Facile synthesis of regio-isomeric naphthofurans and benzodifurans

Article abstract of DOI:10.1016/j.tet.2004.11.022

Naphtho[1,2-b]furans 1a-f, naphtho[2,1-b]furans 2a-f, benzo[1,2-b:5,4- b′]difurans 3a-b, benzo[1,2-b:4,5-b′]difurans 4a-b, and benzo[1,2-b:4,3-b′]difurans 5a-b were synthesized by base-catalyzed cyclization reaction of the corresponding o-alkoxybenzoylarene derivatives. The o-alkoxybenzoylarenes were obtained from the etherification reaction of the o-hydroxybenzoylarenes, which were prepared either by the reaction of methoxyarenes with benzoyl chloride in the presence of aluminum chloride or by photo-Fries rearrangement of aryl benzoates. Graphical Abstract.

Full text of DOI:10.1016/j.tet.2004.11.022

Tetrahedron 61 (2005) 545–553
Facile synthesis of regio-isomeric naphthofurans
and benzodifurans
*
Kwanghee Koh Park and Jinsuk Jeong
Department of Chemistry, Chungnam National University, Daejeon 305-764, South Korea
Received 12 October 2004; revised 8 November 2004; accepted 8 November 2004
Available online 26 November 2004
Abstract—Naphtho[1,2-b]furans 1a–f, naphtho[2,1-b]furans 2a–f, benzo[1,2-b:5,4-b0]difurans 3a–b, benzo[1,2-b:4,5-b0]difurans 4a–b, and
benzo[1,2-b:4,3-b0]difurans 5a–b were synthesized by base-catalyzed cyclization reaction of the corresponding o-alkoxybenzoylarene
derivatives. The o-alkoxybenzoylarenes were obtained from the etherification reaction of the o-hydroxybenzoylarenes, which were prepared
either by the reaction of methoxyarenes with benzoyl chloride in the presence of aluminum chloride or by photo-Fries rearrangement of aryl
benzoates.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
nyl compounds of type B (Scheme 1).5b–d For the efficient
synthesis of variously substituted benzodifurans and
naphthofurans, availability of the corresponding starting
materials A or B and facile methods of dehydrative
cyclization reaction of the precursors are the key factors.
Arene ring-fused furans have attracted widespread interest
in view of their presence in natural products, and their
biological and pharmacological activities.1–4 Among
arenofurans, benzofurans have been the subject of the
most extensive studies and numerous synthetic methods
have been developed for them.1,2,5–7 Compared to benzo-
furans, the reports on the synthesis of naphthofurans3,5,8 and
benzodifurans4,9–11 are rather limited, though many of the
extended arenofurans exhibit interesting biological proper-
ties3,4 and have potential applications as fluorescent dyes
and probes, and as photosensitizers.9,12
We have been interested in the preparation of various
alkoxybenzoylarene derivatives A and their photocycliza-
tion reaction leading to benzo[b]furan6 and benzodifuran
ring systems.10,11 However, we could not obtain naphth0o-
furans and benzodifurans other than benzo[1,2-b:5,4-b ]-
difuran from the photocyclization reactions of the
corresponding alkoxybenzoylarenes.11 In this paper, we
describe facile syntheses of regioisomeric naphthofurans
1–2 and benzodifurans 3–5 by base-catalyzed dehydrative
cyclization reaction of appropriate o-alkoxybenzoylarene
derivatives.
A major route for the synthesis of various arene ring-fused
furan derivatives is the intramolecular formation of a furan
moiety starting from properly substituted arene compounds
via dehydrative cyclization of either o-alkoxycarbonyl
compounds of type A2,4b–d,6,7a,8b–e,9–11 or a-aryloxycarbo-
Scheme 1. A major route for the synthesis of arene ring-fused furan
derivatives.
Keywords: Naphtho[1,2-b]furan; Naphtho[2,1-b]furan; Benzo[1,2-b:4,5-
b0]difuran; Benzo[1,2-b:5,4-b0]difuran; Benzo[1,2-b:4,3-b0]difuran.
* Corresponding author. Tel.: C82 42 821 5479; fax: C82 42 823 1360;
e-mail: khkoh@cnu.ac.kr
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.11.022

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K. K. Park, J. Jeong / Tetrahedron 61 (2005) 545–553
2. Results and discussion
yield: Crouse et al. reported that photoirradiation of
1-naphthyl benzoate gave the o-isomer 6 with 47% yield
without the para isomer,13 while Gu et al. reported that both
isomers were obtained with 1:1 ratio.14 1-Benzoyl-2-
naphthol 7 was obtained in 77% yield from the reaction
of 2-methoxynaphthalene with benzoyl chloride in the
presence of AlCl3. The corresponding reaction of 1-meth-
oxynaphthalene gave 4-benzoyl-1-methoxynaphthalene in
94% yield without formation of any 2-benzoylated products.
It is noteworthy that the AlCl3-catalyzed benzoylation
reaction of 2-methoxynaphthalene gives demethylated
product 7, while the same reaction of 1-methoxynaphtha-
lene gives non-demethylated product, 4-benzoyl-1-methoxy-
naphthalene. Such selective demethylation of methoxy
group ortho to carbonyl group had previously been reported
in the reaction of aryl methyl ether with AlCl3.15
2.1. Synthesis of naphthofurans 1 and 2
Regioisomeric o-hydroxybenzoylnaphthalenes 6 and 7, the
starting materials for the naphthofurans 1 and 2, were
prepared as shown in Scheme 2. 2-Benzoyl-1-naphthol 6
was prepared in 48% yield from photo-Fries rearrangement
of 1-naphthyl benzoate in methanol, which also gave the
p-isomer, 4-benzoyl-1-naphthol as a co-product in 31%
o-Alkoxybenzoylnaphthalenes 8 and 9 were prepared with
91–99% yields by reacting o-benzoylnaphthols 6 and 7 with
alkyl halide in the presence of potassium carbonate in
acetone. It is known that o-alkoxy-substituted benzo-
phenones photocyclize readily to benzo[b]furans via
intramolecular d-hydrogen abstraction.6,9–11 Thus, we
attempted photocyclization reaction of 8a and 9a to obtain
the corresponding naphthofurans. However, irradiation of a
solution of 8a or 9a in various solvents (benzene, methanol,
t-butanol, or cyclohexane) with either 350 or 254 nm lamps
did not produce any significant amounts of cyclized
products and most of the starting materials were recovered.
