Metal-Free-Mediated Oxidation Aromatization of 1,4-Dihydropyridines to Pyridines
2H), 6.74-6.72 (m, 2H), 5.59 (s, 1H), 5.17 (s, 1H),
4.09-4.04 (m, 4H), 3.82 (s, 3H), 3.78 (s, 3H), 2.29 (s,
6H), 1.21 (t, J=7.2 Hz, 6H); 13C NMR (100 MHz,
CDCl3) δ: 167.9, 153.2, 143., 123.7, 122.4, 110.4, 102.7,
62.6, 60.1, 59.5, 55.5, 37.8, 19.7, 18.4, 14.3, 13.5.
(400 MHz, CDCl3) δ: 7.65 (d, J=8.0 Hz, 2H), 7.39 (d,
J=8.0 Hz, 2H), 4.10 (q, J=7.2 Hz, 4H), 2.62 (s, 6H),
0.91 (t, J=7.2 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ:
167.3, 155.9, 144.7, 140.3, 131.2, 130.9, 128.7, 127.9,
126.6 (q, J=270.0 Hz), 125.0, 124.9, 61.5, 23.0, 13.5.
HRMS m/z (ESI) calcd for C20H21F3NO4 [M+H]+
396.1417, found 396.1410.
Diethyl 4-(3,4-dimethoxyphenyl)-2,6-dimethylpyri-
dine-3,5-dicarboxylate (3b): White solid; 1H NMR (400
MHz, CDCl3) δ: 7.04-7.00 (m, 1H), 6.93 (d, J=8.0 Hz,
1H), 6.70 (d, J=7.6 Hz, 1H), 4.10-4.00 (m, 4H), 3.87
(s, 3H), 3.65 (s, 3H), 2.64 (s, 6H), 0.96 (t, J=7.2 Hz,
6H); 13C NMR (100 MHz, CDCl3) δ: 167.3, 155.8,
152.4, 146.2, 130.9, 127.2, 123.4, 121.7, 113.0, 61.2,
60.5, 55.9, 23.1, 13.5. HRMS m/z (ESI) calcd for
C21H26NO6 [M+Na]+ 410.1574, found 410.1567.
Diethyl 4-(4-chlorophenyl)-2,6-dimethyl-1,4-dihy-
dropyridine-3,5-dicarboxylate (4a): Pale yellow solid;
1H NMR (400 MHz, CDCl3) δ: 7.21 (d, J=8.4 Hz, 2H),
7.16 (d, J=8.4 Hz, 2H), 6.24 (s, 1H), 4.96 (s, 1H), 4.14
-4.02 (m, 4H), 2.28 (s, 6H), 1.21 (t, J=7.2 Hz, 6H);
13C NMR (100 MHz, CDCl3) δ: 167.5, 146.3, 144.3,
131.5, 129.3, 127.8, 103.4, 59.7, 39.1, 19.3, 14.1.
Diethyl 4-(4-cyanophenyl)-2,6-dimethyl-1,4-dihy-
dropyridine-3,5-dicarboxylate (7a): Pale yellow solid;
1H NMR (400 MHz, CDCl3) δ: 7.53-7.50 (m, 2H),
7.41-7.39 (m, 2H), 5.65 (brs, 1H), 5.04 (s, 1H), 4.22-
4.03 (m, 4H), 2.35 (s, 6H), 1.21 (t, J=7.2 Hz, 6H); 13C
NMR (100 MHz, CDCl3) δ: 167.1, 153.0, 144.4, 131.8,
128.9, 119.3, 109.8, 103.3, 59.9, 40.3, 19.7, 14.2.
Diethyl 4-(4-cyanophenyl)-2,6-dimethylpyridine-3,
5-dicarboxylate (7b): Colorless oil; 1H NMR (400 MHz,
CDCl3) δ: 7.70 (d, J=8.4 Hz, 2H), 7.40 (d, J=8.4 Hz,
2H), 4.04 (q, J=7.2 Hz, 4H), 2.70 (s, 6H), 0.97 (t, J=
7.2 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ: 166.6,
155.8, 131.8, 129.1, 118.1, 112.8, 61.8, 22.4, 13.6.
HRMS m/z (ESI) calcd for C20H21N2O4 [M + H] +
353.1501, found 353.1496.
Diethyl 4-(4-chlorophenyl)-2,6-dimethylpyridine-3,
1
5-dicarboxylate (4b): Pale yellow oil; H NMR (400
Diethyl
2,6-dimethyl-1,4-dihydropyridine-3,5-di-
MHz, CDCl3) δ: 7.35 (d, J=8.4 Hz, 2H), 7.21-7.19 (m,
2H), 4.04 (q, J=7.2 Hz, 4H), 2.60 (s, 6H), 0.97 (t, J=
7.2 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ: 167.4,
155.5, 145.0, 134.8, 134.7, 129.5, 129.4, 128.4, 128.3,
126.9, 61.5, 58.3, 52.2, 30.8, 22.7, 13.6. HRMS m/z
(ESI) calcd for C19H21ClNO4 [M + H] + 362.1154,
found 362.1151.
carboxylate (8a): Pale yellow solid; 1H NMR (400 MHz,
CDCl3) δ: 9.08 (s, 1H), 4.48 (q, J=7.2 Hz, 4H), 3.25 (s,
6H), 2.20 (s, 2H), 1.45 (t, J=7.2 Hz, 6H); 13C NMR
(100 MHz, CDCl3) δ: 162.1, 159.9, 146.6, 126.7, 63.1,
19.6, 14.1.
