Oxidative coupling of methoxynaphthylenediols

Article abstract of DOI:10.1016/j.tet.2005.04.058

The oxidative coupling of a mixture of 1-methoxy-7-methyl-4,5- naphthylenediol and 4-methoxy-7-methyl-1,5-naphthylenediol using lead(IV) oxide gives the symmetrical bisnaphthalene indigos diosindigo A and diosindigo B together with the corresponding unsymmetrical isomer. Oxidation of the first two by nitric acid gives the binaphthyldiquinones mamegakinone and biramentaceone, respectively; the third gives the unsymmetrical diquinone rotundiquinone. Similar oxidations of related naphthylenediols are described.

Full text of DOI:10.1016/j.tet.2005.04.058

Tetrahedron 61 (2005) 6568–6574
Oxidative coupling of methoxynaphthylenediols
*
Bhim C. Maiti, Oliver C. Musgrave and Douglas Skoyles
Chemistry Department, The University, Old Aberdeen AB24 3UE, UK
Received 28 February 2005; revised 7 April 2005; accepted 21 April 2005
Abstract—The oxidative coupling of a mixture of 1-methoxy-7-methyl-4,5-naphthylenediol and 4-methoxy-7-methyl-1,5-naphthylenediol
using lead(IV) oxide gives the symmetrical bisnaphthalene indigos diosindigo A and diosindigo B together with the corresponding
unsymmetrical isomer. Oxidation of the first two by nitric acid gives the binaphthyldiquinones mamegakinone and biramentaceone,
respectively; the third gives the unsymmetrical diquinone rotundiquinone. Similar oxidations of related naphthylenediols are described.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
formed the cyclic phenylboronate 4 which, on being treated
with acetic anhydride and sodium acetate followed by
water, produced a mixture of the diacetoxynaphthols 5 and
7. Subsequent methylation with diazomethane gave a
similar mixture of the methoxy diacetates 6 (w80%) and
8 (w20%), which we were unable to separate. However, as
will be apparent later, the presence of the minor component
had no discernible effect on the formation of the derived
bisnaphthalene indigos. We have previously described the
preparation of the diacetates of the other components
required, the methoxynaphthylene diols 10, 11, and 18.8
The intensely coloured bisnaphthalene indigo ‘Russig’s
Blue’ 21,2 is readily prepared by the lead(IV) oxide-induced
oxidative coupling of 4-methoxy-l-naphthol 1. Two sym-
metrically substituted derivatives of 2, namely diosindigo A
133 and diosindigo B 20,4 which occur naturally in woods of
the Diospyros species, have been synthesised in a similar
manner and converted by further oxidation into the
corresponding orange-red binaphthyldiquinones mamega-
kinone 16 and biramentaceone 223,5,6 which are found
naturally in Diospyros and Euclea species.7 We now
describe the preparation of unsymmetrically substituted
analogues of these quinones.
Of these starting materials the two methoxynaphthylene
diacetates derived from juglone were the more accessible.
The alkaline hydrolysis of a 1:1 mixture of 6 and the
isomeric diacetate of 10 gave a mixture of the diols 10 and
17. Treatment of this with lead(IV) oxide produced an
intense blue mixture of the corresponding bisnaphthalene
indigos which we separated by preparative TLC into the two
symmetrically substituted quinones 12 (33%) (Scheme 2)
and 19 (37%) (Scheme 3) and the unsymmetrical isomer 23
(17%) (Scheme 4). The first pair were identical with
specimens prepared from the diols 10 and 17 separately. The
poor solubility of the strongly hydrogen-bonded symmetri-
cal quinone 12 prevented the measurement of its NMR
signals and we characterised it as the leucoacetate 14. The
other symmetrical quinone 19 showed the expected NMR
signals while the unsymmetrical quinone 23 gave a more
complicated spectrum with the signals for the two types of
hydroxy group, at d 8.78 and 13.45, being particularly
distinctive. An additional, yellow quinone isolated during
the purification of the above blue compounds proved to be
5-methoxy-1,4-naphthoquinone 9. This was derived from
the minor contaminant 8 present in the methoxy diacetate 6.
The hydrolysis of 8 produced the 1,4-naphthylenediol which
2. Discussion
One of the starting materials required for the syntheses, the
methoxynaphthylene diacetate 6, was prepared by the
sequence8 shown in Scheme 1. The dihydrojuglone 3
Keywords: Naphthalenes; Quinones; Coupling reactions; Oxidation.
*
Corresponding author. Tel.: C44 1224 313003; fax: C44 1224 272921;
e-mail: o.c.musgrave@abdn.ac.uk
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.04.058

B. C. Maiti et al. / Tetrahedron 61 (2005) 6568–6574
6569
Scheme 1.
Scheme 2.