The failure of the photocyclization reaction made us to try
base-catalyzed cyclization reaction and the reaction
Scheme 2. Preparation of o-benzoylhydroxynaphthalenes 6 and 7.
Scheme 3. Synthesis of naphtho[1,2-b]furan derivatives 1a–f.

K. K. Park, J. Jeong / Tetrahedron 61 (2005) 545–553
547
Scheme 4. Synthesis of naphtho[2,1-b]furan derivatives 2a–f.
provided naphthofurans 1 and 2 in excellent yields
(84–99%). The synthetic routes are summarized in
Schemes 3 and 4.
type B starting material,5b–d or by cyclofragmentation of
epoxysulfone.5a Chatterjea et al. reported that 9a is cyclized
to 2-ethoxycarbonyl-1-phenylnaphtho[2,1-b]furan by
sodium/ethanol.8d However, repetition of the reaction by
us gave not only the reported product, but also its
hydrolyzed product, 1-phenylnaphtho[2,1-b]furan-2-carb-
oxylate and decarboxylated product 2a with poorly
reproducible products ratios.
Depending on the a-substituent in the alkyl halide, the
reactions of 6 and 7 with alkyl halides in the presence of
K2CO3 in acetone either stop at the alkylation stage or
further proceed to the cyclization/dehydration step. When
the a-substituent is ethoxycarbonyl, o-alkoxybenzoyl-
naphthalene 8a and 9a were obtained at reflux temperature
of acetone. Treatment of 8a and 9a with KOH in dioxane at
30 8C produced Ia and IIa, respectively.16 Acidification of
the salts Ia and IIa with aq HCl resulted in decarboxylative
dehydroxylation to provide 3-phenylnaphtho[1,2-b]furan 1a
and 1-phenylnaphtho[2,1-b]furan 2a, respectively: 1a and/
or 2a had been previously prepared either by cyclodehydra-
tion of the corresponding 2-naphthyloxy-1-phenylethanone,
The naphthofurans 1b and 2b were obtained in overall
yields of 82 and 97% yields, respectively, from the two-step
reactions of 6 and 7 with bromoacetonitrile involving
isolated 8b and 9b intermediates. The one-step reaction of 6
to produce 1b in refluxing acetone solution without isolating
the intermediate 8b gave much low yield, 41%. When the
a-substituents in the alkyl halide are benzoyl and napthoyl
groups, alkylation and then cyclization/dehydration
Scheme 5. Preparation of dibenzoyldihydroxybenzenes 10–12.9,10,15

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K. K. Park, J. Jeong / Tetrahedron 61 (2005) 545–553
reactions proceeded in one pot at refluxing temperature of
acetone to give the corresponding naphthofurans 1c–f and
2c–f in 87–99% yields.17
described for the synthesis of naphthofurans 1 and 2, which
are shown in Scheme 6. For cyano-derivatives 3a–5a,
alkylated intermediates 13–15 were isolated and cycliza-
tion/dehydration of the intermediates gave the desired
products with the overall yields of 69–83%. For 3b–5b,
alkylation and dehydrative cyclization reactions proceeded
in one pot at refluxing temperature of acetone to give the
corresponding benzodifurans in 85–97% yields: the syn-
thesis of 3b from the same starting materials, but by phase
transfer catalytic method or microwave irradiation had been
reported.4d
2.2. Synthesis of regioisomeric benzodifuran derivatives
3–5
Regioisomeric dihydroxydibenzoylbenzenes 10–12, start-
ing materials for the synthesis of the benzodifurans 3–5,
were prepared by the reported procedures (Scheme 5).9,10,15
The reaction of 1,3-dimethoxybenzene with benzoyl
chloride in the presence of aluminum chloride provided
1,5-dibenzoyl-2,4-dihydroxybenzene 10 in 35% yield.9,10
2,5-Dibenzoyl-1,4-dihydroxybenzene 11 and 2,3-diben-
zoyl-1,4-dihydroxybenzene 12 were obtained in two steps
from 1,4-dimethoxybenzene and separated.15
The symmetrical nature of the compounds 3–5 is manifested
in their NMR spectra. Based on the symmetry of the
compounds, the expected number of 13C NMR peaks is 11
for 3a, 10 for 4a and 5a, 15 for 3b, and 14 for 4b and 5b. The
actual carbon numbers present in the compounds are 24 for
the a series and 36 for the b series. The observed number of
peaks in the 13C NMR spectra exactly matches the expected
number or one less number due to overlapping.
Alkylation of 10–12 to dialkoxydibenzoylbenzenes 13–15
and subsequent dehydrative cyclization reactions of 13–15
to produce 3–5 were carried out in the same manner
Scheme 6. Synthesis of various regioisomeric benzodifurans 3–5.

K. K. Park, J. Jeong / Tetrahedron 61 (2005) 545–553
549
3. Conclusions
AlCl3 (1.80 g, 13.9 mmol) in dichloromethane (30 mL), and
stirred for 20 h at room temperature under nitrogen
atmosphere. Then the reaction mixture was poured to a
beaker containing ice water (45 mL) and conc HCl (15 mL)
and stirred for 1 h. The organic layer was separated and the
aqueous layer was extracted with dichloromethane three
times. The organic layers were combined, dried with
anhydrous sodium sulfate and concentrated. The residue
was purified by silica gel column chromatography (eluent:
5:1 hexane–ethyl acetate) and then recrystallization from
dichloromethane to afford 1-benzoyl-2-naphthol 7 (1.22 g,
Facile synthetic methods for various regioisomeric naphtho-
furans 1 and 2 and benzodifurans 3–5 have been developed.