Diethyl 2,6-dimethylpyridine-3,5-dicarboxylate (8b):
1
Pale yellow oil; H NMR (400 MHz,CDCl3) δ: 8.70 (s,
Diethyl 4-(4-fluorophenyl)-2,6-dimethyl-1,4-dihy-
dropyridine-3,5-dicarboxylate (5a): Pale yellow solid;
1H NMR (400 MHz, CDCl3) δ: 7.25-7.21 (m, 2H),
6.91-6.85 (m, 2H), 5.65 (brs, 1H), 4.96 (s, 1H), 4.13-
4.04 (m, 4H), 2.33 (s, 6H), 1.22 (t, J=7.2 Hz, 6H); 13C
NMR (100 MHz, CDCl3) δ: 167.5, 161.4 (d, J=242.0
Hz), 143.7, 143.6, 129.4 (d, J=8.0 Hz), 114.5 (d, J=
21.0 Hz), 104.2, 59.8, 39.1, 19.6, 14.2.
Diethyl 4-(4-fluorophenyl)-2,6-dimethylpyridine-3,
5-dicarboxylate (5b): Colorless oil; 1H NMR (400 MHz,
CDCl3) δ: 7.59-7.55 (m, 2H), 7.14-7.09 (m, 2H),
4.46 (q, J=7.2 Hz, 2H), 4.14 (q, J=7.2 Hz, 2H), 2.61
(s, 3H), 2.36 (s, 3H), 1.43 (t, J=7.2 Hz, 3H), 1.06 (t,
J=7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ: 168.2
(d, J=9.0 Hz), 163.3 (d, J=247.0 Hz), 155.2 (d, J=
13.0 Hz), 143.0, 135.7, 130.3, 130.2, 130.0, 128.6,
127.3, 115.4 (d, J=22.0 Hz), 61.7, 23.0, 16.9, 13.9 (d,
J=49.0 Hz). HRMS m/z (ESI) calcd for C19H21FNO4
[M+H]+ 346.1449, found 346.1443.
1H), 4.45 (q, J=7.2 Hz, 4H), 2.87 (s, 6H), 1.42 (t, J=
7.2 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ: 165.6,
162.0, 123.4, 61.6, 24.5, 14.3. HRMS m/z (ESI) calcd
for C13H18NO4 [M+H]+ 252.1230, found 252.1232.
Dimethyl 4-isopropyl-2,6-dimethyl-1,4-dihydropy-
ridine-3,5-dicarboxylate (9a): White solid; 1H NMR
(400 MHz, CDCl3) δ: 5.67 (s, 1H), 4.02 (s, 1H), 3.89 (d,
J=6.4 Hz, 1H), 3.71 (s, 6H), 2.31 (s, 6H), 1.62-1.54
(m, 1H), 0.74-0.73 (m, 6H); 13C NMR (100 MHz,
CDCl3) δ: 169.1, 160.5, 146.4, 144.8, 101.5, 53.5, 50.8,
38.8, 35.4, 19.3, 18.3.
Dimethyl
2,6-dimethylpyridine-3,5-dicarboxylate
1
(9b): White solid; H NMR (400 MHz, CDCl3) δ: 8.70
(s, 1H), 3.94 (s, 6H), 2.86 (s, 6H); 13C NMR (100 MHz,
CDCl3) δ: 166.0, 162.5, 140.9, 122.5, 52.2, 24.8. HRMS
m/z (ESI) calcd for C11H14NO4 [M+H]+ 224.0917,
found 224.0423.
Dimethyl 2,6-dimethyl-4-(2-nitrophenyl)pyridine-
1
3,5-dicarboxylate (10b): Pale yellow oil; H NMR (400
Diethyl 4-(4-(trifluoromethyl)phenyl)-2,6-dimethyl-
1,4-dihydropyridine-3,5-dicarboxylate (6a): Pale yellow
solid; H NMR (400 MHz, CDCl3) δ: 7.48-7.39 (m,
4H), 5.68 (s, 1H), 5.05 (brs, 1H), 4.10 (q, J=7.2 Hz,
4H), 2.35 (s, 6H), 1.22 (t, J=6.8 Hz, 6H); 13C NMR
(100 MHz, CDCl3) δ: 167.3, 151.6, 144.2, 128.3, 124.8,
124.8, 124.7, 103.6, 59.9, 39.8, 19.6, 18.4, 14.2.
MHz, CDCl3) δ: 7.74-7.70 (m, 1H), 7.54-7.51 (m,
1H), 7.47-7.43 (m, 1H), 6.56 (d, J=8.0 Hz, 1H), 3.39
(s, 6H), 2.68 (s, 6H); 13C NMR (100 MHz, CDCl3) δ:
167.3, 161.5, 156.2, 135.1, 130.9, 130.5, 129.0, 128.8,
127.6, 65.6, 52.1, 29.7, 23.1, 19.2, 14.0. HRMS m/z
(ESI) calcd for C17H17N2O6 [M+H]+ 345.1081, found
345.1079.
1
Diethyl 2,6-dimethyl-4-(4-(trifluoromethyl)phenyl)-
pyridine-3,5-dicarboxylate (6b): Colorless oil; H NMR
3-Ethyl 5-methyl 4-(2,3-dichlorophenyl)-2,6-dimeth-
1
ylpyridine-3,5-dicarboxylate (11b): Yellow oil; 1H NMR
Chin. J. Chem. 2014, 32, 1245—1250
© 2014 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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