Diels-Alder reactions of chromone-3-carboxaldehydes with ortho-benzoquinodimethane. New synthesis of benzo[b]xanthones

Article abstract of DOI:10.1016/S0040-4020(01)01131-0

An efficient new route to the benzo[b]xanthone system has been developed and applied to the synthesis of several new derivatives. The cycloaddition reactions of chromone-3-carboxaldehydes 12, reacting as dienophiles, with ortho-benzoquinodimethane 7 gave a diastereomeric mixture of cycloadducts 8 and 9. The formation of these compounds results from the Diels-Alder reactions of 12 and 7 followed by the in situ deformylation. The oxidation of adducts 8 and 9 with dimethyl sulfoxide in the presence of iodine gave the novel benzo[b]xanthones 11 in good yields.

Full text of DOI:10.1016/S0040-4020(01)01131-0

TETRAHEDRON
Pergamon
Tetrahedron 58 (2002) 105±114
Diels±Alder reactions of chromone-3-carboxaldehydes with
ortho-benzoquinodimethane. New synthesis of benzo[b]xanthones
p
Angela Sandulache, Artur M. S. Silva and Jose A. S. Cavaleiro
Â
Department of Chemistry, University of Aveiro, Campus Universitario de Santiago, 3810-193 Aveiro, Portugal
Received 2 August 2001; revised 19 September 2001; accepted 12 November 2001
AbstractÐAn ef®cient new route to the benzo[b]xanthone system has been developed and applied to the synthesis of several new
derivatives. The cycloaddition reactions of chromone-3-carboxaldehydes 12, reacting as dienophiles, with ortho-benzoquinodimethane 7
gave a diastereomeric mixture of cycloadducts 8 and 9. The formation of these compounds results from the Diels±Alder reactions of 12 and 7
followed by the in situ deformylation. The oxidation of adducts 8 and 9 with dimethyl sulfoxide in the presence of iodine gave the novel
benzo[b]xanthones 11 in good yields. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
followed by oxidation constitute a new method for the
synthesis of novel benzo[b]xanthones.
The enone moiety of the parent chromone does not function
as dienophile in cycloaddition reactions. However, the
presence of an electron-withdrawing substituent at C-3
enhances the dienophilicity of such 2,3-double bond.
These 3-substituted chromones are very versatile molecules,
reacting as Michael acceptors, with concomitant opening of
the pyrone ring; some of them can react as heterodienes and
as dienophiles. The majority of the reactions of this type of
chromones are nucleophilic additions leading mainly to new
heterocyclic compounds as condensation products.1
The great interest on xanthones is due to their abundance in
nature5 and mainly to their important biological properties,
such as inhibitors of monoamineoxygenase enzymes
(MAO-A and MAO-B),5 acting as anti-in¯ammatory, anti-
oxidant and anti-ulcer agents,6 as bronchodilatators in the
treatment of asthma7 and also as in vivo and in vitro anti-
tumour drugs.8 However the most prominent activities of
this type of compounds are shown by some xanthone
based analogues of the anthracycline anti-tumour agents9
and the antibiotic bikaverin 1, a natural fungal metabolite
with a benzo[b]xanthone skeleton.10 Some synthetic
benzo[b]xanthone analogues like 2, 3 and 4 (Scheme 1)
proved to be cytotoxic in vitro against a human breast
cancer MCF-7 cell line11 and against leukaemia L1210
cells.12
Although chromone-3-carboxaldehydes constitute the most
studied class of chromones bearing electron-withdrawing
substituent at C-3,2 their use as 2p components in cyclo-
addition reactions are scarce. They have been only used as
dienophiles in Diels±Alder reactions with electron-rich
dienes (2,3-dimethyl-1,3-butadiene and 1-methoxy-3-
(trimethylsilyloxy)-1,3-butadieneÐDanishefsky's diene),
giving xanthone-type compounds.3 Chromones bearing a
3-cyano substituent have also been used as dienophiles
in the same type of cycloaddition reactions with the
Danishefsky's diene, in order to prepare xanthone deriva-
tives possessing important biological activities.4 We
describe here for the ®rst time Diels±Alder reactions of
chromone-3-carboxaldehydes with ortho-benzoquino-
dimethane, followed by oxidation of the formed cyclo-
adducts, leading to benzo[b]xanthones. Our results
con®rm that chromone-3-carboxaldehydes can be used as
dienophiles; the corresponding cycloaddition reactions
General synthetic approaches to xanthones involve the
connection of two aryl fragments to form the internal
pyranone ring.9,11,13 Besides these classical syntheses,
other methods have been also developed, such as cyclo-
additon reactions of 2-styrylchromones with appropriate
dienophiles14 and photooxidative cyclizations of 2-styryl-
chromones.15 Other synthesis of benzo[b]xanthone type
compounds have been carried out by photooxidative
cyclizations of appropriate styrylxanthones,16 by irradiation
of 2-benzyl- and 2-benzhydryl-3-benzoylchromones with
UV light17 and by decomposition of ortho-carboxynaph-
thalenediazonium tetra¯uoroborates in the presence of
phenols.18 A few speci®c synthetic methods were also
developed for the synthesis of bikaverin 1.10,19 We describe
here a new method for the synthesis of novel benzo[b]-
xanthones 11, from Diels±Alder reactions of chromone-3-
carboxaldehydes 12, as dienophiles, with the highly reactive
Keywords: Diels±Alder reactions; chromone-3-carboxaldehydes; ortho-
benzoquinodimethane; benzo[b]xanthones; oxidation reactions.
Corresponding author. Tel.: 1351-234370714; fax: 1351-234370084;
p
e-mail: arturs@dq.ua.pt
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(01)01131-0

106
A. Sandulache et al. / Tetrahedron 58 (2002) 105±114
Scheme 1.
diene ortho-benzoquinodimethane 7, followed by oxidation
of the obtained cycloadducts 8 and 9.
into account the dienophilicity of chromones bearing
electron withdrawing substituents at C-3, we carried out
Diels±Alder reactions of chromone-3-carboxaldehydes 12
with ortho-benzoquinodimethane 7, obtaining a diastereo-
meric mixture of benzo[b]-1,6,6a,12a-tetrahydroxanthones,
8 and 9, in good yields (Table 2, Scheme 3). These cyclo-
addition reactions might give rise to the expected adduct
13, a b-ketoaldehyde which was prone to deformylation
under the reactions conditions, yielding the mixture of
diastereomers 8 and 9, which could be separated by thin
layer chromatography (TLC). This type of deformylation
was already reported by Wallace et al.,3 from reactions
carried out at high temperatures. In some cases, small
amounts of the opened compound 10a,f,g were also
isolated (Table 2); however when using 6-nitrochromone-
3-carboxaldehyde 12j as starting material the opened
compound 10j was formed in appreciable amount
(38.5%). This fact seems to indicate that the pyran ring
opening is facilitated by the presence of an electron with-
drawing substituent in the para position of the heterocyclic
oxygen.
2. Results and discussion
2.1. Chemistry
Initial experiments considered the Diels±Alder reactions of
the unsubstituted chromone 5 with ortho-benzoquinodi-
methane 7, formed in situ by thermal extrusion of sulfur
dioxide from 1,3-dihydrobenzo[c]thiophene 2,2-dioxide
6,20 with or without a Lewis acid as catalyst (Table 1,
Scheme 2). Low yields have been obtained in all cases,
and when AlCl3, TiCl4 or higher pressure was used the
cycloadducts 8a and 9a were not isolated. The formation
of the trans-diastereomer 8a can be explained by a thermal
enolisation of the cis-diastereomer 9a. The benxo[b]-
xanthone 11a and (2-hydroxyphenyl)-2-naphthylketone
10a were also isolated in almost all cases. Presumably
xanthone 11a has been obtained by the in situ oxidation of
cycloadducts 8a and 9a, whereas 10a involves the pyran
ring opening during the oxidation process.
From the reaction of 5-acetoxychromone-3-carboxaldehyde
12h with ortho-benzoquinodimethane 7 four compounds
8h (32%), 9h (21%) and 8i (12.5%), 9i (9.5%) have
Since the yields obtained were not acceptable and taking
Table 1. Reaction conditions and yields obtained in the Diels±Alder reactions of the unsubstituted chromone 5 with ortho-benzoquinodimethane 7
Entry
Sulfone 6 (equiv.)
Catalyst
Pressure (atm)
Time (h)
Yield (%)
8a19a
10a
11a
5a
54
83
55.5
38.5
68
1
2
3
4
5
2.5
1.5
2
1.5
1.5
±
±
±
4.5
±
±
±
72
20
26
24
14
17
6.5
15
10
11.5
5.5
±
7.5
±
12.5
7.5
±
11
14
ZnCl2
TiCl4
AlCl3
±
a
Recovered starting material.
Scheme 2.

A. Sandulache et al. / Tetrahedron 58 (2002) 105±114
107
Table 2. Conditions and yields obtained in the Diels±Alder reactions of the
chromone-3-carboxaldehydes 12 with ortho-benzoquinodimethane 7
To circumvent the bromination step during the conversion
of the diastereomeric mixture of 8 and 9 into 11, we decided
to perform this transformation with DMSO/I2, a reagent
mixture which has been used by our group in the cyclode-
hydrogenation of 20-hydroxychalcones and 20-hydroxycin-
Entry
R1
R2
R3
R4 Time (h)
Yield (%)
8
9
10
namylideneacetophenones
into
the
corresponding
1
2
3
4
5
6
7
8
9
10
a
b
c
d
e
f
g
h
i
H
H
H
H
H
H
CH3
Cl
Br
Br
H
H
H
H
NO2
H
H
H
H
H
OCH3
H
H
H
H
H
H
H
H
Br
H
H
H
H
H
6:30
5:30
5
3:30
5
5:30
5
4:30
5
51 44
50.5 43.5
4
±
±
±
±
2.3
chromones.21 In this way the expected benzo[b]xanthones
11 have been obtained in very good yields (88±98%).
