SnCl4-mediated oxidative biaryl coupling reaction of 1-naphthol and subsequent ring closure of 2,2′-binaphthol to the dinaphthofuran framework

Article abstract of DOI:10.1016/j.tet.2004.05.077

A simple method for the direct synthesis of 2,2′-binaphthols 2 and dinaphtho[1,2-b;2′,1′-d]furans 3 under mild conditions was developed, utilizing a biaryl coupling reaction via electron donor-acceptor complexes of 1-naphthols with SnCl₄. Heating of the complex in a sealed tube for (18-24 h) afforded the corresponding o-o coupled product 2 in excellent yield. Prolonged reaction (56-65 h) under the same conditions afforded 3 in high yield in one step. We also found that in the case of α-naphthol without substituents other than a hydroxyl group at the C-1 position, regioselective o-o coupling reaction proceeded. The products 2a, 2b and 2g should be useful as synthetic intermediates for naturally occurring 3,3′-bijuglone, 3,3′-biplumbagin and elliptinone.

Full text of DOI:10.1016/j.tet.2004.05.077

Tetrahedron 60 (2004) 6295–6310
SnCl4-mediated oxidative biaryl coupling reaction of 1-naphthol
and subsequent ring closure of 2,20-binaphthol to the
dinaphthofuran framework
*
Tetsuya Takeya, Hirohisa Doi, Tokutaro Ogata, Tsuyoshi Otsuka, Iwao Okamoto
and Eiichi Kotani
Showa Pharmaceutical University, 3-3165 Higashi-tamagawagakuen, Machida, Tokyo 194-8543, Japan
Received 16 April 2004; revised 26 May 2004; accepted 26 May 2004
Available online 17 June 2004
Abstract—A simple method for the direct synthesis of 2,20-binaphthols 2 and dinaphtho[1,2-b;20,10-d]furans 3 under mild conditions was
developed, utilizing a biaryl coupling reaction via electron donor–acceptor complexes of 1-naphthols with SnCl4. Heating of the complex in
a sealed tube for (18–24 h) afforded the corresponding o–o coupled product 2 in excellent yield. Prolonged reaction (56–65 h) under the
same conditions afforded 3 in high yield in one step. We also found that in the case of a-naphthol without substituents other than a hydroxyl
group at the C-1 position, regioselective o–o coupling reaction proceeded. The products 2a, 2b and 2g should be useful as synthetic
intermediates for naturally occurring 3,30-bijuglone, 3,30-biplumbagin and elliptinone.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
method required elevated temperature (350–400 8C) and a
long reaction time.
Since the construction of the biaryl substructure is of
importance for the synthesis of a variety of natural products,
including binaphthoquinones, lignans, alkaloids, flavonoids,
and coumarins,1 and binaphthols are useful as chirality
inducers,2 we have been focused on the oxidative biaryl
coupling of hydroxyarenes. Nature makes extensive use
of this coupling reaction for the selective construction of
complex compounds from simple starting materials such as
naphthols and phenols.3
On the other hand, stannic chloride or tin tetrachloride
(SnCl4; SC) is used extensively in organic synthesis as a
Lewis acid for enhancing a variety of organic reactions. For
example, it is used to promote electrophilic aromatic
substitutions including Friedel–Craft alkylation,11a nucleo-
philic additions such as the Evans aldol11b reaction and the
Mukaiyama–Michael11c reaction, and pericyclic reactions
such as the Diels–Alder reaction11d and ene reaction.11e SC
is classified as hard Lewis acid according to hard and soft
acids and bases (HSAB) theory, and therefore interacts
preferentially with hard oxygen (O-donor) and nitrogen
bases (N-donor). Since it is known that SC as an inorganic
acceptor forms s-type12 or p-type13 electron donor–
acceptor (EDA) complexes with aryl donors (naphthol,
etc.), charge transfer (CT) interactions might play an
important role in these electron-transfer reactions. In
addition, many studies on thermal and photochemical
reactions via EDA complexes have been reported.14 In
contrast, there have been only a few reports to date on
oxidative reactions with SC (applications of SnCl4).15
Although coupling reactions of 1-naphthols (NPOH) for
preparation of 2,20-binaphthols (BNPOH) by utilizing metal
salts,4 Lewis acids,5 electrolytic methods,6 thermal dis-
proportionation7 and aerobic oxidation8 have been studied
extensively, poor selectivity and low yield of the desired
products, accompanied with side reactions, have often been
reported, so that the reactions are difficult to control.
Synthesis of the dinaphthofuran (DNF) framework requires
generally two steps, namely, the biaryl coupling of NPOH
and subsequent ring closure of the resulting BNPOH.
Although a number of authors have obtained the DNF
framework in two steps,9 only one example of such
synthesis in one step has been recorded.7 However, this
In preliminary communications,16 we reported the direct
synthesis of BNPOH and the DNF framework utilizing
oxidative coupling reaction via the EDA complex of NPOH
with SC. We now provide greater detail and experimental
procedures, and also describe some ancillary studies.
Keywords: Naphthol; Coupling reactions; Tin tetrachloride; Biaryls.
*
Corresponding author. Tel.: þ81427211579; fax: 81427211579;
e-mail address: takeya@ac.shoyaku.ac.jp
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.05.077

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T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310
2. Results and discussion
SnCl4 dissolved in the solvent to the solution of 1a
immediately afforded a yellow-green solution. This obser-
vation suggests the formation of the EDA complex of SnCl4
with 1-naphthol 1a. New (charge transfer) absorption band
was observed at 486 nm in the absorption spectra of the
SnCl4 complex with 1a in CH2Cl2.12 The biaryl coupling
reaction of 1a using SnCl4 in CH2Cl2 did not proceed at
23 8C (room temperature), but the mixture changed into a
deep-red colored solution with heating at 100 8C, and the
biaryl coupling reactions proceeded.
We investigated the oxidative biaryl coupling reaction of
NPOHs 1a–1h17 (including precursors for the synthesis of
natural products) and the naphthol ethers 1i–j with several
Lewis acids under various conditions. To determine the
optimum conditions for the coupling reaction, detailed
preliminary experiments were done with NPOH 1a as a
model substrate17. Several Lewis acids (SnCl4, TiCl4,
AlCl3, etc.) as an electron acceptors and various solvents
(CH2Cl2, MeNO2, THF, benzene, DMF, etc.) were investi-
gated, and the results are summarized in Table 1 and
Scheme 1.
We found that the nature of the major product changed
drastically with the reaction time. In contrast to the above
reaction for 24 h, prolonged reaction (56 h) under the same
conditions selectively afforded DNF 3a in 92% yield in one
step from 1a (entry 6). In addition, we found also that the
coupling reaction proceeds in the presence of a catalytic
amount of SC. For example, the reaction 1a with SC
(0.25 equiv.) in CH2Cl2 or MeNO2 gave the results shown in
entries 11 and 13. In addition, the transformations of 1a to
3a proceeded stoichiometrically overall, as discussed below
(refer to Table 3, entry 2).
The efficiency of this reaction is highly dependent upon the
nature of the solvent, with solvents having a low donor
number,18 such as CH2Cl2 and MeNO2, being particularly
favorable. The conversion of 1a to 2a was completely
inhibited in DMF and THF. The best result was obtained
with SnCl4 (1.3 equiv.) in CH2Cl2 as a solvent at 100 8C in a
sealed tube. That is, the reaction of 1a using SnCl4 in
CH2Cl2 afforded only the o–o coupled product (2a;
BNPOH) in an almost quantitative yield (Table 1, entry
4). A similar result was obtained in the dark. The addition of
The optimized protocol was subsequently extended to a
Table 1. Biaryl coupling reactions via the EDA complex of 1-naphthols 1 with acceptora
Entry
Substrate
Acceptor (1.3 equiv.)
Solvent
Temperature (8C)
Time (h)
Product (isolated yield, %)
Recovered
2
3
4
5
6
1 (%)
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1b
1c
1d
1d
1e
1i
—
—
CH2Cl2
MeNO2
MeNO2
CH2Cl2
CH2Cl2
CH2Cl2
MeNO2
MeNO2
MeNO2
CH2Cl2
CH2Cl2
MeNO2
MeNO2
MeNO2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
Benzene
DMF
100
80
23
100
100
100
100
80
24
7
100
100
100
—
—
—
—
—
—
9
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
TiCl4
TiCl4
AlCl3
AlCl3
Ag2O
Ag2O
Ag2O
Ag2O
12
24
48
56
0.8
1.5
70
76
96
3.5
21
6
97
84
Trace
13
92
60
82
9
80
Trace
86
59
86
66
57
4
14
10b
11c
12b
13c
14
15
16
17
18
19
20
21
22
23
24
25d
26d
27e
28e
29f
30f
31f
32f
100
100
80
80
100
23
100
100
100
100
100
100
100
100
100
100
100
100
100
23
12
—
7
23
84
98
—
—
—
—
38
84
77
93
—
100
100
88
—
83
—
—
—
—
—
3
32
18
65
48
24
48
48
24
24
24
24
0.5
24
24
1
98
52
1i
1j
4
4
1a
1a
1a
1a
1a
1a
1a
1a
1b
1d
1e
48
10
THF
CH2Cl2
MeNO2
CH2Cl2
MeNO2
CHCl3
CHCl3
CHCl3
CHCl3
69
17
38
86
35
20
12
Trace
7
23
23
23
0.5
1
1
30
75
a
The reactions of naphthols (1 mmol) with SnCl4 (1.3 equiv.) were carried out using an argon-saturated solvent in a sealed tube with stirring under normal
laboratory light. Similar results were obtained in the dark.
With SnCl4 (0.5 equiv.).
b
c
d
e
f
With SnCl4 (0.25 equiv.).
This reaction was carried out with TiCl4 (1.3 equiv.) in place of SnCl4 under the same conditions as above.
This reaction was carried out with AlCl3 (1.3 equiv.) under the same conditions as above.
With Ag2O (1.5 equiv.) in CHCl3 under air.

