO2 (289.3): C 78.87; H
5.23; N 4.84. Found: C 78.75; H 5.21; N 4.80.
Diethyl 4-phenyl-1,4-dihydropyridine-3,5-dicarboxylate (12) [4]. Colorless oil, yield 65%
(method A). MS: m/z = 301 (M+, 30%), 224 (80%), 168 (50%); IR: 3329, 3103, 2981,
1
1699, 1603, 1492, 1372, 1292, 1189, 1076, 754, 708; H NMR (400 MHz, CDCl3): 
7.35 (dd, 2H J = 7.8, 1.4), 7.31 (d, 2H, J = 5.2), 7.23 (t, 2H, J = 7.8), 7.15 (tt, 1H, J = 7.8,
1.4), 6.52 (t, 1H, J = 5.4), 4.89 (s, 1H), 4.12–4.02 (m, 4H), 1.19 (t, 6H, J = 6.8);
13C NMR (100 MHz, CDCl3):  167.0, 146.8, 133.4, 128.4, 128.0, 126.4, 108.8, 60.1,
37.6, 14.2. Anal. calc. for C17H19NO4 (301.35): C 67.76; H 6.36; N 4.65. Found: C 67.75;
H 6.31; N 4.60.
4-Phenyl-1,4-dihydropyridine-3,5-dicarbonitrile (14). Yellow needles from ethanol, yield
76% (method A), mp 176–178 °C. MS: m/z = 207 (M+, 50%), 130 (100%); IR: 3228,
1
3106, 3001, 2206, 1670, 1609, 1510, 1452, 1246, 1074, 756, 700; H NMR (400 MHz,
CDCl3):  7.43 (t, 2H, J = 7.8), 7.35 (t, 1H, J = 7.6), 7.31 (d, 2H, J = 7.6), 4.49 (s, 1H);
13C NMR (150 MHz, DMSO-d6):  143.6, 137.6, 128.9, 127.8, 127.7, 119.3, 85.4, 40.0.
Anal. calc. for C13H9N3 (207.2): C 75.35; H 4.38; N 20.28. Found: C 75.25; H 4.31; N
20.30.
Oxidation of 1,4-dihydropyridines 2a–c and 6a: General procedure
To a stirred cold (0–5 °C) solution of nitric acid (6 mL, 70%), the appropriate
dihydropyridine derivatives 2a–c and 6a (1 mmol) was added portionwise within 5 min
as solids. After stirring for an additional 15 min under cooling, the reaction mixture was
kept at room temperature for 30 min, then poured onto crushed ice (ca. 10 g) and treated
S12

with saturated solution of Na2CO3 to achieve a pH 8. The product was then extracted with
CHCl3 (3 × 50 mL) and dried over anhydrous sodium sulfate. The solvent was then
removed in vacuo and the crude product was purified by crystallization from ethanol to
give 15a–d.
3,5-Dibenzoyl-4-phenylpyridine (15a). Colorless needles from ethanol, mp 190–192 °C,
yield 0.28 g (76%). MS: m/z = 363 (M+, 100%), 258 (25%), 105 (100%); IR: 3057, 3028,
1
1663, 1594, 1573, 1447, 1318, 1276, 1228, 1180, 1013, 916, 816, 706; H NMR
(400 MHz, CDCl3):  8.86 (s, 2H), 7.59 (dd, 4H, J = 8.0, 1.6), 7.44 (tt, 2H, J = 7.6, 1.6),
7.29 (t, 4H, J = 7.8), 7.05 (m, 2H), 6.99 (m, 3H); 13C NMR (100 MHz, CDCl3):  195.8,
149.8, 146.8, 136.6, 135.4, 134.8, 133.7, 129.7, 129.3, 128.8, 128.4, 128.3; Anal. calc.for
C25H17NO2 (363.4): C 82.63; H 4.72; N 3.85. Found: C 82.54; H 4.69; N 3.90.
4-(p-Chlorophenyl)-3,5-dibenzoylpyridine (15b). Colorless needles from ethanol, mp
180–182 °C, yield 0.28 g (70%). MS: m/z = 399 (M + 2, 25%), 397 (M+, 100%), 292
(20%), 105 (100%); IR: 3059, 2969, 1658, 1595, 1493, 1447, 1289, 1092, 1006, 840; 1H
NMR (400 MHz, DMSO-d6):  8.89 (s, 2H), 7.68 (dd, 4H, J = 7.8, 1.2), 7.58 (t, 2H, J =
13
7.6), 7.42 (t, 4H, J = 7.6), 7.15 (d, 2H, J = 8.4), 7.02 (d, 2H, J = 8.4); C NMR (100
MHz, DMSO-d6):  195.1, 149.6, 144.6, 136.2, 134.9, 134.0, 133.8, 133.4, 130.7, 129.7,
128.7, 128.1. Anal. calc.for C25H16ClNO2 (397.9): C 75.47; H 4.05; N 3.52. Found: C
75.38; H 4.09; N 3.47.
3,5-Dibenzoyl-4-p-tolylpyridine (15c). Colorless needles from ethyl acetate, mp 150–
152 °C, yield 0.27 g (72%); IR: 3156, 2995, 1655, 1626, 1568, 1485, 1370, 1203, 1176,
1137, 1000, 836; LCMS: m/z = 378 (M + 1); MS: m/z = 377 (M+, 100%), 275 (40%), 105
(85%); 1H NMR (400 MHz, CDCl3):  8.84 (s, 2H), 7.64 (d, 4H, J = 7.2), 7.48 (t, 2H, J =
7.4), 7.32 (t, 4H, J = 7.8), 6.96 (d, 2H, J = 8.4), 6.81 (d, 2H, J = 8.4), 2.10 (s, 3H);
13C NMR (100 MHz, CDCl3):  196.0, 149.9, 146.7, 138.8, 136.6, 135.4, 133.7, 131.9,
129.8, 129.1, 129.0, 128.4, 21.0. Anal. calc.for C26H19NO2 (377.5): C 82.74; H 5.07; N
3.71. Found: C 82.68; H 5.00; N 3.67.
S13

