A simple method for the synthesis of 4-aryl-9-oxynaphthofuranone lignans

Article abstract of DOI:10.1039/a605288f

The 9-aryl-4-oxynaphthofuran-1(3H)-one system is generally synthesized in two steps from α-aryl-o-toluic acid derivatives. The method involves a tandem conjugate addition-Dieckmann type condensation between α-lithiated α-aryl-o-toluic acid derivatives and

Full text of DOI:10.1039/a605288f

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A simple method for the synthesis of 4-aryl-9-oxynaphthofuranone
lignans
Kazuhiro Kobayashi,* Kouji Maeda, Tomokazu Uneda, Osamu Morikawa and
Hisatoshi Konishi
Department of Materials Science, Faculty of Engineering, Tottori University,
Tottori 680, Japan
The 9-aryl-4-oxynaphthofuran-1(3H )-one system is generally synthesized in two steps from á-aryl-
o-toluic acid derivatives. The method involves a tandem conjugate addition–D ieckmann type
condensation between á-lithiated á-aryl-o-toluic acid derivatives and 2-furan-2(5H )-one as a key step
followed by simple dehydrogenation or dehydration, and can be applied to the synthesis of two natural
lignans (neojusticidin A and neojusticidin B).
We have recently reported the synthesis of 9-arylnaphtho[2,3-
c]furan-1(3H)-one derivatives including natural lignans, such as
collinusin, dehydrodimethylretrodendrin and justicidin B.1f The
key step in our procedure was the reaction of o-aroylbenzyl-
lithiums with furan-2(5H)-one. As a extension of this study we
now describe a simple and general approach to the synthesis of
naphtho[2,3-c]furan-1(3H)-one derivatives carrying a methoxy
(or hydroxy) substituent at the 9-position and an aryl substitu-
ent at the 4-position, including natural lignans such as neojusti-
cidin A 14 and neojusticidin B 15, which is based on reactions
of α-lithiated α-aryl-o-toluic acid derivatives with 2-furan-
2(5H)-one and conceptually similar to that of Harrowven.1c
These natural products were first isolated from Justicia procum-
bens Linn. var. leucantha Honda and characterized by Okigawa,
Maeda and Kawano in 1970.2 Few methods have been reported
for the simple construction of this skeleton,3 though a notable
approach to neojusticidin B 15 from 3,4:3Ј,4Ј-bis(methylene-
dioxy)benzophenone involving nine steps has been recorded by
Horii, Tsujiuchi, Kanai and Momose,3c and a number of inter-
esting methods have been reported to prepare other types of
arylnaphthofuranone lignans.1 So we have been aiming to
Scheme 1 Reagents and conditions: i, 2LDA, Ϫ78 ЊC, THF; ii, furan-
2(5H)-one, Ϫ78 ЊC to RT; iii, 10% Pd–C, p-cymene, reflux
develop a simple and general method to synthesize this class of
compounds.
We envisioned two potential entries to this system by start-
ing with readily available materials. One approach (Scheme 1),
in which interaction of α-lithiated product of ethyl o-
benzylbenzoate 1 with furan-2(5H)-one leading the dihydro
derivative 2 followed by dehydrogenation should give us a rapid
access to the system 3, parallels the MIRC route to oxyaromatic
compound utilizing ortho-toluate carbanions.4 The second
approach (Scheme 2) would involve treating 3-aryl-3-lithio-
isobenzofuran-1(3H)-ones, lithio derivatives of 3-arylisobenzo-
furan-1(3H)-ones 4–8, with furan-2(5H)-one which would be
expected to give the desired compounds 10–15 by the sub-
sequent dehydration of the resulting 4-hydroxy derivatives 9.