Scheme 3.
was oxidised immediately by lead(IV) oxide to the
corresponding 1,4-naphthoquinone 9 (Scheme 1) and so
did not participate in the phenolic coupling reactions.
preparative TLC into the symmetrical quinones diosindigo
A 13 (39%) and diosindigo B 20 (37%). The structure of the
third component, the unsymmetrical quinone 24 (17%),
follows from its NMR signals which are similar to those9 of
diosindigo A plus those4 of diosindigo B.
The application of the above hydrolysis with subsequent
oxidation procedure to a mixture of the methyl-substituted
methoxynaphthylene diacetates corresponding to the diols
11 and 18 gave the expected mixture of bisnaphthalene
indigos (Schemes 2, 3 and 4) which we separated by
The oxidative coupling of two different phenols having
similar reactivity would be expected to give the two
symmetrical and the unsymmetrical products in the ratio

6570
B. C. Maiti et al. / Tetrahedron 61 (2005) 6568–6574
Scheme 4.
of 1:1:2. The much lower yields of the unsymmetrical
bisnaphthalene indigos obtained in the present work
indicate that the isomeric naphthols concerned react with
lead(IV) oxide at differing rates. We attribute this to the
difference in their hydroxylation patterns, the peri hydroxy
groups of the 1,8-naphthylenediol systems in 10 and 11
providing stronger coordination to the metal than is possible
with the 1,5-substituted isomers 17 and 18. The rapid
formation of a transient complex such as 27 between the
diol 10 and lead(IV) oxide and the subsequent intra-
molecular coupling of its two naphthalene nuclei would
effectively prevent much of the 1,8-dihydroxy compound 10
from coupling with the 1,5-dihydroxy isomer 17. If four-
fifths of the 1,8-isomer were removed from the reaction in
this way the theoretical yields of each of the two
symmetrical bisnaphthalene indigos would be 40% and
that of the unsymmetrical quinone would be reduced to
20%. These values are in good agreement with those
obtained experimentally and provide support for the above
argument.
Scheme 5.

B. C. Maiti et al. / Tetrahedron 61 (2005) 6568–6574
6571
The bisnaphthalene indigos 12, 19, and 23 underwent
oxidative demethylation readily on being treated with nitric
acid, giving the corresponding binaphthyldiquinones 15, 21
and 25. The dimethyl analogues 13, 24 and 20 behaved in a
similar manner giving the naturally occurring diquinones7
mamegakinone 16, rotundiquinone 26, and biramentaceone
22 (Schemes 2–4). Each of the unsymmetrical diquinones
25 and 26 showed two distinctive NMR signals for their
hydroxy protons. In the mass spectrometer the molecular
ions from the bijuglones 15, 21 and 25 underwent cleavage
of their quinone rings with the formation of characteristic10
fragment radical-ions with m/z 120 (C7H4O2) and 92
(C6H4O). The corresponding ions from their dimethyl
counterparts 16, 22, and 26 had the expected m/z values of
134 and 106. We succeeded in reconverting the diquinone
mamegakinone 16 into the monoquinone diosindigo A 13
by reductively methylating it using tin(II) chloride and
phosphoryl(V) chloride in methanolic hydrochloric acid8
and then oxidising the resulting binaphthyltetraol with
lead(IV) oxide (Scheme 2).
mixture was added to 1 M sulphuric acid (10 ml) and shaken
with chloroform (5!5 ml). The dried chloroform solution
was warmed with lead(IV) oxide (500 mg, 2.42 mmol) for
5 min, filtered hot, and the deep blue filtrate was treated
twice more with lead(IV) oxide (50 mg) in the same
manner. The chloroform solution was then subjected to
preparative TLC in order to separate the components of the
mixture of bisnaphthalene indigos.
3.3. Oxidative demethylation reactions
A suspension of the bisnaphthalene indigo (10 mg) in 4 M
nitric acid (1.5 ml) was heated on the steam-bath for 0.5 h
and then poured into water (7 ml). The resulting solid was
crystallised from light 0petroleum to give the substituted
2,20-binaphthyl-1,4:10,4 -diquinone (65–93%).
3.4. Reductive acetylation of quinones
A mixture of the quinone (4 mg), acetic anhydride (1 ml),
zinc dust (50 mg) and anhydrous sodium acetate (50 mg)
was boiled under reflux for 30–60 min and added to hot
water. Extraction with chloroform gave the corresponding
leucoacetate.
