Molecules 2005, 10, X
1276
26.0 (C-3'), 22.2 (C-4'), 13.7 (C-5'). Shifts with identical superscripts (*,∝) within a data set are
interchangeable.
Cyclization of 3,5-dimethoxy-2-hexanoyl-phenylacetic acid methyl ester (8) with ethoxide, to give the
naphthol (10) and the naphthoquinone (11) by auto-oxidation.
A solution of 3,5-dimethoxy-2-hexanoyl-phenylacetic acid methyl ester (8, 95mg, 0.31 mmol) in
dry EtOH (10 mL), was added dropwise, over 7 min, to a refluxing solution of sodium ethoxide
(prepared from Na (0.42 g) in 10 mL of dry EtOH) under N2. After a further 10 min at reflux the
reaction mixture was cooled, diluted with ether (30 mL), neutralized with HCl (1M) and then extracted
with aqueous NaHCO3 (5%; 3×30 mL) giving a light pink aqueous phase and a yellow organic phase.
The ethereal phase was dried (MgSO4) and concentrated in vacuo to give a crude mixture, which was
purified by flash chromatography on a silica column (r = 6 mm, l = 20 cm, silica gel 0.040-0.063 mm;
Pet. Sp/EtOAc 25:75), giving 3-butyl-2-hydroxy-5,7-dimethoxy-1,4-naphthoquinone (11) (47 mg, 0.16
mmol, 52%) as a bright yellow solid and 2-butyl-6,8-dimethoxy-naphthalene-1,3-diol (10) (21 mg,
0.076 mmol, 25%) as a yellow oil, which auto-oxidized to the naphthoquinone (11) over several days
on exposure to air.
2-Butyl-6,8-dimethoxy-naphthalene-1,3-diol (10): TLC: Rf 0.48 [EtOAc/ Pet. Sp, 25:75 (v/v)]. IR: ν
OMe OH
(cm-1): 3402 (s, br), 2932 s, 2858 m, 2362 w, 1636 s, 1597 s, 1448
1
4'
m, 1404 m, 1371 s, 1338 w, 1246 w, 1209 m, 1150 m, 1107 m,
1'
8a
1041 m. ESI-MS (+ve ion, cv 50V) m/z: 277 (M+H, 100%), 263
4a
6
3
MeO
OH
(M-CH3+H, 10%), 220 (2%), 205 (2%). UV (MeOH) λmax (log ε):
245 (4.90), 292 (3.91). 1H-NMR (CDCl3): 9.43 (1H, s, 1-OH), 6.55 (1H, s, 4-H), 6.50 (1H, d, 2.1 Hz,
5-H), 6.28 (1H, d, 2.1 Hz, 7-H), 3.98 (3H, s, 8-OCH3), 3.85 (3H, s, 6-OCH3), 2.74 (2H, t, 7.5 Hz, 1'-
13
H), 1.58 (2H, m, 2'-H), 1.44 (2H, m, 3'-H), 0.94 (3H, t, 7.2 Hz, 4'-H). C APT-NMR (CDCl3): 157.5
(C-6)*, 157.0 (C-8) *, 154.6 (C-3)∝, 152.9 (C-1)∝, 135.9 (C-4a), 112.1 (C-2), 106.2 (C-8a), 100.8 (C-4)
98.0 (C-5), 95.4 (C-7), 56.0 (C-8-OCH3), 55.3 (C-6-OCH3), 31.5 (C-2'), 22.9 (C-1')∆, 22.8 (C-3')∆, 14.1
(C-4'). Shifts with identical superscripts (*,∝,∆) are interchangeable.
3-Butyl-2-hydroxy-5,7-dimethoxy-1,4-naphthoquinone (11): TLC: Rf 0.28 [EtOAc/ Pet. Sp, 25:75
OMe
O
(v/v)]. mp: 160oC. IR: ν (cm-1): 3209 m, 2932 m, 2359 m, 1655 m,
1638 s, 1595 m, 1460 m, 1321 s, 1209 s, 1157 m, 1126 w, 1034 w.
EIMS m/z: 290 (M+•, 100%), 248 (M-C3H6, 43%), 233 (M-
(CH2)3CH3, 13%), 219 (35%), 165 (22%). HREI-MS m/z: found
5
4'
1'
3
4a
8a
MeO
OH
1
O
290.1163 (C16H18O5 requires 290.1154). UV (MeOH) λmax (log ε):
1
212 (4.68), 261 (4.51), 304 (4.29). H-NMR (CDCl3): 7.25 (1H, d, 2.4 Hz, 8-H), 6.75 (1H, d, 2.4 Hz,
5-H), 3.96 (3H, s, 5-OCH3)*, 3.93 (3H, s, 7-OCH3)*, 2.56 (2H, t, 7.5 Hz, 1'-H), 1.50 (2H, m, 2'-H),
13
1.40 (2H, m, 3'-H), 0.92 (3H, t, 7.2 Hz, 4'-H). C APT-NMR (CDCl3): 183.6 (C-4)*, 181.7 (C-1)*,
163.7 (C-7)∝, 161.7 (C-5)∝, 150.9 (C-2), 133.2 (C-8a), 126.2 (C-3), 114.2 (C-4a), 105.2 (C-6), 103.0
(C-8), 56.4 (C-5-OCH3)∆, 55.8 (C-7-OCH3)∆, 30.5 (C-2'), 23.2 (C-1'), 22.9 (C-3'), 13.8(C-4'). Shifts
with identical superscripts (*,∝,∆) within a data set are interchangeable.