52
54
54
44
42
42
37
41
H
2.2. NMR spectroscopy
OCH3
OAc
OH
H
42
32
49.5
23
48.5 2.4
21
40
±
±
1
The most important features of the H NMR spectra of the
benzotetrahydroxanthones 8 and 9 are the resonances
appearing in their aliphatic region, due to H-1, H-6, H-6a
and H-12a. However the resonances which immediately
j
5
12.5 38.5
Scheme 3.
been isolated. Compounds 8h and 9h are the expected
cycloadducts (two diastereomers), while the presence of 8i
and 9i suggests that a deacetylation process also
accompanied the cycloaddition reaction.
indicate the presence of the trans 8 or the cis 9 cycloadducts
are those of H-6a; in the case of 9 they appear as narrow
multiplets (d 4.89±5.05 ppm) while in the case of 8 they
appears as a double doublet of doublets (d 4.53±4.73 ppm).
3
The coupling constants JH6a±H12a,12±13 Hz in the latter
Procedures for the transformation of the benzo[b]-
1,6,6a,12a-tetrahydroxanthones, 8 and 9, into benzo[b]-
xanthones 11 have also been attempted. Oxidation of
these cycloadducts with chloranil and with sulphur were
unsuccessful, while treatment of the 8c and 9c mixture
with an excess of limonene and 10% Pd/C gave 11c in
28.5% yield; benzylic bromination with NBS
(2.05 equiv.), in the presence of AIBN, followed by
dehydrobromination by treatment with triethylamine, has
afforded benzoxanthone 13c contaminated with a small
amount of another product. TLC analysis of this mixture
revealed the presence of two very close spots and their
case indicate a trans con®guration of these two protons.
In the case of compounds 9 the coupling constants
3JH6a±H12a,2±3 Hz, measured in some cases from the signal
of H-12a, suggest a cis con®guration of these protons. This
con®guration was con®rmed by the close proximity of H-6a
and H-12a found in the NOESY spectra of these adducts 9.
The resonances of all other protons of compounds 8 and 9,
mainly those of the referred aliphatic region, and their
coupling constants were determined by the aid of COSY,
HETCOR (or HSQC), HMBC and NOESY spectra. These
2D spectra also allowed the unequivocal assignment of the
carbon resonances; those of the quaternary carbons were
mainly assigned by the connectivities found in the HMBC
spectra (Fig. 1). In the case of compounds 8i and 9i the
presence of a hydroxyl proton involved in a hydrogen
bond with the carbonyl group was identi®ed by the
resonance at d 11.66±11.82 ppm.
1
separation by preparative TLC was not successful. The H
NMR spectrum of this mixture revealed that the minor
component is quite similar to that due to 13c (there are
minor shifts in the resonances of similar protons). The
main difference is in the resonance of H-6 which is missing
for the unknown compound. Based on these data and on the
fact that the mass spectrum of this mixture presented peaks
with the pro®le of a chlorobromobenzoxanthone derivative,
m/z at 258 (35Cl, 79Br) and 260 (35Cl, 81Br), we believe that
this new compound is the 6-bromo-10-chlorobenzo[b]-
xanthone.
The 1H NMR spectra of compounds 10a,f,g,j present signals
in the aromatic region and another at d 12.06±12.76 ppm
for 10a,f,j and at d 10.80 ppm for 10g. These data together
with a carbon resonance at d 199.7±201.5 ppm indicate that

108
A. Sandulache et al. / Tetrahedron 58 (2002) 105±114
COSY and NOESY (mixing time of 800 ms) experiments,
while 13C assignments were made using 2D HETCOR or
HSQC and HMBC experiments (long range C/H coupling
constants were optimised to 4 and 7 Hz). Mass spectra (EI,
70 eV) were measured on VG Autospec Q an M mass spec-
trometers. Elemental analyses were obtained on a LECO
932 CHN analyser. Preparative TLC was carried on Riedel
silica gel 60 DGF254, and column chromatography on Merck
silica gel 60, 70±230 mesh.
Figure 1. Important connectivities found in the HMBC spectra of the
cycloadducts 8 and 9.
3.2. General procedure for chromone-3-carboxalde-
hydes 12
The chromone-3-carboxaldehydes 12 used in this work have
been prepared by Vilsmeir formylation of appropriate
20-hydroxyacetophenones.22 However, the procedure has
been slightly improved. Phosphorous oxychloride
(30 mmol) was added to dry DMF (10 mL) and the
resulting mixture stirred for 15 min. Then the appropriate
20-hydroxyacetophenone (10 mmol) was added and the
reaction mixture kept at 608C for 16 h for 20-hydroxy-40-
methoxyacetophenone and 60-acetoxy-20-hydroxyaceto-
phenone and 4±5 h for the others. After this period the
reaction mixture was poured into an ice water mixture and
stirred for 2 h. The obtained solid was removed by ®ltration,
taken in chloroform (100 mL) and washed with water. The
solvent was evaporated to dryness and the residue
recrystallised from ethanol, giving chromone-3-carboxalde-
hydes 12 in good yields (61±94%). It is important to notice
that using our procedure the yield of compounds 12e (94%),
12f (61%), 12g (77%) and 12j (69%) signi®cantly increased
in relation with literature data.23
Figure 2. Important connectivities found in the HMBC spectra of the
benzoxanthones 11.
the cycloadducts 8a,f,g,j and 9a,f,g,j have been oxidised
with concomitant pyran ring opening. The signals at d
10.80±12.76 ppm are due to the resonances of hydroxyl
protons (20-OH) involved in intramolecular hydrogen
bonds with a carbonyl group. The resonance of the 20-OH
of 10g appears at lower frequency value relatively to those
of 10a,f,j, this is probably due to the steric effect between
the 60-methoxyl group and the 2-naphthyl group. This effect
implies lack of conjugation between the 2-naphthyl and the
carbonyl groups, decreasing the strength of the hydrogen
bond.22 The connectivities found in the HMBC spectra of
compounds 10a,f,g,j (20-OH!C-10, C-20 and C-30; H-1!C-
3, C-8 and C-10; H-4!C-2, C-9 and C-5) allowed the
con®rmation for the resonance assignments of protonated
carbons and the unequivocal assignment of those of
quaternary carbons.
3.3. General procedure for the Diels±Alder reactions of
chromone-3-carboxaldehydes 12with ortho-
benzoquinodimethane 7: synthesis of cycloadducts
benzo[b]-1,6,6a,12a-tetrahydroxanthones 8 and 9
The most deshielded protons of compounds 11 are H-1 (d
8.87±8.96 ppm) and H-11 (d 8.13±8.45 ppm, save for 11g,i
which have substituents at that position and for 11j since its
spectrum was run in a different solvent), due to the
mesomeric and anisotropic deshielding effect of the
carbonyl group. The unequivocal assignment of H-1 and
its differentiation of H-6 (d 7.80±8.04 ppm) was not only
based in their frequency values, but also on the con-
nectivities found in the HMBC spectra of these compounds,
as shown in Fig. 2. These connectivities allowed the con-
®rmation of some protonated carbons and the unequivocal
assignments of the quaternary carbons (C-1a, C-5a, C-6a,
C-7a, C-12 and 12a).
Chromone-3-carboxaldehydes 12 (1.15 mmol) and 1,3-
(212.5 mg,
dihydrobenzo[c]thiophene 2,2-dioxide
6
1.26 mmol) in 1,2,4-trichlorobenzene (5 mL) were re¯uxed
at 2508C, under nitrogen for the appropriate reaction time
(Table 2). After reaction cooling, the solvent was removed
by column chromatography (silica gel, light petroleum as
eluent) and then the cycloadducts were eluted with dichloro-
methane. The solvent was evaporated to dryness and the
residue was separated by preparative TLC, using an appro-
priate mixture of solvents (with polarities ranging from light
petroleum to chloroform). The cycloadducts 8 and 9 were
recrystallised from ethanol.
3. Experimental
3.1. General
3.3.1. trans-Benzo[b]-1,6,6a,12a-tetrahydroxanthone (8a)
(51%). Mp 180±1828C; H NMR d 2.90±3.00 (m, 1H,
1
H-12a), 3.00 (dd, Jˆ15.1, 9.0 Hz, 1H, H-1), 3.30 (dd,
Jˆ16.0, 10.4 Hz, 1H, H-6), 3.43 (dd, Jˆ16.0, 6.0 Hz, 1H,
H-6), 3.50 (dd, Jˆ15.1, 3.6 Hz, 1H, H-1), 4.60 (ddd,
Jˆ12.8, 10.4, 6.0 Hz, 1H, H-6a), 7.02 (d, Jˆ8.3 Hz, 1H,
H-8), 7.05 (ddd, Jˆ7.6, 7.2, 1.0 Hz, 1H, H-10), 7.18±7.22
(m, 4H, H-2,3,4,5), 7.51 (ddd, Jˆ8.3, 7.2, 1.8 Hz, 1H, H-9),
7.94 (dd, Jˆ7.6, 1.8 Hz, 1H, H-11); 13C NMR d 28.0 (C-1),
36.0 (C-6), 46.0 (C-12a), 77.2 (C-6a), 117.8 (C-8), 120.7
(C-11a), 121.5 (C-10), 126.4 and 126.7 (C-3 and C-4), 127.2
(C-11), 129.0 and 129.1 (C-2 and C-5), 132.6 (C-5a), 133.8
Melting points were determined on a Reichert Thermovar
1
apparatus ®tted with a microscope and are uncorrected. H
and 13C NMR spectra were recorded in CDCl3, if not stated
otherwise, on Bruker AMX 300 and DRX 300 spectro-
meters operating at 300.13 and 75.47 MHz, respectively;
the chemical shifts are expressed in d (ppm) values relative
to TMS as internal reference and the coupling constants (J)
1
are expressed in Hz. H Assignments were made using 2D

A. Sandulache et al. / Tetrahedron 58 (2002) 105±114
109
(C-1a), 136.0 (C-9), 161.1 (C-7a), 193.6 (C-12); MS (EI)
m/z (rel. int.) 251 [(M11)1, 42], 250 (M1z, 100), 249
[(M21)1, 52], 232 (43), 231 (73), 130 (29), 129 (41), 128
(40), 121 (55), 120 (24), 115 (34), 92 (27), 77 (8). Anal.
