eluent to give products 3 and salicaldehydes 5, respectively. 5 could
be reused as the starting material. The products were further
recrystallized from ethyl acetate/hexane.
being concentrated, the residue was diluted with ethyl acetate (20
mL), then washed with water (10 mL) and brine (10 mL). The
organic layer was dried over anhydrous Na2SO4 and filtrated
through diatomite. The filtrate was concentrated to achieve 8 as
pale yellow solids. Mp 169-172 °C; 1H NMR (CDCl3, 400 MHz)
δ 8.78 (d, J ) 2.0 Hz, 1H), 8.31 (dd, J1 ) 2.4 Hz, J2 ) 9.6 Hz,
1H), 7.64 (d, J ) 1.6 Hz, 1H), 7.54 (s, 2H), 7.35 (dd, J1 ) 2.0 Hz,
J2 ) 8.8 Hz, 1H), 7.21 (d, J ) 8.0 Hz, 2H), 7.11 (d, J ) 9.6 Hz,
1H), 7.01 (d, J ) 8.4 Hz, 2H), 6.76 (d, J ) 8.8 Hz, 1H), 5.27 (s,
1,4-Dihydropyridine 3a: colorless crystals; mp 124-125 °C;
1H NMR (CDCl3, 400 MHz) δ 7.73 (d, J ) 12.6 Hz, 1H), 7.67 (s,
2H), 7.45 (m, 3H), 7.30 (m, 3H), 7.22 (t, J ) 7.2 Hz, 1H), 7.13 (t,
J ) 7.2 Hz, 1H), 6.95 (d, J ) 7.6 Hz, 1H), 5.51 (d, J ) 12.6 Hz,
1H), 5.23 (s, 1H), 4.17 (q, J ) 7.2 Hz, 2H), 4.09 (q, J ) 7.2 Hz,
4H), 1.27 (t, J ) 7.2 Hz, 3H), 1.17 (t, J ) 7.2 Hz, 6H) ppm; 13C
NMR (CDCl3, 100 MHz) δ 167.3, 166.7, 160.1, 154.1, 143.0, 136.2,
136.0, 131.8, 129.9, 128.3, 126.2, 124.8, 120.4, 118.0, 109.8, 101.8,
60.2, 59.9, 33.5, 14.3, 14.2 ppm; IR (KBr) V 2980, 1705, 1647,
1598, 1582, 1486, 1280, 1228, 1126, 754, 691 cm-1; MS (ESI)
m/z 514.2 ([M + Na]+); HRMS (ESI) calcd for C28H29NO7 ([M +
Na]+) 514.1842, found 514.1838.
1H), 4.09 (m, 4H), 2.37(s, 3H), 1.18 (t, J ) 7.2 Hz, 6H) ppm; 13
C
NMR (CDCl3, 100 MHz) δ 166.2, 156.0, 151.1, 141.4, 140.38,
140.35, 139.7, 136.9, 136.5, 135.3, 131.5, 130.4, 128.3, 121.6,
121.4, 120.2, 119.0, 108.8, 60.3, 33.8, 20.8, 14.2 ppm; IR (KBr) V
2918, 1699, 1608, 1578, 1536, 1516, 1473, 1344, 1268, 1234, 1209
cm-1; MS (ESI) m/z 674.1 ([M + Na]+); HRMS (ESI) calcd for
C30H26BrN3O9 ([M + Na]+) 674.0743, found 674.0740.
1,4-Dihydropyridine 3s: pale green crystals; mp 96-97 °C; 1H
NMR (CDCl3, 400 MHz) δ 7.73 (d, J ) 12.0 Hz, 1H), 7.29 (dd, J1
) 2.0 Hz, J2 ) 8.0 Hz, 1H), 7.27 (s, 2H), 7.16 (m, 1H), 7.09 (m,
1H), 6.90 (dd, J1 ) 1.2 Hz, J2 ) 8.0 Hz, 1H), 5.58 (d, J ) 11.6
Hz, 1H), 5.20 (s, 1H), 4.18 (q, J ) 7.6 Hz, 2H), 4.04 (m, 4H),
3.69 (m, 1H), 1.38 (s, 3H), 1.36 (s, 3H), 1.27 (t, J ) 7.2 Hz, 3H),
1.14 (t, J ) 7.2 Hz, 6H) ppm; 13C NMR (CDCl3, 100 MHz) δ
167.3, 166.8, 160.4, 153.1, 137.6, 136.0, 131.3, 127.8, 124.9, 117.6,
107.9, 101.4, 59.8, 59.7, 55.5, 32.6, 21.9, 14.2, 14.1 ppm; IR (KBr)
V 2980, 1712, 1646, 1581, 1480, 1439, 1320, 1117, 1031 948, 780
cm-1; MS (ESI) m/z 480.2 ([M + Na]+); HRMS (ESI) calcd for
C25H31NO7 ([M + Na]+) 480.1985, found 480.1980.