T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310
6297

6298
T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310
Scheme 2.
Scheme 3.
Table 2. Reactions of the naphthols with acceptora
Entry
Substrate
Acceptor
Solvent
Temperature (8C)
Time (h)
Product (isolated yield, %)b
Recovered
2
3
7
8
9
10
1 (%)
1
2
3
4
1f
1f
1f
1g
1h
1f
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
Ag2O
Ag2O
CH2Cl2
MeNO2
MeNO2
CH2Cl2
CH2Cl2
CHCl3
100
100
100
100
100
23
121
4.3
15
121
121
1
1
16
2
1
58
24
—
8
Trace
c
9
12
5
30
25
6
18
58
52
5
4
6b
7b
30
—
c
c
—
1h
CHCl3
23
3
a
The reactions of naphthols (1 mmol) with SnCl4 (1.3 equiv.) were carried out using an argon-saturated solvent in a sealed tube with stirring under normal
laboratory light. Similar results were obtained in the dark.
With Ag2O (1.5 equiv.) under air.
b
c
Along with a complex mixture including polymers.

T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310
Table 3. Reactions of the naphthols 2 and 7 with SnCl4 at 100 8Ca
6299
range of substrates (Table 1). For NPOHs 1b and 1d
substituted with a methoxyl group at the R5 position on ring
A, the biaryl coupling took place smoothly to afford the
corresponding BNPOH 2 in excellent yields (entries 14 and
16). However, in the case of NPOH 1c, the coupling
reaction did not occur to yield p-naphthoquinone 4c (entry
15).12m In the case of NPOH 1e substituted with alkyl
(methyl) in place of the R5 methoxyl group, 2e was obtained
in CH2Cl2, but the yield was lower (52%) (entry 18).
Alternatively, in the case of the naphthol-ethers 1i and 1j
corresponding to 1a and 1b, the coupled products were
hardly obtained under similar conditions, and entry 20
shows that prolonged reaction gave 3a in only 4% yield.
These results show that the hydroxyl group in NPOHs,
including 1a,b,d,e, is important for the coupling reaction, in
contrast with the previous report on the Scholl reaction.19
Next, the oxidation of 1a,b,d,e using the well-known Ag2O
as a coupling reagent were conducted in CHCl3 at 23 8C. In
all cases, the yield and selectivity of coupling products in
the reactions with Ag2O were lower, in comparison with the
cases using SC (entries 29–32).
Entry
NPOH
Solvent
Time (h)
Product
(%)b
Recovered
3
8
2 (%)
1
2a
2a
2b
2d
2e
2f
2h
7f
7g
CH2Cl2
CH2Cl2
MeNO2
CH2Cl2
CH2Cl2
MeNO2
CH2Cl2
MeNO2
MeNO2
2
2.5
8
63
23
7
118
1.5
1
98
21
—
72
30
—
68
14
58
—
—
2c
3
d
—
91
4
5
6
d
—
29
11
—
—
7
8d
9
82
80
a
The reaction mixture was vigorously stirred with SnCl4 (1.3 equiv.) using
an argon-saturated solvent at 100 8C under normal laboratory light in a
sealed tube. Similar results were obtained in the dark.
Isolated yield.
With SnCl4 (0.25 equiv.).
Along with a complex mixture including polymers.
b
c
d
It is known that in the case of 2-substituted naphthalenes
such as 2-naphthol, the regioselective coupling reaction
proceed comparatively easily to afford the corresponding
1,10-binaphthol.4i,8a,b However, regioselective ortho/ortho-
coupling is more difficult to control in the reaction of
1-substituted naphthalenes such as 1-naphthol. There are
many reports on the oxidative coupling reaction of
a-naphthol 1h.4 In general, the coupling reaction by
means of chemicals, such as FeCl3,4f,i MnO2,4g benzoyl
peroxide4a and electrolysis6a is known to produce a
preponderance of the p–p coupled product 10 over the
o–o coupled product 2h. The formation process of 2h is
generally believed to involve the naphthoxy radical.
Poutsma et al. reported only that thermolysis of 1h at
400 8C afforded predominantly the o–o coupled products,
Next, the reactions of 1f, 1g and 1h, which lack the
methoxyl group on ring A, were carried out (Schemes 2 and
3 and Table 2). These coupling reactions were very sluggish
in CH2Cl2. A longer period of reaction of 1f–g (121 h)
afforded BNPOH 2f–g and the naphthol trimers 7f–g and
8f–g in very low yields (Table 2, entries 1 and 4). In
contrast with these results, the reaction of 1f for 4.3 h in
MeNO2 in place of CH2Cl2 gave 2f (16%) and 3f (8%)
(entry 2), and similar reaction for 15 h afforded 8, with the
disappearance of 1f (entry 3). However, polymeric com-
pounds were formed in both cases. In the cases of 1f using
Ag2O, the o–o coupled product 2f (25%) and the o–p
coupled product 9f (30%) were obtained (entry 6).
Scheme 4.

6300
T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310
2h (27%) and 3h (33%), and 10 (3.8%), together with
by-products.7 We examined the reaction of 1h with SC in
CH2Cl2. Interestingly, the ortho/ortho coupling reaction
proceeded regioselectively to afford 2h6a in 30% yield,
along with 10 (4%)24h and the recovered 1h (52%) (Table 2,
entry 5). This result provides some clues to the reaction
mechanism via EDA complex formation of NPOH 1 with
SC. The reason for this regioselectivity is discussed below.
(3) The reaction of 1h without a substituent other than the
hydroxyl group regioselectively afforded 2h as a major
product.
(4) BNPOHs 2b, 2e and 2g having a methyl group on ring
A or B could not be converted to the corresponding
DNFs 3b, 3e and 3g. The reason for this is considered
as follows: in the case of 2b, it is due to the steric
hindrance of a methyl group at the R6 position; in the
cases of 2e and 2g, it is owing to side-chain oxidation,
including C–H bond cleavage20 of the methyl group,
which is preferred to hydroxyl group deprotonation on
ring A.
(5) The different yields of 2 or 3, the formation of different
products, and the different reaction times in the present
reactions with SC are a consequence of the structural
differences. In particular, the methoxyl group at R5 on
ring A plays an important role in the oxidation of
NPOH. That is, the methoxyl group is considered not
only to activate the NPOH ring for the formation of
the EDA complex with SC, but also to inhibit the
production of polymeric compounds, including 8, via
reaction at the substituted position (R5 position). This
consideration is also supported by the electrochemical
studies described below.
In order to confirm the formation process of DNF 3 from
NPOH 1 via BNPOH 2, the ring closure of 2 with SnCl4
(1.3 equiv.) was carried out as shown in Scheme 4 and Table
3. Both 2a and 2d gave the corresponding 3a and 3d in high
yields. In the cases of 2f and 2h, the yields of the
corresponding DNF 3 were poor. However, the reactions
of 2b and 2e did not afford the corresponding furans 3
(entries 3 and 5). When a catalytic amount (0.25 equiv.) of
SC was used, non-reacted 2a (72%) was recovered with the
formation of 3a (21%) in the reaction of 2a (entry 2). This
result indicated that the conversion of 2 to 3 proceeded
stoichiometrically. Furthermore, the naphthol trimers 7f–g
could be easily converted to the corresponding furans 8f–g
by the reaction with SC (Scheme 4).
The noteworthy features of the present reactions with SC are
as follows (Scheme 5).
2.1. Electrochemistry of naphthol derivatives 1, 2 and 7
(1) BNPOH 2a, 2b and 2d were obtained in a compara-
tively short time (18–24 h) in satisfactory to excellent
yield by the reactions of the corresponding NPOH 1a,
1b and 1d with SC (1.3 equiv.), while prolonged
reaction (56–65 h) of 1a and 1d under the same
conditions gave DNF 3a and 3d in high yield. These
reactions can be conveniently performed with electron-
rich NAP having a methoxyl group at the R5 position
on ring A.
(2) However, there is an exception in the case of 1c as a
substrate; the coupling reaction to 2c did not take place.
The reason for this may be that 1c is much more
oxidizable than the other compounds because it has
the lowest oxidation potential (0.82 V vs Ag/AgCl), as
described below.
In general, electron-donating or electron-accepting ability is
reflected in the oxidation or reduction potential one of
compounds.21 Therefore, the oxidation potentials (the half-
wave potential (E1/2), V vs Ag/AgCl) of the first one-
electron transfer from 1, 2 or 7 in argon-saturated CH2Cl2
and MeNO2 were measured by cyclic voltammetry (CV).
In all cases, irreversible waves were observed. The results
are summarized in Table 4. On the other hand, the first half-
wave reduction potential of SC in CH2Cl2 was also
measured by CV. The irreversible wave was observed, but
it was not clear.
The oxidation potentials of 1, 2 and 7 in MeNO2 showed
lower values than those in CH2Cl2, i.e. a solvent effect of
MeNO2 was observed. In fact, the oxidations with SC in
Scheme 5.