Reactions of the benzylic anions of isobenzofuran-1(3H)-one5
and its 3-substituted derivatives (such as CN 6 or SO2Ph 7) with
Michael acceptors have been reported to give polycyclic com-
pounds, some of which were elegantly elaborated to provide
syntheses of useful natural products.8 It is somewhat surprising
that there have been so far few reports on the synthesis utilizing
the benzylic anions of 3-arylisobenzofuran-1(3H)-ones.9,10
These approaches required the efficient preparation of the
starting materials ethyl o-benzylbenzoate 1 and its substituted
derivatives, and 3-arylisobenzofuranones 4–8. Compound 1
was prepared by the normal esterification of commercially
available o-benzylbenzoic acid. In order to obtain its substi-
tuted derivatives and compounds 4–8 we initially attempted the
route developed by Arnold, Mellows and Sammes.11 Unfort-
unately, we were not able to obtain these compounds in good
isolated yields and a modifying procedure was therefore
attempted. After several unsuccessful attempts, it was found
that the use of the corresponding dimethyl acetals in place of 2-
bromobenzaldehyde methylene acetals produced the desired
compounds in satisfactory yields. Thus, bromine–lithium ex-
change between the appropriately substituted 2-bromobenzalde-
hyde dimethyl acetals and butyllithium followed by in situ
trapping of the resulting lithium compounds with aromatic
aldehydes afforded the corresponding benzhydrol derivatives,
which were transformed into the corresponding lactol deriv-
atives upon exposure to aq. H2SO4. Oxidation of these lactols
with Na2Cr2O7 gave the desired lactones 4–8 (30–50% yields
from o-bromobenzaldehydes), hydrogenolysis of which then
afforded substituted o-(arylmethyl)benzoic acids (quantitative).
Finally, the usual acidic esterification of these carboxylic acids
afforded the corresponding esters (80–90%).
The o-toluate 1 was lithiated with 2 equivalents of lithium
diisopropylamide (LDA) in THF at Ϫ78 ЊC to give a solution
of the deep-red α-anion, which was then treated with furan-
2(5H)-one. The characteristic colour disappeared immediately,
J. Chem. Soc., Perkin Trans. 1, 1997
443

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Table 1 Preparation of 4-aryl-9-oxynaphtho[2,3-c]furan-1(3H)-one
derivatives
Starting Dehydration Methylation
Product
Entry material conditionsa
conditionsb
(yield/%)c
1
2
3
4
5
6
7
1
4
4
5
6
7
8
—
A
A
A
A
B
—
—
A
A
A
B
3 (56)
10 (51)
11 (51)
12 (62)
13 (56)
14 (50)d
15 (52)e
B
B
a
b
A: I2, CHCl3, B: SOCl2, pyridine. A: CH2N2, Et2O, B: MeI, K2CO3,
acetone. c Yields refer to overall yields of purified products (preparative
d
TLC on SiO2) starting from 1 and 4–8. Neojusticin A (i.e., justicidin
D, ref. 2). e Neojusticin B (i.e., justicidin C, ref. 2).
furanone carbonyls appeared to be rather sluggish at this tem-
perature, and overnight stirring at room temperature was
required to afford the corresponding dihydroxynaphtho-
furanone adducts 9 satisfactorily. Attempts to speed up the
cyclization by the addition of co-solvent (TMEDA or HMPA)
were met with a considerable lowering in the yield of the prod-
ucts. It was also found that the use of 2 equivalents of LDA was
required for satisfactory production of the products. These
products were also not further purified because of the reasons
described for the adduct 2. Their IR spectra (~3350, ~1780,
~1720 and ~1670 cmϪ1) showed that each of these products was
an equilibrium mixture of 9A and 9B. These were then immedi-
ately subjected to dehydration with iodine (followed by O-
methylation with diazomethane for the preparation of 11–13)
to give the expected products 10–13 in reasonable isolated
yields from the arylisobenzofuranones 4–6 (see Table 1, entries
2, 3, 4 and 7, respectively).