The starting materials for the syntheses, regioisomeric
o-hydroxybenzoylarenes, were prepared either by the
reaction of methoxyarenes with benzoyl chloride in the
presence of aluminum chloride or by photo-Fries rearrange-
ment of aryl benzoates, depending on the positions of the
substituents. The allkylation of o-hydroxybenzoylarenes
followed by cyclization/dehydration reactions afforded the
desired arenofurans in excellent yields.
1
77%): mp 139–141 8C (lit. 141.05 8C;18 135–137 8C8d); H
NMR (CDCl3) d 11.20 (s, 1H), 7.93 (d, 1H, JZ9 Hz), 7.74
(d, 1H, JZ8 Hz), 7.62 (d, 2H, JZ8 Hz), 7.55 (t, 1H, JZ
7 Hz), 7.40 (t, 2H, JZ8 Hz), 7.31–7.22 (m, 3H), 7.15 (t, 1H,
JZ8 Hz).
4. Experimental
4.1. General
The same reaction using 1-methoxynaphthalene (0.200 g,
1.26 mmol) instead of 2-methoxynapthalene gave 94%
yield (0.309 g) of 4-benzoyl-1-methoxynaphthalene:20 1H
NMR (CDCl3) d 8.39–8.33 (m, 2H), 7.83 (d, 2H, JZ8 Hz),
7.61–7.42 (m, 6H), 6.78 (d, 1H, JZ8 Hz), 4.05 (s, 3H).
1
Melting points are uncorrected. H and 13C NMR spectra
were obtained at 400 and 100 MHz, respectively, using
tetramethylsilane (in CDCl3) or residual undeuterated
solvent (in DMSO-d6 and D2O) as an internal standard.
4.4. Preparation of 1a and 2a
4.2. Preparation of 2-benzoyl-1-naphthol 6
A solution of ethyl bromoacetate (1.21 g, 7.25 mmol) in
acetone (50 mL) was added to the reaction mixture of
benzoylnaphthol (6 or 7, 1.50 g, 6.04 mmol) and potassium
carbonate (3.34 g, 24.2 mmol) in acetone (100 mL) and
heated at reflux for 2 h under nitrogen atmosphere. After
removing potassium carbonate by filtration, the reaction
mixture was concentrated. To the residue, water was added
and extracted with dichloromethane. The organic layer was
dried, concentrated, and then purified by silica gel column
chromatography (eluent: 5:1 hexane–ethyl acetate) to give
the alkylated compound, 8a or 9a.
Benzoyl chloride (3.51 g, 25.0 mmol) in dichloromethane
(50 mL) was added slowly to a solution of 1-naphthol
(3.00 g, 20.8 mmol) and pyridine (6.58 g, 83.2 mmol) in
dichloromethane (250 mL) and refluxed for 3 h under
nitrogen atmosphere. The reaction mixture was washed
with 10% aqueous HCl and then dried with anhydrous
sodium sulfate. The concentrated reaction mixture was
purified by silica gel column chromatography (eluent: 9:1
hexane–ethyl acetate) to give 1-naphthyl benzoate (4.75 g,
92%): mp 58–59 8C (lit.13 47–48 8C). A methanol solution
(870 mL) of 1-naphthyl benzoate (4.75 g, 19.1 mmol) in a
quartz vessel was purged with nitrogen for 1 h and then
irradiated under nitrogen with 254 nm mercury lamps using
RPR-100 photochemical reactor (Southern New England
Ultraviolet Company) for 17 h. The reaction mixture was
concentrated and purified by silica gel column chroma-
tography eluting with 9:1 hexane–ethyl acetate to provide
2.28 g (48%) of 2-benzoyl-1-naphthol 6 and 1.47 g (31%) of
4-benzoyl-1-napththol.
1
4.4.1. Compound 8a. Yield, 99%; mp 68–70 8C; H NMR
(CDCl3) d 8.43 (dd, 1H, JZ6, 3 Hz), 7.90–7.85 (m, 3H),
7.68 (d, 1H, JZ8 Hz), 7.61–7.56 (m, 3H), 7.47–7.42 (m,
3H), 4.59 (s, 2H), 4.18 (q, 2H, JZ7 Hz), 1.23 (t, 3H, JZ
7 Hz); 13C NMR (CDCl3) d 196.16, 168.41, 153.47, 137.17,
135.77, 133.26, 130.08, 128.33, 127.90, 127.76, 127.64,
127.01, 126.79, 125.72, 123.99, 123.30, 72.36, 61.15, 14.11.
IR (KBr): 1758, 1662, 1281, 1196, 1100 cmK1. Anal. Calcd
for C21H18O4: C, 75.43; H, 5.43%. Found: C, 75.46; H,
5.41%.
2-Benzoyl-1-naphthol 6: mp 70–72 8C (lit. 63–64 8C;13
70.85 8C18); 1H NMR (CDCl3) d 13.95 (s, 1H), 8.52 (d, 1H,
JZ8 Hz), 7.75 (d, 1H, JZ8 Hz), 7.71 (d, 2H, JZ8 Hz),
7.64 (t, 1H, JZ8 Hz), 7.61–7.49 (m, 5H), 7.21 (d, 1H, JZ
9 Hz).
4.4.2. Compound 9a. Yield, 98%; mp 78–80 8C (lit.8d oil);
1H NMR (CDCl3) d 7.93–7.88 (m, 3H), 7.85–7.81 (m, 1H),
7.57–7.52 (m, 2H), 7.44–7.35 (m, 4H), 7.18 (d, 1H, JZ
9 Hz), 4.63 (s, 2H), 4.16 (q, 2H, JZ7 Hz), 1.20 (t, 3H, JZ
7 Hz); 13C NMR (CDCl3) d 197.08, 168.46, 152.22, 137.69,
133.42, 131.60, 131.04, 129.67, 129.22, 128.43, 128.02,
127.43, 124.49, 124.20, 123.87, 113.63, 66.47, 61.30, 14.11.