T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310
6301
Table 4. Oxidation potentials in the first wave of the naphthol derivatives 1,
2 and 7 in CH2Cl2 or MeNO2
position, and –Me at R5 decreased the oxidation potential
due to their electron-donating effect (compare the oxidation
potential of 1h with that of 1d, 1e or 1f); (ii) in contrast,
–Me at R3 or R6 slightly increased the oxidation potential
(compare 1a with 1b or 1f with 1g); (iii) –OMe at R1 has no
influence on the oxidation potential, presumably due to
hydrogen-bond formation (compare 1a with 1d)25; (iv) the
effect of the hydroxyl group on ring A is similar to that
of –OMe at the same position (compare 1a with 1i or 1b
with 1j). Among these substituents, –OMe at R5 showed the
strongest substituent effect, namely, electron-donating
effect, and in fact the oxidation potential of 1d (þ0.95 V)
is greatly shifted towards lower potential at 0.21 V as
compared with that of 1h (þ1.16 V).
a
Entry
Naphthol
CH2Cl2
ox
MeNO2
ox
þE
þE
1/2
1/2
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1g
1h
1i
0.95
1.02
0.82
0.95
1.10
1.09
1.14
1.16
0.97
1.08
0.84
1.02
0.77
0.87
0.64
0.70
0.93
0.89
0.93
1.06
0.78
0.88
0.65
0.87
0.58
0.78
0.83
0.72
0.88
0.68
0.65
9
10
11
12
13
14
15
16
17
18
19
1j
2a
2b
2d
2e
2f
2g
2h
7f
b
—
Furthermore, we examined the electrochemical reaction of
1a in argon-saturated CH2Cl2 under constant potential
conditions in an undivided cell (Scheme 6). Since the first
wave onset oxidation potential and the half-wave oxidation
potential of 1a are 0.75 and 0.95 V (vs Ag/AgCl), anodic
oxidation was conducted at the corresponding potentials.
The reaction at 0.80 or 0.95 V gave 4a in a yield of 60 or
34% and 6b in a yield of 23 or 11%, respectively (Scheme
6). These results are clearly different from those of the
reaction with SC.
0.83
1.09
1.04
1.01
0.75
0.75
7g
a
Potentials (V) are vs Ag/AgCl; all substrates were measured in the range
of about 0.0–2.0 V. The oxidation potentials of anodic current (E) were
obtained by cyclic voltammetry of 0.1 mM solutions of the substrates
in an argon-saturated solvent (CH2Cl2 or MeNO2) containing 0.1 M
n-Bu4NClO4 as a supporting electrolyte at a Pt (platinum)-electrode. The
voltage scan rate in cyclic voltammetry was 100 mV s21 at 23 8C.
ox
The electrochemical studies suggested that NPOH 1a–d
having –OMe at the R5 position (oxidation potentials range
from 0.82 to 1.02 V) are stronger donors than 1e–h. In
addition, they interact strongly with SC, and one-electron
transfer to SC takes place more easily to form the
corresponding radical cation species.
E
1/2
Oxidation potential of 2d could exactly not be measured since 2d is
¼the first half-wave oxidation potential.
b
poorly soluble in CH2Cl2.
MeNO2 proceeded more rapidly than those in CH2Cl2 in all
cases. However, complex mixtures including polymeric
compounds were observed in almost all cases. The
oxidation potential of 2d could not be measured exactly,
because of the poor solubility of 2d in CH2Cl2.
2.2. Proposed mechanism for the SC-mediated oxidative
reaction of NPOH
The proposed mechanism for the SC-mediated oxidative
reaction of 1 to 2 or 3 is illustrated in Scheme 7. This is
slightly revised from the mechanism proposed in our
previous report, on the basis of further experiments and
novel information described below. The additional experi-
ments showed that the oxidative coupling of 1 proceeded
with a catalytic cycle of SC, while the transformations of 2
to 3 proceeded stoichiometrically. In addition, the reaction
of 1-naphthol 1h without any substituent gave regioselec-
tively the o–o coupled product 2h as described above. In
particular, this result provides a clue for analysis of the
mode of coordination in the EDA complex formed by
NPOH 1 with SC.
The oxidation potentials of NPOH 1, except for 1i
(þ0.97 V) and 1j (þ1.08 V), in CH2Cl2 increased in the
order of 1c (þ0.82 V),1a¼1d (þ0.95 V),1b
(þ1.02 V),1f (þ1.09 V),1e (þ1.10 V),1g (1.14 V),1h
(þ1.16 V) (Table 4). NPOH 1c having two methoxyl groups
showed the lowest oxidation potential, whereas 1h, which
lacks a methoxyl group, showed the highest oxidation
potential among NPOHs 1. The oxidation potentials of
BNPOH 2 are slightly lower than or almost equal to those of
the corresponding monomers 1 (entries 11–17). The
trimeric furans 7f–g have the lowest oxidation potential
of all the compounds (entries 18–19).
A comparison of the oxidation potentials of NPOH 1
indicated that a methoxyl (–OMe) or a methyl (–Me) group
has a different substituent effect depending on the
substituted position as follows: (i) –OMe at the R5 or R4
It is known that SC forms six coordination complexes, as a
s-type EDA complex, with hydroxyarenes12k and aromatic
aldehydes12c,h,l as an O-donor, etc., or with pyridine12i and
Scheme 6.

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T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310

T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310
6303
2,20-bipyridine12j as an N-donor, etc. There are two limiting
modes of complexation of NPOH 1 with SC: the 2:1
complex or the 1:1 complex (1 to SnCl4). Yamamoto and
co-workers reported that the s-type EDA complex is formed
between SC and two hydroxyl moieties as O-donors in
1,10-binaphthol.12a In addition, Denmark et al.12c,d showed
by 13C NMR and 119Sn NMR spectral studies that an
octahedral 2:1 complex (aldehyde or HMPA to SnCl4) is the
coordinated species present upon combination of 4-tert-
butylbenzaldehyde or HMPA (hexamethylphosphorus tri-
amide) with SC. From the regioselective formation of 2h
and the above information, we believe that an octahedral 2:1
complexes can form rather than the 1:1 complexes proposed
previously by us, in the coordination of 1 with SC as shown
in Scheme 7. This reaction is initiated by the formation of
the EDA complex A of two NPOH 1 with SC. Solvents such
as CH2Cl2 and MeNO2 receive one-electron transfer from
the anion radical species (SC–z) and subsequent one-proton
transfer from the NPOH site to reform SC. The regioselec-
tive ortho/ortho coupling for the formation of 2 proceeds via
radical D, which is the s-type complex involving SC and
two carbonyl moieties.
The formation mechanism of 3 from 1 can be rationalized in
terms of biaryl coupling within radical D and subsequent
ring closure to form the DNF ring, based on the results listed
in Table 3, entries 1, 2, 4 and 6. Although the exact mode of
ring closure is not clear, we believe that it may proceed via
radical pathways22 involving the formation of H2O (the
naphthoxy radical-induced reaction) as shown by the bold
arrows, rather than nonradical pathways8b (the Lewis acid-
promoted dehydration pathway) because of the formation of
polymeric compounds (including 8) as described above
(Table 2, entries 1–3 and Table 3, entry 6). In this step, SC
is inactivated by the resulting H2O. In the present oxidation,
SC plays an important role. That is, it acts not only as a
characteristic Lewis acid catalyst, but also as a mediator for
electron transfer. Alternatively, CH2Cl2 and MeNO2 used as
Table 5. 13C and 1H NMR spectral data (d/ppm) for compounds 2f,a 3f,a 7fb and 7gb
Carbon
No.
2f
3f
7f
7g
13C
1Hc
13C
1Hc
13C
1Hc
13C
1Hc
1
2
3
4
4a
5
6
6a
6b
6c
7
151.2
121.3
112.6
130.3
127.9
150.5
103.6
149.3
105.8
104.0
150.0
125.8
117.5
118.2
120.9
120.9
150.5
105.1
106.7
150.1
121.5
115.8
123.48
122.1
123.52
114.9
148.3
107.5
150.3
109.9
125.1
146.8
126.3
116.1
123.67
120.4
106.4
123.69
147.8
128.0
6.85 d (8.5)
6.96 d (8.5)
7.14 d (8.6)
7.20 d (8.6)
6.85s
7.49 d (8.5)
7.79 d (8.5)
8.26 d (8.8)
8.11 d (8.8)
8.06 d (9.2)
8.71 d (9.2)
7.99 d (9.2)
8.80 d (9.2)
6.67 d (8.5)
6.70 d (8.5)
103.1
150.4
115.8
118.2
117.5
125.8
150.0
104.0
8.11 d (8.8)
8.26 d (8.8)
8
8a
9
6.89 d (8.5)
6.87 d (8.5)
104.2
149.1
113.7
152.0
108.2
154.1
108.0
152.6
112.3
151.4
107.2
154.5
7.12s
10
10a
11
12
12a
12b
13a
13b
10
6.96 d (8.5)
6.85 d (8.5)
105.8
149.3
115.0
151.0
151.0
115.0
151.2
121.3
112.6
130.3
127.9
150.5
103.6
103.1
150.4
115.8
151.8
107.4
130.3
111.0
127.2
149.3
104.15d
104.17d
149.7
115.1
152.1
113.7
131.0
111.9
129.8
147.1
125.4
107.3
151.8
114.1
20
30
7.49 d (8.5)
7.79 d (8.5)
7.59 d (8.6)
7.74 d (8.6)
7.66 d (8.5)
7.63 d (8.5)
40
4a0
50
600
6.67 d (8.5)
6.70 d (8.5)
6.92 d (8.6)
6.96 d (8.6)
7
6.93s
80
8a0
Otherse,f
1
Assignment based on H–1H COSY, 1H–13C COSY and HMBC spectra.
a
Data recorded in CDCl3 at 500 MHz (1H NMR) and 125 MHz (13C NMR).
b
Data recorded in CD3SOCD3 at 500 MHz (1H NMR) and 125 MHz (13C NMR).
Coupling constants (J in Hz) are given in parentheses.
c
d
Interchangeable.
e
13C NMR; 2f: 55.9 (5- and 50-OMe), 56.4 (8- and 80-OMe). 3f: 56.8 (1 and 12-OMe), 55.9 (4- and 9-OMe). 7f: 57.0 (1-OMe), 55.3 (4-OMe), 56.28 (7-OMe),
55.7 (10-OMe), 55.6 (50-OMe), 56.31 (80-OMe). 7g: 15.6 (3-Me), 15.9 (8-Me), 15.5 (60-Me), 55.9 (1-OMe), 60.5 (4-OMe), 60.2 (7-OMe or 50-OMe), 56.8
(10-OMe), 60.3 (7-OMe or 50-OMe), 56.2 (80-OMe).
f
1H NMR; 2f: 3.96 (s, 5- and 50-OMe), 3.99 (s, 8- and 80-OMe), 9.86 (s, 1- and 10-OH).03f: 4.23 (s, 1- and 12-OMe), 4.03 (s, 4- and 9-OMe). 7f: 4.10 (s,
1-OMe), 4.16 (s, 4-OMe), 3.53 (s, 7-OMe), 3.96 (s, 10-OMe), 3.99 (s, 50-OMe), 4.01 (s, 8 -OMe), 10.63 (s, 11-OH), 9.94 (s, 10-OH). 7g: 2.45 (s, 3-Me), 2.62
(s, 8-Me), 2.49 (s, 60-Me), 3.64 (s, 1-OMe), 3.90 (s, 4-OMe), 3.71 (s, 7-OMe), 4.17 (s, 10-OMe), 3.91 (s, 50-OMe), 4.08 (s, 80-OMe), 10.35 (s, 11-OH), 9.73 (s,
10-OH).