Calcd for C17H14O2: C, 81.58; H, 5.68. Found: C, 81.51; H,
5.65.
3.00 (m, 1H, H-12a), 3.00 (dd, Jˆ15.0, 9.0 Hz, 1H, H-1),
3.29 (dd, Jˆ16.1, 10.4 Hz, 1H, H-6), 3.43 (dd, Jˆ16.1,
6.1 Hz, 1H, H-6), 3.50 (dd, Jˆ15.0, 3.4 Hz, 1H, H-1),
4.60 (ddd, Jˆ12.8, 10.4, 6.1 Hz, 1H, H-6a), 6.99 (d,
Jˆ8.8 Hz, 1H, H-8), 7.18±7.21 (m, 4H, H-2,3,4,5), 7.45
(dd, Jˆ8.8, 2.7 Hz, 1H, H-9), 7.89 (d, Jˆ2.7 Hz, 1H,
H-11); 13C NMR d 27.9 (C-1), 35.8 (C-6), 45.8 (C-12a),
77.7 (C-6a), 119.6 (C-8), 121.4 (C-11a), 126.5 (C-11 and
C-3 or C-4), 126.7 (C-3 or C-4), 127.0 (C-10), 129.0 and
129.1 (C-2 and C-5), 132.3 (C-5a), 133.5 (C-1a), 135.8
(C-9), 159.6 (C-7a), 192.5 (C-12); MS (EI) m/z (rel. int.)
287 [(M11)1, 37Cl, 11], 286 (M1z, 37Cl, 44), 285 [(M21)1,
37Cl; (M11)1, 35Cl; 35], 284 (M1z, 35Cl, 99), 283 [(M21)1,
35Cl, 29], 268 (16), 267 (40), 266 (37), 265 (82), 249 (14),
231 (9), 157 (33), 156 (15), 155 (67), 154 (16), 130 (38), 129
(100), 128 (63), 127 (32), 126 (20), 116 (22), 115 (34), 104
(15), 103, (10), 102 (11), 101 (10), 99 (12), 98 (9), 91 (11),
77 (22). Anal. Calcd for C17H13ClO2: C, 71.71; H, 4.60.
Found: C, 71.49; H, 4.83.
3.3.2. cis-Benzo[b]-1,6,6a,12a-tetrahydroxanthone (9a)
(44%). Mp 124±1258C; H NMR d 2.87±3.09 (m, 3H,
1
2£H-1 and H-12a), 3.19 (dd, Jˆ18.0, 4.4 Hz, 1H, H-6),
3.30 (dd, Jˆ18.0, 3.3 Hz, 1H, H-6), 4.92±4.96 (m, 1H,
H-6a), 6.96 (d, Jˆ8.4 Hz, 1H, H-8), 7.03 (ddd, Jˆ7.7, 7.3,
1.0 Hz, 1H, H-10), 7.11±7.18 (m, 4H, H-2,3,4,5), 7.47 (ddd,
Jˆ8.4, 7.3, 1.7 Hz, 1H, H-9), 7.93 (dd, Jˆ7.7, 1.7 Hz, 1H,
H-11); 13C NMR d 26.2 (C-1), 32.8 (C-6), 44.8 (C-12a),
75.0 (C-6a), 118.0 (C-8), 119.2 (C-11a), 121.5 (C-10),
126.2 and 126.5 (C-3 and C-4), 127.5 (C-11), 128.8 and
129.3 (C-2 and C-5), 131.7 (C-5a), 133.7 (C-1a), 136.0
(C-9), 160.9 (C-7a), 194.8 (C-12); MS (EI) m/z (rel. int.)
251 [(M11)1, 21], 250 (M1z, 100), 249 [(M21)1, 25], 232
(30), 231 (90), 130 (17), 129 (56), 128 (51), 121 (74), 120
(13), 115 (21), 104 (23), 92 (21), 77 (12). Anal. Calcd for
C17H14O2: C, 81.58; H, 5.68. Found: C, 81.57; H, 5.67.
3.3.6.
cis-10-Chlorobenzo[b]-1,6,6a,12a-tetrahydro-
1
xanthone (9c) (42%). Mp 136±1378C; H NMR d 2.91
(dd, Jˆ12.1, 4.0 Hz, 1H, H-1), 2.97 (ddd, Jˆ8.8, 4.0,
2.0 Hz, 1H, H-12a), 3.06 (dd, Jˆ12.1, 8.8 Hz, 1H, H-1),
3.20 (dd, Jˆ18.0, 4.5 Hz, 1H, H-6), 3.30 (dd, Jˆ18.0,
3.4 Hz, 1H, H-6), 4.93±4.96 (m, 1H, H-6a), 6.92 (d,
Jˆ8.8 Hz, 1H, H-8), 7.12±7.20 (m, 4H, H-2,3,4,5), 7.41
(dd, Jˆ8.8, 2.6 Hz, 1H, H-9), 7.88 (d, Jˆ2.6 Hz, 1H,
H-11); 13C NMR d 26.0 (C-1), 32.7 (C-6), 44.5 (C-12a),
75.3 (C-6a), 119.7 (C-8), 120.1 (C-11a), 126.4 and 126.7
(C-3 and C-4), 126.8 (C-11), 127.1 (C-10), 128.8 and 129.3
(C-2 and C-5), 131.5 (C-5a), 133.4 (C-1a), 135.9 (C-9),
159.3 (C-7a), 193.6 (C-12); MS (EI) m/z (rel. int.) 287
[(M11)1, 37Cl, 8], 286 (M1z, 37Cl, 32), 285 [(M21)1,
37Cl; (M11)1, 35Cl; 24], 284 (M1z, 35Cl, 73), 283
[(M21)1, 35Cl, 18], 268 (12), 267 (31), 266 (27), 265
(59), 249 (9), 231 (6), 157 (24), 156 (15), 155 (55), 154
(18), 130 (36), 129 (100), 128 (64), 127 (31), 126 (22),
116 (10), 115 (30), 104 (32), 103 (13), 102 (10), 101 (9),
99 (11), 98 (10), 91 (7), 78 (13), 77 (16). Anal. Calcd for
C17H13ClO2: C, 71.71; H, 4.60. Found: C, 71.83; H, 4.72.
3.3.3. trans-10-Methylbenzo[b]-1,6,6a,12a-tetrahydro-
xanthone (8b) (51%). Mp 159±1618C; H NMR d 2.32
1
(s, 3H, CH3), 2.86±2.98 (m, 2H, H-1 and H-12a), 3.26
(dd, Jˆ15.9, 10.2 Hz, 1H, H-6), 3.39 (dd, Jˆ15.9, 6.0 Hz,
1H, H-6), 3.43±3.54 (m, 1H, H-1), 4.53 (ddd, Jˆ12.5, 10.2,
6.0 Hz, 1H, H-6a), 6.91 (d, Jˆ8.4 Hz, 1H, H-8), 7.16±7.21
(m, 4H, H-2,3,4,5), 7.31 (dd, Jˆ8.4, 1.9 Hz, 1H, H-9), 7.72
(d, Jˆ1.9 Hz, 1H, H-11); 13C NMR d 20.4 (s, CH3), 28.1
(C-1), 36.0 (C-6), 46.0 (C-12a), 77.3 (C-6a), 117.6 (C-8),
120.3 (C-11a), 126.4 and 126.6 (C-3 and C-4), 126.7 (C-11),
129.0 and 129.1 (C-2 and C-5), 130.9 (C-10), 132.6 (C-5a),
133.8 (C-1a), 137.1 (C-9), 159.2 (C-7a), 193.8 (C-12); MS
(EI) m/z (rel. int.) 265 [(M11)1, 27], 264 (M1z, 73), 263
[(M21)1, 32], 246 (34), 245 (100), 231 (10), 135 (59), 134
(35), 130 (16), 129 (38), 128 (47), 127 (22), 115 (22), 104
(10), 91 (11), 78 (27), 77 (27); Anal. Calcd for C18H16O2: C,
81.79; H, 6.10. Found: C, 81.76; H, 6.13.
3.3.4.
cis-10-Methylbenzo[b]-1,6,6a,12a-tetrahydro-
3.3.7. trans-10-Bromobenzo[b]-1,6,6a,12a-tetrahydro-
xanthone (8d) (54%). Mp.2948C; H NMR d 2.87±2.97
1
1
xanthone (9b) (43%). Mp 123±1248C; H NMR d 2.31
(s, 3H, CH3), 2.89 (dd, Jˆ13.0, 2.9 Hz, 1H, H-1), 2.91±
2.96 (m, 1H, H-12a), 3.06 (dd, Jˆ13.0, 5.1 Hz, 1H, H-1),
3.18 (dd, Jˆ18.0, 4.2 Hz, 1H, H-6), 3.29 (dd, Jˆ18.0,
3.3 Hz, 1H, H-6), 4.89±4.92 (m, 1H, H-6a), 6.86 (d,
Jˆ8.4 Hz, 1H, H-8), 7.09±7.18 (m, 4H, H-2,3,4,5), 7.29
(dd, Jˆ8.4, 2.4 Hz, 1H, H-9), 7.72 (d, Jˆ2.4 Hz, 1H,
H-11); 13C NMR d 20.4 (CH3), 26.2 (C-1), 32.9 (C-6),
44.8 (C-12a), 74.9 (C-6a), 117.7 (C-8), 118.8 (C-11a),
126.2 and 126.5 (C-3 and C-4), 127.0 (C-11), 128.7 and
129.2 (C-2 and C-5), 131.0 (C-10), 131.7 (C-5a), 133.8
(C-1a), 137.1 (C-9), 158.9 (C-7a), 195.1 (C-12); MS (EI)
m/z (rel. int.) 265 [(M11)1, 34], 264 (M1z, 100), 263
[(M21)1, 29], 246 (35), 245 (76), 135 (80), 134 (37), 130
(13), 129 (44), 128 (49), 127 (18), 115 (17), 104 (21), 78 (29),
77 (15). Anal. Calcd for C18H16O2: C, 81.79; H, 6.10. Found:
C, 81.80; H 6.09.