Scheme 2 Reagents and conditions: i, 2LDA, Ϫ78 ЊC, THF; ii, furan-
2(5H)-one, Ϫ78 ЊC to RT; iii, I2, CHCl3, RT or SOCl2, pyridine, RT;
iv, CH2N2, 0 ЊC or K2CO3, MeI, acetone, reflux
Having established a simple and efficient route to 9-methoxy-
4-arylnaphtho[2,3-b]furan-1(3H)-ones, we next turned our
attention to the corresponding reactions using 3-(benzo-
dioxolyl)isobenzofuran-1(3H)-ones 7 and 8 yielding natural
lignans neojusticidin A 14 and neojusticidin B 15, respectively.
However, the reactions starting from compounds 7 and 8 under
similar conditions described above gave rise to the desired
products 14 and 15 only in considerably lower yields (ca. 15%
yield each). The lower yield may be ascribed to the instability of
the methylenedioxy moiety under these reaction conditions. We
reasoned that dehydration of the corresponding adducts with
thionyl chloride in pyridine, followed by the subsequent
O-methylation with iodomethane in acetone in the presence of
potassium carbonate, should not affect the methylenedioxy
moiety and afford the desired products in good yields. As
expected, dehydration and O-methylation under these modified
conditions proceeded more cleanly than those under the initial
ones to give compounds 14 and 15 in satisfactory yields (entries
indicating that the addition of the anion to furan-2(5H)-one in
the manner of 1,4-addition was complete. The following intra-
molecular cyclization of the resulting enolate intermediate pro-
ceeded smoothly by allowing the reaction mixture to warm up
to room temperature to afford the dihydronaphthofuranone
adduct 2. With 1 equivalent of LDA the sequence appeared to
proceed not so cleanly as judged by TLC of the reaction mix-
ture, and the product after dehydrogenation 3 (vide infra) was
obtained only in a low yield. Every attempt to isolate this
adduct in a pure form resulted in failure, because it was not only
sparingly soluble in organic solvents, such as diethyl ether or
dichloromethane, but also unstable under purification con-
ditions. Therefore, after the production of compound 2 was
briefly confirmed on the basis of its IR spectrum (3354, 1781,
1720 and 1671 cmϪ1), which seemed to indicate that it was an
equilibrium mixture of 2A and 2B, it was subjected to the next
step without any purification. Dehydrogenation of 2 was suc-
cessively achieved with 10% Pd on activated carbon in refluxing
p-cymene to give 4-phenyl-9-hydroxynaphtho[2,3-b]furan-
1(3H)-one 3 in a satisfactory yield (entry 1 in Table 1). We next
subjected the derivatives of 1, carrying methoxy substituents on
the benzene rings, to this sequence. However, the reactions
using these starting materials each gave an intractable mixture
of products. Although we have no firm explanation at this
point, this may be attributed to the lower reactivity of the tolu-
ate carbonyl group caused by the methoxy substituents. These
results indicate that the strategy of Scheme 1 is unlikely to pro-
vide a general production of 4-aryl-9-oxynaphthofuranone
derivatives, and we turned our attention to an alternative
approach starting with 3-arylisobenzofuranones 4–8.
1
5 and 6 in Table 1, respectively). IR and H NMR data as well
as melting points for these products are consistent with those
reported in the literature.2a
The methodology described in this paper allows very rapid
access to the 4-aryl-9-oxynaphtho[2,3-c]furan-1(3H)-one nu-
cleus from readily available starting materials, and is applicable
to the synthesis of natural lignans, neojusticidin A and neojus-
ticidin B. Although the yields of the products are not so high,
the convenience of this approach makes it attractive.
