An expeditious synthesis of polyhydroxylated 2-arylbenzo[b]furans

Article abstract of DOI:10.1016/S0040-4020(01)00462-8

An expeditious synthesis of polyhydroxylated 2-arylbenzo[b]furans is described. The key steps are the conversion of the corresponding polymethoxylated stilbenes into diarylethanoid molecules (epoxide or alcohol) that were demethylated and cyclised using boron tribromide to give the target polyhydroxylated 2-arylbenzo[b]furans.

Full text of DOI:10.1016/S0040-4020(01)00462-8

TETRAHEDRON
Pergamon
Tetrahedron 57 ,2001) 5585±5589
An expeditious synthesis of polyhydroxylated
2-arylbenzo[b]furans
Romain Dupont and Philippe Cotellep
 Â
Laboratoire de Chimie Organique Physique associe au CNRS, ENSCL, Universite de Lille 1, F-59655 Villeneuve d'Ascq, France
Received 29 January 2001; revised 30 March 2001; accepted 24 April 2001
AbstractÐAn expeditious synthesis of polyhydroxylated 2-arylbenzo[b]furans is described. The key steps are the conversion of the
corresponding polymethoxylated stilbenes into diarylethanoid molecules ,epoxide or alcohol) that were demethylated and cyclised using
boron tribromide to give the target polyhydroxylated 2-arylbenzo[b]furans. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Natural polyphenols containing a 2-phenylbenzo[b]furan
unit such as moracins1 or norlignans2 ,Scheme 1) often
exhibit interesting biological activities. This has stimulated
numerous studies3 on the synthesis of the 2-phenylbenzo[b]-
furan skeleton.
In order to design the best 1,2-diarylethanoid unit, we
synthesised three model molecules, i.e. 2-,2-methoxy-
phenyl)-1-,4-methoxyphenyl)ethanone 1a, 1,2-epoxy-1-,2-
methoxyphenyl)-2-,4-methoxyphenyl)ethane 2a and 2-,3-
chlorobenzoyloxy)-1-,2-methoxyphenyl)-2-,4-methoxy
phenyl)ethanol 3a ,Scheme 2). We have chosen these
models since the known 2-,4-hydroxyphenyl)benzofuran
5a8 presents an easily interpretable 1H NMR spectrum.
The proton H3 appears as a doublet at 7.04 ppm with a
As a part of our studies on the synthesis of new biologically
active polyhydroxylated compounds,4 we have shown that
boron tribromide may promote a tandem deprotection±
cyclisation of 2-methoxyphenylacetones5 and 2-hydroxy-
3-arylpropenoic acids6 leading respectively to 2-methyl
and 2-carboxybenzo[b]furans in moderate yields. These
results led us to evaluate the synthesis of natural or synthetic
polyhydroxylated 2-phenylbenzo[b]furans from 1,2-diaryl-
ethanoid units and boron tribromide. The acid-catalysed
tandem deprotection±cyclisation of diarylethanoid units is
well documented7 but the reported procedure generally
requires hard conditions ,concentrated acid, high tempera-
ture) and gives variable yields. Our new approach might be
of particular interest due to the limited number of steps
involved ,®ve steps from the commercially available benzyl
alcohols) and its simplicity.
5
coupling constant of Jˆ0.85 Hz, the phenyl protons as
two doublets at 6.97 and 7.78 ppm ,3Jˆ8.8 Hz) and the
other aromatic protons as two broad singlets at 7.14±7.31
and 7.48±7.59 ppm. Compound 1a was prepared according
to Clader et al.9 Compounds 2a and 3a were obtained from
the reaction of the corresponding E-stilbene 4a and
mcpba.10 The structure of 3a was unambiguously estab-
lished from the NMR data ,1H, 13C and 1H±13C correlation).
Compound 3a was obtained from the nucleophilic substi-
tution of the epoxide 2a by m-chlorobenzoic acid. Under
neutral conditions, this reaction is known to follow a
second-order kinetics and the nucleophile reacts on the
less hindered position to give 3a. The crude product
Scheme 1.
Keywords: boron and compounds; dealkylation; cyclisation; benzofurans.