(m, 1H, H-12a), 2.93 (dd, Jˆ14.6, 8.9 Hz, 1H, H-1), 3.28
(dd, Jˆ16.0, 10.4 Hz, 1H, H-6), 3.42 (dd, Jˆ16.0, 6.1 Hz,
1H, H-6), 3.49 (dd, Jˆ14.6, 2.9 Hz, 1H, H-1), 4.58 (ddd,
Jˆ12.8, 10.4, 6.1 Hz, 1H, H-6a), 6.93 (d, Jˆ8.8 Hz, 1H,
H-8), 7.17±7.20 (m, 4H, H-2,3,4,5), 7.57 (dd, Jˆ8.8,
2.5 Hz, 1H, H-9), 8.03 (d, Jˆ2.5 Hz, 1H, H-11); 13C NMR
d 27.9 (C-1), 35.8 (C-6), 45.8 (C-12a), 77.6 (C-6a), 114.1
(C-10), 119.9 (C-8), 121.9 (C-11a), 126.5 and 126.8 (C-3
and C-4), 129.6 (C-11), 132.3 (C-5a), 133.5 (C-1a), 138.6
(C-9), 160.0 (C-7a), 192.3 (C-12); MS (EI) m/z (rel. int.)
331 [(M11)1, 81Br, 22], 330 (M1z, 81Br, 81), 329 [(M21)1,
81Br; (M11)1, 79Br; 35], 328 (M1z, 79Br, 78), 327 [(M21)1,
79Br, 18], 313 (10), 312 (24), 311 (54), 310 (25), 309 (51),
249 (16), 231 (11), 202 (13), 201 (41), 200 (17), 199 (42),
198 (11), 172 (11), 170 (10), 164 (9), 130 (39), 129 (100),
128 (72), 127 (32), 121 (10), 116 (24), 115 (39), 105 (10),
104 (11), 103 (12), 102 (8), 91 (12), 77 (15). Anal. Calcd
for C17H13BrO2: C, 62.03; H, 3.98. Found: C, 61.81; H,
4.07.
3.3.5. trans-10-Chlorobenzo[b]-1,6,6a,12a-tetrahydro-
xanthone (8c) (52%). Mp 182±1848C; H NMR d 2.89±
1

110
A. Sandulache et al. / Tetrahedron 58 (2002) 105±114
3.3.8.
cis-10-Bromobenzo[b]-1,6,6a,12a-tetrahydro-
3.3.11. trans-9-Methoxybenzo[b]-1,6,6a,12a-tetrahydro-
xanthone (8f) (44%). Mp 184±1868C; H NMR d 2.86±
1
1
xanthone (9d) (42%). Mp 158±1608C; H NMR d 2.90
(dd, Jˆ12.1, 3.4 Hz, 1H, H-1), 2.93±2.99 (m, 1H, H-12a),
3.05 (dd, Jˆ12.1, 9.0 Hz, 1H, H-1), 3.19 (dd, Jˆ18.0,
4.2 Hz, 1H, H-6), 3.30 (dd, Jˆ18.0, 3.3 Hz, 1H, H-6),
4.92±4.95 (m, 1H, H-6a), 6.86 (d, Jˆ8.8 Hz, 1H, H-8),
7.09±7.17 (m, 4H, H-2,3,4,5), 7.54 (dd, Jˆ8.8, 2.5 Hz,
1H, H-9), 8.03 (d, Jˆ2.5 Hz, 1H, H-11); 13C NMR d 26.0
(C-1), 32.7 (C-6), 44.4 (C-12a), 75.2 (C-6a), 114.2 (C-10),
120.1 (C-8), 120.6 (C-11a), 126.4 and 126.6 (C-3 and C-4),
128.8 and 129.3 (C-2 and C-5), 130.0 (C-11), 131.4 (C-5a),
133.4 (C-1a), 138.6 (C-9), 159.8 (C-7a), 193.4 (C-12); MS
(EI) m/z (rel. int.) 331 [(M11)1, 81Br, 24], 330 (M1z, 81Br,
88), 329 [(M21)1, 81Br, (M11)1, 79Br, 36], 328 (M1z, 79Br,
90), 327 [(M21)1, 79Br, 19], 313 (9), 312 (30), 311 (62),
310 (31), 309 (59), 249 (15), 231 (9), 201 (45), 200 (18), 199
(44), 172 (9), 170 (8), 130 (35), 129 (100), 128 (71), 127
(29), 121 (7), 116 (9), 115 (30), 104 (26), 103 (10), 77 (11).
Anal. Calcd for C17H13BrO2´0.25H2O: C, 61.13; H, 4.04.
Found: C, 61.28; H, 4.29. HRMS (EI) calcd for
C17H1381BrO2: 330.0078. Found: 330.0091.
2.97 (m, 1H, H-12a), 2.91 (dd, Jˆ22.8, 11.4 Hz, 1H, H-1),
3.27 (dd, Jˆ16.0, 10.1 Hz, 1H, H-6), 3.40 (dd, Jˆ16.0,
6.0 Hz, 1H, H-6), 3.49 (dd, Jˆ22.8, 11.4 Hz, 1H, H-1),
3.85 (s, 3H, OCH3), 4,57 (ddd, Jˆ12.1, 10.1, 6.0 Hz, 1H,
H-6a), 6.46 (d, Jˆ2.4 Hz, 1H, H-8), 6.61 (dd, Jˆ8.8, 2.4 Hz,
1H, H-10), 7.17±7.22 (m, 4H, H-2,3,4,5), 7.87 (d,
Jˆ8.8 Hz, 1H, H-11); 13C NMR d 28.1 (C-1), 36.0 (C-6),
45.6 (C-12a), 55.6 (OCH3), 77.8 (C-6a), 100.6 (C-8), 110.1
(C-10), 114.6 (C-11a), 126.4 and 126.6 (C-3 and C-4), 128.9
and 129.1 (C-2 and C-5), 129.0 (s, C-11), 132.6 (C-5a),
134.0 (C-1a), 163.1 (C-7a), 166.0 (C-9), 192.1 (C-12); MS
(EI) m/z (rel. int.) 281 [(M11)1, 30], 280 (M1z, 100), 279
[(M21)1, 55], 262 (19), 261 (55), 249 (7), 152 (15), 151
(84), 150 (24), 130 (15), 129 (33), 128 (36), 127 (18), 122
(19), 115 (22), 107 (14), 104 (4), 94 (7), 79 (12), 77 (9).
Anal. Calcd for C18H16O3: C, 77.12; H, 5.75. Found: C,
77.17; H, 5.72.
3.3.12.
cis-9-Methoxybenzo[b]-1,6,6a,12a-tetrahydro-
1
xanthone (9f) (41%). Mp 182±1848C; H NMR d 2.87
(dd, Jˆ12.5, 2.3 Hz, 1H, H-1), 2.83±2.89 (m, 1H, H-12a),
3.03 (dd, Jˆ12.5, 6.0 Hz, 1H, H-1), 3.19 (dd, Jˆ18.0,
4.3 Hz, 1H, H-6), 3.29 (dd, Jˆ18.0, 3.1 Hz, 1H, H-6),
3.81 (s, 3H, OCH3), 4.91±4.94 (m, 1H, H-6a), 6.40 (d,
Jˆ2.4 Hz, 1H, H-8), 6.60 (dd, Jˆ8.8, 2.4 Hz, 1H, H-10),
7.10±7.17 (m, 4H, H-2,3,4,5), 7.86 (d, Jˆ8.8 Hz, 1H,
H-11); 13C NMR d 26.4 (C-1), 33.0 (C-6), 44.5 (C-12a),
55.6 (OCH3), 75.4 (C-6a), 100.8 (C-8), 110.3 (C-10),
113.0 (C-11a), 126.3 and 126.5 (C-3 and C-4), 128.8,
129.2 and 129.3 (C-2, C-5 and C-11), 131.7 (C-5a), 133.9
(C-1a), 162.9 (C-7a), 166.1 (C-9), 193.7 (C-12); MS (EI)
m/z (rel. int.) 281 [(M11)1, 30], 280 (M1z, 100), 279
[(M21)1, 43], 262 (18), 261 (54), 249 (5), 152 (15), 151
(87), 150 (22), 130 (14), 129 (43), 128 (48), 127 (19), 122
(18), 115 (20), 107 (15), 104 (17), 95 (9), 79 (13), 77 (10).
Anal. Calcd for C18H16O3: C, 77.12; H, 5.75. Found: C,
77.43; H, 5.76.
3.3.9.
trans-8,10-Dibromobenzo[b]-1,6,6a,12a-tetra-
1
hydroxanthone (8e) (54%). Mp 190±1928C. H NMR d
2.95 (dd, Jˆ16.1, 11.6 Hz, 1H, H-1), 2.97±3.06 (m, 1H,
H-12a), 3.39 (dd, Jˆ16.2, 10.4 Hz, 1H, H-6), 3.49 (dd,
Jˆ16.1, 4.1 Hz, 1H, H-1), 3.54 (dd, Jˆ16.2, 6.0 Hz, 1H,
H-6), 4.66 (ddd, Jˆ13.1, 10.4, 6.0 Hz, 1H, H-6a), 7.18±
7.21 (m, 4H, H-2,3,4,5), 7.87 (d, Jˆ2.4 Hz, 1H, H-9),
8.00 (d, Jˆ2.4 Hz, 1H, H-11); 13C NMR d 27.9 (C-1),
35.7 (C-6), 45.5 (C-12a), 78.4 (C-6a), 112.7 (C-8), 114.0
(C-10), 122.5 (C-11a), 126.6 and 126.8 (C-3 and C-4), 128.9
(C-2 or C-5), 129.1 (C-11 and C-2 or C-5), 132.1 (C-5a),
133.2 (C-1a), 141.1 (C-9), 156.7 (C-7a), 191.6 (C-12); MS
(EI) m/z (rel. int.) 410 (M1z, 81Br, 11), 409 (40), 408 (M1z,
79Br81Br, 70), 407 (19), 406 (M1z, 79Br, 41), 405 (7), 392
(14), 391 (27), 390 (24), 389 (41), 388 (14), 387 (24), 281
(17), 280 (10), 279 (30), 278 (12), 277 (18), 199 (15), 197
(12), 143 (10), 141 (8), 130 (31), 129 (100), 128 (59), 127
(23), 116 (21), 115 (27), 91 (8), 77 (10). Anal. Calcd
for C17H12Br2O2: C, 50.03; H, 2.96. Found: C, 50.08; H,
3.14.
