4046
H. Cao et al. / Tetrahedron 68 (2012) 4042e4047
potassium bromide pellets with a Bruker Vector 22 spectrometer.
Mass spectra were recorded on a Shimadzu GCeMS-QP5050A
spectrometer at an ionization voltage of 70 eV equipped with a DB-
WAX capillary column (internal diameter: 0.25 mm, length: 30 m).
Elemental analyses were performed with a Vario EL elemental
analyzer. TLC was performed by using commercially prepared
100e400 mesh silica gel plates (GF254) and visualization was
effected at 254 nm.
4.2.7. Methyl 7-(4-fluorophenyl)-2,5-dioxo-5,6,7,8-tetrahydro-2H-
chromene-4-carboxylate (3ga). 1H NMR (400 MHz, CDCl3)
d
7.21e7.24 (m, 2H), 7.06e7.10 (m, 2H), 6.23 (s, 1H), 3.95 (s, 3H),
3.51e3.58 (m, 1H), 3.07e3.09 (m, J¼8.0 Hz, 2H), 2.74e2.88 (m, 2H).
13C NMR (100 MHz, CDCl3)
191.3, 174.1, 165.7, 160.9, 158.5, 145.6,
d
136.4, 128.1, 128.0, 116.2, 116.0, 112.4, 53.2, 43.8, 37.5, 36.1. MS (EI)
m/z (%): 316, 267, 223, 194, 77. C17H13O5: calcd C, 64.56; H, 4.14;
found: C, 64.09; H, 4.17.
4.2.8. Ethyl 7-methyl-2,5-dioxo-5,6,7,8-tetrahydro-2H-chromene-4-
carboxylate (3bb). 1H NMR (400 MHz, CDCl3)
d 6.17 (s, 1H),
4.2. General procedure for the synthesis of methyl 2,5-dioxo-
5,6,7,8-tetrahydro-2H-chromene-4-carboxylate (3aa)
4.38e4.43 (m, 2H), 2.86e2.82 (m, 1H), 2.57e2.67 (m, 2H),
2.30e2.44 (m, 1H), 2.23e2.27 (m, 11.8 Hz, 1H), 1.36 (t, J¼7.2 Hz, 3H),
1.17 (d, J¼6.4 Hz, 3H). 13C NMR (100 MHz, CDCl3)
d 192.3, 174.7,
To the mixture of cyclohexane-1,3-dione (1a 0.5 mmol) and di-
methyl but-2-ynedioate (2a 0.6 mmol), was added the solution of
DABCO (2 mol %) in DMF (2.0 mL). The reaction mixture was stirred at
ꢀ20 ꢁC for 1 h. The solvent was removed and the crude product was
separated by column chromatography to give a pure sample of 3aa.
165.4, 158.9, 146.1, 112.0, 111.9, 62.6, 44.8, 36.3, 27.8, 20.7, 13.9. MS
(EI) m/z (%): 250, 221, 177, 93, 45.C13H14O5: calcd C, 62.39; H, 5.64;
found: C, 62.87; H, 5.61.
4.2.9. Ethyl
mene-4-carboxylateethyl (3cb). 1H NMR (400 MHz, CDCl3)
1H), 4.40 (q, J¼7.2 Hz, 2H), 2.75 (s, 2H), 2.45 (s, 2H), 1.37 (t, J¼7.2 Hz,
3H), 1.16 (s, 6H). 13C NMR (100 MHz, CDCl3)
192.3, 173.98, 165.37,
7,7-dimethyl-2,5-dioxo-5,6,7,8-tetrahydro-2H-chro-
d
6.18 (s,
4.2.1. Methyl 2,5-dioxo-5,6,7,8-tetrahydro-2H-chromene-4-
carboxylate (3aa). 1H NMR (400 MHz, CDCl3)
d
6.19(s, 1H), 3.93(s,
3H), 2.91(t, J¼6.0 Hz, 2H), 2.58 (t, J¼6.0 Hz, 2H), 2.15e2.21(m, 2H);
13C NMR (100 MHz, CDCl3)
192.4, 175.4, 165.9, 158.7, 145.9, 112.4,
d
159.17,146.06,111.7,111.4, 62.5, 50.6, 42.1, 32.5, 28.2,13.9. MS (EI) m/
z (%): 264, 235, 191, 43; C14H16O5: calcd 63.63; H, 6.10; found: C,
64.01; H, 6.08.
d
112.1, 53.2, 36.5, 28.5, 19.8. MS (EI) m/z (%): 222, 194, 163, 138, 93.