All the above coupling reactions producing the
bisnaphthalene indigos utilise methoxynaphthylenediols in
which the aromatic ring with the hydroxy and methoxy
groups carries no other substituents. We have noticed that
the presence of a methyl group adjacent to the methoxy
group has a deleterious effect on such reactions. Thus the
oxidative coupling of the methoxynaphthylene diol 11 with
the isomeric diol8 29 derived from plumbagin (Scheme 5)
gave only two products, diosindigo A 13 (76%) and the
cross-coupled bisnaphthalene indigo 30 (10%). The poor
solubility of the latter prevented the measurement of its
NMR spectrum and we characterised it as its leuco-acetate
31. When we treated the methoxydiol 29 alone with
lead(IV) oxide the products were plumbagin 32 (23%) and
3,30-biplumbagin 33 (0.3%), both apparently resulting from
heterolytic oxidative demethylation reactions. It appears
that the presence of the two methyl groups in the postulated
complex 28 largely inhibits the normal coupling reaction.
3.4.1. 1-Hydroxy-4,5-naphthylene phenylboronate 4. A
mixture of 1,4,5-naphthalene triol11 3 (2 g, 11.36 mmol),
phenylboronic anhydride (1.18 g, 11.36 mmol) and benzene
(100 ml) was boiled under reflux using a Dean-Stark
apparatus until the evolution of water was complete.
Concentration of the solution gave a solid which crystallised
from benzene to yield the phenylboronate 4 (1.8 g,
6.87 mmol, 61%) as needles, mp 200–202 8C (Found: MC
262.0798. C, 73.0; H, 4.0%. C16H1111BO3 requires M
262.0801. C, 73.3; H, 4.2%); m/z 262 (100%, M), 233 (19,
MKCHO) and 131 (4, M2C); nmax/cmK1 3210 (OH), 1638,
1618 and 1602 (aromatic C]C) and 1330 (B–O); lmax/nm
319 (log 3 3.71), 334 (3.73) and 348 (3.73); dH [(CD3)2CO]
6.85 (2H, s, H-2 and -3), 6.99 (1H, dd, JZ1.8 Hz, H-6),
7.20–7.63 (4H, m, H-7 and m- and p-H’s of Ph), 7.75 (1H,
dd, JZ1.8 Hz, H-8) and 7.90–8.18 (2H, m, o-H’s of Ph).
3. Experimental
3.1. General
3.4.2. Reaction of 1-hydroxy-4,5-naphthylene phenyl-
boronate 4 with acetic anhydride and sodium acetate. A
mixture of the phenylboronate (410 mg, 1.57 mmol), acetic
anhydride (5.4 g, 52.95 mmol) and anhydrous sodium
acetate (80 mg, 0.98 mmol) was kept for 27 h at 20 8C,
poured into water and extracted with chloroform. The
chloroform solution, after being washed with aqueous
sodium hydrogen carbonate and evaporated, afforded a
solid which crystallised from benzene to give a mixture of
4,8-diacetoxy-1-naphthol 5 and 5,8-diacetoxy-1-naphthol 7
(110 mg, 0.43 mmol, 27%) as needles, mp 154–156 8C
(Found: MC, 260.0684. Calcd for C14H12O5: M, 260.0684);
m/z 260 (l.5%, M), 218 (5, MKCH2CO), 176 (100, 218-
CH2CO) and 147 (3.5, 176-CHO); nmax/cmK1 3440 (OH)
and 1750 (aryl acetate C]O); lmax/nm 292infl (log 3 3.70),
303.5 (3.79), 317 (3.75) and 331 (3.67).
Operations involving the formation of the free naphthols,
particularly those in alkaline solution, were performed
under nitrogen. IR spectra were measured for potassium
bromide discs and UV–vis spectra were obtained for
1
solutions in ethanol or, where indicated, in chloroform. H
NMR spectra were measured at 100 MHz for solutions in
deuterochloroform or, where indicated, in perdeutero-
acetone with tetramethylsilane as internal standard. Mass
spectra were measured using EI at 70 eV. TLC was
performed on silica gel (Merck GF254). ‘Light petroleum’
refers to the fraction with bp 60–80 8C. The reaction
products were colourless solids unless stated otherwise.
3.2. Oxidative coupling reactions
3.4.3. Methylation of the mixture of diacetoxynaphthols 5
and 7. A solution ofdiazomethane [fromN-nitrosomethylurea
(2 g, 19.4 mmol) in ether (30 ml)] was added to a solution of
the mixture of diacetoxynaphthols (100 mg, 0.38 mmol) in
A mixture of the methoxynaphthylene diacetates (ca.