3.3.13.
trans-11-Methoxybenzo[b]-1,6,6a,12a-tetra-
1
hydroxanthone (8g) (42%). Mp 193±1948C; H NMR d
2.88±2.98 (m, 1H, H-12a), 2.98 (dd, Jˆ11.1, 3.0 Hz, 1H,
H-1), 3.24 (dd, Jˆ16.3, 10.2 Hz, 1H, H-6), 3.40 (dd,
Jˆ16.3, 6.0 Hz, 1H, H-6), 3.47 (dd, Jˆ11.1, 7.5 Hz, 1H,
H-1), 3.94 (s, 3H, OCH3), 4.56 (ddd, Jˆ13.0, 10.2,
6.0 Hz, 1H, H-6a), 6.54 (dd, Jˆ8.4, 0.8 Hz, 1H, H-8),
6.62 (dd, Jˆ8.4, 0.8 Hz, 1H, H-10), 7.17±7.23 (m, 4H,
H-2,3,4,5), 7.41 (t, Jˆ8.4 Hz, 1H, H-9); 13C NMR d 28.1
(C-1), 36.0 (C-6), 46.6 (C-12a), 56.1 (OCH3), 77.2 (C-6a),
103.8 (C-8), 109.9 (C-10), 126.0 (C-11a), 126.3 and 126.6
(C-3 and C-4), 129.0 and 129.1 (C-2 and C-5), 132.5 (C-5a),
134.1 (C-1a), 135.9 (C-9), 160.8 (C-11), 162.6 (C-7a), 192.3
(C-12); MS (EI) m/z (rel. int.) 281 [(M11)1, 27], 280 (M1z,
100), 279 [(M21)1, 36], 262 (21), 261 (52), 247 (9), 231
(8), 151 (54), 150 (47), 130 (14), 129 (27), 128 (30), 127
(15), 122 (24), 115 (20), 107 (28), 104 (9), 91 (7), 77 (10).
Anal. Calcd for C18H16O3: C, 77.12; H, 5.75. Found: C,
77.13; H, 5.79.
3.3.10. cis-8,10-Dibromobenzo[b]-1,6,6a,12a-tetrahydro-
xanthone (9e) (37%). Mp 160±1628C; 1H NMR d 2.90 (dd,
Jˆ14.1, 4.5 Hz, 1H, H-1), 3.04 (ddd, Jˆ10.3, 4.5, 2.8 Hz,
1H, H-12a), 3.11 (dd, Jˆ14.1, 10.3 Hz, 1H, H-1), 3.24 (dd,
Jˆ18.1, 4.9 Hz, 1H, H-6), 3.37 (dd, Jˆ18.1, 3.9 Hz, 1H,
H-6), 5.02±5.06 (m, 1H, H-6a), 7.14±7.21 (m, 4H,
H-2,3,4,5), 7.85 (d, Jˆ2.5 Hz, 1H, H-9), 8.00 (d,
Jˆ2.5 Hz, 1H, H-11); 13C NMR d 25.9 (C-1), 32.2 (C-6),
44.2 (C-12a), 76.2 (C-6a), 113.0 (C-8), 114.0 (C-10), 121.4
(C-11a), 126.4 and 126.7 (C-3 and C-4), 128.8 and 129.3
(C-2 and C-5), 129.4 (C-11), 131.4 (C-5a), 133.1 (C-1a),
141.2 (C-9), 156.4 (C-7a), 192.5 (C-12); MS (EI) m/z (rel.
int.) 410 (M1z, 81Br, 61), 409 (32), 408 (M1z, 79Br81Br,
100), 407 (27), 406 (M1z, 79Br, 60), 392 (22), 391 (39),
390 (37), 389 (62), 388 (22), 387 (35), 281 (20), 280
(12), 279 (35), 278 (17), 277 (20), 276 (9), 199 (12), 197
(19), 143 (8), 141 (8), 130 (38), 129 (97), 128 (58), 127 (23),
116 (10), 115 (24), 104 (21), 103 (8), 91 (8), 77 (13).
Anal. Calcd for C17H12Br2O2: C, 50.03; H, 2.96. Found:
C, 49.69; H 3.09.
3.3.14. cis-11-Methoxybenzo[b]-1,6,6a,12a-tetrahydrox-
anthone (9g) (48.5%). Mp 116±1188C; H NMR d 2.83±
1
2.90 (m, 1H, H-12a), 2.91 (dd, Jˆ13.5, 6.2 Hz, 1H, H-1),

A. Sandulache et al. / Tetrahedron 58 (2002) 105±114
111
3.04 (dd, Jˆ13.5, 4.7 Hz, 1H, H-1), 3.15 (dd, Jˆ18.1,
3.9 Hz, 1H, H-6), 3.25 (dd, Jˆ18.1, 3.0 Hz, 1H, H-6),
3.91 (s, 3H, OCH3), 4.86±4.89 (m, 1H, H-6a), 6.53 (t,
Jˆ8.2 Hz, 2H, H-8,10), 7.08±7.15 (m, 4H, H-2,3,4,5),
7.35 (t, Jˆ8.2 Hz, 1H, H-9); 13C NMR d 26.3 (C-1), 32.6
(C-6), 45.7 (C-12a), 56.0 (OCH3), 74.2 (C-6a), 103.8 (C-8),
109.3 (C-11a), 110.0 (C-10), 126.1 and 126.3 (C-3 and C-4),
128.7 and 129.1 (C-2 and C-5), 131.6 (C-5a), 133.8 (C-1a),
135.8 (C-9), 161.1 (C-11), 162.4 (C-7a), 193.7 (C-12); MS
(EI) m/z (rel. int.) 281 [(M11)1, 28], 280 (M1z, 100), 279
[(M21)1, 34], 262 (23), 261 (58), 247 (9), 231 (7), 151 (49),
150 (38), 130 (10), 129 (28), 128 (32), 127 (13), 122 (18),
115 (14), 107 (25), 104 (9), 77 (7). Anal. Calcd for
C18H16O3: C, 77.12; H, 5.75. Found: C, 77.13; H 5.73.
(C-1), 35.7 (C-6), 45.5 (C-12a), 76.9 (C-6a), 107.2 (C-8),
107.9 (C-11a), 109.5 (C-10), 126.6 and 126.7 (C-3 and C-4),
129.0 and 129.1 (C-2 and C-5), 132.4 (C-5a), 133.3 (C-1a),
138.3 (C-9), 161.1 (C-7a), 162.2 (C-11), 199.5 (C-12); MS
(EI); m/z (rel. int.) 267 [(M11)1, 20], 266 (M1z, 100), 265
[(M21)1, 22], 248 (32), 247 (62), 137 (59), 136 (12), 130
(8), 129 (26), 128 (26), 115 (12), 108 (9), 104 (7). Anal.
Calcd for C17H12O3: C, 76.68; H, 5.30. Found: C, 76.62; H,
5.49.
3.3.18. cis-11-Hydroxybenzo[b]-1,6,6a,12a-tetrahydro-
xanthone (9i) (40%). Mp 139±1418C; H NMR d 2.95
1
(ddd, Jˆ12.4, 6.3, 2.5 Hz, 1H, H-12a), 2.97 (dd, Jˆ16.9,
6.3 Hz, 1H, H-1), 3.12 (dd, Jˆ16.9, 12.4 Hz, 1H, H-1), 3.21
(dd, Jˆ17.8, 4.0 Hz, 1H, H-6), 3.31 (dd, Jˆ17.8, 3.2 Hz,
1H, H-6), 4.90±4.94 (m, 1H, H-6a), 6.42 (dd, Jˆ8.3, 0.7 Hz,
1H, H-8), 6.53 (dd, Jˆ8.3, 0.7 Hz, 1H, H-10), 7.11±7.20
(m, 4H, H-2,3,4,5), 7.36 (t, Jˆ8.3 Hz, 1H, H-9), 11.66 (s,
1H, OH); 13C NMR d 25.5 (C-1), 32.7 (C-6), 44.3 (C-12a),
74.5 (C-6a), 106.5 (C-11a), 107.5 (C-8), 109.5 (C-10), 126.4
and 126.7 (C-3 and C-4), 128.7 and 129.3 (C-2 and C-5),
131.5 (C-5a), 133.3 (C-1a), 138.2 (C-9), 160.9 (C-7a), 162.6
(C-11), 201.1 (C-12); MS (EI) m/z (rel. int.) 267 [(M11)1,
27], 266 (M1z, 100), 265 [(M21)1, 25], 248 (44), 247 (69),
137 (68), 136 (20), 130 (13), 129 (39), 128 (40), 115 (17),
108 (20), 104 (18). Anal. Calcd for C17H12O3: C, 76.68; H,
5.30. Found: C, 76.65; H, 5.34.
3.3.15. trans-11-Acetoxybenzo[b]-1,6,6a,12a-tetrahydro-
xanthone (8h) (32%). Mp 163±1658C; H NMR d 2.42
1
(s, 3H, OCOCH3), 2.87±3.02 (m, 2H, H-1 and 12a), 3.35±
3.47 (m, 1H, H-1), 3.26 (dd, Jˆ16.1, 10.3 Hz, 1H, H-6),
3.42 (dd, Jˆ16.1, 6.0 Hz, 1H, H-6), 4.63 (ddd, Jˆ12.9,
10.3, 6.0 Hz, 1H, H-6a), 6.69 (dd, Jˆ8.1, 1.1 Hz, 1H,
H-8), 6.95 (dd, Jˆ8.4, 1.1 Hz, 1H, H-10), 7.17±7.20 (m,
4H, H-2,3,4,5), 7.48 (dd, Jˆ8.4, 8.1 Hz, 1H, H-9); 13C
NMR d 21.1 (OCOCH3), 27.8 (C-1), 35.9 (C-6), 46.2
(C-12a), 76.9 (C-6a), 113.5 (C-11a), 116.0 (C-8,10), 126.4
and 126.7 (C-3 and C-4), 128.9 and 129.0 (C-2 and C-5),
132.3 (C-5a), 133.6 (C-1a), 135.7 (C-9), 150.1 (C-11), 162.1
(C-7a), 169.7 (OCOCH3), 191.9 (C-12); MS (EI) m/z (rel.
int.) 308 (M1z, 100), 267 (19), 266 (100), 265 (15), 248 (26),
247 (38), 137 (56), 136 (14), 130 (10), 129 (30), 128 (25),
127 (10), 115 (14), 108 (9), 85 (33), 83 (50). Anal. Calcd for
C19H16O4: C, 74.01; H, 5.23. Found: C, 73.74; H, 5.17.