4-Benzoyl-1-napththol: mp 164–165 8C (lit. 166–167 8C19);
1H NMR (DMSO-d6) d 11.10 (br s, 1H), 8.33 (d, 1H, JZ
8 Hz), 8.26 (dd, 1H, JZ8, 2 Hz), 7.71 (d, 2H, JZ8 Hz),
7.63 (t, 1H, JZ8 Hz), 7.60–7.49 (m, 5H), 6.92 (d, 1H, JZ
8 Hz).
To the reaction flask containing potassium hydroxide
(0.280 g, 5.00 mmol) in dioxane (20 mL), 8a–9a (0.500 g,
1.50 mmol) was added and stirred at 30 8C for 1 h. The
reaction mixture was concentrated under reduced pressure
to give a solid residue. The solid residue was dissolved in
water (10 mL), acidified with aq HCl, stirred for 1 h at
80 8C, and then extracted with ether. The ether layers were
4.3. Reaction of 2-methoxynaphthalene with benzoyl
chloride: preparation of 7
A solution of 2-methoxynaphthalene (1.00 g, 6.32 mmol)
and benzoyl chloride (1.06 g, 7.58 mmol) in dichloro-
methane (30 mL) was added slowly to the suspension of

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K. K. Park, J. Jeong / Tetrahedron 61 (2005) 545–553
dried, concentrated, and then purified by silica gel column
chromatography (eluent: 5:1 hexane–ethyl acetate) to give
1a–2a.
chromatography (eluent: 5:1 hexane–ethyl acetate) to give
8b–9b.
4.5.1. Compound 8b. Yield, 91%; oil; 1H NMR (CDCl3) d
8.29–8.26 (m, 1H), 7.94–7.91 (m, 1H), 7.84–7.81 (m, 2H),
7.76 (d, 1H, JZ8 Hz), 7.68–7.58 (m, 3H), 7.49–7.43 (m,
3H), 4.84 (s, 2H); 13C NMR (CDCl3) d 195.68, 152.25,
136.97, 135.81, 133.59, 130.15, 128.47, 128.26, 128.08,
127.55, 127.48, 125.59, 125.22, 122.61,115.11, 60.57 (one
sp2 carbon is missing due to overlap). IR (neat): 1662, 1597,
1447, 1338, 1281, 1246, 1090 cmK1. Anal. Calcd for
C19H13NO2: C, 79.43; H, 4.56; N, 4.88%. Found: C, 79.50;
H, 4.63; N, 4.85%.
4.4.3. Compound 1a. Yield, 91%; mp 111–113 8C; 1H
NMR (CDCl3) d 8.33 (d, 1H, JZ8 Hz), 7.93 (d, 1H, JZ
8 Hz), 7.90 (s, 1H), 7.86 (d, 1H, JZ9 Hz), 7.71–7.66 (m,
3H), 7.59 (t, 1H, JZ8 Hz), 7.52–7.45 (m, 3H), 7.37 (t, 1H,
JZ8 Hz); 13C NMR (CDCl3) d 151.31, 140.38, 132.11,
131.40, 128.91, 128.18, 127.58, 127.39, 126.35, 125.27,
123.57, 123.42, 121.83, 121.53, 120.03, 118.66. IR (KBr):
1558, 1521, 1445, 1387, 1128 cmK1. Anal. Calcd for
C18H12O: C, 88.50; H, 4.95%. Found: C, 88.52; H, 4.92%.
4.4.4. Compound 2a. Yield, 84%; oil; 1H NMR (CDCl3) d
7.98 (d, 1H, JZ8 Hz), 7.93 (d, 1H, JZ8 Hz), 7.76 (d, 1H,
JZ9 Hz), 7.69 (d, 1H, JZ9 Hz), 7.68 (s, 1H), 7.62–7.58 (m,
2H), 7.53–7.46 (m, 3H), 7.42 (t, 1H, JZ8 Hz), 7.34 (t, 1H,
JZ8 Hz); 13C NMR (CDCl3) d 153.04, 141.59, 133.02,
130.72, 129.79, 128.82, 128.51, 128.24, 127.78, 125.89,
125.86, 124.37, 124.27, 123.30, 120.65, 112.58. IR (KBr):
1525, 1489, 1386, 1225, 1109 cmK1. Anal. Calcd for
C18H12O: C, 88.50; H, 4.95%. Found: C, 88.64; H, 4.84%.
4.5.2. Compound 9b. Yield, 99%; mp 90–91 8C; 1H NMR
(CDCl3) d 8.01 (d, 1H, JZ9 Hz), 7.90–7.87 (m, 1H), 7.84–
7.81 (m, 2H), 7.59 (t, 1H, JZ7 Hz), 7.55–7.52 (m, 1H),
7.47–7.39 (m, 5H), 4.75 (s, 2H); 13C NMR (CDCl3) d
196.31, 150.69, 137.35, 133.90, 131.55, 131.46, 130.04,
129.56, 128.72, 128.19, 127.81, 125.61, 125.43, 124.52,
114.85, 114.31, 55.35. IR (KBr): 1665, 1592, 1579, 1509,
1281, 1242, 1219 cmK1. Anal. Calcd for C19H13NO2: C,
79.43; H, 4.56; N, 4.88%. Found: C, 79.46; H, 4.63; N,
4.89%.
