systems such as 1,4-dimethoxynaphthalene and 5,8-dimethoxy-
quinoline, the oxidative demethylation reaction of 1,4-
dimethoxybenzene did not proceed. This suggests that the
reaction sites are the benzylic positions on the fused ring
and that the reaction intermediate would be somewhat
stabilized by the fused ring.
Table 2. the Oxidative Demethylations of
1,4-Methoxybenzenes under Optimized Conditionsa
In summary, we have demonstrated a mild oxidative
demethylation of fused 1,4-dimethoxybenzenes to 1,4-
quinones using NBS in the presence of aqueous THF and a
catalytic amount of sulfuric acid. We can also control two
reactions, bromination or oxidative demethylation, because
different pathways are followed depending on the presence
or absence of a catalytic mount of sulfuric acid. However,
the oxidative demethylation of an unfused ring system such
as 1,4-dimethoxybenzene does not proceed under the opti-
mized reaction conditions. Further studies on synthetic
applications to various anticancer and antibiotic agents such
as lavendamycin and streptonigrin derivatives,11 as well as
on the development of the diagnostic agent of quinoline-
5,8-dione derivatives as a tumor marker, are in process in
our laboratories.
Acknowledgment. This research was supported by the
Korea Research Foundation for the 21st Century.
Supporting Information Available: 1H and 13C NMR
spectra of 2, 2c, 1,4-naphthoquinone, and 2-ethyl-9,10-
anthraquinone. This material is available free of charge via
OL006952R
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1.0 mmol) was added to a well-stirred mixture of NBS (196 mg, 1.1 mmol)
in a solution of THF (15 mL), water (5 mL), and sulfuric acid (0.05 mL)
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of 2-methylquinoline-5,8-dione (2).
a All reactions were performed with a 1.0 mmol reaction scale using 1.1
equiv of NBS in the presence of THF (25 mL), water (5 mL), and H2SO4
(0.05 mL) for 5 min at 20 °C. b Isolated yield. c Reaction time was 15 min.
d Reactant was recovered yield of >80%.
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9,10-dimethoxyanthracene, which has no pyridine moieties,
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naphthoquinone and 2-ethyl-9,10-anthraquinone. Although
the electron density on the benzene ring of 1,4-dimethoxy-
benzene is higher than that of the benzene ring of fused
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