3.3.19.
trans-10-Nitrobenzo[b]-1,6,6a,12a-tetrahydro-
1
xanthone (8j) (23%). Mp 215±2188C; H NMR d 3.00
(dd, Jˆ16.4, 11.9 Hz, 1H, H-1), 3.03±3.12 (m, 1H,
H-12a), 3.35 (dd, Jˆ16.0, 10.3 Hz, 1H, H-6), 3.51 (dd,
Jˆ16.0, 6.1 Hz, 1H, H-6), 3.50±3.60 (m, 1H, H-1), 4.73
(ddd, Jˆ13.0, 10.3, 6.1 Hz, 1H, H-6a), 7.16 (d, Jˆ9.2 Hz,
1H, H-8), 7.20±7.23 (m, 4H, H-2,3,4,5), 8.37 (dd, Jˆ9.2,
2.9 Hz, 1H, H-9), 8.83 (d, Jˆ2.9 Hz, 1H, H-11); 13C NMR d
27.8 (C-1), 35.7 (C-6), 45.8 (C-12a), 78.4 (C-6a), 119.2
(C-8), 120.2 (C-11a), 123.8 (C-11), 126.7 and 127.0
(C-3,4), 128.9 and 129.0 (C-2,5), 130.4 (C-9), 131.8
(C-5a), 133.1 (C-1a), 142.2 (C-10), 165.0 (C-7a), 191,5
(C-12); MS (EI) m/z (rel. int.) 296 [(M11)1, 28], 295
(M1z, 100), 294 [(M21)1, 21], 277 (39), 276 (65), 230
(16), 202 (6), 166 (31), 150 (9), 130 (32), 129 (100), 128
(87), 127 (29), 120 (16), 115 (32), 104 (22), 91 (17), 77 (12).
Anal. Calcd for C17H13NO4´0.25H2O: C, 68.04; H, 4.50; N,
4.67. Found: C, 67.93; H, 4.66; N, 4.83. HRMS (EI) calcd
for C17H13NO4: 295.0845. Found: 295.0836.
3.3.16. cis-11-Acetoxybenzo[b]-1,6,6a,12a-tetrahydro-
xanthone (9h) (21%). Mp 142±1438C; H NMR d 2.39
1
(s, 3H, OCOCH3), 2.83±2.93 (m, 1H, H-1), 2.87 (ddd,
Jˆ12.6, 6.2, 2.4 Hz, 1H, H-12a), 3.07 (dd, Jˆ17.1,
12.6 Hz, 1H, H-1), 3.17 (dd, Jˆ18.1, 4.6 Hz, 1H, H-6),
3.29 (dd, Jˆ18.1, 3.3 Hz, 1H, H-6), 4.94±4.97 (m, 1H,
H-6a), 6.68 (dd, Jˆ8.2, 2.1 Hz, 1H, H-8), 6,87 (dd, Jˆ8.2,
1.1 Hz, 1H, H-10), 7.08±7.18 (m, 4H, H-2,3,4,5), 7.44 (t,
Jˆ8.2 Hz, 1H, H-9); 13C NMR d 21.1 (OCOCH3), 26.0
(C-1), 32.7 (C-6), 45.3 (C-12a), 74.6 (C-6a), 112.1
(C-11a), 116.07 and 116.14 (C-8 and C-10), 126.3 and
126.6 (C-3 and C-4), 128.8 and 129.3 (C-2 and C-5),
131.5 (C-5a), 133.6 (C-1a), 135.6 (C-9), 150.7 (C-11),
162.0 (C-7a), 169.7 (OCOCH3), 193.1 (C-12); MS (EI)
m/z (rel. int.) 308 (M1z, 36), 267 (19), 266 (100), 265
(21), 256 (18), 249 (10), 248 (45), 247 (61), 168 (41), 149
(26), 137 (65), 136 (16), 130 (12), 129 (44), 128 (38), 127
(13), 118 (19). Anal. Calcd for C19H16O4´0.25H2O: C, 71.84;
H, 5.35. Found: C, 71.54; H, 5.72. HRMS (EI) calcd for
C19H16O4: 308.1049. Found: 308.1061.
3.3.20.
cis-10-Nitrobenzo[b]-1,6,6a,12a-tetrahydro-
xanthone (9j) (12.5%).24 1H NMR (500.13 MHz) d 2.96
(dd, Jˆ15.9, 5.9 Hz, 1H, H-1), 3.03±3.07 (m, 1H, H-1),
3.11 (ddd, Jˆ10.5, 5.9, 2.3 Hz, 1H, H-12a), 3.26 (dd,
Jˆ18.0, 4.5 Hz, 1H, H-6), 3.32±3.38 (m, 1H, H-6), 5.07±
5.09 (m, 1H, H-6a), 7.10 (d, Jˆ9.1 Hz, 1H, H-8), 7.14±7.20
(m, 4H, H-2,3,4,5), 8.34 (dd, Jˆ9.1, 2.8, 1H, H-9), 8.83 (d,
Jˆ2.8 Hz, 1H, H-11); 13C NMR (125.76 MHz) d 25.8
(C-1), 32.4 (C-6), 44.3 (C-12a), 76.1 (C-6a), 119.3 (C-8),
120.2 (C-11a), 124.2 (C-11), 126.7 and 126.9 (C-3 and C-4),
128.9 and 129.3 (C-2 and C-5), 130.4 (C-9), 131.0 (C-5a),
132.8 (C-1a), 142.3 (C-10), 164.8 (C-7a), 192.4 (C-12).
3.3.17.
trans-11-Hydroxybenzo[b]-1,6,6a,12a-tetra-
1
hydroxanthone (8i) (49.5%). Mp 167±1698C; H NMR d
2.92 (dd, Jˆ16.5, 11.7 Hz, 1H, H-1), 3.04 (ddd, Jˆ12.8,
11.7, 5.2 Hz, 1H, H-12a), 3.26 (dd, Jˆ16.0, 10.5 Hz, 1H,
H-6), 3.42 (dd, Jˆ16.0, 6.0 Hz, 1H, H-6), 3.50 (dd, Jˆ16.5,
5.2 Hz, 1H, H-1), 4.57 (ddd, Jˆ12.8, 10.5, 6.0 Hz, 1H,
H-6a), 6.48 (dd, Jˆ8.3, 0.7 Hz, 1H, H-8), 6.54 (d,
Jˆ8.3 Hz, 1H, H-10), 7.18±7.21 (m, 4H, H-2,3,4,5), 7.39
(t, Jˆ8.3 Hz, 1H, H-9), 11.82 (s, 1H, OH); 13C NMR d 27.7
3.3.21. (2-Hydroxyphenyl)-2-naphthylketone (10a) (4%).
Mp 79±808C; 1H NMR d 6.90 (ddd, Jˆ8.0, 7.2, 1.0 Hz, 1H,

112
A. Sandulache et al. / Tetrahedron 58 (2002) 105±114
H-50), 7.11 (dd, Jˆ8.3, 1.0 Hz, 1H, H-30), 7.54 (ddd, Jˆ8.3,
7.2, 1.5 Hz, 1H, H-40), 7.59 (dt, Jˆ6.9, 2.5 Hz, 1H, H-7),
7.63 (dt, Jˆ6.9, 2.5 Hz, 1H, H-6), 7.68 (dd, Jˆ8.0, 1.5 Hz,
1H, H-60), 7.78 (dd, Jˆ8.4, 1.6 Hz, 1H, H-3), 7.93 (dd,
Jˆ6.9, 2.5 Hz, 1H, H-5), 7.95 (dd, Jˆ6.9, 2.5 Hz, 1H,
H-8), 7.98 (d, Jˆ8.4 Hz, 1H, H-4), 8.19 (d, Jˆ1.6 Hz, 1H,
H-1), 12.06 (s, 1H, 20-OH); 13C NMR d 118.4 (C-30), 118.7
(C-50), 119.3 (C-10), 125.3 (C-3), 127.0 (C-7), 127.8 (C-5),
128.2 (C-6), 128.4 (C-4), 129.2 (C-8), 130.4 (C-1), 132.1
(C-2), 133.7 (C-60), 134.8 (C-10), 135.1 (C-9), 136.3
(C-40), 163.2 (C-20), 201.5 (CvO); MS (EI) m/z (rel. int.)
249 [(M11)1, 25], 248 (M1z, 94), 247 [(M21)1, 100], 231
(17), 189 (8), 155 (31), 129 (9), 128 (57), 127 (54), 126 (15),
124 (12), 121 (40), 101 (9), 93 (12). Anal. Calcd for
C17H12O2: C, 82.24; H, 4.87. Found: C, 81.90; H, 4.49.