Experimental
The lithiation products of the 3-arylisobenzofuranones 4–6,
generated in situ by the treatment with 2 equivalents of LDA in
THF at Ϫ78 ЊC, were also treated with furan-2(5H)-one. The
addition of the anions to furan-2(5H)-one in the 1,4-addition
manner proceeded smoothly. However, the intramolecular con-
densation of the resulting enolate intermediates with the benzo-
The mps were recorded with a Laboratory Devices MEL-
TEMP II melting point apparatus and are uncorrected. The IR
spectra were determined for KBr disks with a Perkin-Elmer
1600 Series FT IR spectrometer. The H NMR spectra were
determined using SiMe4 as an internal reference with a JEOL
JNM-GX270 FT NMR spectrometer operating at 270 MHz in
1
444
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CDCl3. J Values are given in Hz. Low-resolution mass spectra
were recorded on a JEOL AUTOMASS 20 spectrometer or a
JEOL JMS-AX505 HA spectrometer. Column chromatography
was carried out on Merck Kieselgel 60 F254. Thin layer chrom-
Ϫ78 ЊC (cooling bath temperature), under an argon atmos-
phere, was added a solution of the benzofuranone 4 (0.41 g, 1.5
mmol) in THF (2.2 cm3). After 5 min, furan-2(5H)-one (0.25 g,
3.0 mmol) was added dropwise via a syringe to the deep red
solution of the resulting carbanion; the solution turned orange
immediately and was allowed to warm to room temperature.
Stirring was continued overnight, after which time the reaction
mixture was worked up in a similar manner as described above.
The crude product was dissolved in CHCl3 (9 cm3) containing
iodine (75 mg, 0.30 mmol) and the mixture was stirred for 10 h
under an argon atmosphere. The resulting mixture was diluted
with CHCl3 (30 cm3), washed successively with aqueous
Na2S2O3 and brine, dried (MgSO4), and evaporated to yield a
yellow solid. Purification of this by preparative TLC on SiO2
afforded the 9-hydroxynaphthofuranone 10 (0.26 g, 51%) as a
white solid: Rf 0.48 (1:2, EtOAc–hexane); mp 173–173.5 ЊC
(Et2O–CHCl3) (Found: C, 71.15; H, 4.8. C20H16O5 requires C,
71.4; H, 4.8%); νmax/cmϪ1 3407 and 1729; δH 3.88 (3 H, s), 3.97
(3 H, s), 5.28 (1 H, d, J 14.6), 5.30 (1 H, d, J 14.6), 6.85 (1 H, d,
J 1.8), 6.87 (1 H, dd, J 8.3 and 1.8), 7.02 (1 H, dd, J 1.8), 7.55–
7.65 (2 H, m), 7.75–7.8 (1 H, m), 8.4–8.5 (1 H, m) and 8.61 (1 H,
s); m/z 336 (M+, 79%) and 262 (100).
atography (TLC) was carried out on Merck Kieselgel 60 PF254
.
All of the solvents used were dried over appropriate drying
agents and distilled under argon prior to use. Furan-2(5H)-one
was commercially available.
Ethyl o-benzylbenzoate 112
This compound was prepared by the acid-catalysed esterifi-
cation of commercially available o-benzylbenzoic acid, bp 170–
180 ЊC (bath temp.)/0.7 Torr; νmax/cmϪ1 1717; δH 1.29 (3 H, t, J
7.3), 4.28 (2 H, q, J 7.3), 4.38 (2 H, s), 7.2–7.3 (7 H, m), 7.41 (1
H, dd, J 7.6 and 1.5) and 7.88 (1 H, dd, J 7.6 and 1.5).