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T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310
solvents may also act as one-electron and one-proton
acceptors23 from the anion radical species (SC–z) and
NPOH, playing the same role as that of O2 reported
previously by us.16b The difference of reactivities in CH2Cl2
or MeNO2 may be based on the difference of one-electron
accepting ability from the anion radical species (SC–z).
in the molecule: six aromatic methoxyls, and 30 aromatic
carbons, ten of which were protonated, ten quaternary, and
ten bearing oxygen (Table 5). The reaction of 7f with SC
gave the trimer 8f in 82% yield (refer to Scheme 4).
Accordingly, the above data proved that 7f has a naphthol
trimer structure with a dinaphthofuran unit and a naphthol
unit. The structure of 7g was also elucidated by similar
analysis.
2.3. Structure of the novel trimeric furan 7f
The structure of 7f was elucidated by means of detailed
1
analyses of the H and 13C NMR spectra with the aid of
various 2D NMR experiments, and also by chemical
transformation to 8f as shown in Scheme 4.
3. Conclusion
In conclusion, SC-mediated oxidation of NPOHs 1 made it
possible to control the synthesis in the direction of either
BNPOH or the DNF framework. For example, the reaction
of 1a, 1b, or 1d with SC for a short time (18–24 h) afforded
the corresponding BNPOH 2a, 2b or 2d in excellent yield,
while prolonged reaction (56–65 h) of 1a or 1d under the
same conditions gave DNF 3a or 3d in high yield. For
the formation of BNPOH and DNF frameworks through the
present oxidation, NPOHs such as 1a, 1b, 1d substituted
with –OMe at the R5 position in the range of oxidation
potential from 0.95 to 1.02 V in CH2Cl2, are concluded to be
the best substrates. The resulting products 2a, 2b and 2g
would be useful synthetic0 intermediates for naturally
occurring 2,20-bijuglone, 3,3 -biplumpugin and elliptinone.
We will report the syntheses of these natural products in the
following article.
All 1H and 13C0NMR signal assignments, except for those of
the carbons C6 and C70, were confirmed by means of H–H
COSY, C–H COSY and HMBC spectral analyses and by
comparison of the spectra with those of the reference
compounds 2f and 3f (which were synthesized by us) (refer
to Table 5 and Figures 1 and 2).
4. Experimental
4.1. General
Figure 1. Long range 1H–13C correlations of 7f in the HMBC spectrum.
All melting points are uncorrected. IR and UV spectra were
recorded on a JASCO IR-700 and a JASCO Ubest-55
1
spectrometer. H and 13C NMR spectra were recorded on
JEOL JNM-AL300 and JNM-alpha 500 spectrometers,
with tetramethylsilane as an internal standard (CDCl3,
CD3COCD3 and CD3SOCD3 solution). Mass spectra were
recorded on a JEOL JMS-D300 or a Shimadzu QP-5000
spectrometer. Elemental analyses were done using a Yanaco
CHN-MT-3 apparatus. Merck Kieselgel 60 (230–400
mesh), Wako silica gel C-200 (200 mesh) and Merck
Kieselgel 60 F254 were used for flash column chroma-
tography, column chromatography and thin-layer chroma-
tography (TLC), respectively. Each organic extract was
dried over MgSO4 or Na2SO4. Oxidation and reduction
potentials were measured on a Yanaco P-1100 voltammetric
analyzer by cyclic voltammetry. Storage and handling of
SnCl4: SnCl4 should be stored in container with silica gel,
blue, middle granule to minimize exposure to moisture. The
container should be flushed with N2 or Ar and tightly sealed.
Perform all manipulations under N2 or argon. All reactions
were carried out in the anhydrous state.
Figure 2. NOE interactions observed in the NOESY spectrum of 7f.
The 1H NMR spectrum of 7f showed the following features:
(i) two pairs of ortho-coupled aromatic protons at d 8.06 (d,
J¼9.2 Hz) and d 8.71 (d, J¼9.2 Hz) assignable to protons at
C1 and C6, and aromatic protons at d 7.59 (d, J¼8.6 Hz0) and
d 7.74 (d, J¼8.6 Hz) assignable to the protons at C3 and
C40; (ii) a singlet (d 3.53) of C(7)-OMe, presumably due to
the shielding effect of the dinaphthofuran ring, was
observed at higher field as compared with the other singlet
signals of Ar-OMe at d 3.96, 3.99, 4.01, 4.10 and 4.16. The
13C NMR spectrum of 7f displayed signals for all 36 carbons
4.2. The oxidation potentials of 1a–h, 2a–b, 2d–h and
7f–g, the reduction potential of SnCl4, and the charge-
transfer absorptions of the EDA complex of 1a with
SnCl4
The oxidation potentials shown in Table 4, and the reduction
potential of SnCl4 were measured by cyclic voltammetry

