M. I. L. Soares, T. M. V. D. Pinho e Melo / Tetrahedron Letters 49 (2008) 4889–4893
4893
chromatography [hexane] to remove 1,2,4-trichlorobenzene followed by
elution with ethyl acetate–hexane.
References and notes
6. 2,3-Diethyl
7,8-dimethyl 4-methyl-1H,4H-pyrrolo[1,2-d][1,2,4]triazine-2,3,7,8-
1. (a) Pinho e Melo, T. M. V. D.; Soares, M. I. L.; Rocha Gonsalves, A. M. d’A.; McNab,
H. Tetrahedron Lett. 2004, 45, 3889–3893; (b) Pinho e Melo, T. M. V. D.; Soares,
Maria I. L.; Rocha Gonsalves, A. M. d’A.; Paixão, J. A.; Matos Beja, A.; Ramos Silva,
M. J. Org. Chem. 2005, 70, 6629–6638; (c) Pinho e Melo, T. M. V. D.; Soares, M. I.
L.; Nunes, C. M. Tetrahedron 2007, 63, 1833–1841.
2. (a) Pinho e Melo, T. M. V. D.; Soares, M. I. L.; Rocha Gonsalves, A. M. d’A.
Tetrahedron Lett. 2006, 47, 791–794; (b) Pinho e Melo, T. M. V. D.; Soares, M. I. L.;
Nunes, C. M.; Paixão, J. A.; Matos Beja, A.; Ramos Silva, M. J. Org. Chem. 2007, 72,
4406–4415; (c) General procedure for [8+2] cycloadditions of diazafulvenium
tetracarboxylate 12a. Yellowish oil. IR (film) 1735, 1696, 1400, 1215 cmÀ1
.
1H
NMR (CDCl3, 300 MHz): 1.26–1.35 (6H, m), 1.62–1.73 (3H, m), 3.82 (3H, s), 3.84
(3H, s), 4.17–4.27 (4H, m), 5.28–5.41 (1H, m), 6.28 (1H, br s), 6.54 (1H, br s), 7.16
(1H, s); 13C NMR (CDCl3, 75.5 MHz): 14.3, 14.4, 14.5, 51.5, 51.7, 62.2, 62.8, 63.1,
63.7, 110.5, 116.6, 123.2, 130.0, 154.5, 154.9, 163.6, 163.8; MS (EI) 397 (M+,
21%), 365 (100), 251 (45), 221 (24), 209 (23), 196 (26), 177 (40),164 (35) and 147
(20). HRMS (EI) m/z 397.1488 (C17H23N3O8 [M+], 397.1485).
7. Vishwakarma, L. C.; Stringer, O. D.; Davis, F. A. Org. Synth. 1993, Coll.Vol. VIII,
546–550.
8. Dimethyl
[3,4-f]indolizine-7,8-dicarboxylate 13b. Brown foam. IR (KBr) 1707, 1393,
1187 cmÀ1 1H NMR (CDCl3, 300 MHz): 1.49 (3H, d, J = 7.2 Hz), 2.35 (3H, s),
methide 22 under conventional heating.
pyrazolo[1,5-c][1,3]thiazole-6,7-dicarboxylate
A
suspension of 2,2-dioxo-1H,3H-
21 (0.87 mmol) and
4,6-dimethyl-1,3-dioxo-2-phenyl-2,3,3a,4,9,9a-hexahydro-1H-pyrrolo-
dipolarophile (1.74 mmol) in 1,2,4-trichlorobenzene (2.5 mL) was heated at
reflux under dry nitrogen for 3–4 h. After cooling to room temperature, the
mixture was purified by flash chromatography [hexane] to remove 1,2,4-
trichlorobenzene followed by elution with ethyl acetate–hexane.
3. (a) Sutcliffe, O. B.; Storr, R. C.; Gilchrist, T. L.; Rafferty, P.; Crew, A. P. A. Chem.
Commun. 2000, 675–676; (b) Sutcliffe, O. B.; Storr, R. C.; Gilchrist, T. L.;
Rafferty, P. J. Chem. Soc., Perkin Trans. 1 2001, 1795–1806.
4. (a) Lindström, P.; Tierney, J.; Wathey, B.; Westman, J. Tetrahedron 2001,
57, 9225–9283; (b) Kappe, C. O. Angew. Chem., Int. Ed. 2004, 43, 6250–
6284.
.
3.11 (1H, dd, J = 8.6 and 16.6 Hz), 3.38 (1H, dd, J = 1.1 and 9.3 Hz), 3.51–3.60 (1H,
m), 3.94–3.99 (1H, m), 5.01 (1H, dq, J = 1.0 and 7.2 Hz), 7.01–7.04 (2H, m, Ar-H),
7.34–7.42 (3H, m, Ar-H); 13C NMR (CDCl3, 75.5 MHz): 10.0, 20.4, 22.3, 36.9, 46.0,
47.7, 51.4, 51.5, 112.2, 112.8, 126.2, 128.8, 129.1, 129.3, 131.2, 132.7, 164.6,
165.7, 176.1, 177.2; m/z (EI) 410 (M+, 20%), 378 (100), 292 (36) and 216 (40).
HRMS (EI) m/z 410.1474 (C22H22N2O6 [M+], 410.1478).
9. Dimethyl
6-methyl-1,3-dioxo-2-phenyl-2,3,3a,4,9,9a-hexahydro-1H-pyrrolo[3,4-
f]indolizine-7,8-dicarboxylate 18. Yellowish foam. IR (KBr) 1712, 1390,
1212 cmÀ1 1H NMR (CDCl3, 300 MHz): 2.34 (3H, s), 2.95–3.02 (1H, m), 3.51–
.
5. General procedure for
[8p+2p] cycloadditions of azafulvenium methides.
3.52 (2H, m), 3.80 (6H, s), 3.81–3.94 (2H, m), 4.56–4.60 (1H, m), 6.96–7.00 (2H,
m, Ar-H), 7.37–7.40 (3H, m, Ar-H); 13C NMR (CDCl3, 75.5 MHz): 10.2, 23.1, 38.3,
40.2, 41.3, 51.5, 111.9, 112.7, 126.3, 128.9, 129.2, 130.9, 131.2, 133.2, 164.5,
165.6, 176.0, 176.8; m/z (EI) 396 (M+, 22%), 364 (100), 278 (28), 217 (24) and
131 (11). HRMS (EI) m/z 396.1324 (C21H20N2O6 [M+], 396.1321).
A
suspension of 2,2-dioxo-1H-pyrrolo[1,2-c]thiazole-6,7-dicarboxylate (0.5
mmol) and dipolarophile (2–4 equiv) in 1,2,4-trichlorobenzene (1 mL) was
irradiated in the microwave reactor (CEM Focused Synthesis System, Discover
S-Class) with the temperature set to 260 °C for the time indicated in each case.
After cooling to room temperature, the mixture was purified by flash