3-(3,4-Dimethoxyphenyl)isobenzofuran-1(3H)-one 4,13 5,6-
dimethoxy-3-phenylisobenzofuran-1(3H)-one 5,14 5,6-dimethoxy-
3-(3,4-dimethoxyphenyl)isobenzofuran-1(3H)-one 6, 7-(1,3-
benzodioxol-5-yl)furo[3,4-f]-1,3-benzodioxol-5(7H)-one 711 and
5,6-dimethoxy-3-(1,3-benzodioxol-5-yl)isobenzofuran-1(3H)-one
89
These compounds were prepared by a modification (using
dimethyl acetals in place of ethylene acetals) of the method
reported by Sammes et al.11 Data for these compounds are as
follows. Compound 4: mp 145–146 ЊC (hexane–Et2O) (lit.,13
148 ЊC); νmax/cmϪ1 1743; δH 3.81 (3 H, s), 3.88 (3 H, s), 6.36 (1
H, s), 6.68 (1 H, s), 6.86 (2 H, s), 7.33 (1 H, d, J 7.6), 7.56 (1 H,
dd, J 7.6 and 7.3), 7.66 (1 H, dd, J 7.6 and 7.3) and 7.97 (1 H, d,
J 7.6). Compound 5: mp 137–137.5 ЊC (benzene–Et2O) (lit.,14
112 ЊC); νmax/cmϪ1 1742; δH 3.88 (3 H, s), 3.96 (3 H, s), 6.28 (1
H, s), 6.68 (1 H, s) and 7.25–7.4 (6 H, m). Compound 6: mp
180–181 ЊC (hexane–CH2Cl2) (Found: C, 65.2; H, 5.6. C18H18O6
requires C, 65.45; H, 5.5%); νmax/cmϪ1 1750; δH 3.81 (3 H, s),
3.89 (6 H, s), 3.97 (3 H, s), 6.24 (1 H, s), 6.65–6.7 (2 H, m), 6.86
(1 H, d, J 8.8), 6.87 (1 H, d, J 8.8) and 7.35 (1 H, s). Compound
7: mp 145–146 ЊC (MeOH) (lit.,11 146–147 ЊC). Compound 8:
4-(3,4-Dimethoxyphenyl)-9-methoxynaphtho[2,3-c]furan-1(3H)-
one 11
The hydroxynaphthofuranone 10 (0.13 g, 0.4 mmol) was treated
with diazomethane (25 mmol) in Et2O (20 cm3) at 0 ЊC for 3 h to
give, after purification by preparative TLC on SiO2, the 9-
methoxynaphthofuranone 11 in almost quantitative yield, Rf
0.69 (1:1, EtOAc–hexane); mp 219–221 ЊC (Et2O–CHCl3)
(Found: C, 71.95; H, 5.2%. C21H18O5 requires C, 72.0; H,
5.2%); νmax/cmϪ1 1765; δH 3.87 (3 H, s), 3.98 (3 H, s), 4.42 (3 H,
s), 5.18 (1 H, d, J 12.5), 5.21 (1 H, d, J 12.5), 6.85 (1 H, d, J 1.8),
6.90 (1 H, dd, J 8.3 and 1.8), 7.03 (1 H, d, J 8.3), 7.55–7.6 (2 H,
m), 7.7–7.8 (1 H, m) and 8.45–8.55 (1 H, m); m/z 350 (M+,
100%).
mp 157–157.5 ЊC (hexane–CH2Cl2) (lit.,9 157.5–158 ЊC); νmax
/
6,7,9-Trimethoxy-4-phenylnaphtho[2,3-c]furan-1(3H)-one 12
This compound was prepared from the benzofuranone 5 as
described for the preparation of the 9-methoxynaphtho-
furanone 11 without isolation of the corresponding 9-hydroxy
derivative; Rf 0.61 (1:1, EtOAc–hexane); mp 147–148 ЊC
(Et2O–CHCl3) (Found: C, 71.7; H, 4.9. C21H18O5 requires C,
72.0; H, 5.2%); νmax/cmϪ1 1749; δH 3.79 (3 H, s), 4.06 (3 H, s),
4.39 (3 H, s), 5.12 (2 H, s), 6.95 (1 H, s), 7.35–7.4 (2 H, m), 7.45–
7.6 (3 H, m) and 7.7–7.75 (1 H, m); m/z 350 (M+, 100%).
cmϪ1 1761; δH 3.90 (3 H, s), 3.96 (3 H, s), 5.97 (2 H, s), 6.19 (1 H,
s), 6.60 (1 H, s), 6.67 (1 H, s), 6.82 (2 H, br s) and 7.33 (1 H, s).