0.25 mmol) was boiled under reflux for 0.5 h with 3%
methanolic potassium hydroxide (5 ml) under nitrogen. The

6572
B. C. Maiti et al. / Tetrahedron 61 (2005) 6568–6574
ether (20 ml) and the mixture was kept for four days at
20 8C. Evaporation of the solvent and crystallisation of
the residue from light petroleum/chloroform gave a
mixture of 4-methoxy-1,5-naphthylene diacetate 6 (80%)
and 5-methoxy-l,4-naphthylene diacetate 8 (20%) (92 mg,
0.34 mmol, 88%) as needles, mp 107–112 8C (Found: MC,
274.0840. Calcd for C15H14O5: M, 274.0841); m/z 274
(26%, M), 232 (20, MKCH2CO) and 190 (100, 232-
CH2CO); nmax/cmK1 1757 (aryl acetate C]O); lmax/nm
298 (log 3 3.88), 312 (3.78) and 326.5 (3.64); dH 2.40 and
2.47 (each 3H, s, CH3CO2Ar), 3.98 (3H, s, CH3OAr) and
6.75–7.85 (5H, m, ArH).
and -80), 8.30 (1H, s, H-3), 8.49 (1H, s, H-30), 8.78 (1H, s,
OH at C-50) and 13.45 (1H, s, OH at C-8).
(c) The slowest-moving0 blue product crystallised from
chloroform to give 5,5 -dihydroxy-4,40-dimethoxy-2,20-
binaphthyl-1,10-quinone 19 (11 mg, 0.029 mmol, 37%) as
deep blue needles, mp 259–260 8C (decomp.) (Found: MC,
376.09433, C22H16O6 requires M, 376.0946); m/z 378 (45%,
MC2H), 376 (100, M), 361 (67, MKMe), 346 (20, 361-
Me) and 345 (40, MKMeO); nmax/cmK1 3340 (ArOH),
1605 (quinone C]O) and 1588 (aromatic C]C); lmax/nm
(CHCl3) 286 (log 3 4.18), 316infl (3.98) and 668 (4.28); dH
4.13 (6H, s, MeO at C-4 and -40), ca. 7.11 (2H, m, H-6 and
-60), ca. 7.36 (2H, m, H-7 and0 -70), ca. 7.76 (2H, m, H-8
and -80), 8.40 (2H, s, H-3 and -3 ) and 8.83 (2H, s, OH at C-5
and -50). This was identical with an authentic specimen
prepared from 4-methoxy-1,5-naphthylene diacetate by the
same procedure.
3.4.4. Oxidative coupling of 1-methoxynaphthylene-4,5-
diol 10 with 4-methoxy-naphthylene-1,5-diol 17. A
mixture of 4-methoxy-1,5-naphthylene diacetate 6 (27 mg,
0.10 mmol, containing 20% of 5-methoxy-1,4-naphthylene
diacetate 8) and 1-methoxy-4,5-naphthylene diacetate8
(10 diacetate) (22 mg, 0.085 mmol) was hydrolysed and
oxidatively coupled as above. Preparative TLC afforded
three blue products.
The mother-liquor from the above crystallisations, on being
subjected to TLC using chloroform, gave a solid which
afforded 5-methoxy-1,4-naphthoquinone 9 (2.5 mg) as
12
yellow needles, mp 184–185 8C (lit.,
186 8C) (Found:
(a). The fastest-moving compound crystallised from chloro-
form to give 8,80-dihydroxy-4,40-dimethoxy-2,20-
binaphthyl-1,10-quinone 12 as deep blue needles (10 mg,
0.027 mmol, 33%), mpO350 8C (lit.,6 (350 8C) (Found:
MC, 376.0947. C, 69.9; H, 4.0%. C22H16O6 requires: M
376.0947. C, 70.2; H, 4.3%); m/z 376 (50%, M), 361 (32,
MKMe), 346 (22, 361-Me), 345 (100, MKMeO) and 92
(30, C6H4O); nmax/cmK1 1578 (quinone C]O); lmax/nm
(CHCl3) 285 (log 3 4.40), 326infl (4.02), 507 (3.57), 664infl
(4.32) and 703 (4.40). This was identical with an authentic
specimen prepared from 1-methoxy-4,5-naphthylene
diacetate by the same procedure.
MC, 188.0476. C11H8O3 requires M, 188.0473); nmax/cmK1
1673 and 1666 (quinone C]O) and 1624 (aromatic C]C);
lmax/nm 245 (log 3 4.20), 328 (3.05) and 394 (3.58); dH 4.00
(3H, s, MeO at C-5), 6.67 (2H, s, H-2 and -3), ca. 7.32 (1H,
m, H-6) and ca. 7.49 (2H, m, H-7 and -8). This was identical
with an authentic specimen.12
3.4.5. Oxidative demethylation of the bisnaphthalene
indigos 12, 19 and 23. (a) The oxidation product obtained
from the symmetrical quinone 12 c0rystallised from l0ight
petroleum to give 8,80-dihydroxy-2,2 -binaphthyl-1,4:1 ,40-
diquinone 15 as red-brown needles (72%), mp 270–273 8C
(decomp.) (Found: MC, 346.0476. C, 69.1; H, 2.8%.