C11H10O5: calcd C, 59.46; H, 4.54; found: C, 59.09; H, 4.56.
4.2.10. 7-Isopropyl-2,5-dioxo-5,6,7,8-tetrahydro-2H-chromene-4-
4.2.2. Methyl 7-methyl-2,5-dioxo-5,6,7,8-tetrahydro-2H-chromene-
carboxylate (3db). 1H NMR (400 MHz, CDCl3)
d 6.17 (s, 1H), 4.40 (q,
4-carboxylate (3ba). 1H NMR (400 MHz, CDCl3)
d
6.18(s, 1H), 3.93(s,
J¼7.2 Hz, 2H), 2.83e2.89 (m, 1H), 2.63e2.70 (m, 2H), 2.25e2.29 (m,
3H), 2.88e2.92 (m, 1H), 2.58e2.67 (m, 2H), 2.39e2.47 (m, 1H),
1H), 2.07e2.11 (m,1H), 1.67e1.72 (m,1H), 1.36 (t, J¼7.2 Hz, 3H), 0.98
2.23e2.30 (m, 1H),1.18 (d, J¼6.4 Hz, 3H); 13C NMR (100 MHz, CDCl3)
(d, J¼6.4 Hz, 6H). 13C NMR (100 MHz, CDCl3)
d 192.7, 175.3, 165.4,
d
192.4, 174.8, 165.8, 158.8, 145.79, 112.0, 111.9, 53.2, 44.8, 36.3, 27.8,
158.9, 146.1, 112.0, 111.8, 62.6, 40.8, 38.9, 32.3, 31.6, 19.3, 19.3, 13.8.
MS (EI) m/z (%): 278:C15H18O5: calcd C, 64.74; H, 6.52; found: C,
65.11; H, 6.50.
20.7; MS (EI) m/z (%): 236, 177, 138, 93. C12H12O5: calcd C, 61.01; H,
5.12; found: C, 61.42; H, 5.10.
4.2.3. Methyl
mene-4-carboxylate(3ca). 1H NMR (400 MHz, CDCl3)
3.92(s, 3H), 2.76 (s, 2H), 2.44 (s, 2H),1.16 (s, 6H); 13C NMR (100 MHz,
CDCl3) 192.4, 174.0, 165.8, 159.0, 145.6, 111.8, 11.39, 53.1, 50.5, 42.0,
32.5, 28.2; MS (EI) m/z (%): 250, 194, 166, 138, 93; C13H14O5: calcd C,
62.39; H, 5.64; found: C, 61.86; H, 5.66.
7,7-dimethyl-2,5-dioxo-5,6,7,8-tetrahydro-2H-chro-
4.2.11. Ethyl
7-(furan-2-yl)-2,5-dioxo-5,6,7,8-tetrahydro-2H-chro-
7.31e7.32
d
6.18(s, 1H),
mene-4-carboxylate (3fb). 1H NMR (400 MHz, CDCl3)
d
(m, 1H), 6.87 (s, 1H), 6.28e6.30 (m, 1H), 6.08e6.10 (m, 1H), 4.15(d,
J¼7.2 Hz, 2H), 3.49e3.54 (m, 1H), 2.78e2.84 (m, 2H), 2.65e2.72 (m,
d
2H), 1.23 (t, J¼7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3)
d 190.9, 173.3,
166.7, 158.0, 155.5, 141.2, 137.3, 111.7, 110.1, 104.4, 61.0, 44.37, 37.5,
32.0, 13.9. MS (EI) m/z (%): 304, 273, 229, 193, 66; C16H14O6: C,
63.57; H, 4.67; found: C, 63.15; H, 4.70.