3.4. General procedure for the synthesis of
benzo[b]xanthones 11
A mixture of compounds 8 and 9 (0.4 mmol) and iodine
(10.2 mg, 0.04 mmol) in DMSO (5 mL) was re¯uxed for
2 h. After cooling, the reaction mixture was poured into
ice and water. A small amount of Na2S2O3 was added and
the reaction mixture stirred for some minutes. The obtained
yellow solid was ®ltered and washed with water. The
residue was taken in chloroform and washed with water.
The recrystallisation of the obtained residue in ethanol
gave compounds 11 in good yields.
3.4.1. Benzo[b]xanthone (11a) (98%). Mp 214±2158C; 1H
NMR d 7.38 (ddd, Jˆ7.9, 7.0, 0.9 Hz, 1H, H-10), 7.51 (ddd,
Jˆ8.2, 6.9, 1.2 Hz, 1H, H-3), 7.52 (d, Jˆ8.1 Hz, 1H, H-8),
7.63 (ddd, Jˆ8.1, 6.9, 1.3 Hz, 1H, H-4), 7.76 (ddd, Jˆ8.1,
7.0, 1.7 Hz, 1H, H-9), 7.92 (s, 1H, H-6), 7.93 (d, Jˆ8.1 Hz,
1H, H-5), 8.09 (d, Jˆ8.2 Hz, 1H, H-2), 8.34 (dd, Jˆ7.9,
1.7 Hz, 1H, H-11), 8.96 (s, 1H, H-1); 13C NMR d 113.5
(C-6), 117.8 (C-8), 121.0 and 121.3 (C-11a and C-12a),
123.4 (C-10), 125.5 (C-3), 126.3 (C-11), 126.9 (C-5),
128.3 (C-1), 129.0 (C-4), 129.5 (C-1a), 129.7 (C-2), 135.3
(C-9), 136.7 (C-5a), 152.2 (C-6a), 156.7 (C-7a), 178.0
(C-12); MS (EI) m/z (rel. int.) 247 [(M11)1, 23], 246
(M1z, 100), 218 (21), 189 (25). Anal. Calcd for
C17H10O2´0.25H2O: C, 81.35; H, 4.18. Found: C, 81.38; H,
4.31. HRMS (EI) calcd for C17H10O2: 246.0681. Found:
246.0678.
3.3.22. (2-Hydroxy-4-methoxyphenyl)-2-naphthylketone
(10f) (2.3%). Yellowish oil; 1H NMR d 3.89 (s, 3H, OCH3),
6.44 (dd, Jˆ8.9, 2.5 Hz, 1H, H-50), 6.56 (d, Jˆ2.5 Hz, 1H,
H-30), 7.56±7.65 (m, 2H, H-6,7), 7.60 (d, Jˆ8.9 Hz, 1H,
H-60), 7.74 (dd, Jˆ8.3, 1.7 Hz, 1H, H-3), 7.91±7.96 (m,
2H, H-5,8), 7.97 (d, Jˆ8.3 Hz, 1H, H-4), 8.14 (d,
Jˆ1.7 Hz, 1H, H-1), 12.76 (s, 1H, 20-OH); 13C NMR: d
55.7 (OCH3), 101.1 (C-30), 107.5 (C-50), 113.3 (C-10),
125.3 (C-3), 126.9 (C-7), 127.8 (C-5), 128.0 (C-6), 128.3
(C-4), 129.1 (C-8), 129.8 (C-1), 132.2 (C-9), 134.6 (C-10),
135.3 (C-60), 135.5 (C-2), 166.2 and 166.3 (C-20 and C-40),
199.9 (CvO). HRMS (EI) calcd for C18H14O3: 278.0943.
Found 278.0939.
3.3.23. (2-Hydroxy-6-methoxyphenyl)-2-naphthylketone
(10g) (2.4%). Yellowish oil; 1H NMR d 3.48 (s, 3H, OCH3),
6.46 (d, Jˆ8.3 Hz, 1H, H-50), 6.72 (dd, Jˆ8.3, 0.5 Hz, 1H,
H-30), 7.43 (t, Jˆ8.3 Hz, 1H, H-40), 7.53 (ddd, Jˆ8.0, 7.0,
1.2 Hz, 1H, H-7), 7.59 (ddd, Jˆ8.1, 7.0, 1.3 Hz, 1H, H-6),
7.67 (dd, Jˆ8.6, 1.7 Hz, 1H, H-3), 7.85 (d, Jˆ8.6 Hz, 1H,
H-4), 7.88 (d, Jˆ8.1 Hz, 1H, H-5), 7.93(d, Jˆ8.0 Hz, 1H,
H-8), 8.19 (s, 1H, H-1), 10.8 (s, 1H, 20-OH); 13C NMR d
55.3 (OCH3), 102.3 (C-50), 110.4 (C-30), 111.8 (C-10), 125.0
(C-3), 126.4 (C-7), 127.2 (C-4), 127.7 (C-5), 127.9 (C-6),
129.3 (C-8), 129.4 (C-1), 132.4 (C-9), 134.9 (C-10), 135.6
(C-40), 138.1 (C-2), 160.1 (C-60), 161.9 (C-20), 199.7
(CvO). HRMS (EI) calcd for C18H14O3: 278.0943. Found
278.0931.
3.4.2. 10-Methylbenzo[b]xanthone (11b) (97%). Mp 176±
1778C; 1H NMR d 2.46 (s, 3H, CH3), 7.37 (d, Jˆ8.6 Hz, 1H,
H-8), 7.48 (ddd, Jˆ8.2, 6.9, 1.1 Hz, 1H, H-3), 7.53 (dd,
Jˆ8.6, 2.2 Hz, 1H, H-9), 7.59 (ddd, Jˆ8.3, 6.9, 1.2 Hz,
1H, H-4), 7.85 (s, 1H, H-6), 7.89 (d, Jˆ8.3 Hz, 1H, H-5),
8.05 (d, Jˆ8.2 Hz, 1H, H-2), 8.13 (d, Jˆ2.2 Hz, 1H, H-11),
8.91 (s, 1H, H-1); 13C NMR d 20.8 (CH3), 113.4 (C-6),
117.6 (C-8), 120.7 (C-11a), 121.3 (C-12a), 125.4 (C-3),
126.3 (C-11), 127.0 (C-5), 128.3 (C-1), 128.9 (C-4), 129.4
(C-1a), 129.7 (C-2), 133.1 (C-10), 136.5 (C-9), 136.6
(C-5a), 152.3 (C-6a), 154.9 (C-7a), 178.1 (C-12); MS (EI)
m/z (rel. int.) 261 [(M11)1, 29], 260 (M1z, 100), 259
[(M21)1, 20], 232 (9), 231 (25), 203 (7), 202 (17). Anal.
Calcd for C18H12O2´0.25H2O: C, 81.57; H, 4.72. Found: C,
81.67; H, 4.62. HRMS (EI) calcd for C18H12O2: 260.0837.
Found: 260.0831.
3.3.24. (2-Hydroxy-5-nitrophenyl)-2-naphthylketone (10j)
1
(38.5%). Mp 175±1768C; H NMR d 7.23 (d, Jˆ9.2 Hz,
1H, H-30), 7.64 (ddd, Jˆ8.0, 6.8, 1.2 Hz, 1H, H-7), 7.69
(ddd, Jˆ8.1, 6.8, 1.3 Hz, 1H, H-6), 7.80 (dd, Jˆ8.5,
1.7 Hz, 1H, H-3), 7.97 (d, Jˆ8.1 Hz, 1H, H-5), 8.00 (d,
Jˆ8.0 Hz, 1H, H-8), 8.04 (d, Jˆ8.5 Hz, 1H, H-4), 8.24 (d,
Jˆ1.7 Hz, 1H, H-1), 8.42 (dd, Jˆ9.2, 2.7 Hz, 1H, H-40),
8.69 (d, Jˆ2.7 Hz, 1H, H-60), 12.73 (s, 1H, 20-OH); 13C
NMR d 118.2 (C-10), 119.6 (C-30), 124.8 (C-3), 127.5
(C-7), 128.0 (C-5), 129.0 (C-6), 129.1 (C-4), 129.4 (C-8),
129.7 (C-60), 130.9 (C-40), 131.0 (C-1), 132.2 (C-9), 133.5
(C-2), 135.3 (C-10), 139.5 (C-50), 168.0 (C-20), 200.4
(CvO); MS (EI) m/z (rel. int.) 294 [(M11)1, 25], 293
(M1z, 100), 292 [(M21), 79], 276 (11), 246 (16), 218 (4),
189 (10), 166 (8), 155 (45), 128 (52), 127 (74), 126 (12), 120
(13). Anal. Calcd for C17H11NO4´0.25H2O: C, 68.50; H,
3.86; N, 4.70. Found: C, 68.56; H, 4.05; N, 5.10. HRMS
(EI) calcd for C17H11NO4: 293.0688. Found: 293.0682.
3.4.3. 10-Chlorobenzo[b]xanthone (11c) (94%). Mp
2258C; 1H NMR d 7.41 (d, Jˆ8.9 Hz, 1H, H-8), 7.49
(ddd, Jˆ8.2, 6.9, 1.0 Hz, 1H, H-3), 7.59 (ddd, Jˆ8.2, 6.9,
1.0 Hz, 1H, H-4), 7.64 (dd, Jˆ8.9, 2.6 Hz, 1H, H-9), 7.84 (s,
1H, H-6), 7.88 (d, Jˆ8.2 Hz, 1H, H-5), 8.03 (d, Jˆ8.2 Hz,
1H, H-2), 8.28 (d, Jˆ2.6 Hz, 1H, H-11), 8.94 (s, 1H, H-1);
13C NMR d 113.7 (C-6), 119.6 (C-8), 120.8 (C-12a), 122.0
(C-11a), 125.7 (C-3), 126.3 (C-11), 127.1 (C-5), 128.6 (C-1),
129.2 (C-10), 129.3 (C-4), 129.7 (C-1a), 129.8 (C-2), 135.2
(C-9), 136.8 (C-5a), 152.0 (C-6a), 155.1 (C-7a), 176.8
(C-12); MS (EI) m/z (rel. int.) 283 [(M11)1, 37Cl, 8], 282
(M1z, 37Cl, 43), 281 [(M21)1, 37Cl; (M11)1, 35Cl; 25], 280
(M1z, 35Cl, 100), 252 (13), 189 (16). Anal. Calcd for
C17H9ClO2´0.25H2O: C, 71.52; H, 3.33. Found: C, 71.85;
H, 3.54. Found: C, 81.67; H, 4.62. HRMS (EI) calcd for
C17H937ClO2: 282.0262. Found: 282.0261.