C20H10O6 requires M 346.0477. C, 69.4; H, 2.9%); m/z
346 (100%, M), 329 (17, MKOH), 290 (4, MK2CO), 289
(8, MKCO–CHO), 262 (5, 290-CO), 234 (3, 262-CO), 120
(10, C7H4O2)- and 92 (21, C6H4O); nmax/cmK1 1670, 1650
Reductive acetylation of the quinone 12 gave the corre-
sponding leucotetra-acetate 14 which crystallised from
ethanol in needles, mp 251.5–253.5 8C (Found: MC, 546.
C, 66.2; H, 5.0%. C30H26O10 requires M 546. C, 65.9; H,
4.8%); m/z 546 (0.5%, M), 504 (10), 462 (13), 420 (1.5) and
378 (25) (each MKnCH2CO), 444 (13, 462-H2O), 402 (100,
420-H2O), 387 (2, 402-Me), 360 (45, 378-H2O), 346 (11,
and 1635 (quinone C]O) and 1608 (aromatic C]C); lmax
/
nm 256infl (log 3 4.18), 274 (4.19),0434 (3.83) and 560infl
(3.24); dH 7.06 (2H, s, H-3 and -3 ), 7.33 (2H, dd, JZ5,
5 Hz, H-6 and -60), 7.70 (4H, dd, JZ1, 5 Hz, H-5, -50, -7 and
-70) and 11.73 (2H, s, OH at C-8 and -80).
402-2CO), 345 (11, 360-Me) and 331 (5, 346-Me); nmax
/
cmK1 1770 and 1758 (aryl acetate C]O) and 1598
(aromatic C]C); lmax/nm 242 (log 3 4.72), 257infl (4.38),
262infl (4.32), 307 (4.03), 317 (4.02) and 330 (3.95); dH
2.00 (6H, s, CH3CO2Ar at C-1 and -10), 2.35 (6H, s,
CH3CO2Ar at C-8 and -80), 3.98 (6H, s, CH3O at C-4 and
-40), 6.75 (2H, s, H-3 and -30), 7.18 (2H, dd, JZ1.5, 8 Hz,
H-7 and -70), 7.52 (2H, dd, JZ8, 8 0Hz, H-6 and -60) and 8.28
(2H, dd, JZ1.5, 8 Hz, H-5 and -5 ).
(b) The oxidation product from the unsymmetrical quinone
23 crystallised from light 0petroleum to give 50,8-dihydroxy-
2,20-binaphthyl-1,4:10,4 -diquinone 25 as red-brown
needles (70%), mp 247–250 8C (decomp.) (Found: MC,
346.0476. C20H10O6 requires M 346.0477); m/z 348 (10%,
MC2H), 346 (100, M), 329 (13, MKOH), 290 (6, MK
2CO), 289 (10, MKCO–CHO), 262 (7, 290-CO), 120 (8,
C7H4O2) and 92 (16, C6H4O); nmax/cmK1 1670 and 1638
(quinone C]O) and 1600 (aromatic C]C); lmax/nm
240infl (log 3 4.30), 266infl (4.27) and 434 (3.83); dH 7.02
and 7.05 (each 1H, s, H-3 and -30), ca. 7.32 (2H, m, H-60 and
-7), ca. 7.69 (4H, m, H-5, -6, -70 and -80), 11.74 (1H, s, OH at
C-8) and 11.84 (1H, s, OH at C-50).
(b) The next blue product crystallised from light petroleum
/chloroform to yield 50,8-dihydroxy-4,40-dimethoxy-2,20-
binaphthyl-1,10-quinone 23 (5 mg, 0.013 mmol, 17%) as
deep blue needles, mp 244–245 8C (decomp.) (Found: MC,
376.0946. C22H16O6 requires M, 376.0946); m/z 378 (19%,
MC2H), 376 (84, M). 361 (45, MKMe), 345 (100, MK
MeO); nmax/cmK1 3400 (hydrogen-bonded ArOH), 1595
and 1580 (quinone C]O); lmax/nm (CHCl3) 283 (log 3
4.36), 320infl (4.14), 514infl (3.69), 638infl (4.32) and 684
(4.41); dH 4.02 (3H, s, MeO at C-4), 4.15 (3H, s, hydrogen-
bonded MeO at C-40), 6.98–7.78 (6H, m, H-5, -6., -60, -7, -70
(c) The oxidation product from the symmetrical quinone 19
crystallised from light petroleum to give 5,50-dihydroxy-
2,20-binaphthyl-1,4:10,40-diquinone 21 as yellow plates

B. C. Maiti et al. / Tetrahedron 61 (2005) 6568–6574
6573
(65%), mp 267–270 8C (decomp.) (Found: MC, 346.0476.