9-Hydroxy-4-phenylnaphtho[2,3-c]furan-1(3H)-one 3
To a stirred solution of LDA (2 mmol) in dry THF (2.5 cm3) at
Ϫ78 ЊC (cooling bath temperature) under argon, was added
ethyl o-benzylbenzoate 1 (0.24 g, 1.0 mmol) dropwise via a
syringe. The deep-red solution of the resulting carbanion
was stirred for 5 min, after which furan-2(5H)-one (0.17 g, 2.0
mmol) was added dropwise to it via a syringe. The deep-red
colour turned into yellow immediately. The reaction mixture
was then allowed to warm to room temperature. Diethyl ether
(10 cm3) and saturated aqueous NH4Cl (10 cm3) were added to
the mixture after which the layers were separated, and the
aqueous phase was extracted with Et2O (3 × 10 cm3). The com-
bined organic layers were washed with brine, dried (MgSO4),
and evaporated to give a residue (0.40 g). p-Cymene (8.0 cm3)
and 10% palladium-on-activated carbon (0.11 g, 1.0 mg) were
added to the residue and the mixture was heated under reflux
for 3 h. After cooling of the mixture to room temperature the
catalyst was filtered off, and the solvent was removed under
reduced pressure. Separation of the residue by preparative TLC
on SiO2 gave the 9-hydroxynaphthofuranone 3 (0.16 g, 56%)
as a white solid: Rf 0.66 (1:3 EtOAc–hexane); mp 180 ЊC
(decomp.) (hexane–CHCl3) (Found: C, 78.25; H, 4.3. C18H12O3
requires C, 78.25; H, 4.4%); νmax/cmϪ1 3424 and 1745; δH 5.27 (2
H, s), 7.35 (1 H, dd, J 7.9 and 1.6), 7.45–7.65 (6 H, m), 7.7–7.75
(1 H, m), 8.4–8.45 (1 H, m) and 8.65 (1 H, br); m/z 276 (M+,
96%) and 202 (100).
4-(3,4-Dimethoxyphenyl)-6,7,9-trimethoxynaphtho[2,3-c]furan-
1(3H)-one 13
This compound was prepared from the benzofuranone 7 as
described for the preparation of the 9-methoxynaphtho-
furanone 11 without isolation of the corresponding 9-hydroxy
derivatives; Rf 0.43 (1:1, EtOAc–hexane); mp 131–132 ЊC
(Et2O–CH2Cl2) (Found: C, 67.1; H, 5.4. C23H22O7 requires C,
67.3; H, 5.4%); νmax/cmϪ1 1756; δH 3.81 (3 H, s), 3.88 (3 H, s),
4.07 (3 H, s), 4.39 (3 H, s), 5.14 (1 H, d, J 12.0), 5.16 (1 H, d, J
12.0), 6.8–6.95 (2 H, m), 7.0–7.05 (2 H, m) and 7.71 (1 H, s); m/z
410 (M+, 100%).
9-(1,3-Benzodioxol-5-yl)-5-methoxyfuro[3Ј,4Ј:6,7]naphtho-
[2,3-d]-1,3-dioxol-6(8H)-one (Neojusticin A) 14
The benzofuranone 7 (0.15 g, 0.50 mmol) was lithiated, treated
with furan-2(5H)-one (84 mg, 1.00 mmol) and the mixture
worked up in a manner similar to that described for the prepar-
ation of the 9-hydroxynaphthofuranone 10. The crude product
(0.17 g) was dissolved in THF (5 cm3) containing pyridine (0.3
cm3) under an argon atmosphere. SOCl2 (0.12 g, 1.0 mmol) was
then added to the mixture and stirring was continued for 18 h at
room temperature. The mixture was evaporated under reduced
pressure. A solution of the residue (0.17 g) in acetone (12 cm3)
4-(3,4-Dimethoxyphenyl)-9-hydroxynaphtho[2,3-c]furan-1(3H)-
one 10
To a stirred solution of LDA (3.0 mmol) in THF (3.8 cm3) at
J. Chem. Soc., Perkin Trans. 1, 1997
445

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Lett., 1965, 4167; 1967, 3821; (b) Z. Horii, K. Ohkuma, S. Kim and
containing K2CO3 (1.6 g, 12 mmol) and MeI (1.6 g, 11 mmol)
was heated under reflux for 11 h after which it was filtered and
the filtrate was evaporated. The residue was partitioned
between water and CHCl3 (20 cm3 each). The organic layer was
separated, dried (MgSO4) and evaporated to give a yellow solid.