When the solid residues obtained from the reaction of 8a
and 9a with KOH were washed with abs. ethanol several
times to remove potassium hydroxide, the potassium salts of
3-hydroxy-3-phenyl-2,3-dihydronaphtho[1,2-b]furan-2-car-
boxylic acid Ia and 1-hydroxy-1-phenyl-1,2-dihydro-
naphtho[2,1-b]furan-2-carboxylic acid IIa were obtained,
respectively.16
The reaction mixture of potassium carbonate (0.385 g,
2.78 mmol) and 8b–9b (0.200 g, 0.696 mmol) in DMF
(8 mL) was stirred at 60 8C for 3.5 h. After removing
potassium carbonate by filtration, the filtrate was concen-
trated. To the residue, water was added and extracted with
dichloromethane. The organic layer was dried, concen-
trated, and then purified by silica gel column chroma-
tography (eluent: 2:1 hexane–dichloromethane for 1b; 2:1
hexane–ethyl acetate for 2b) to give 1b–2b.
1
4.4.5. Compound Ia. Mp 303 8C (dec); H NMR (D2O) d
8.13 (d, 1H, JZ8 Hz), 7.79 (d, 1H, JZ8 Hz), 7.58 (t, 1H,
JZ8 Hz), 7.52 (t, 1H, JZ8 Hz), 7.35–7.27 (m, 6H), 6.94 (d,
1H, JZ9 Hz), 4.95 (s, 1H); 13C NMR (D2O) d 174.98,
167.37, 156.55, 144.97, 136.51, 129.92, 129.69, 129.25,
128.94, 127.89, 126.09, 123.47, 123.35, 123.23, 121.94,
95.67, 85.23. IR (KBr): 3500–2500 (broad), 1607, 1399,
1064 cmK1. Anal. Calcd for C19H13KO4: C, 66.26; H,
3.80%. Found: C, 66.05; H, 3.95%.
4.5.3. Compound 1b. Yield, 90%; mp 163–164 8C; 1H
NMR (CDCl3) d 8.36 (d, 1H, JZ8 Hz), 7.96 (d, 1H, JZ
8 Hz), 7.80–7.76 (m, 4H), 7.70–7.56 (m, 4H), 7.55–7.50 (m,
1H); 13H NMR (CDCl3) d 152.47, 134.18, 133.16, 129.45,
129.31, 128.66, 128.41, 128.30, 127.40, 127.27, 125.54,
122.80, 120.88, 120.81, 120.71, 118.31, 112.72. IR (KBr):
2217, 1459, 1444, 1378, 1197, 1077 cmK1. Anal. Calcd for
C19H11NO: C, 84.74; H, 4.12; N, 5.20%. Found: C, 84.76;
H, 4.12; N, 5.04%.
4.4.6. Compound IIa. Mp 280–281 8C (dec); 1H NMR
(D2O) d 7.80 (d, 1H, JZ9 Hz), 7.67 (d, 1H, JZ8 Hz), 7.30–
7.25 (m, 3H), 7.16–7.08 (m, 4H), 7.03 (t, 1H, JZ7 Hz), 6.94
(t, 1H, JZ7 Hz), 4.98 (s, 1H); 13C NMR (D2O) d 175.07,
159.07, 145.75, 134.11, 131.75, 130.83, 130.67, 130.01,
128.95, 128.76, 127.46, 125.03, 123.74, 122.46, 114.26,
96.13, 85.49. IR (KBr): 3500–2500 (broad), 1601, 1408,
1239 cmK1. Anal. Calcd for C19H13KO4: C, 66.26; H,
3.80%. Found: C, 66.28; H, 3.79%.
4.5.4. Compound 2b. Yield, 98%; mp 99–102 8C; 1H NMR
(CDCl3) d 7.96–7.90 (m, 3H), 7.68–7.56 (m, 6H), 7.51
(t, 1H, JZ8 Hz), 7.41 (t, 1H, JZ8 Hz); 13C NMR (CDCl3) d
154.19, 135.37, 130.99, 130.53, 129.54, 129.48, 129.39,
129.17, 129.05, 127.82, 127.26, 125.57, 124.51, 122.95,
119.58, 112.20, 112.07. IR (KBr): 2229, 1584, 1530, 1444,
1262, 1218 cmK1. Anal. Calcd for C19H11NO: C, 84.74; H,
4.12; N, 5.20%. Found: C, 84.71; H, 4.12; N, 5.18%.
4.5. Preparation of 1b and 2b
A solution of bromoacetonitrile (0.116 g, 0.967 mmol) in
acetone (5 mL) was added dropwise to the reaction mixture
of benzoylnaphthol, 6–7 (0.200 g, 0.806 mmol) and potass-
ium carbonate (0.446 g, 3.22 mmol) in acetone (10 mL) and
stirred at 30 8C for 3–6 h under nitrogen atmosphere. After
removing potassium carbonate by filtration, the reaction
mixture was concentrated. To the residue, water was added
and extracted with dichloromethane. The organic layer was
dried, concentrated, and then purified by silica gel column
4.6. Preparation of 1c–f and 2c–f
A solution of the corresponding bromoacetophenone or
bromoacetonaphthone (0.484 mmol) in acetone (4 mL) was
added dropwise to the reaction mixture of benzoylnaphthol,
6–7 (0.100 g, 0.403 mmol) and potassium carbonate
(0.223 g, 1.61 mmol) in acetone (4 mL) and heated at reflux
for 2–6 h under nitrogen atmosphere until the benzoyl-
naphthol disappeared. After removing potassium carbonate

K. K. Park, J. Jeong / Tetrahedron 61 (2005) 545–553
551
by filtration, the reaction mixture was concentrated. To the
residue, water was added and extracted with dichloro-
methane. The organic layer was dried, concentrated, and
then purified by silica gel column chromatography (eluent:
dichloromethane for 1c and 1e; 1:1 hexane–dichloro-
methane for 1d, 1f, 2d, and 2e; 2:1 hexane–ethyl acetate
for 2c and 2f) to give the corresponding naphthofurans.
1646, 1545, 1342, 1333, 1014 cmK1. Anal. Calcd for
C25H16O2: C, 86.19; H, 4.63%. Found: C, 86.21; H, 4.71%.