C20H10O6 requires M, 346.0477); m/z 346 (100%, M), 329
(10, MKOH), 290 (3, MK2CO), 289 (8, MKCO–CHO),
262 (5, 290-CO), 234 (3, 262-CO), 120 (8, C7H4O2) and 92
(22, C6H4O); nmax/cmK1 1638 and 1622 (quinone C]O)
and 1602 (aromatic C]C); lmax/nm 247 (log 3 4.31),
267infl (4.27) and 438 (3.94); dH 7.05 (2H, s, H-3 and -30),
7.32 (2H, dd,0JZ5, 5 Hz, H-7 and -70), 7.68 (4H, dd, JZ1,
5 Hz, H-6, -6 , -8 and -80) and 11.83 (2H, s, OH at C-5 and
-50).
OH at C-8 and -80). This was identical with an authentic
specimen.13
(b) The oxidation product from the unsymmetrically
substituted 50,8-dihydroxy-4,40-dimethoxy-6,70-dimethyl-
2,20-binaphthyl-1,10-quinone 24 crystallised from light
petroleum giving 0 50,8-dihydroxy-6,70-dimethyl-2,20-
binaphthyl-1,4:10,4 -diquinone 26 (rotundiquinone14)
(93%) as orange-red needles, mp 239 8C (decomp.)
(Found: MC, 374.0789. C22H14O6 requires M, 374.0790);
m/z 374 (100%, M), 357 (21, MKOH), 318 (10, MK2CO),
317 (11, MKCO–CHO), 290 (13, 318-CO), 262 (3, 290-
CO), 134 (6, C8H6O2) and 106 (16, C7H6O); nmax/cmK1
1666 and 1643 (quinone C]O); lmax/nm 253 (log 3 4.16),
274infl (4.09) and 438 (3.81); dH 2.46 (6H, s, Me at C-6 and
-70), 6.98 (1H, s, H-3), 7.03 (1H, s, H-30), 7.13 and 7.15
(each 1H, br s, H-60 and -7), 7.50 and 7.52 (each 1H, br s,
H-5 and -80), 11.70 (1H. s, OH at C-8) and 11.80 (1H, s, OH
at C-50).
3.4.6. Oxidative coupling of 1-methoxy-7-methyl-4,5-
naphthylenediol 11 with 4-methoxy-7-methyl-1,5-
naphthylenediol 18. A mixture of 1-methoxy-7-methyl-
4,5-naphthylene diacetate8 (11 diacetate) (35 mg,
0.12 mmol) and 4-methoxy-7-methyl-1,5-naphthylene
diacetate8 (18 diacetate) (35 mg, 0.12 mmol) was
hydrolysed and oxidatively coupled as described above.
Three blue products resulted.
(c) The oxidation product from diosindigo B 20 crystallised
from light petroleum 0to 0give 5,50-dihydroxy- 7,70-dimethyl-
2,20-binaphthyl-1,4:1 ,4 -diquinone 22 (biramentaceone) as
orange-red needles (89%), mp 272 8C (decomp.) (Found:
MC, 374.0789. C22H14O6 requires M, 374.0790); m/z 376
(10%, MC2H), 374 (100, M), 357 (28, MKOH), 346 (4,
MKCO), 318 (10, 346-CO), 317 (14, 346-CHO), 303 (5,
318-Me), 290 (12, 318-CO), 262 (5, 290-CO), 187 (6,
(a) The fastest-moving compound crystallised from chloro-
form to yield 8,80-dihydroxy-4,40-dimethoxy-6.60-dimethyl-
2,20-binaphthyl-1,10-quinone (diosindigo A) 13 (19 mg,
0.047 mmol, 39%) as deep blue needles, mp 317 8C
(decomp.) (lit.,3 317 8C decomp.) identical with an authentic
specimen.
(b) The next product 0 crystallised from0 light petroleum
/chloroform to yield 5 , 8-dihydroxy-4,4 -dimethoxy-6,70-
dimethyl-2,20-binaphthyl-1,10-quinone 24 as deep blue
needles (8 mg, 0.020 mmol, 17%), mp 257–258 8C
(decomp.) (Found: MC, 404.1260. C24H20O6 requires M
404.1259); m/z 406 (16%, MC2H), 404 (67, M), 389 (56,
MKMe) and 373 (100, MKMeO); nmax/cmK1 3400
(ArOH) and 1588 (hydrogen-bonded quinone C]O);
lmax/nm (CHCl3) 292 (log 3 4.46), 322infl (4.23), 504infl
(3.67), 665infl (4.50) and 694 (4.54); dH 2.38 (6H, s, Me at
C-60and -70), 4.01 (3H, s, MeO at C-4), 4.13 (3H, s, MeO at
C-4 ), 6.80 (1H, br s, H-7), 6.94 (1H, br s, H-600), 7.10 (1H, br
s, H-5), 7.57 (1H, br s, H-80), 8.26 (1H, s, H-3 ), 8.47 (1H, s,
H-3), 8.69 (1H, s, OH at C-50) and 13.51 (1H, s, OH at C-8).
