2700
S. E. Watson
J ¼ 9.0 Hz), 7.93 (dd, 1H, J ¼ 9.0 and 7.3 Hz), 8.21 (d, 1H, J ¼ 8.0 Hz), 8.43
(s, 1H); 13C NMR (CDCl3) d ¼ 11.91, 15.73, 118.42, 118.62, 118.90, 120.27,
124.73, 125.74, 128.94, 135.91, 137.15, 146.64, 154.83, 154, 83, 175.23;
IR (KBr) 2894, 1652, 1605, 1531, 1322, 1240, 760 cm21. Anal. calcd. for
C15H12O2: C, 80.36; H, 4.96; N, 5.20. Found: C, 80.16; H, 5.21; N, 5.03.
4-Methylpyrrolo[2,3-b]xanthone 1. Crude 3,4-dimethyl-2-nitroxanthone
(2.58 g, 9.6 mmol) was dissolved in dry dimethylformamide (15 mL), and
dimethylformamide dimethylacetal (DMFA) (3.85 mL, 28.8 mmol) and pyrro-
lidine (0.93 mL, 11.52 mmol) were added. The reaction mixture was heated
under an inert atmosphere at 1008C for 2 h. The volatiles were removed
under reduced pressure and the resulting red solid residue was dissolved in
ethyl acetate (10 mL). Hexane (30 mL) was added. The solution was stored
at 2108C for 24 h and filtered to give a brick-red solid (2.66 g, 8.16 mmol,
1
85%). H NMR indicated this material to be a mixture of the pyrrolidine
and dimethylamino enamines 8 and 9.
The crude mixture of enamines was dissolved in dry THF/MeOH (1 : 1,
30 mL) and cooled to 08C. Palladium on carbon (10%, 200 mg) was added.
The reaction mixture was degassed and stirred at 08C under one atmosphere
of hydrogen for 2 h and then allowed to warm slowly to rt. Filtaration
through celite, removal of the solvent, and recrystallization from methanol
provided compound 1 as a pale yellow solid (1.48 g, 5.95 mmol, 62% for
1
two steps): mp ¼ 268 decomp; H NMR (DMSO) d ¼ 2.642 (s, 3H), 3.30
(d, 1H, J ¼ 8.0 Hz), 6.63 (d, 1H, J ¼ 2.0 Hz), 7.355 (dd, 1H, J ¼ 7.2 Hz),
7.60 (d, 1H, J ¼ 8.0 Hz), 7.753 (m, 2H), 8.07 (s, 1H), 8.14 (d, 1H,
J ¼ 7.2 Hz); 13C NMR (CDCl3) d ¼ 12.406, 100.781, 105.880, 115.409,
117.048, 118.505, 120.568, 126.426, 132.450, 133.391, 134.559, 135.348,
136.228, 147.063, 156.410, 177.745; IR (KBr) 3232.2, 2917.52, 1621.82,
1512.99, 1474.62, 1338.18, 1159.94, 868.29, 768.52 cm21. MS (FAB) 256
(M þ Li), 160, 136, 89. HRMS m/z C15H12NO2 256.0954, found 256.0958.
Anal. calcd. for C15H12NO2: C, 80.36; H, 4.96; N, 5.20. Found: C, 80.16;
H, 5.21; N, 5.03.
REFERENCES
1. Batcho, A. D.; Leimgruber, W. Organic Synthesis; Freeman, J. P., Ed.; Wiley:
New York, Col. Vol. VII; pp. 34–41.
2. Frahm, A. W.; Pickert, M. Arch. Pharm. Pharm. Med. Chem. 1998, 331, 177–192.
3. Rewcastle, G. W.; Alwell, G. J.; Beguley, B. C.; Calveley, S. B.; Denny, W. A.
J. Med. Chem. 1989, 32, 793–799.
4. Livingstone, R. In Rodd’s Chemistry of Carbon Compounds, 2nd ed.; Coffey, S.,
Ed.; Elsevier: Amsterdam, 1977; Vol. IV, Part E, pp. 316–333.
5. Goldberg, A. A.; Walker, H. A. J. Chem. Soc. 1953, 1348–1357.
6. (a) For an excellent review, see: Lindley, J. Tetrahedron 1984, 40, 1433–1456;
(b) For additional references, see: Boger, D. L.; Yohannes, D. Tetrahedron. Lett.