4.6.6. Compound 2d. Yield, 99%; mp 122–124 8C (lit.8e
105 8C); 1H NMR (CDCl3) d 7.92 (t, 2H, JZ8 Hz), 7.87 (d,
2H, JZ8 Hz), 7.73 (d, 1H, JZ9 Hz), 7.68 (d, 1H, JZ8 Hz),
7.52–7.43 (m, 6H), 7.33 (t, 1H, JZ8 Hz), 7.19 (d, 2H, JZ
8 Hz), 2.39 (s, 3H); 13C NMR (CDCl3) d 184.14, 152.66,
147.87, 143.14, 134.73, 132.87, 130.99, 130.98, 130.00,
129.85, 129.75, 129.11, 128.72, 128.68, 128.46, 128.14,
126.85, 125.09, 123.21, 121.94, 112.64, 21.72. IR (KBr):
1635, 1606, 1545, 1343, 1182, 1013 cmK1. Anal. Calcd for
C26H18O2: C, 86.16; H, 5.01%. Found: C, 86.14; H, 5.03%.
4.6.1. Compound 1c. Yield, 99%; mp 119–120 8C; 1H
NMR (CDCl3) d 8.42 (d, 1H, JZ8 Hz), 7.98–7.94 (m, 3H),
7.72 (d, 1H, JZ9 Hz), 7.67–7.55 (m, 5H), 7.51 (t, 1H, JZ
7 Hz), 7.44–7.34 (m, 5H); 13C NMR (CDCl3) d 184.75,
151.09, 146.91, 137.51, 133.35, 132.39, 130.97, 130.85,
130.00, 129.82, 128.40, 128.26, 127.99, 126.98, 126.87,
124.86, 123.73, 121.23, 120.99, 119.17 (one carbon is
missing due to overlap). IR (KBr): 1643, 1539, 1490, 1339,
1288, 1213 cmK1. Anal. Calcd for C25H16O2: C, 86.19; H,
4.63%. Found: C, 86.13; H, 4.72%.
4.6.7. Compound 2e. Yield, 87%; mp 144–145 8C (lit.8e
180 8C); 1H NMR (CDCl3) d 8.01 (d, 2H, JZ9 Hz), 7.92 (t,
2H, JZ9 Hz), 7.73 (d, 1H, JZ9 Hz), 7.68 (d, 1H, JZ8 Hz),
7.53–7.42 (m, 6H), 7.32 (t, 1H, JZ8 Hz), 6.88 (d, 2H, JZ
9 Hz), 3.84 (s, 3H); 13C NMR (CDCl3) d 182.91, 163.03,
152.52, 147.98, 132.96, 132.14, 130.95, 130.64, 130.04,
129.81, 129.76, 129.09, 128.64, 128.46, 128.14, 126.80,
125.04, 123.19, 121.90, 113.36, 112.58, 55.43. IR (KBr):
1643, 1600, 1550, 1489, 1255, 1180 cmK1. Anal. Calcd for
C26H18O3: C, 82.52; H, 4.79%. Found: C, 82.47; H, 4.96%.
4.6.2. Compound 1d. Yield, 99%; mp 157–160 8C; 1H
NMR (CDCl3) d 8.41 (d, 1H, JZ8 Hz), 7.95 (d, 1H, JZ
8 Hz), 7.92 (d, 2H, JZ8 Hz), 7.71 (d, 1H, JZ8 Hz), 7.67–
7.56 (m, 5H), 7.45–7.35 (m, 3H), 7.21 (d, 2H, JZ8 Hz),
2.40 (s, 3H); 13C NMR (CDCl3) d 184.36, 150.91, 147.13,
143.25, 134.88, 133.27, 131.08, 130.42, 130.06, 129.99,
128.76, 128.39, 128.25, 128.16, 126.87, 126.82, 124.77,
123.76, 121.27, 120.94, 119.19, 21.73. IR (KBr): 1637,
1605, 1545, 1385, 1340, 1165 cmK1. Anal. Calcd for
C26H18O2: C, 86.16; H, 5.01%. Found: C, 86.16; H, 5.08%.
4.6.8. Compound 2f. Yield, 97%; mp 139–142 8C; 1H
NMR (CDCl3) d 8.48 (s, 1H), 7.96 (dd, 1H, JZ9, 2 Hz),
7.92 (d, 1H, JZ8 Hz), 7.91 (d, 1H, JZ9 Hz), 7.86 (d, 1H,
JZ8 Hz), 7.81 (d, 1H, JZ8 Hz), 7.80 (d, 1H, JZ8 Hz),
7.74 (d, 1H, JZ9 Hz), 7.70 (d, 1H, JZ8 Hz), 7.57–7.30 (m,
9H); 13C NMR (CDCl3) d 184.41, 152.85, 147.86, 135.05,
134.54, 132.75, 132.05, 131.60, 131.33, 130.97, 130.19,
129.71, 129.40, 129.14, 128.68, 128.44, 128.14, 128.12,
127.82, 127.59, 126.89, 126.37, 125.18, 125.12, 123.17,
121.92, 112.64. IR (KBr): 1647, 1623, 1559, 1491, 1361,
1336 cmK1. Anal. Calcd for C29H18O2: C, 87.42; H, 4.55%.
Found: C, 87.38; H, 4.69%.
4.6.3. Compound 1e. Yield, 95%; mp 180–181 8C; 1H
NMR (CDCl3) d 8.42 (d, 1H, JZ8 Hz), 8.04 (d, 2H, JZ
9 Hz), 7.96 (d, 1H, JZ8 Hz), 7.72 (d, 1H, JZ8 Hz), 7.68–
7.57 (m, 5H), 7.45–7.35 (m, 3H), 6.90 (d, 2H, JZ9 Hz),
3.86 (s, 3H); 13C NMR (CDCl3) d 183.24, 163,14, 150.78,
147.24, 133.20, 132.13, 131.17, 130.18, 130.01, 129.97,
128.40, 128.29, 128.14, 126.79, 124.72, 123.74, 121.27,
120.89, 119.17, 113.40, 55.46 (one sp2 carbon is missing
due to overlap). IR (KBr): 1626, 1596, 1543, 1508, 1488,
1165 cmK1. Anal. Calcd for C26H18O3: C, 82.52; H, 4.79%.