M
2C), 135 (6, C8H7O2), 134 (10, C8H6O2) and 106 (20,
C7H6O); nmax/cmK1 1665 and 1645 (quinone C]O); lmax
/
nm (EtOH C10% dioxan) 252 (log 3 4.26), 273infl (4.16)
and 444 (3.90); dH 2.46 (6H, s, Me at C-7 and -70), 7.01 (2H,
s, H-3 and 0-30), 7.13 (2H, br s, H-6 and -60), 7.500 (2H, br s,
H-8 and -8 ) and 11.80 (2H, s, OH at C-5 and -5 ). This was
identical with an authentic specimen15 of biramentaceone
which had mp 272 8C (decomp.).
3.5. Conversion of mamegakinone 16 into diosindigo
A 13
A mixture of mamegakinone 16 (5 mg, 0.013 mmol), tin(II)
chloride dihydrate (5 mg, 0.022 mmol), phosphoryl(V)
chloride (20 mg, 0.13 mmol), 4 M hydrochloric acid
(2 ml) and methanol (10 ml) was boiled under reflux
under nitrogen for 1 h, diluted with water, and extracted
with chloroform. A mixture of the chloroform solution and
lead(IV) oxide (200 mg, 0.97 mmol) was boiled under
reflux for 0.5 h, filtered and evaporated. The resulting blue
solid crystallised from chloroform to give diosindigo A 13
(5 mg, 0.012 mmol, 93%) identical with an authentic
specimen.
(c) The slowest-moving compound crystallised from chloro-
form to give 5,50-dihydroxy- 4,40-dimethoxy-7,70-dimethyl-
2,20-binaphthyl-1,10-quinone (diosindigo B) 20 (18 mg,
0.045 mmol, 37%) as deep blue needles, mp 275 8C
(decomp.) identical with an authentic specimen.8
3.4.7. Oxidative demethylation of the methyl-substituted
bisnaphthalene indigos 13, 20 and 24. (a) The oxidation
product from diosindigo A 13 crystallised from light
petroleum to give 8,80-dihydroxy-6,60-dimethyl- 2,20-
binaphthyl-1,4:10,40-diquinone 16 (mamegakinone) (75%)
as orange-red needles, mp 254–256 8C (decomp.) (lit.,13
256 8C decomp.) (Found: MC, 374.0793. C22H14O6
requires M, 374.0790); m/z 374 (100%, M), 357 (20, MK
OH), 318 (11, MK2CO), 317 (14, MKCO–CHO), 290 (13,
318-CO), 262 (6, 290-CO), 135 (5, C8H7O2), 134 (13,
C8H6O2) and 106 (25, C7H6O); nmax/cmK1 1661, 1642 and
1627 (quinone C]O); lmax/nm (EtOH C10% dioxan) 253
(log 3 4.27), 272infl (4.20) and 440 (3.85); dH 2.47 (6H, s,
Me at C-6 and -60), 6.98 (2H, s, H-3 and0-30), 7.13 (2H, br s,
H-7 and -70), 7.50 (2H, br s, H-5 and -5 ) and 11.69 (2H, s,
3.5.1. Oxidative coupling of 1-methoxy-7-methyl-4,5-
naphthylenediol 11 with 1-methoxy-2-methyl-4,5-
naphthylenediol 29. A mixture of 1-methoxy-7-methyl-
4,5-naphthylene diacetate (11 diacetate)8 (30 mg,
0.10 mmol) and 1-methoxy-2-methyl-4,5-naphthylene
diacetate (29 diacetate)8 (30 mg, 0.10 mmol) was
hydrolysed and oxidised as described above. TLC afforded
two products the faster-moving of which crystallised
from chloroform to give diosindigo A 13 (16 mg,
0.04 mmol, 76%) identical with an authentic specimen.
The slower-moving product crystallised from light

6574
B. C. Maiti et al. / Tetrahedron 61 (2005) 6568–6574
petroleum/chloroform to give 8,80-dihydroxy-4,40-
dimethoxy-30,6-dimethyl-2,20-binaphthyl-1,10-quinone 30
(4 mg, 0.01 mmol, 10%) as deep blue needles, mpO360 8C
(Found: (MKMe)C, 389.1023. C23H17O6 requires (MK
Me), 389.1025); m/z 404 (6%, M), 389 (16, MKMe), 388
(45, 389-H), 375 (6, MKCHO), 374 (75, 389-Me), 373
(100, MKMeO), 360 (14, 388-CO), 359 (56, 388-CHO),
358 (18, 389-MeO), 357 (16, 388-MeO), 345 (11, 373-CO)
and 343 (14, 374-MeO); nmax/cmK1 1580 and 1572
(hydrogen-bonded quinone C]O); lmax/nm (CHCl3) 291
(log 3 4.52), 337infl (4.23), 516infl (3.91) and 692 (4.49).