Corresponding author. Tel.: 133-320-33-72-31; fax: 133-320-33-63-09; e-mail: philippe.cotelle@univ-lille1.fr
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020,01)00462-8

5586
R. Dupont, P. Cotelle / Tetrahedron 57 12001) 5585±5589
Scheme 2.
Table 1. Stilbenes 4 and 2-arylbenzo[b]furans 5 prepared
Entry
Yield in 4a
Starting material
R4
R5
R0
R0
4
Yield in 5c
b
R3
3
1
2
3
4
5
6
7
8
9
10
1a
2a
3a
2a13a
2b
2c
3d
3e
H
H
H
H
H
H
H
OMe
H
H
H
H
H
H
H
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
13
58
65
50
51
21
64
40
48
66
71
71
71
70
80
72
84
71
86
H
H
H
OMe
H
H
H
OMe
H
H
H
H
H
H
H
OMe
OMe
OMe
H
OMe
OMe
H
H
OMe
2f
3g
H
a
Unoptimised yields in crude stilbenes 4 form the corresponding commercially available benzylalcohols.
For the structures of compounds 2, 3, 4 and 5 see Scheme 3.
Overall yields in 2-arylbenzo[b]furans 5 calculated from the puri®ed starting material ,entries 1±3) or from the crude stilbenes 4 ,other entries).
b
c
,mixture of 2a and 3a) of the reaction of crude 4a ,E/Zˆ4)
was also tested in order to evaluate the relevance of an
exhaustive puri®cation at this early step. The results
reported in Table 1 ,entries 1±3) led us to choose the
`epoxide/alcohol' strategy since 1a gave 5a in only 13%
yield whereas 5a was obtained in 58 and 65% yields from
2a and 3a, respectively. The unseparated products of the
oxidation of 4a with mcpba were converted into 5a in
50% yield ,entry 4). Consequently, stilbene 4 was not
separated from its Z isomer before oxidation and the oxida-
tion products ,2 and 3) were not puri®ed prior to cyclisation.
The yields in 5 are given for the transformation 4!5.
Oxidation of 4 with mcpba gave variable amounts of
epoxide 2 ,the trans isomer was the major product in the
same proportions than the E isomer of the starting stilbene
4) and alcohol 3 ,as mixtures of diastereoisomers and in
some cases regioisomers). The main product is indicated
in Table 1, column 2.
Stilbenes 4 were synthesised in three steps from the
commercially available benzyl alcohols as depicted in
Scheme 3. The known benzyl bromides11±15 were obtained
from the reaction of the corresponding benzyl alcohols
with 48% aqueous HBr16 or with phosphorus tribromide15
in 88±96% yields. The phosphonium bromides were
obtained by treatment of the corresponding benzyl bromides
0
0
Scheme 3. For 4 RxˆRy ˆH or OCH3; for 5 RxˆRy ˆH or OH; ,a) HBr 48% or PBr3 88±96%; ,b) P,C6H5)3, toluene, re¯ux, 4 h, 75±90%; ,c) MeOH, MeONa,
then 4-methoxy or 3,4-dimethoxybenzaldehyde, 76±96%; ,d) mcpba, CH2Cl2, NaHCO3; ,e) BBr3, CH2Cl2, 208C, 21±66%.

R. Dupont, P. Cotelle / Tetrahedron 57 12001) 5585±5589
5587
with triphenylphosphine in re¯uxed toluene17 in 75±90%
yields. The stilbenes 418±22 were obtained by a classical
Wittig reaction22 in variable mixtures of E and Z isomers.
The crude stilbenes were used without further puri®cation
except for 4a. The epoxidation of the stilbenes was carried
out according to Moyna et al.10 to give variable mixtures of
epoxides 2 ,cis and trans isomers) and alcohols 3 ,erythro
and threo isomers). The epoxidation products were used
without further puri®cation except for 2a and 3a.
yellow powder: dH ,200 MHz, CDCl3; Me4Si): 3.81 ,3H, s,
OMe), 3.84 ,3H, s, OMe), 3.89 ,3H, s, OMe), 3.94 ,3H, s,
OMe), 6.78±6.87 ,3H, m), 6.99±7.14 ,4H, m), 7.31 ,1H, d,
3Jˆ16.2 Hz); Elemental analysis calcd for C18H20O4: C,
71.98; H, 6.71; found: C, 72.02; H, 6.89.