Purification of this by preparative TLC gave neojusticidin A 14
(95 mg, 50%) as a white solid, Rf 0.47 (1:1, EtOAc–hexane); mp
271–272 ЊC (Et2O–CHCl3) (lit.,2a 273–275 ЊC); νmax/cmϪ1 1761;
δH 4.33 (3 H, s), 5.11 (1 H, d, J 14.9), 5.12 (1 H, d, J 14.9), 6.05–
6.1 (4 H, m), 6.75 (1 H, dd, J 8.7 and 1.8), 6.77 (1 H, s), 6.95 (1
H, d, J 8.7), 6.99 (1 H, s) and 7.71 (1 H, s); m/z 378 (M+, 100%).
T. Momose, J. Chem. Soc., Chem. Commun., 1968, 653; (c) Z. Horii,
M. Tsujiuchi, K. Kanai and T. Momose, Chem. Pharm. Bull., 1977,
25, 1803; (d) J. Krepelka, I. Vancurova and J. Holubek, Collect.
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4 e.g. F. M. Hauser and R. Rhee, J. Am. Chem. Soc., 1977, 99, 4533;
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Tetrahedron Lett., 1992, 33, 1655.
5 W. Trueb and G. H. Eugster, Helv. Chim. Acta, 1972, 55, 969;
N. J. P. Broom and P. G. Sammes, J. Chem. Soc., Chem. Commun.,
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6 G. A. Kraus and H. Sugimoto, Tetrahedron Lett., 1978, 2263;
J. N. Freskos and J. S. Swenton, J. Chem. Soc., Chem. Commun.,
1985, 658; B. L. Chenard, M. G. Dolson, A. D. Sercel and
J. S. Swenton, J. Org. Chem., 1984, 49, 318; R. A. Russell, A. I. Day,
B. A. Pilley, P. J. Leavy and R. N. Warrener, J. Chem. Soc., Chem.
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7 F. M. Hauser and R. P. Rhee, J. Org. Chem., 1978, 43, 180;
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4-(1,3-Benzodioxol-5-yl)-6,7,9-trimethoxynaphtho[2,3-c]furan-
1(3H)-one (Neojusticin B) 15
This compound was prepared from the benzofuranone 8 as
described for the preparation of neojusticidin A 14. Data for
15, Rf 0.58 (1:1, EtOAc–hexane); mp 265–268 ЊC (Et2O–
CHCl3) (lit.,2a 262–265 ЊC); νmax/cmϪ1 1754; δH 3.84 (3 H, s),
4.06 (3 H, s), 4.38 (3 H, s), 5.13 (2 H, s), 6.06 (1 H, d, J 1.5), 6.09
(1 H, d, J 1.5), 6.80 (1 H, dd, J 8.7 and 1.8), 6.81 (1 H, s), 6.97 (1
H, d, J 8.7), 6.99 (1 H, s) and 7.70 (1 H, s); m/z 394 (M+, 100%).
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Acknowledgements
We wish to thank Mrs Miyuki Tanmatsu (this Department) for
help in determining the mass spectra.
References
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Paper 6/05288F
Received 29th July 1996
Accepted 10th October 1996
3 For syntheses of compounds having this skeleton, see (a)
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446
J. Chem. Soc., Perkin Trans. 1, 1997