T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310
6305
using an Ag/AgCl reference electrode at a platinum
electrode with 0.1 M tetrabutylammonium perchlorate as a
supporting electrolyte in an argon-saturated solvent
(CH2Cl2 or MeNO2). The charge-transfer absorption
described in the text were measured soon after mixing
1a (7.65£1025 M) with SnCl4 (7.98£1025 M) in argon-
saturated CH2Cl2.
149.6, 150.8, 156.7. MS m/z: 218 (Mþ). HR-MS calcd for
C13H14O3: 218.0943. Found: 218.0956.
4.3.3. 1,4,5-Trimethoxy-2-methylnaphthalene (1j). A
solution of SnCl2·2H2O (2.9 g) in conc. HCl (2.9 ml) was
added to a solution of 5-methoxy-2-methyl-1,4-naphtho-
quinone17 (667 mg, 3.5 mmol) in 95% EtOH (28 ml) under
a nitrogen atmosphere at 0 8C, and the mixture was stirred at
ambient temperature for 30 min. To the reaction mixture
was added Me2SO4 (4.79 ml), followed by 25% KOH
solution (44.8 ml), and the whole was stirred for 15 min.
The reaction mixture was poured into ice water and acidified
with dilute HCl, and the whole was extracted with ether.
The organic layer was washed with H2O, then dried with
Na2SO4, and concentrated. The residue was subjected to
flash chromatography (AcOEt–hexane¼1:8) to yield
(549 mg, 72%), as light yellow crystals (hexane), mp
68.5–69 8C (lit.24f 69–70 8C). IR (KBr) cm21: 2930, 2840,
4.3. Synthesis of 1-naphthols 1a–j
1-Naphthols 1a,17a,b 1b,17c 1c,17d–f 1f,17g and 1g17h were
synthesized according to the protocol reported previously,
and 1d and 1h are commercially available (Tokyo Kasei
Chemical Industries, Ltd., Japan).
4.3.1. 4-Methyl-l-naphthol (1e). A solution of 4-methy1-1-
naphthalenecarboxaldehyde (100 mg, 0.59 mmol) and
m-chloroperbenzoic acid (303 mg, 1.76 mmol, purity;80%)
in CH2C12 (10 ml) was rapidly stirred for 19 h. Aqueous
sodium thiosulfate (4 ml, 10% solution) was introduced, and
after being stirred for 30 min the mixture was poured into an
additional 8 ml of aqueous thiosulfate and vigorously
shaken. The phases were separated, the aqueous phase
was extracted with CH2Cl2, and the organic phase was
washed successively with aqueous thiosulfate and brine,
dried, and evaporated to give 6.87 g (29.7 mmol, 99%) of
crude formate. The crude formate was dissolved in acetone
(10 ml) and cooled in an ice bath, ice-cold 10% aqueous
HCl (3 ml) was added, and the whole was refluxed for 4 h.
The reaction mixture was poured into ice-water and
extracted with CH2C12. The organic phase was washed
sequentially with water and brine, then dried, and
evaporated. The residue was subjected to flash chroma-
tography (AcOEt–hexane¼1:10) to yield 1e (81 mg, 87%),
as colorless needles (petroleum ether), mp 81–81.5 8C
(lit.24g 80–81 8C). IR (KBr) cm21: 3434, 3374, 1589, 1513.
1H NMR (CDCl3) d: 2.61 (3H, s, 4-Me), 5.08 (1H, s, 1-OH),
6.72 (1H, d, J¼7.5 Hz, 2-H), 7.13 (1H, dd, J¼0.9, 7.5 Hz,
3-H), 7.47–7.57 (2H, m, 6 and 7-H), 7.92–7.95 (1H, m,
5-H), 8.19–8.22 (1H, m, 8-H). LR-MS m/z: 158 (Mþ).
HR-MS calcd for C11H10O: 158.0729. Found: 158.0771.
1
1601. H NMR (CDCl3) d: 2.41 (3H, s, Me), 3.81 (3H, s,
OMe), 3.91 (3H, s, OMe), 3.94 (3H, s, OMe), 6.63 (1H, s,
C3-H), 6.79 (1H, d, J¼7.5 Hz, C6-H), 7.37 (1H, dd, J¼7.5,
8.2 Hz, C7-H), 7.66 (1H, dd, J¼0.9, 8.3 Hz, C8-H). 13C
NMR (CDCl3) d: 16.1, 56.3, 56.8, 60.9, 105.7, 109.4, 114.4,
117.0, 126.4, 126.5, 131.4, 147.1, 153.0, 157.3. MS m/z: 232
(Mþ). HR-MS calcd for C14H16O3: 232.1100. Found:
232.1075.
4.4. General procedure for oxidative reaction of
naphthols 1, 2 and 7 with various acceptors such as
SnCl4, TiCl4 and AlCl3 in CH2Cl2 or MeNO2 as a solvent
The acceptor (1.3, 0.5 or 0.25 equiv.) was added to a
solution of the naphthol (1 mmol) in the solvent listed above
(20 ml) and the mixture was stirred for 20 min at room
temperature under normal laboratory light in an argon
atmosphere. Then, the reaction mixture was heated in a
sealed tube with stirring until disappearance of the naphthol,
except in the cases where the starting material was
recovered. The reaction mixture was poured into ice
water, 10% HCl was added, and the whole was extracted
with CHCl3. The organic layer was washed with H2O, then
dried and concentrated. The residue was subjected to flash
column chromatography on silica gel with the designated
solvents as follows: AcOEt–hexane (1:6; for 2a and 3a in
Table 1); CH2Cl2–hexane (2:1; for 2f, 7f and 8f in Table 2);
CH2Cl2–hexane (2:1; for 2f, 3f and 8f in Table 2); CH2Cl2–
hexane (2:1; for 2g, 7g and 8g in Table 2); CH2Cl2–hexane
(2:1; for 2h and 10 in Table 2). Yields for 2a–b, 2d, 2e–h,
3a, 3d, 3f–g, 6d, 5c, 5d, 7f–g, 8f–g, 10 are listed in Tables
1–3. Similar results were obtained when the reactions were
carried out in the dark.
4.3.2. 1,4,5-Trimethoxynaphthalene (1i). A solution of
SnCl2·2H2O (2.9 g) in conc. HCl (2.9 ml) was added to
a solution of 5-methoxy-1,4-naphthoquinone (667 mg,
3.5 mmol) in 95% EtOH (28 ml) under a nitrogen
atmosphere at 0 8C, and the mixture was stirred at ambient
temperature for 30 min. To the reaction mixture was added
Me2SO4 (4.79 ml), followed by 25% KOH solution
(44.8 ml), and the whole was stirred for 15 min. The
reaction mixture was poured into ice water and acidified
with dilute HCl, and the whole was extracted with ether.
The organic layer was washed with H2O, then dried with
Na2SO4, and concentrated. The residue was subjected to
flash chromatography (AcOEt–hexane¼1:8) to yield 1i
(549 mg, 72%), as a light blue amorphous powder (MeOH),
4.4.1. 4,40,8,80-Tetramethoxy-2,20-di-1,10-naphthol (2a).
Colorless needles (CHCl3–hexane), mp 207–209 8C. IR
(KBr) cm21: 3348, 1646, 1606, 1584. 1H NMR (CDCl3) d:
3.95 (6H, s, 4 and 40-OMe0), 4.03 (6H, s, 8 and 80-OMe), 6.87
(2H, d, J¼8.6 Hz, 7 and 7 -H), 6.92 (2H, s, 3 and 30-H), 7.35
(2H, t, J¼8.6 Hz, 6 and 60-H), 7.89 (2H, d, J¼8.6 Hz, 5 and
50-H), 9.87 (2H, s, 1 and 10-OH). 13C NMR (CDCl3) d: 56.0
(C4 and C40-OMe), 56.1 (C8 and C80-OMe), 105.2 (C7 and
C70), 109.4 (C3 and C30), 115.7 (C8a and C8a0), 116.0 (C5
and C50), 119.4 (C2 and C20), 125.0 (C6 and C60), 1270.6
(C4a and C4a0), 144.7 (C1 and C10), 147.6 (C4 and C4 ),
mp 117–118 8C (lit.24e 116–117.5 8C). IR (KBr) cm21
:
1
2944, 2908, 2832, 1595. H NMR (CDCl3) d: 3.92 (3H, s,
OMe), 3.94 (3H, s, OMe), 3.97 (3H, s, OMe), 6.73 (1H, d,
J¼8.5 Hz, Ar-H), 6.79 (1H, d, J¼8.5 Hz, Ar-H), 6.91 (1H,
d, J¼7.8 Hz, Ar-H), 7.83 (1H, dd, J¼7.8, 8.5 Hz, Ar-H),
7.86 (1H, d, J¼8.5 Hz, Ar-H). 13C NMR (CDCl3) d: 55.8,
56.4, 57.4, 104.2, 106.7, 107.1, 114.6, 118.4, 125.9, 128.8,