A. Sandulache et al. / Tetrahedron 58 (2002) 105±114
113
3.4.4. 10-Bromobenzo[b]xanthone (11d) (96%). Mp 206±
2088C; 1H NMR d 7.37 (d, Jˆ8.9 Hz, 1H, H-8), 7.51 (ddd,
Jˆ8.2, 6.9, 1.1 Hz, 1H, H-3), 7.62 (ddd, Jˆ8.3, 6.9, 1.3 Hz,
1H, H-4), 7.79 (dd, Jˆ8.9, 2.5 Hz, 1H, H-9), 7.86 (s, 1H,
H-6), 7.89 (d, Jˆ8.3 Hz, 1H, H-5), 8.04 (d, Jˆ8.2 Hz, 1H,
H-2), 8.45 (d, Jˆ2.5 Hz, 1H, H-11), 8.89 (s, 1H, H-1); 13C
NMR d 113.7 (C-6), 116.4 (C-10), 119.9 (C-8), 120.8
(C-12a), 122.3 (C-11a), 125.8 (C-3), 127.1 (C-5), 128.6
(C-1), 129.3 (C-4), 129.4 (C-11), 129.6 (C-1a), 129.8
(C-2), 136.8 (C-5a), 138.0 (C-9), 151.9 (C-6a), 155.4
(C-7a), 176.8 (C-12); MS (EI) m/z (rel. int.) 327
[(M11)1, 81Br, 22], 326 (M1z, 81Br, 100), 325 [(M21)1,
81Br, (M11)1, 79Br, 23], 324 (M1z, 79Br, 99), 298 (7), 296
(7), 217 (8), 190 (6), 189 (36), 188 (7), 187 (12), 163 (10),
95 (13), 78 (15). Anal. Calcd for C17H9BrO2´0.25H2O: C,
61.88; H, 2.88. Found: C, 62.10; H, 2.71. HRMS (EI) calcd
for C17H981BrO2: 325.9765. Found: 325.9771.
276 (M1z, 100), 275 [(M21)1, 38], 259 (10), 248 (14),
247 (72), 246 (24), 231 (10), 230 (38), 218 (17), 189 (27),
176 (10), 138(10), 109 (19), 95 (17). Anal. Calcd for
C18H12O3´0.25H2O: C, 76.92; H, 4.45. Found: C, 76.26; H,
4.54. HRMS (EI) calcd for C18H12O3: 276.0786. Found:
276.0778.
3.4.8. 11-Hydroxybenzo[b]xanthone (11i) (91%). Mp
212±2148C; 1H NMR d 6.81 (dd, Jˆ8.3, 0.8 Hz, 1H,
H-10), 6.94 (dd, Jˆ8.3, 0.8 Hz, 1H, H-8), 7.52 (ddd,
Jˆ8.3, 6.8, 1.2 Hz, 1H, H-3), 7.62 (t, Jˆ8.3 Hz, 1H, H-9),
7.64 (ddd, Jˆ8.3, 6.8, 1.2 Hz, 1H, H-4), 7.87 (s, 1H, H-6),
7.92 (d, Jˆ8.3 Hz, 1H, H-5), 8.07 (d, Jˆ8.3 Hz, 1H, H-2),
8.89 (s, 1H, H-1), 12.69 (s, 1H, OH); 13C NMR d 106.9
(C-8), 108.3 (C-11a), 110.3 (C-10), 113.5 (C-6), 120.1
(C-12a), 125.7 (C-3), 127.1 (C-5), 127.9 (C-1), 129.5
(C-1a,4), 129.8 (C-2), 137.1 (C-5a), 137.4 (C-9), 151.9
(C-6a), 156.7 (C-7a), 162.3 (C-11), 183.0 (C-12); MS (EI)
m/z (rel. int.) 263 [(M11)1, 27], 262 (M1z, 100), 205 (10),
176 (9). HRMS (EI) calcd for C17H10O3: 262.0630. Found:
262.0635.
3.4.5. 8,10-Dibromobenzo[b]xanthone (11e) (94%). Mp
1
266±2688C; H NMR d 7.55 (ddd, Jˆ8.0, 6.9, 1.0 Hz,
1H, H-3), 7.66 (ddd, Jˆ8.2, 6.9, 1.2 Hz, 1H, H-4), 7.94
(d, Jˆ8.2 Hz, 1H, H-5), 8.04 (s, 1H, H-6), 8.05 (d,
Jˆ8.0 Hz, 1H, H-2), 8.08 (d, Jˆ2.5 Hz, 1H, H-9), 8.42 (d,
Jˆ2.5 Hz, 1H, H-11), 8.91 (s, 1H, H-1); 13C NMR d 112.6
(C-8), 114.3 (C-6), 116.3 (C-10), 120.3 (C-12a), 123.2
(C-11a), 126.1 (C-3), 127.2 (C-5), 128.8 (C-1), 129.0
(C-11), 129.6 (C-4), 129.9 (C-2), 130.1 (C-1a), 137.0 (C-
5a), 140.6 (C-9), 151.7 (C-6a), 152.3 (C-7a), 176.2 (C-12);
MS (EI) m/z (rel. int.) 407 [(M11)1, 81Br, 15], 406 (M1z,
81Br, 60), 405 (28), 404 (M1z, 79Br81Br, 100), 403 (15), 402
(M1z, 79Br, 61), 269 (13), 267 (14), 216 (20), 202 (8), 188
(18), 187 (29), 114 (10), 107 (10), 94 (9). Anal. Calcd for
C17H8Br2O2´0.25H2O: C, 47.32; H, 2.55. Found: C, 47.40;
H, 2.19. HRMS (EI) calcd for C17H881Br2O2: 405.8850.
Found: 405.8856.
3.4.9. 10-Nitrobenzo[b]xanthone (11j) (92%). Mp 258±
1
2608C; H NMR (CDCl31TFA) d 7.61 (ddd, Jˆ8.3, 7.0,
1.1 Hz, 1H, H.3), 7.73 (d, Jˆ9.2 Hz, 1H, H-8), 7.71±7.76
(m, 1H, H-4), 8.00 (d, Jˆ8.4 Hz, 1H, H-5), 8.05 (s, 1H,
H-6), 8.14 (d, Jˆ8.3 Hz, 1H, H-2), 8.64 (dd, Jˆ9.2,
2.8 Hz, 1H, H-9), 9.00 (s, 1H, H-1), 9.24 (d, Jˆ2.8 Hz,
1H, H-11); 13C NMR (CDCl31TFA) d 114.7 (C-6), 119.6
(C-12a), 120.0 (C-8), 120.2 (C-11a), 124.1 (C-11), 126.9
(C-3), 127.4 (C-5), 129.6 (C-1), 130.2 (C-2), 130.4
(C-9,1a), 130.7 (C-4), 137.8 (C-5a), 143.5 (C-10), 151.7
(C-6a), 160.4 (C-7a), 179.3 (C-12); MS (EI) m/z (rel. int.)
292 [(M11)1, 27], 291 (M1z, 100), 261 (12), 245 (33), 217
(14), 205 (10), 190 (11), 189 (49), 188 (11), 187 (19), 163
(10), 114 (9). Anal. Calcd for C17H9NO4´0.25H2O: C, 67.94;
N, 4.66; H, 3.33. Found: C, 67.87; N, 5.01; H, 3.62. HRMS
(EI) calcd for C17H9NO4: 291.0532. Found: 291.0526.
3.4.6. 9-Methoxybenzo[b]xanthone (11f) (88%). Mp 190±
1
1928C; H NMR d 3.95 (s, 3H, OCH3), 6.88 (d, Jˆ2.3 Hz,
1H, H-8), 6.92 (dd, Jˆ8.8, 2.3 Hz, 1H, H-10), 7.49 (ddd,
Jˆ8.2, 6.9, 1.2 Hz, 1H, H-3), 7.60 (ddd, Jˆ8.2, 6.9, 1.3 Hz,
1H, H-4), 7.84 (s, 1H, H-6), 7.90 (d, Jˆ8.2 Hz, 1H, H-5),
8.06 (d, Jˆ8.2 Hz, 1H, H-2), 8.28 (d, Jˆ8.8 Hz, 1H, H-11),
8.91 (s, 1H, H-1); 13C NMR d 55.9 (OCH3), 100.2 (C-8),
112.7 (C-10), 113.3 (C-6), 115.1 (C-11a), 121.5 (C-12a),
125.4 (C-3), 127.0 (C-5), 128.2 (C-1), 128.6 (C-11), 128.8
(C-4), 129.6 (C-1a), 129.7 (C-2), 136.4 (C-5a), 152.4
(C-6a), 158.6 (C-7a), 165.5 (C-9), 177.0 (C-12); MS (EI)
m/z (rel. int.) 277 [(M11)1, 25], 276 (M1z, 100), 233 (11),
205 (11), 176 (7). HRMS (EI) calcd for C18H12O3: 276.0786.
Found: 276.0780.
Acknowledgements
Thanks are due to the University of Aveiro and `FundacËaÄo
Ã
para a Ciencia e Tecnologia', for funding the Organic
Chemistry Research Unit. A. Sandulache also thanks FCT
for a grant (BD/19670/99) and the Dunarea de Jos Univer-
sity, Galati, Romania for her leave of absence.
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