4.1.4. 1,2-Epoxy-1-'2-methoxyphenyl)-2-'4-methoxy-
phenyl)ethane 2a. 48% yield; white powder: dH
,200 MHz, CDCl3; Me4Si): 3.80 ,d, 1H, 4Jˆ1.90 Hz),
4
3.834 ,s, 3H), 3.841 ,s, 3H), 4.33 ,d, 1H, Jˆ1.90 Hz),
3
6.90±7.08 ,m, 2H), 6.96 ,d, 2H, Jˆ8.90 Hz), 7.29±7.39
3
3. Conclusion
,m, 2H), 7.35 ,d, 2H, Jˆ8.90 Hz); dC,50 MHz, CDCl3;
Me4Si): 55.39 ,q), 55.43 ,q), 58.1 ,d), 62.3 ,d), 110.2 ,d),
114.0 ,d), 120.8 ,d), 125 ,s), 125.9 ,d), 127.1 ,d), 128.9 ,d),
129.6 ,s), 158.1 ,s), 159.8 ,s); MS ,EI) m/z ,%): 256 ,13),
227 ,40), 151 ,68), 135 ,42), 121 ,100), 91 ,17), 77 ,18);
Elemental analysis calcd for C16H16O5: C, 74.98; H, 6.29;
found: C, 75.25; H, 6.08.
We have successfully obtained by this method seven
hydroxylated 2-phenylbenzo[b]furans in 17±57% overall
yields ,from the corresponding benzyl alcohols) in ®ve
steps. This strategy may be easily applied to the synthesis
of some norlignans that possess a 2-phenylbenzo[b]furan
skeleton. This expeditious, inexpensive and simple method
for the synthesis of polyhydroxylated 2-phenylbenzo[b]fur-
ans may be of particular interest in the obtention of poten-
tially biologically active synthetic polyphenols. Some of
them are currently being tested as HIV-integrase inhibitors.
4.1.5. 2-'3-Chlorobenzoyloxy)-1-'2-methoxyphenyl)-2-
'4-methoxyphenyl)ethan-1-ol 3a. 31% yield; yellow oil;
dH ,200 MHz, CDCl3; Me4Si): 3.73 ,s, 3H), 3.75 ,s, 3H),
3
3
5.22 ,d, 1H, Jˆ7.0 Hz), 6.31 ,d, 1H, Jˆ7.0 Hz), 6.73±
3
6.87 ,m, 2H), 6.77 ,d, 2H, Jˆ8.90 Hz), 7.10±7.24 ,m,
3
3
2H), 7.20 ,d, 2H, Jˆ8.90 Hz), 7.36 ,dd, 1H, Jˆ7.95 Hz,
3Jˆ7.65 Hz), 7.52 ,ddd, 1H, 3Jˆ7.95 Hz, 4Jˆ1.90 Hz,
4Jˆ1.30 Hz), 7.97 ,ddd, 1H, 3Jˆ7.65 Hz, 4Jˆ1.60 Hz,
4Jˆ1.30 Hz), 8.08 ,dd, 1H, 4Jˆ1.90 Hz, 4Jˆ1.60 Hz);
dC,50 MHz, CDCl3; Me4Si): 55.0 ,q), 55.1, ,q), 73.8 ,d),
79.0 ,d), 110.3 ,d), 113.3 ,d), 120.5 ,d), 127.8 ,d), 128.1
,d), 128.3 ,d), 128.6 ,d), 128.9 ,s), 129.56 ,d), 129.63 ,d),
132.0 ,s), 132.8 ,d), 133.3 ,s), 134.3 ,s), 156.4 ,s), 159.2 ,s),
164.7 ,s); MS ,Vision 2000): 257 ,M2C6H4ClCO2);
Elemental analysis calcd for C23H21ClO5: C, 66.93; H,
5.13; found: C, 66.95; H, 5.47.
4. Experimental
4.1. General
TLC analyses were performed on a 3£10 cm plastic sheet
precoated with silica gel 60F254 ,Merck) ,Solvent system:
ethyl acetate/hexane 1:4). SiO2, 200±400 mesh ,Merck) was
used for column chromatography. Melting points were
obtained on a Reichert Thermopan melting point apparatus,
equipped with a microscope and are uncorrected. NMR
spectra were obtained on an AC 200 Bruker spectrometer
in the appropriate solvent with TMS as internal reference.