Found: C, 82.58; H, 4.67%.
4.7. Preparation of 3a, 4a and 5a
Dibenzoyldihydroxybenzenes 10–12 are available from our
earlier studies.10,15 A solution of bromoacetonitrile
(0.166 g, 1.38 mmol) in acetone (5 mL) was added dropwise
to the reaction mixture of dibenzoyldihydroxybenzene
10–12 (0.200 g, 0.628 mmol) and potassium carbonate
(0.694 g, 5.02 mmol) in acetone (10 mL) and heated at
reflux for 2–12 h under nitrogen atmosphere until the
dibenzoyldihydroxybenzene disappeared. After removing
potassium carbonate by filtration, the reaction mixture was
concentrated. To the residue, water was added and extracted
with dichloromethane. The organic layer was dried,
concentrated, and then purified by silica gel column
chromatography (eluent: 1:1 hexane–dichloromethane for
13; 1:9 hexane–ethyl acetate for 15) to give 13 and 15 with
87 and 99% yields, respectively. In case of 14, the reaction
mixture was concentrated and the residue was washed with
water to remove potassium carbonate. Further washing of
the residue with cold methanol provided 14 with 80% yield.
4.6.4. Compound 1f. Yield, 91%; mp 162–164 8C; 1H
NMR (CDCl3) d 8.55 (s, 1H), 8.42 (d, 1H, JZ8 Hz), 8.04
(dd, 1H, JZ8, 2 Hz), 7.97 (d, 1H, JZ7 Hz), 7.88–7.84 (m,
3H), 7.75–7.55 (m, 7H), 7.51 (t, 1H, JZ7 Hz), 7.38 (t, 2H,
JZ7 Hz), 7.32–7.28 (m, 1H); 13C NMR (CDCl3) d 184.59,
151.14, 147.15, 135.18, 134.71, 133.38, 132.23, 132.01,
131.04, 130.85, 129.99, 129.46, 128.44, 128.30, 128.24,
127.87, 127.63, 127.00, 126.93, 126.46, 125.42, 124.91,
123.82, 121.31, 120.98, 119.23 (one carbon is missing due
to overlap). IR (KBr): 1739, 1635, 1545, 1361, 1292,
1191 cmK1. Anal. Calcd for C29H18O2: C, 87.42; H, 4.55%.
Found: C, 87.44; H, 4.63%.
4.6.5. Compound 2c. Yield, 99%; mp 140–143 8C (lit.8e
137 8C); H NMR (CDCl3) d 7.95–7.90 (m, 4H), 7.73 (d,
1
1H, JZ9 Hz), 7.68 (d, 1H, JZ8 Hz), 7.51–7.42 (m, 7H),
7.39–7.30 (m, 3H); 13C NMR (CDCl3) d 184.59, 152.85,
147.67, 137.35, 132.73, 132.28, 131.39, 130.99, 130.25,
129.77, 129.62, 129.15, 128.69, 128.47, 128.25, 127.97,
126.92, 125.14, 123.19, 121.91, 112.65. IR (KBr): 1653,
1
4.7.1. Compound 13. Mp 179–180 8C; H NMR (DMSO-
d6) d 7.75 (d, 4H, JZ7 Hz), 7.66 (t, 2H, JZ7 Hz), 7.53 (t,
4H, JZ7 Hz), 7.52 (s, 1H), 7.31 (s, 1H), 4.09 (s, 4H); 13C
NMR (DMSO-d6) d 193.05, 156.88, 136.84, 133.45, 131.38,

552
K. K. Park, J. Jeong / Tetrahedron 61 (2005) 545–553
129.19, 128.58, 122.76, 115.45, 99.38, 54.29. IR (KBr):
1661, 1600, 1447, 1262, 1196, 1040 cmK1. Anal. Calcd for
C24H16N2O4: C, 72.72; H, 4.07; N, 7.07%. Found: C, 72.74;
H, 4.03; N, 7.04%.
mixture of dibenzoyldihydroxybenzene 10–12 (0.300 g,
0.942 mmol) and potassium carbonate (1.04 g, 7.54 mmol)
in acetone (10 mL) and heated at reflux for 15–24 h under
nitrogen atmosphere until the starting material disappeared.
After concentrating the reaction mixture, the residue was
washed with water and then recrystallized from 2:1
acetone–CH2Cl2 to give 3b and 4b with 97 and 85% yields,
respectively. In case of 5b, the reaction mixture was filtered
to remove potassium carbonate and then concentrated. To
the residue, water was added and extracted with dichloro-
methane. The organic layer was dried, concentrated, and
then purified by silica gel column chromatography (eluent:
1:1 hexane–dichloromethane) to give 5b with 93% yield.
1
4.7.2. Compound 14. Mp 245–247 8C; H NMR (DMSO-
d6) d 7.82 (d, 4H, JZ8 Hz), 7.72 (t, 2H, JZ7 Hz), 7.57 (t,
4H, JZ7 Hz), 7.47 (s, 2H), 5.13 (s, 4H); 13C NMR (DMSO-
d6) d 193.42, 148.14, 135.95, 134.03, 131.37, 129.39,
128.82, 115.82, 114.20, 54.37. IR (KBr): 1664, 1596, 1448,
1411, 1217, 1049 cmK1. Anal. Calcd for C24H16N2O4: C,
72.72; H, 4.07; N, 7.07%. Found: C, 72.89; H, 4.11; N,
6.92%.