357-CO), 317 (9, 346-CHO), 187 (7, M2C), 149 (6,
C8H5O3), 121 (25, C7H5O2), 120 (20, C7H4O2) and 92
(33, C6H4O). This was identical (MS, UV and IR) with an
authentic specimen.16
Acknowledgements
We are indebted to Professor G. S. Sidhu and Dr. S. Natori
for specimens and to Dr. T. J. Lillie for experimental
assistance.
Reductive acetylation gave the corresponding leucotetra-
acetate 31 which crystallised from ethanol as needles
(Found: MC, 574.1841. C32H30O10 requires M, 574.1839);
m/z 574 (2%, M), 532 (20, MKCH2CO), 490 (22, 532-
CH2CO), 472 (5, 490-H2O), 448 (3, 490-CH2CO), 430 (100,
448-H2O), 415 (7, 430-Me), 406 (35, 448-CH2CO) and 388
(45, 406-H2O); nmax/cmK1 1775 and 1765 (aryl acetate
C]O) and 1610 (aromatic C]C); lmax/nm 242 (log 3
4.84), 253infl (4.70), 282infl (4.35), 290infl (4.34), 313infl
(4.21) and 328infl (4.07); dH 1.94 and 2.00 (each 3H, s,
MeCO2Ar at C-1 and -10), 2.34 (6H, s, MeCO2Ar at C-8 and
-80), 2.45 and 2.52 (each 3H, s, Me at C-30 and -6), 3.93 and
3.95 (each 3H, s, MeO at C-4 0and -40), 6.66 (1H, s, H-3),
6.98–7.10 (2H, m, H-7 and -7 ), 7.25–7.48 (1H, m, H-60)
and 7.98–8.14 (2H, m, H-5 and -50).
References and notes
1. Russig, F. J. Prakt. Chem. 1900, 62, 30–60.
2. Goldschmidt, S.; Wessbecher, H. Ber. 1928, 61, 372–377.
3. Musgrave, O. C.; Skoyles, D. J. Chem. Soc., Perkin Trans. 1
1974, 1128–1136.
4. Maiti, B. C.; Musgrave, O. C. J. Chem. Soc., Perkin Trans. 1
1986, 675–681.
5. Maiti, B. C.; Musgrave, O. C.; Skoyles, D. J. Chem. Soc.,
Chem. Commun. 1976, 244–245.
6. Laatsch, H. Liebigs Ann. Chem. 1980, 1321–1347.
7. Thomson, R. H. Naturally Occurring Quinones III; Chapman
and Hall: London, 1987; pp 165, 166.
3.5.2. Oxidative coupling of 1-methoxy-2-methyl-4,5-
naphthylenediol 29. 1-Methoxy-2-methyl-4,5-naphthylene
diacetate (29 diacetate)8 (0.5 g, 1.74 mmol) was hydrolysed
and oxidised with lead(IV) oxide as described above.
Separation of the products by TLC using chloroform on
silica gel containing oxalic acid gave, as the major product,
plumbagin 32 (73 mg, 0.39 mmol, 23%), identical with an
authentic specimen.
8. Maiti, B. C.; Musgrave, O. C.; Skoyles, D. Tetrahedron 2005,
61, 1765–1771.
9. van der Vijver, L. M.; Gerritsma, K. W. Phytochemistry 1974,
13, 2322–2323.
10. Lillie, T. J.; Musgrave, O. C.; Skoyles, D. J. Chem. Soc.,
Perkin Trans. 1 1976, 2155–2161.
11. Willstatter, R.; Wheeler, A. S. Ber. 1914, 47, 2796–2801.
12. Hayes, N. F.; Thomson, R. H. J. Chem. Soc. 1955, 904–907.
13. Yoshihira, K.; Tezuka, M.; Natori, S. Chem. Pharm. Bull.
1971, 19, 2308–2313.
The minor product crystallised from light petroleum to give
8,80-dihydroxy-3,300-dimethyl-2,20-binaphthyl-1,4:10,40-
diquinone 33 (3,3 -biplumbagin) (1 mg, 0.0027 mmol,
0.3%) as yellow needles, mp 214–216 8C (lit.,16 214–
216 8C); m/z 374 (100%, M), 373 (9, MKH), 359 (92,
MKMe), 357 (56, MKOH), 346 (7, MKCO), 345 (9,
MKCHO), 331 (31, 359-CO), 330 (7, 345-Me), 329 (13,
14. van der Vijver, L. M.; Gerritsma, K. W. Pharm. Weekbl. 1976,
111, 1273–1285; Chem. Abstr. 1977, 86, 68368g.
15. Krishnamoorthy, V.; Thomson, R. H. Phytochemistry 1969, 8,
1591–1594.
16. Sankaram, A. V. B.; Sidhu, G. S. Indian J. Chem. 1974, 12,
519–520.