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T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310
156.2 (C8 and C80). LR-MS m/z: 406 (Mþ). HR-MS calcd
for C24H22O6: 406.1416. Found: 406.1433. Anal. calcd for
C24H22O6: C, 70.92; H, 5.46. Found: C, 70.82; H, 5.43.
80-H). 13C NMR (CDCl3) d: 18.81 (C4 and C40-Me), 115.13
(C2 and C20), 122.95 (C8 and C80), 124.15 (C5 and C500),
124.73 (C8a and C8a0), 125.61 (C6 0and C60, or C7 and C70),
126.80 (C6 and C60, or C7 and C7 ), 127.41 (C4 and C4 ),
128.07 (C3 and C30), 133.54 (C4a and C4a0), 147.46 (C1 and
C10). LR-MS m/z: 314 (Mþ). HR-MS calcd for C22H18O2:
314.1302. Found: 314.1292. Anal. calcd for C22H18O2: C,
84.05; H, 5.77. Found: C, 84.00; H, 5.79.
4.4.2. 1,5,8,12-Tetramethoxydinaphtho[1,2-b:10,20-d]-
furan (3a). Colorless needles (CHCl3–hexane), mp 300–
1
303 8C. IR (KBr) cm21: 1692, 1589. H NMR (CDCl3) d:
4.15 (6H, s, 5 and 8-OMe), 4.27 (6H, s, 1 and 12-OMe), 7.09
(2H, d, J¼7.9 Hz, 2 and 11-H), 7.34 (2H, s, 6 and 7-H), 7.47
(2H, t, J¼7.9, 8.2 Hz, 3 and 7-H), 8.01 (2H, d, J¼8.2 Hz, 4
and 9-H). 13C NMR (CDCl3) d: 56.0 (C5- and C8-OMe),
56.3 (C1 and C12-OMe), 96.2 (C6 and C7), 106.6 (C2 and
C11), 114.7 (C12a and C13b), 115.3 (C4 and C9), 119.7
(C6a and C6b), 125.2 (C3 and C10), 126.7 (C4a and C8a),
145.8 (C12b and C13a), 151.7 (C5 and C8), 155.0 (C1 and
C12). LR-MS m/z: 388 (Mþ). HR-MS calcd for C24H20O5:
388.1311. Found: 388.1334. Anal. calcd for C24H20O5: C,
74.21; H, 5.19. Found: C, 74.19; H, 5.18.
4.4.7. 1-Methoxy-7-methyl-1,4-naphthoquinone (4c).
Yellow needles (CHCl3–hexane), mp 169.5–170 8C
1
(lit.24c 166.5–167.5 8C). IR (KBr) cm21: 1651, 1599. H
NMR (CDCl3) d: 2.48 (3H, s, 7-Me), 4.00 (3H, s, 5-OMe),
6.84 (2H, s, 2 and 3-H), 7.11 (1H, s, 6-H), 7.55 (1H, s, 8-H).
LR-MS m/z: 202 (Mþ). HR-MS calcd for C12H10O3:
202.0627. Found: 202.0614. Anal. calcd for C12H10O3: C,
71.28; H, 4.98. Found: C, C, 71.30; H, 4.95.
4.4.8. 5,50,8,80-Tetramethoxy[2,20]di-1,10-naphthol (2f).
Colorless needles (hexane–AcOEt), mp 257–260.5 8C. IR
(KBr) cm21: 3358. 1H NMR (CDCl3) d: 3.96 (6H, s, 5 and
50-OMe), 3.99 (6H, s, 8 and 80-OMe), 6.67 (02H, d, J¼8.5 Hz,
6 and 60-H), 6.70 (2H, d, J¼8.5 Hz, 7 and 7 -H), 7.49 (2H, d,
J¼8.5 Hz, 3 and 30-H), 7.79 (2H, d, J¼8.5 Hz, 4 and 40-H),
9.86 (2H, s, 1 and 10-OH). 13C NMR (CDCl3) d: 55.9 (5 and
50-OMe), 56.4 (8 and 80-OMe), 1003.1 (C7 and C70), 1030.6
(C6 and C60), 112.6 (C3 and C3 ), 115.8 (C8a and C8a ),
121.3 (C2 and C20), 127.9 (C4a and C4a0), 130.3 (C4 and
C40), 150.39 (C8 and C80), 150.46 (C5 and C50), 151.2 (C1
and C10). LR-MS m/z: 406 (Mþ). HR-MS calcd for
C24H22O6: 406.1416. Found: 406.1433. Anal. calcd for
C24H22O6: C, 70.92; H, 5.46. Found: C, 71.10; H, 5.44.
Anal. calcd for C24H22O6: C, 70.92; H, 5.46. Found: 70.62;
H, 5.48.
4.4.3. 4,40,8,80-Tetramethoxy-3,30-dimethyl[2,20]di-1,10-
naphthol (2b). Colorless needles (CHCl3–MeOH), mp
251–252 8C. IR (KBr) cm21: 3372, 1606. 1H NMR (CDCl3)
d: 2.10 (6H, s, 3 and 30-Me), 3.87 (6H, s, 4 and 40-OMe),
3.99 (3H, s, 8 and 80-OMe), 6.77 (2H, d, 0J¼7.7 Hz, 7 and
70-H), 7.35 (2H, dd, J¼7.7, 7.9 Hz, 6 and 6 0-H), 7.74 (2H, d,
J¼7.9 Hz, 5- and 50-H), 9.380(2H, s, 1 and 1 -OH). 13C NMR
(CDCl3) d: 13.2 (C3 and C3 -Me), 56.0 (C8 and C80-OMe),
61.2 (C4 and C40-OMe), 103.6 (C7 and C70), 114.1 (C8a and
C8a0), 115.8 (C5 and C50), 120.2 (C2 and C20), 125.5 (C6
and C60), 128.7 (C4a and C4a0), 130.0 (C3 and C30), 1460.2
(C1 and C10), 147.1 (C4 and C40), 156.5 (C8 and C8 ).
LR-MS m/z: 434 (Mþ). HR-MS calcd for C26H26O6:
434.1730. Found: 434.1766. Anal. calcd for C26H26O6: C,
71.87; H, 6.03. Found: C, C, 71.67; H, 6.00.
4.4.4. 4,40-Dimethoxy[2,20]binaphthalenyl-1,10-diol (2d).
4.4.9. 1,4,9,12-Tetramethoxydinaphtho[1,2-b;20,10-d]-
furan (3f). Pale yellow amorphous powder (ether–hexane),
Colorless needles (benzene), mp 223–224 8C (lit.24a 206–
1
1
207 8C). IR (KBr) cm21: 3434, 1596. H NMR (CDCl3) d:
mp 202–203.5 8C. IR (KBr) cm21: 2922, 1578, 1456. H
3.99 (6H, s, 4 and 40-OMe), 5.44 (2H, s, 1 and 10-OH), 6.73
(2H, s, 3 and 30-H), 7.58–7.61 (4H, m, Ar-H), 8.28–8.30
(4H, m, Ar-H). LR-MS m/z: 346 (Mþ). HR-MS calcd for
C22H18O4: 346.1200. Found: 346.1222. Anal. calcd for
C22H18O4: C, 76.29; H, 5.24. Found: C, C, 76.19; H, 5.22.
NMR (CDCl3) d: 4.03 (6H, s, 4 and 9-OMe), 4.23 (6H, s, 1
and 12-OMe), 6.85 (2H, d, J¼8.5 Hz, 3 and 10-H), 6.96
(2H, d, J¼8.5 Hz, 2 and 11-H), 8.11 (2H, d, J¼8.8 Hz, 6 and
7-H), 8.26 (2H, d, J¼8.8 Hz, 5 and 8-H). 13C NMR (CDCl3)
d: 55.9 (4 and 9-OMe), 56.8 (1 and 12-OMe), 104.0 (C3 and
C10), 105.8 (C2 and C11), 115.0 (C12a and C13b), 117.5
(C5 and C8), 118.2 (C6 and C7), 120.9 (C6a and C6b),
125.8 (C4a and C8a), 149.3 (C1 and C12), 150.0 (C4 and
C9), 151.0 (C12b and C13a). LR-MS m/z: 388 (Mþ).
HR-MS calcd for C24H26O5: 388.1305. Found: 388.1341.
Anal. calcd for C24H20O5: C, 74.21; H, 5.19. Found: C,
74.31; H, 5.17.
4.4.5. 5,8-Dimethoxydinaphtho[1,2-b;20,10-d]furan (3d).
Light blue needles (benzene), mp 215.5–216.5 8C (lit.24b
216–217 8C). IR (KBr) cm21: 1598, 1583. 1H NMR
(CDCl3) d: 4.12 (6H, s, 5 and 8-OMe), 7.23 (2H, s, 6 and
7-H), 7.54 (2H, ddd, J¼1.3, 7.0, 8.4 Hz, 2 and 11-H, or 3
and 10-H), 7.67 (2H, ddd, J¼1.3, 7.0, 8.4 Hz, 2 and 11-H, or
3 and 10-H), 8.37 (2H, broad d, J¼8.5 Hz, 1 and 12-H, or 4
and 9-H), 8.47 (2H, broad d, J¼7.7 Hz, 1 and 12-H, or 4 and
9-H). LR-MS m/z: 328 (Mþ). HR-MS calcd for C22H16O3:
328.1095. Found: 328.1146. Anal. calcd for C22H16O3: C,
80.47; H, 4.91. Found: 80.37; H, 4.93.
4.4.10. 12-(10-Hydroxy-50,80-dimethoxynaphthalen-20-
yl)-1,4,7,10-tetramethoxy-13-oxa-dibenzo[a,g]fluoren-
11-ol (7f). Light brown amorphous powder (CHCl3–
MeOH), mp 263–265 8C. IR (KBr) cm21: 3346, 1612,
1449. 1H NMR (CD3SOCD3) d: 3.53 (3H, s, 7-OMe),
3.96 (3H, s, 10-OMe), 3.99 (3H, s, 50-OMe), 4.01 (3H, s,
80-OMe), 4.10 (6H, each s, 1- and 4-OMe), 6.87 (1H, d, J¼
8.5 Hz, 90-H), 6.89 (1H, d, J¼8.5 Hz, 80-H), 6.92 (1H, d, J¼
8.6 Hz, 6 -H), 6.96 (1H, d, J¼8.6 Hz, 7 -H), 7.14 (1H, d, J¼
8.6 Hz, 20-H), 7.20 (1H, d, J¼8.6 Hz, 30-H), 7.59 (1H, d, J¼
8.6 Hz, 3 -H), 7.74 (1H, d, J¼8.6 Hz, 4 -H), 8.06 (1H, d, J¼
9.2 Hz, 5-H), 8.71 (1H, d, J¼9.2 Hz, 6-H), 9.94 (1H, s,
4.4.6. 4,40-Dimethyl[2,20]binaphthalenyl-1,10-diol (2e).
Colorless amorphous powder (CHCl3–hexane), mp 219–
1
220 8C. IR (KBr) cm21: 3054, 2938, 1603, 1573, 1504. H
NMR (CDCl3) d: 2.67 (6H, d, J¼0.7 Hz, 4 and 40-Me), 5.59
(2H, s, 1 and 10-OH), 7.23 (2H, 0d, J¼0.7 Hz, 3 and 30-H),
7.55–7.65 (4H, m, 6, 60, 7 and 7 -H), 8.00 (2H, dd, J¼1.5,
7.5 Hz, 5 and 50-H), 8.36 (2H, dd, J¼1.5, 7.5 Hz, 8 and