4.7.3. Compound 15. Mp 147–150 8C; 1H NMR (CDCl3) d
7.70 (d, 4H, JZ8 Hz), 7.53 (t, 2H, JZ8 Hz), 7.39 (t, 4H,
JZ8 Hz), 7.25 (s, 2H), 4.63 (s, 4H); 13C NMR (CDCl3) d
193.44, 149.29, 136.73, 133.80, 131.78, 129.41, 128.44,
115.74, 114.30, 54.77. IR (KBr): 1739, 1669, 1597, 1470,
1450, 1292 cmK1. Anal. Calcd for C24H16N2O4: C, 72.72;
H, 4.07; N, 7.07%. Found: C, 72.74; H, 4.05; N, 7.05%.
4.8.1. Compound 3b. Mp 228–230 8C (lit.4d 208–209 8C);
1H NMR (CDCl3) d 7.90 (s, 1H), 7.86 (s, 1H), 7.85 (d, 4H,
JZ7 Hz), 7.49–7.43 (m, 6H), 7.36–7.30 (m, 10H); 13C
NMR (CDCl3) d 185.29, 154.83, 148.04, 136.84, 132.67,
130.37, 129.85, 129.67, 129.09, 128.41, 128.00, 126.38,
115.01, 95.61 (one carbon is missing due to overlap). IR
(KBr): 1653, 1542, 1445, 1331, 1236 cmK1. Anal. Calcd for
C36H22O4: C, 83.38; H, 4.28%. Found: C, 83.39; H, 4.30%.
The reaction mixture of potassium carbonate (0.558 g,
4.04 mmol) and 13–15 (0.200 g, 0.504 mmol) in DMF
(8 mL) was stirred at 60 8C for 2–20 h until the starting
material disappeared. After concentrating the reaction
mixture, the residue was washed with water and then cold
methanol to give 3a and 4a with 92 and 86% yields,
respectively. In case of 5a, the reaction mixture was filtered
to remove potassium carbonate and then concentrated. To
the residue, water was added and extracted with dichloro-
methane. The organic layer was dried, concentrated, and
then purified by silica gel column chromatography (eluent:
2:1 hexane–dichloromethane) to give 5a with 84% yield.
4.8.2. Compound 4b. Mp 259–260 8C; 1H NMR (CDCl3) d
7.91 (d, 4H, JZ8 Hz), 7.88 (s, 2H), 7.54 (dd, 4H, JZ8,
2 Hz), 7.49 (t, 2H, JZ7 Hz), 7.45–7.33 (m, 10H); 13C NMR
(CDCl3) d 185.26, 151.71, 148.59, 136.87, 132.81, 130.42,
129.80, 129.69, 129.08, 128.52, 128.46, 128.06, 104.17 (one
carbon is missing due to overlap). IR (KBr): 1640, 1554,
1445, 1333, 1235 cmK1. Anal. Calcd for C36H22O4: C,
83.38; H, 4.28%. Found: C, 83.34; H, 4.25%.
4.8.3. Compound 5b. Mp 185–187 8C; 1H NMR (CDCl3) d
7.82 (s, 2H), 7.70 (d, 4H, JZ7 Hz), 7.40 (t, 2H, JZ8 Hz),
7.25 (t, 4H, JZ8 Hz), 6.90 (d, 4H, JZ7 Hz), 6.85 (t, 2H,
JZ8 Hz), 6.69 (t, 4H, JZ8 Hz); 13C NMR (CDCl3) d
185.60, 152.16, 148.67, 136.90, 132.41, 131.21, 129.57,
129.48, 127.93, 127.85, 127.26, 121.66, 112.94 (one carbon
is missing due to overlap). IR (KBr): 1653, 1545, 1377,
1268, 1243 cmK1. Anal. Calcd for C36H22O4: C, 83.38; H,
4.28%. Found: C, 83.44; H, 4.32%.
4.7.4. Compound 3a. Mp 295–297 8C; 1H NMR (CDCl3) d
8.15 (s, 1H), 7.81 (s, 1H), 7.73 (d, 4H, JZ8 Hz), 7.63–7.52
(m, 6H); 13C NMR (CDCl3) d 155.78, 133.16, 129.94,
129.59, 128.39, 127.86, 125.01, 123.93, 114.21, 111.86,
96.15. IR (KBr): 2221, 1626, 1568, 1448, 1342, 1200 cmK1
.
Anal. Calcd for C24H12N2O2: C, 79.99; H, 3.36; N, 7.77%.
Found: C, 79.96; H, 3.28; N, 7.65%.
4.7.5. Compound 4a. Mp 290–291 8C; 1H NMR (CDCl3) d
7.96 (s, 2H), 7.75 (d, 4H, JZ8 Hz), 7.63–7.53 (m, 6H); 13C
NMR (CDCl3) d 152.91, 133.14, 129.99, 129.59, 128.26,
127.79, 126.83, 125.53, 111.93, 104.14. IR (KBr): 2227,
1571, 1483, 1445, 1419, 1221 cmK1. Anal. Calcd for
C24H12N2O2: C, 79.99; H, 3.36; N, 7.77%. Found: C, 79.95;
H, 3.34; N, 7.67%.
Acknowledgements
This work was supported by Grant No. R05-2003-000-
10459-0 from the Basic Research Program of the Korea
Science and Engineering Foundation.
4.7.6. Compound 5a. Mp 211–214 8C; 1H NMR (CDCl3) d
7.80 (s, 2H), 7.12–7.06 (m, 6H), 6.94 (t, 4H, JZ8 Hz); 13C
NMR (CDCl3) d 153.65, 134.18, 129.17, 128.55, 128.25,
128.05, 126.16, 118.95, 113.23, 111.71. IR (KBr): 2226,
1559, 1462, 1447, 1412, 1050 cmK1. Anal. Calcd for
C24H12N2O2: C, 79.99; H, 3.36; N, 7.77%. Found: C, 79.91;
H, 3.34; N, 7.64%.
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