Mass spectra were recorded on a Ribermag R 10-10 spectro-
meter ,Electron Impact, 60 eV) or on a Finnigan MAT
Vision 2000 spectrometer [for the MALDI ,mass assisted
laser desorption ionisation)]. Elemental analyses were
performed by CNRS laboratories ,Vernaison) and were
within 0.4% of the theoretical value.
4.1.6. 1,2-Epoxy-1-'2,3-dimethoxyphenyl)-2-'4-methoxy-
phenyl)ethane 2b. White powder: dH ,200 MHz, CDCl3;
3
Me4Si): 3.79 ,d, 1H, Jˆ1.90 Hz), 3.81 ,s, 3H), 3.82 ,s,
3
3H), 3.87 ,s, 3H), 4.23 ,d, 1H, Jˆ1.90 Hz), 6.86±6.94
,m, 2H), 6.92 ,d, 2H, 3Jˆ8.60 Hz), 7.11 ,dd, 1H,
4
3
3Jˆ8.60 Hz, Jˆ1.60 Hz), 7.30 ,d, 2H, Jˆ8.60 Hz).
4.1.1. 'E)-2,5,40-Trimethoxystilbene 4c. 97% yield; yellow
oil: dH ,200 MHz, CDCl3; Me4Si): 3.82 ,3H, s, OMe), 3.83
,3H, s, OMe), 3.85 ,3H, s, OMe), 6.81±6.83 ,2H, m), 6.93
,2H, d, Jˆ8.9 Hz), 7.11 ,1H, d, Jˆ16.5 Hz), 7.21 ,1H, d,
4Jˆ2.55 Hz), 7.42 ,1H, d, 3Jˆ16.5 Hz), 7.52 ,2H, d,
3Jˆ8.9 Hz); Elemental analysis calcd for C17H18O3: C,
75.53; H, 6.71; found: C, 75.45; H, 6.76.
4.1.7. 1,2-Epoxy-1-'2,5-dimethoxyphenyl)-2-'4-methoxy-
phenyl)ethane 2c. White powder; dH ,200 MHz, CDCl3;
3
Me4Si): 3.69 ,d, 1H, Jˆ1.90 Hz), 3.76 ,s, 3H), 3.79 ,s,
3
3
3
3H), 3.81 ,s, 3H), 4.28 ,d, 1H, Jˆ1.90 Hz), 6.82 ,d, 2H,
4Jˆ1.60 Hz), 6.90 ,d, 1H, 4Jˆ1.90 Hz), 6.93 ,d, 2H,
3
3Jˆ8.60 Hz), 7.31 ,d, 2H, Jˆ8.60 Hz).
4.1.8. 2-'3-Chlorobenzoyloxy)-1-'2,4,5-trimethoxyphenyl)-
2-'4-methoxyphenyl)ethan-1-ol 3d. Yellow oil; dH
,200 MHz, CDCl3; Me4Si): 3.67 ,s, 3H), 3.71 ,s, 3H), 3.72
4.1.2. 'E)-2,3040-Trimethoxystilbene 4e. 96% yield; white
powder: dH ,200 MHz, CDCl3; Me4Si): 3.897 ,3H, s, OMe),
3.903 ,3H, s, OMe), 3.95 ,3H, s, OMe), 6.85 ,d, 1H,
3Jˆ8.2 Hz), 6.90 ,1H, dd, 3Jˆ8.2 Hz, 4Jˆ1.6 Hz), 6.97
3
,s, 3H), 3.75 ,s, 3H), 5.07 ,d, 1H, Jˆ7.0 Hz), 6.36 ,d, 1H,
3Jˆ7.0 Hz), 6.56 ,d, 1H, 3Jˆ8.60 Hz), 6.71 ,d, 2H,
3Jˆ8.90 Hz), 6.98 ,d, 1H, 3Jˆ8.60 Hz), 7.14 ,d, 2H,
3Jˆ8.90 Hz), 7.30 ,dd, 1H, 3Jˆ7.95 Hz, 3Jˆ7.65 Hz),
7.46 ,ddd, 1H, 3Jˆ7.95 Hz, 4Jˆ2.20 Hz, 4Jˆ1.30 Hz),
7.92 ,ddd, 1H, 3Jˆ7.65 Hz, 4Jˆ1.60 Hz, 4Jˆ1.30 Hz),
3
4
4
,1H, tdd, Jˆ7.55 Hz, Jˆ1.2 Hz, Jˆ0.45 Hz), 7.06 ,1H,
3
4
m), 7.07,1H, d, Jˆ16.45 Hz), 7.10,1H, d, Jˆ1.60 Hz),
7.24,1H, ddd, 3Jˆ8.2 Hz, 3Jˆ7.4 Hz, 4Jˆ1.7 Hz),
7.34,1H, d, 3Jˆ16.45 Hz), 7.58,1H, dd, 3Jˆ7.65 Hz,
4Jˆ1.75 Hz); Elemental analysis calcd for C17H18O3: C,
75.53; H, 6.71; found: C, 75.15; H, 6.65.