4.2.4. Methyl
7-isopropyl-2,5-dioxo-5,6,7,8-tetrahydro-2H-chro-
6.16 (s, 1H),
mene-4-carboxylate (3da). 1H NMR (400 MHz, CDCl3)
d
3.92 (s, 3H), 2.84e2.89 (m,1H), 2.63e2.74 (m, 2H), 2.26e2.34 (m,1H),
4.2.12. Dimethyl 6-methyl-2-oxo-2H-pyran-4,5-dicarboxylate
2.03e2.10 (m, 1H), 1.70e1.74 (m, 1H), 1.00 (d, J¼8.0 Hz, 6H); 13C NMR
(3ha). 1H NMR (400 MHz, CDCl3)
d
6.49 (s, 1H), 3.90 (s, 3H), 3.84
(100 MHz, CDCl3)
d192.8, 175.5, 165.8, 158.8, 145.7, 111.9, 111.8, 53.0,
(s, 3H), 2.49 (s, 3H). 13C NMR (100 MHz, CDCl3)
d
167.0, 164.7, 164.6,
40.6, 38.8, 32.2, 31.6,19.3,19.2; MS (EI) m/z (%): 264, 205,194,166,138,
159.7,145.7,113.7,109.1, 53.2, 52.7,19.3. MS (EI) m/z (%): 221,195,125,
93, 69; C14H16O5: calcd C, 63.63; H, 6.10; found: C, 63.97; H, 6.12.
93, 43. C10H10O6: calcd C, 53.10; H, 4.46; found: C, 53.41; H, 4.44.
4.2.5. Methyl 2,5-dioxo-7-phenyl-5,6,7,8-tetrahydro-2H-chromene-
4.2.13. Diethyl 6-methyl-2-oxo-2H-pyran-4,5-dicarboxylate
4-carboxylate(3ea). 1H NMR (400 MHz)
d
7.36e7.39 (m, 2H),
(3ib). 1H NMR (400 MHz, CDCl3):
d
6.45 (s, 1H), 4.32 (q, J¼7.2 Hz,
7.25e7.27 (m, 2H), 6.19 (s, 1H), 3.92 (s, 3H), 3.51e3.57 (m, 1H),
2H), 2.46 (s, 3H), 4.22 (q, J¼7.2 Hz, 2H), 1.32 (t, J¼7.2 Hz, 3H), 1.29 (t,
3.08e3.12 (m, 2H), 2.74e2.86 (m, 2H). 13C NMR (100 MHz, CDCl3)
J¼7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3):
d 168.1, 165.1, 164.8,
d
191.7, 174.5, 165.7, 158.7, 145.7, 140.8, 129.1, 127.7, 126.5, 112.2,
160.0, 147.4, 113.8, 109.7, 63.0, 62.4, 19.3, 14.1.
112.0, 53.2, 43.7, 38.0, 35.9, 14.1. MS (EI) m/z (%): 298, 228, 193, 77,
55; C17H14O5: calcd C, 68.45; H, 4.73; found: C, 68.07; H, 4.75.
4.2.14. Dimethyl 6-methyl-2-oxo-2H-pyran-4,5-dicarboxylate
(3ha). 1H NMR (400 MHz, CDCl3)
6.49 (s, 1H), 3.90 (s, 3H), 3.84
(s, 3H), 2.49 (s, 3H). 13C NMR (100 MHz, CDCl3)
167.0, 164.7, 164.6,
159.7, 145.7, 113.7, 109.1, 53.2, 52.7, 19.3. MS (EI) m/z (%): 221, 195,
125, 93, 43. C10H10O6: calcd C, 53.10; H, 4.46; found: C, 53.41; H,
4.44.
d
4.2.6. Methyl 7-(furan-2-yl)-2,5-dioxo-5,6,7,8-tetrahydro-2H-chro-
d
mene-4-carboxylate (3fa). 1H NMR (400 MHz, CDCl3)
d
7.37 (s, 1H),
6.33 (s, 1H), 6.20 (s, 1H), 6.12 (d, J¼3.0 Hz, 1H), 3.93 (s, 3H),
3.63e3.68 (m,1H), 3.15e3.20 (m, 2H), 2.82e2.91 (m,1H), 2.75e2.90
(m, 1H). 13C NMR (100 MHz, CDCl3)
d 190.9, 173.6, 165.7, 158.6, 153.7,
145.6, 142.3, 112.3, 112.1, 110.4, 105.7, 53.2, 40.9, 33.2, 31.6. MS (EI)
m/z (%): 288, 261, 227, 194, 94, 66; C15H12O6: C, 62.50; H, 4.20;
found: C, 62.11; H, 4.22.
4.2.15. Diethyl 6-methyl-2-oxo-2H-pyran-4,5-dicarboxylate
(3ib). 1H NMR (400 MHz, CDCl3):
d
6.45 (s, 1H), 2.46 (s, 3H), 4.32
(q, J¼7.2 Hz, 2H), 4.22 (q, J¼7.2 Hz, 2H), 1.32 (t, J¼7.2 Hz, 3H), 1.29 (t,