3,5-Dibenzoyl-4-(naphthalen-1-yl)pyridine (15d). Yellow needles, yield 0.33 g (80%),
mp 181–182 °C. MS: m/z = 413 (M+). IR: 3059, 3004, 1658, 1593, 1569, 1539, 1449,
1316, 1298, 1278, 1205, 1174, 1010, 903, 806, 782, 712; 1H NMR (400 MHz, CDCl3): δ
9.02 (s, 2H), 7.55 (tt, 2H, J = 7.2, 2.4), 7.44 (d, 1H, J = 8.0), 7.42–7.40 (m, 4H), 7.38–
7.34 (m, 2H), 7.30–7.25 (m, 2H), 7.16–7.13 (m, 2H), 7.11–7.07 (m, 4H); 13C NMR
(100 MHz, CDCl3): δ 195.6, 150.4, 145.9, 136.5, 136.3, 133.1, 132.8, 132.2, 130.6,
129.4, 129.1, 128.7, 128.1, 127.9, 126.6, 126.0, 125.4, 124.4. HRMS = 413.1409
(C29H19NO2 requires 413.1410).
References
1. Elassar, A.-Z. A.; El-Khair, A. A. Tetrahedron 2003, 59, 8463–8480.
doi:10.1016/S0040-4020(03)01201-8
2. Riyadh, S. M.; Abdelhamid, I. A.; Al-Matar, H. M.; Hilmy, N. M.; Elnagdi, M.
H. Heterocycles 2008, 75, 1849–1905. doi:10.3987/REV-07-625
3. Böhme, H., Willinger, G. Arch. Pharm. 1969, 302, 974–985.
doi:10.1002/ardp.19693021215
4. Mai, A.; Valente, S.; Meade, S.; Carafa, V.; Tardugno, M.; Nebbioso, A.;
Galmozzi, A.; Mitro, N.; De Fabiani, E.; Altucci, L.; Kazantsev, A. J. Med.
Chem. 2009, 52, 5496–5504. doi:10.1021/jm9008289
S14

O
O
Ph
Ph
N
H
Compound 2a
O
O
Ph
Ph
N
H
Compound 2a
S15

Cl
O
O
Ph
Ph
N
H
Compound 2b
Cl
O
O
Ph
Ph
N
H
Compound 2b
S16

O
O
Ph
Ph
N
H
Compound 2c
O
O
Ph
Ph
N
H
Compound 2c
S17

O
O
S
S
N
H
Compound 2d
O
O
S
S
N
H
Compound 2d
S18

O
O
O
O
N
H
Compound 2e
O
O
O
O
N
H
Compound 2e
S19

O
O
Ph
Ph
N
Ph
Compound 2f
O
O
Ph
Ph
N
Ph
Compound 2f
S20

O
O
Ph
Ph
N
OH
Compound 2g
O
O
Ph
Ph
N
OH
Compound 2g
S21

O
O
O
O
N
Ph
Compound 2h
O
O
O
O
N
Ph
Compound 2h
S22

O
O
O
O
N
OMe
Compound 2i
O
O
O
O
N
OMe
Compound 2i
S23

O
O
N
Cl
Cl
OMe
Compound 2j
O
O
N
Cl
Cl
OMe
Compound 2j
S24

O
O
S
S
N
OMe
Compound 2k
O
O
S
S
N
OMe
Compound 2k
S25

O
O
S
S
N
Compound 2l
O
O
S
S
N
Compound 2l
S26

Compound 2m
Compound 2m
S27

O
O
N
Compound 2n
O
O
N
Compound 2n
S28

O
O
N
COOH
Compound 2o
O
O
N
COOH
Compound 2o
S29

O
O
N
Ph
Compound 4a
O
O
N
Ph
Compound 4a
S30