7.87 (d, 2H, J = 8.0 Hz), 7.58 (t, 1H, J = 7.6 Hz), 7.45 (t, 2H, J = 7.6 Hz),
6.62 (s, 1H), 4.59 (s, 1H), 2.44 (s, 3H), 2.35 (s, 3H), 1.91 (s, 3H). 13
C
NMR (CDCl3, 100 MHz): 193.2, 158.0, 149.7, 147.7, 139.1, 133.3,
129.6, 128.7, 126.9, 118.9, 118.1, 113.9, 112.4, 14.7, 13.9, 12.7.
Compound 4c: white solid; 1H NMR (DMSO, 400 MHz): 9.99 (s, 1H),
8.13 (d, 1H, J = 8.4 Hz), 8.08 (d, 1H, J = 8.4 Hz), 7.73 (d, 2H, J = 7.4
Hz), 7.65-7.42 (m, 5H), 6.87 (s, 1H), 2.43 (s, 3H). 13C NMR (DMSO, 100
MHz): 191.8, 161.0, 150.6, 142.7, 139.4, 133.2, 129.3, 129.2, 127.7,
124.9, 123.7, 123.2, 122.9, 120.9, 119.5, 117.9, 100.2, 15.2. Compound
4d: orange oil; 1H NMR (CDCl3, 400 MHz): 7.68 (d, 2H, J = 7.6 Hz),
7.38 (t, 1H, J = 7.6 Hz), 7.26 (t, 2H, J = 7.6 Hz), 5.61 (s, 1H), 3.95 (s,
3H), 3.78 (s, 3H), 2.15 (s, 3H), 1.71 (s, 3H). 13C NMR (CDCl3, 100
MHz): 192.9, 157.1, 144.1, 139.6, 138.8, 136.3, 133.4, 131.2, 129.6,
128.7, 123.5, 118.0, 108.9, 61.6, 60.9, 13.8, 12.6.
14. NMR analysis of the mother liquors indicated the presence of a
substantial amount of quinones hydroxybenzofurans 4, but not of their
isomers 3.
15. Typical procedure for the synthesis of 5: NaBH4 (0.92 mmol) was added
to a solution of 4 (0.46 mmol) in anhydrous MeOH (5 mL) and the
mixture was stirred at r.t. for 2 hours. The reaction was concentrated
under reduced pressure, washed with aq. solution of HCl 1N (10 mL) and
extracted with DCM (2x 10 mL). The combined organic layers were
washed with brine (10 mL), dried over MgSO4, concentrated under
reduced pressure and purified by flash silica gel column chromatography
(DCM/ether as eluent) to give alcohol 5. 5a: white solid; 1H NMR
(DMSO, 400 MHz): 8.93 (s, 1H), 7.43 (d, 2H, J = 7.6 Hz), 7.31 (t, 2H, J
= 7.6 Hz), 7.22-7.17 (m, 2H), 6.76 (d, 1H, J = 2.4 Hz), 6.57 (dd, 1H, J =
2.4 Hz, J = 7.6 Hz), 5.88 (d, 1H, J = 3.5 Hz), 5.78 (d, 1H, J = 3.5 Hz),
2.46 (s, 3H). 13C NMR (DMSO, 100 MHz): 153.0, 151.7, 147.9, 144.8,
128.6, 128.4, 127.1, 126.2, 118.5, 111.9, 110.8, 105.9, 67.3, 12.8. 5b:
white solid; 1H NMR (CDCl3, 400 MHz): 7.27-7.13 (m, 6H), 6.45 (s,
1H), 6.14 (s, 1H), 4.37 (s, 1H), 2.31 (s, 3H), 2.28 (s, 3H), 1.96 (s, 3H).
13C NMR (CDCl3, 100 MHz): 153.8, 149.1, 148.2, 142.8, 128.3, 127.1,
126.6, 126.1, 118.6, 117.2, 113.2, 112.2, 68.0, 14.7, 13.0, 12.5. 5c:
yellow solid; 1H NMR (DMSO, 400 MHz): 9.72 (s, 1H), 8.13 (d, 1H, J =
8.4 Hz), 8.05 (d, 1H, J = 8.4 Hz), 7.55 (t, 1H, J = 7.5 Hz), 7.47 (d, 2H, J
= 7.5 Hz), 7.41 (t, 1H, J = 7.5 Hz), 7.33 (t, 2H, J = 7.5 Hz), 7.22 (t, 1H, J
= 7.5 Hz), 6.97 (s, 1H), 5.98 (s, 1H), 5.91 (s, 1H), 2.57 (s, 3H). 13C NMR
(DMSO, 100 MHz): 150.4, 148.9, 144.9, 142.8, 128.5, 127.1, 127.0,
126.3, 123.9, 123.6, 123.5, 122.6, 121.1, 119.9, 119.3, 101.0, 67.4, 12.9.
5d: orange solid; 1H NMR (CDCl3, 400 MHz): 7.27-7.15 (m, 5H), 6.12
(s, 1H), 5.59 (s, 1H), 4.01 (s, 3H), 3.84 (s, 3H), 2.34 (brs, 1H), 2.24 (s,
3H), 1.99 (s, 3H). 13C NMR (CDCl3, 100 MHz): 153.3, 143.3, 142.7,
140.1, 135.8, 134.8, 128.3, 127.2, 126.1, 123.4, 117.2, 108.9, 67.9, 61.5,
60.9, 13.1, 12.4.
16. Cheng, X. M.; Liu, X. W. J. Comb. Chem. 2007, 9, 906-8.
17. Bernatek, E. Acta Chem. Scand. 1956, 10, 273-278.