T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310
6307
10-OH), 10.63 (1H, s, 11-OH). 13C NMR (CD3SOCD3) d:
55.34 (4-OMe), 55.64 (50-OMe), 55.66 (10-OMe), 56.28
(7-OMe), 56.31 (80-OMe), 57.00 (1-OMe), 104.15 (C60 or
C70), 104.17 (C600 or C70), 104.19 (C9), 105.12 (C2), 106.74
(C3), 107.39 (C2 ), 107.53 (C8), 108.23 (C12), 111.03 (C400),
113.48 (C13b), 113.73 (C10a), 114.93 (C6c), 115.09 (C8a ),
115.78 (C5), 121.46 (C4a)0, 122.09 (C6a), 123.48 (C6),
123.52 (C6b), 127.19 (C4a ), 130.29 (C30), 148.28 (C7),
149.05 (C10), 149.27 (C50), 149.31 (C13a), 149.73 (C800),
150.09 (C4), 150.54 (C1), 151.20 (C11), 151.75 (C1 ),
154.08 (C12a). LR-MS m/z: 606 (Mþ). HR-MS calcd for
C36H30O9: 606.1881. Found: 606.1887. Anal. calcd for
C36H30O9: C, 71.28; H, 4.98. Found: C, 70.98; H, 5.05.
(CD3SOCD3) d: 15.50 (C60-Me), 15.59 (C3-Me), 15.88 (C8-
Me), 55.88 (C1-OMe), 56.21 (C80-OMe), 56.82 (C10-OMe),
60.21 (C7 or C50-OMe), 60.25 (C7 or C50-OMe), 60.48
(C4-OMe), 106.43 (C6b), 107.21 (C12), 107.31 (C70),
107.97 (C9), 109.92 (C2),0 110.87 (C40), 112.28 (C10a),
112.45 (C13b), 113.67 (C2 ), 114.10 (C8a0), 116.07 (C5),
120.36 (C6a), 123.67 (C6), 123.69 (C6c), 125.05 (C3),
125.43 (C600), 126.30 (C4a), 127.96 (C8), 129.77 (C4a0),
131.03 (C3 ), 146.84 (C4), 147.14 (C50), 147.81 (C7),
149.82 (C13a), 150.29 (C1), 151.41 (C11), 151.75 (C80),
152.10 (C10), 152.59 (C10), 154.48 (C12a). LR-MS m/z:
648 (Mþ). HR-MS calcd for C39H36O9: 648.2349. Found:
648.2386. Anal. calcd for C39H36O9: C, 72.21; H, 5.59.
Found: C, 72.41; H, 5.60. Anal. calcd for C39H36O9: C,
72.21; H, 5.59. Found: C, C, 72.15; H, 5.61.
4.4.11. 1,4,8,11,13,16-Heptamethoxydinaphtho[2,1-d;
20,10-d0]naphtho[1,2-b;3,4-b0]difuran (8f). Pale brown
needles (CHCl3–MeOH), mp 221–223 8C. IR (KBr)
cm21: 1582, 1459. 1H NMR (CDCl3) d: 4.05 (3H, s,
OMe), 4.06 (3H, s, OMe), 4.20 (3H, s, OMe), 4.26 (3H, s,
OMe), 4.29 (3H, s, OMe), 4.29 (3H, s, OMe), 6.84 (1H, d,
J¼8.6 Hz, Ar-H), 6.88 (1H, d, J¼8.6 Hz, Ar-H), 6.977 (1H,
d, J¼8.5 Hz, Ar-H), 6.984 (1H, d, J¼8.5 Hz, Ar-H), 7.06
(1H, d, J¼8.6 Hz, Ar-H), 7.10 (1H, d, J¼8.6 Hz, Ar-H),
8.23 (1H, d, J¼9.3 Hz, Ar-H), 8.42 (1H, d, J¼8.7 Hz,
Ar-H), 8.66 (1H, d, J¼8.7 Hz, Ar-H), 8.89 (1H, d, J¼
9.3 Hz, Ar-H). 13C NMR (CDCl3) d: 55.6 (Ar-OMe), 55.9
(Ar-OMe), 56.7 (Ar-OMe), 56.9 (Ar-OMe), 57.0 (Ar-OMe),
103.7, 104.1, 105.4, 105.6, 105.7, 106.7, 109.6, 112.6,
113.2, 114.5, 114.7, 116.7, 118.1, 119.1, 119.9, 121.1,
123.1, 124.5, 124.9, 125.7, 149.19, 149.23, 149.4, 149.7,
149.9, 150.5, 150.9, 151.2, 151.5. LR-MS m/z: 588 (Mþ).
HR-MS calcd for C36H28O8: 588.1776. Found: 588.1807.
Anal. calcd for C36H28O8: C, 73.46; H, 4.79. Found: C,
73.56; H, 4.77.
4.4.14. 1,4,8,11,13,16-Heptamethoxy-2,9,15-trimethyldi-
naphtho[2,1-d:20,10-d0]naphtho[1,2-b:3,4-b0]difuran (8g).
Red amorphous powder (hexane–AcOEt), mp 147–148 8C.
IR (KBr) cm21: 2926, 1620, 1586, 1452. 1H NMR (CDCl3)
d: 2.56 (3H, s, Me), 2.56 (3H, s, Me), 2.68 (3H, s, Me), 3.73
(3H, s, OMe), 3.985 (3H, s, OMe), 3.988 (3H, s, OMe), 4.27
(3H, s, OMe), 4.31 (3H, s, OMe), 4.33 (3H, s, OMe), 6.885
(1H, s, Ar-H), 6.888 (1H, s, Ar-H), 7.00 (1H, s, Ar-H), 8.05
(1H, d, J¼9.2 Hz, Ar-H), 8.22 (1H, d, J¼8.6 Hz, Ar-H),
8.66 (1H, d, J¼8.6 Hz, Ar-H), 9.02 (1H, d, J¼9.2 Hz,
Ar-H). LR-MS m/z: 630 (Mþ). HR-MS calcd for C39H34O8:
630.2244. Found: 630.2261. Anal. calcd for C39H34O8: C,
74.27; H, 5.43. Found: C, 74.17; H, 5.40.
4.4.15. 2,20-Binaphthalenyl-1,10-diol (2h). Colorless
powder (benzene–hexane), mp 222–223 8C (lit.10 221–
223 8C). IR (KBr) cm21: 3051, 1599, 1568. 1H NMR
(CDCl3) d: 5.66 (2H, s, Ar-OH), 7.39 (2H, d, J¼8.27 Hz,
Ar-H), 7.55–7.60 (6H, m, Ar-H), 7.86–7.89 (2H, m, Ar-H),
8.32–8.35 (2H, m, Ar-H). LR-MS m/z: 286 (Mþ). Anal.
calcd for C20H14O2: C, 83.90; H, 4.93. Found: C, 83.98; H,
4.90.
4.4.12. 5,50,8,80-Trimethoxy-6,60-dimethyl[2,20]di-1,10-
naphthol (2g). Colorless needles (ether–hexane), mp
229–232 8C. IR (KBr) cm21: 0 3378, 1618. 1H NMR
(CDCl3) d: 2.43 (6H, s, 6 and 6 -Me), 3.87 (6H, s, 5 and
500-OMe), 3.88 (6H, s, 8 and 80-OMe), 6.00 (2H, s, 7 and
7 -H), 7.51 (2H, d, J¼8.5 Hz, 3 and 30-H), 7.62 (2H, d,
J¼8.5 Hz, 4 and 40-H), 90.77 (2H, s, 1 and 10-0OH). 13C NMR
(CDCl3) d: 16.2 (6 and 6 -Me), 56.3 (8 and 8 -OMe), 61.0 (5
and 50-OMe), 107.1 (C7 and C70), 112.4 (C3 and C30), 1140.8
(C8a and C8a0), 119.8 (C2 and C20), 125.5 (C4a and C4a0),
130.4 (C6 and C60), 130.9 (C4 and C40),0148.0 (C8 and C8 ),
151.5 (C5 and C50), 152.3 (C1 and C1 ). LR-MS m/z: 434
(Mþ). HR-MS calcd for C26H26O6: 434.1730. Found:
434.1746. Anal. calcd for C26H26O6: C, 71.87; H, 6.03.
Found: C, 71.52; H, 6.01.
4.4.16. Dinaphtho[1,2-b;20,10-d]furan (3h). Colorless
needles (ethanol), mp 179–180 8C (lit.7 178–180 8C). IR
1
(KBr) cm21: 2935, 1570. H NMR (CDCl3) d: 7.50–7.59
(4H, m, 2, 20-H and 3, 30-H), 7.69 (2H, d, J¼8.25 Hz, 5,50-H
or 6,60-H), 7.80 (2H, d, J¼08.25 Hz, 5,50-H or 6,60-H), 7.88–
7.91 (2H, m, 1,10-H or 4,4 -H), 8.19–8.22 (2H, m, 1,10-H or
4,40-H). LR-MS m/z: 268 (Mþ).
4.4.17. 1,10-Binaphthalenyl-4,40-diol (10). Colorless
powder (benzene), mp 293–294 8C (lit.6a 296–298 8C). IR
1
(KBr) cm21: 3385, 1593. H NMR (CD3COCD3) d: 7.04
(2H, d, J¼7.53 Hz, 2, 20-H), 7.27 (2H, d, J¼7.53 Hz, 3,
30-H), 7.28–7.29 (4H, m, Ar-H), 7.42–7.47 (2H, m, Ar-H),
8.35 (2H, broad d, J¼8.27 Hz, Ar-H), 9.15 (2H, s, Ar-OH).
LR-MS m/z: 286 (Mþ). Anal. calcd for C20H14O2: C, 83.90;
H, 4.93. Found: C, 84.01; H, 4.95.
4.4.13. 12-(1-Hydroxy-5,8-dimethoxy-6-methylnaphtha-
len-2-yl)-1,4,7,10-tetramethoxy-3,8-dimethyl-13-oxadi-
benzo[a,g]fluoren-11-ol (7g). Pale green amorphous
powder (CHCl3–hexane), mp 249–251 8C. IR (KBr)
1
cm21: 3372, 1619, 1581. H NMR (CD3SOCD3) d: 2.45
(3H, s, 3-Me), 2.49 (3H, s, 60-Me), 2.62 (3H, s, 8-Me), 3.64
(3H, s, 1-OMe), 3.71 (3H, s, 7-OMe), 03.90 (3H, s, 4-OMe),
3.91 (3H, s, 50-OMe), 4.08 (3H, s, 8 -OMe), 4.17 (3H, s,
10-OMe), 6.85 (1H, s, 2-H), 6.93 (1H, s, 70-H), 7.12 (1H, s,
9-H), 7.63 (1H, d, J¼8.5 Hz, 40-H), 7.66 (1H, d, J¼8.5 Hz,
30-H), 7.99 (1H, d, J¼9.2 Hz, 5-H), 8.80 (1H, d, J¼9.2 Hz,
6-H), 9.73 (1H, s, 10-OH), 10.35 (1H, s, 11-OH). 13C NMR
4.5. General procedure for oxidation of 1-naphthols with
Ag2O
A mixture of selected 1-naphthols 1 (2.3 mmol) in CHCl3
(10 ml) containing 1.5 equiv. of Ag2O (80 mg, 0.344 mmol)
was stirred at 23 8C in an air atmosphere. The solvent was
removed and the residue was subjected to flash column