General Procedure for Transformation of Dihydropyridines
3 to 6. To a solution of 3 (1 mmol) in CH2Cl2 (15 mL) was added
pyrrolidine (5 mmol), and the mixture was stirred overnight at room
temperature. After completion, the mixture was diluted with CH2-
Cl2 (15 mL), washed with dilute hydrochloric acid (1 N, 5 mL)
and then brine (15 mL), dried over anhydrous Na2SO4, and filtrated
through diatomite. After the filtrate was concentrated in vacuum,
the product was crystallized from ethyl acetate.
Procedure for the Synthesis of 1,4-Dihydropyridine 9. To a
solution of 6c (1 mmol) and Et3N (3 mmol) in CH2Cl2 (15 mL)
was added dropwise a solution of trifluomethyl sulfinic anhydride
(1.5 mmol) in CH2Cl2 (5 mL) at -50 °C for 30 min. The mixture
was stirred for 2 h and then treated with brine. The organic layer
was dried over anhydrous Na2SO4 and evaporated under vacuum.
The crude product was purified by flash column chromatography
on silica gel (ethyl acetate/hexane, 1:10) and then recrystallized
from ethyl acetate/hexane to give pure product as colorless crystals.
Mp 117-120 °C; 1H NMR (CDCl3, 400 MHz) δ 7.66 (s, 2H), 7.55
(d, J ) 2.4 Hz, 1H), 7.36 (dd, J1 ) 2.8 Hz, J2 ) 8.8 Hz, 1H), 7.26
(d, J ) 8.4 Hz, 2H), 7.20 (d, J ) 8.4 Hz, 2H), 7.10 (d, J ) 8.8 Hz,
1H), 5.29 (s, 1H), 4.12 (m, 4H), 2.39 (s, 3H), 1.16 (t, J ) 7.2 Hz,
6H) ppm; 13C NMR (CDCl3, 125 MHz) δ 166.2, 146.2, 141.0,
140.6, 137.4, 136.8, 135.0, 131.3, 130.5, 121.2, 121.0, 118.5 (q,
JC-F ) 317.3 Hz), 108.8, 60.5, 33.0, 20.9, 14.1 ppm; IR (KBr) V
2983, 1714, 1696, 1595, 1575, 1522, 1473, 1425, 1241, 1199, 1140,
1077, 611 cm-1; MS (ESI) m/z 640.0 ([M + Na]+); HRMS (ESI)
calcd for C25H23BrF3NO7S ([M + Na]+) 640.0223, found 640.0212.
1,4-Dihydropyridine 6a: pale yellow crystals; mp 150-151 °C;
1H NMR (CDCl3, 400 MHz) δ 8.49 (b, 1H), 7.68 (s, 2H), 7.27 (d,
J ) 8.0 Hz, 2H), 7.19 (d, J ) 8.0 Hz, 2H), 7.10 (m, 2H), 6.95 (d,
J ) 8.0 Hz, 1H), 6.87 (t, J ) 7.2 Hz, 1H), 5.13 (s, 1H), 4.13 (m,
4H), 2.39 (s, 3H), 1.16 (t, J ) 7.2 Hz, 6H) ppm; 13C NMR (CDCl3,
100 MHz) δ 167.9, 152.9, 140.7, 136.8, 133.6, 130.5, 128.8, 128.1,
121.1, 118.2, 109.7, 60.8, 30.3, 20.9, 14.1 ppm; IR (KBr) V 3449,
2983, 1698, 1679, 1594, 1578, 1514, 1474, 1429, 1305, 1282, 1209,
1083, 1064, 823 cm-1; MS (ESI) m/z 430.1 ([M + Na]+); HRMS
(ESI) calcd for C24H25NO5 ([M + Na]+) 430.1625, found 430.1620.
Procedure for the Synthesis of 1,4-Dihydropyridine 8. A
mixture of 6c (1 mmol), 2,4-dinitrochlorobenzene (1 mmol), and
K2CO3 (2 mmol) in CH3CN (15 mL) was refluxed for 2 h. After
Acknowledgment. We thank the National Natural Science
Foundation of China (No. 20272051), the Natural Science
Foundation of Zhejiang Province (R404109), as well as the
Specialized Research Fund for Doctoral Program of Higher
Education (20050335101).
Supporting Information Available: Detailed experimental
procedures, characterizaton data, copies of 1H and 13C NMR spectra
for all products, and crystallographic information files (CIF) for
compound 3a. This material is available free of charge via the
JO7013593
7782 J. Org. Chem., Vol. 72, No. 20, 2007