6308
T. Takeya et al. / Tetrahedron 60 (2004) 6295–6310
chromatography on silica gel with the designated solvents as
follows: AcOEt–hexane (1:6; for 2a, 1a and 5a in Table 1);
AcOEt–hexane (1:5; for 2b and 4b in Table 1); AcOEt–
hexane (1:5; for 2d and 6d in Table 1); CH2Cl2–hexane
(2:1; for 2f and 9f in Table 2). Yields for 2a, 5a, 2b, 6b, 2d,
5d, 2e, 2h and 9f are listed in Tables 1 and 2.
OMe), 6.63 (1H, d, J¼8.4 Hz, Ar-H), 6.66 (1H, d, J¼
8.3 Hz, Ar-H), 6.68 (1H, d, J¼8.3 Hz, Ar-H), 6.74 (1H, d,
J¼8.6 Hz, Ar-H), 6.97 (1H, d, J¼8.1 Hz, Ar-H), 7.24 (1H,
d, J¼8.1 Hz, Ar-H), 7.35 (1H, d, J¼8.4 Hz, Ar-H), 7.71
(1H, d, J¼8.6 Hz, Ar-H), 9.59 (1H, s, OH), 9.83 (1H, s,
OH). MS m/z: 406 (Mþ). HR-MS calcd for C24H22O6:
406.1416. Found: 406.1440. Anal. calcd for C24H22O6: C,
70.92; H, 5.46. Found: C, 70.68; H, 5.47.
4.5.1. 5-Methoxy-1,4-naphthoquinone (4a). Yellow
needles (ether–hexane), mp 187–189 8C (lit.17a 180–
185 8C). IR (KBr) cm21: 1655, 1581. H NMR (CDCl3) d:
4.5.6. 5,50,8,80-Trimethoxy-6,60-dimethyl-2,40-di-1,10-
naphthol (9g). Colorless needles, mp 246–247 8C (ether–
hexane). IR (KBr) cm21: 3336, 1612. 1H NMR (CDCl3) d:
2.34 (3H, s, Me), 2.43 (3H, s, Me), 3.00 (3H, s, OMe), 3.89
(3H, s, OMe), 3.96 (3H, s, OMe), 4.06 (3H, s, OMe), 6.56
(1H, s, Ar-H), 6.64 (1H, s, Ar-H), 6.91 (1H, d, J¼8.1 Hz,
Ar-H), 7.25 (1H, d, J¼8.1 Hz, Ar-H), 7.43 (1H, d, J¼
8.5 Hz, Ar-H), 7.55 (1H, d, J¼8.5 Hz, Ar-H), 9.50 (1H, s,
OH), 9.74 (1H, s, OH). 13C NMR (CDCl3) d: 16.1, 16.7,
56.1, 56.4, 60.4, 61.0, 106.7, 107.5, 110.1, 111.1, 114.0,
115.4, 124.7, 124.8, 126.3, 126.8, 129.4, 129.8, 130.6,
132.3, 147.9, 149.2, 150.9, 152.3, 154.5. MS m/z: 434 (Mþ).
HR-MS calcd for C26H26O6: 434.1730. Found: 434.1758.
Anal. calcd for C26H26O6: C, 71.87; H, 6.03. Found: C,
71.97; H, 6.01.
1
4.02 (3H, s, OMe), 6.88 (2H, s, Ar-H), 7.32 (1H, dd, J¼1.8,
7.8 Hz, Ar-H), 7.67–7.76 (2H, m, Ar-H). 13C NMR
(CDCl3) d: 56.5 (C5-OMe), 118.0, 119.2, 119.7, 134.1,
135.0, 136.2, 140.9, 159.6, 184.4 (C1 or C4), 185.2 (C1 or
C4). HR-MS calcd for C11H8O3: 188.0471. Found:
188.0486. Anal. calcd for C11H8O3: C, 70.21; H, 4.29.
Found: C24H18O6: C, 70.41; H, 4.31.
4.5.2. 4,8,40,80-Tetramethoxy[2,20]binaphthalenylidene-
1,10-dione (5a). Deep purple needles (CHCl3–hexane),
1
mp 261–262 8C. IR (KBr) cm21: 1613, 1581, 1564. H
NMR (CDCl3) d: 3.99 (6H, s, 8 and 80-OMe), 4.01 (6H, s, 4
and 40-OMe), 7.00 (2H, d,0J¼8.2 Hz, 7 and 70-H), 7.41 (2H,
dd, J¼0.9, 7.5 Hz, 5 and 50-H), 7.52 (2H, t, J¼8.2 Hz, 6 and
60-H), 7.92 (2H, s, 3 and 3 -H). 13C NMR (CDCl3) d: 55.90
(4 and 40-OMe), 56.32 (8 and 80-OMe), 102.28 (C3 and C30),
112.46 (C7 and C70), 114.61 (C5 and C50), 120.630(C8a and
C8a0), 133.35 (C4a and C4a0), 133.83 (C6 and C6 ), 134.49
(C2 and C20), 155.42 (C4 and C40), 159.90 (C8 and C80),
189.49 (C1 and C10). LR-MS m/z: 404 (Mþ). HR-MS calcd
for C24H20O6: 404.1254. Found: 404.1267. Anal. calcd for
C24H20O6: C, 71.28; H, 4.98. Found: C, 71.08; H, 4.95.
4.6. Anodic oxidation of NPOH 1a
A solution of 1a (58 mg, 0.142 mmol) in CH2Cl2 (30 ml)
was oxidized at 0.80 or 0.95 V (vs Ag-AgCl) under an argon
atmosphere for 1 h in the presence of n-Bu4N·ClO4 (1.02 g)
as a supporting salt using platinum mesh as an anode and a
cathode, and an Ag-AgCl reference electrode, in a divided
cell (H-shaped glass cell) through glass filters. Based on CV
curves, the oxidation potential of 1a was 0.78 or 0.95 V vs
Ag-AgCl (the first onset oxidation potential or the first half-
wave oxidation potential in CV). The solvent was
evaporated and the residue was purified by flash column
chromatography on silica gel using hexane–AcOEt (2:1)
as an eluent to give 4a (60 or 34%) and 6a (23 or 11%),
respectively. 6a: yellow needles (CHCl3–hexane), mp
4.5.3. 4,40-Dimethoxy[2,20]binaphthalenylidene-1,10-
dione (5d). Deep blue needles (benzene), mp 257–258 8C
(lit.24a 257–258 8C). IR (KBr) cm21: 1606, 1584, 1561. 1H
NMR (CDCl3) d: 4.08 (6H, s, 4 and 40-OMe), 7.48 (2H,
broad t, J¼7.7 Hz, 7 and 70-H), 7.61 (2H, broad t, J¼7.7 Hz,
6 and 60-H), 7.79 (2H, broad d, J¼7.7 Hz, 8 and 80-H), 8.17
(2H, broad d, J¼7.7 Hz, 5 and 50-H), 8.42 (2H, s, 3 and
30-H). LR-MS m/z: 344 (Mþ). HR-MS calcd for C22H16O4:
344.1044. Found: 344.1029. Anal. calcd for C22H16O4: C,
76.73; H, 4.68. Found: C, 76.93; H, 4.69.
1
202–204 8C. IR (KBr) cm21: 1644, 1604, 1570. H NMR
(CDCl3) d: 3.99 (6H, s, 5 and 50-OMe), 6.95 (2H, s, 2 and
20-H), 7.33 (2H, d, J¼08.2 Hz, 6 and 60-H), 7.71 (2H, t,
J¼7.9, 8.2 Hz, 7 and 7 -H), 7.76 (2H, d, J¼7.9 Hz, 8 and
80-H). 13C NMR (CDCl3) d: 56.5 (C5 and C50-OMe), 118.2
(C6 and C60), 119.10 (C8 and C80), 119.8 (C5a and C50a),
134.2 (C8a and C8a ),0134.8 (C2 and C20), 135.2 (C7 and
C700), 146.8 (C3 and C3 ), 160.1 (C5 and C50), 182.1 (C4 and
C4 ), 184.4 (C1 and C10). LR-MS m/z: 374 (Mþ). HR-MS
calcd for C22H14O6: 374.0790. Found: 374.0762. Anal.
calcd for C22H14O6: C, 70.59; H, 3.77. Found: C, 70.49; H,
3.78.
4.5.4. 5,50-Dimethoxy-2,20-dimethyl[3,30]binaphtho-
quinone (6b). Yellow needles (CHCl3–hexane), mp 261–
1
263 8C. IR (KBr) cm21: 1659, 1588. H NMR (CDCl3) d:
2.00 (6H, s, 2 and 20-Me), 3.95 (3H, s, 5 and 50-OMe), 7.28
(2H, dd, J¼0.9, 8.2 Hz, 6 and 60-H), 7.69 (2H, dd, J¼7.7 Hz,
7 and 70-H), 7.81 (2H, dd, J¼1.1, 07.5 Hz, 8 and 80-H). 13C
NMR (CDCl3) d: 13.8 (C2 and C2 -Me), 56.3 (C8 and C80-
OMe), 1017.7 (C6 and C60), 119.3 (C8 and C80), 119.7 (C5a
and C5a ), 134.2 (C8a and C8a0), 134.9 (C7 and0 C70), 142.8
(C2 and C20, or C3 and C30), 142.9 (C2 and C2 , or C3 and
C300), 159.7 (C5 and C50), 182.0 (C4 and C40), 184.8 (C1 and
C1 ). LR-MS m/z: 402 (Mþ). HR-MS calcd for C24H18O6:
402.1103. Found: 402.1131. Anal. calcd for C24H18O6: C,
71.64; H, 4.51. Found: C24H18O6: C, 71.54; H, 4.52.
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