4
4
8.02 ,dd, 1H, Jˆ1.90 Hz, Jˆ1.60 Hz).
4.1.9. 2-'3-Chlorobenzoyloxy)-1-'2-methoxyphenyl)-2-
'3,4-dimethoxyphenyl)ethan-1-ol 3e. Yellow oil: dH
4.1.3. 'E)-2,5,3040-Trimethoxystilbene 4g. 96% yield; pale

5588
R. Dupont, P. Cotelle / Tetrahedron 57 12001) 5585±5589
,200 MHz, CDCl3; Me4Si): 3.66 ,s, 3H), 3.68 ,s, 3H), 3.75
4.2.3. 5,6-Dihydroxy-2-'4-hydroxyphenyl)benzo[b]furan
5d. Brown powder; mpˆ2558C; dH ,200 MHz, acetone-d6;
Me4Si): 6.84 ,d, 1H, 5Jˆ0.85 Hz), 6.91 ,d, 2H, 3Jˆ8.7 Hz),
3
3
,s, 3H), 5.25 ,d, 1H, Jˆ7.0 Hz), 6.22 ,d, 1H, Jˆ7.0 Hz),
4
3
6.63 ,d, 1H, Jˆ1.9 Hz), 6.69 ,d, 1H, Jˆ8.3 Hz), 6.71±
3
4
5
3
6.83 ,m, 2H), 6.84 ,dd, 1H, Jˆ8.3 Hz, Jˆ1.9 Hz), 7.09±
7.19 ,m, 2H), 7.31 ,dd, 1H, 3Jˆ7.95 Hz, 3Jˆ7.65 Hz), 7.46
,ddd, 1H, 3Jˆ7.95 Hz, 4Jˆ1.90 Hz, 4Jˆ1.30 Hz), 7.93 ,ddd,
6.97 ,s, 1H), 7.00 ,d, 1H, Jˆ0.85 Hz), 7.66 ,d, 2H, Jˆ
8.7 Hz), 7.82 ,s, 1H), 8.02 ,s, 1H), 8.65 ,s, 1H); dC,50 MHz,
acetone-d6; Me4Si): 98.4 ,d), 100.1 ,d), 105.8 ,d), 116.5 ,d),
122.4 ,s), 123.6 ,s), 126.5 ,d), 143.2 ,s), 144.5 ,s), 149.9 ,s),
155.8 ,s), 158.4 ,s).; MS ,EI) m/z ,%):242 ,100), 241 ,11),
226 ,16), 139 ,15), 121 ,30); elemental analysis calcd for
C14H10O4: C, 69.42; H, 4.16; found: C, 69.38; H, 4.21.
3
4
4
1H, Jˆ7.65 Hz, Jˆ1.60 Hz, Jˆ1.30 Hz), 8.04 ,dd, 1H,
4
4Jˆ1.90 Hz, Jˆ1.60 Hz).
4.1.10.
1,2-Epoxy-1-'2,3-dimethoxyphenyl)-2-'3,4-di-
methoxyphenyl)ethane 2f. Yellow oil: dH ,200 MHz,
CDCl3; Me4Si): 3.78 ,d, 1H, 3Jˆ1.9 Hz), 3.82 ,s, 3H),
3.87 ,s, 3H), 3.89 ,s, 3H), 3.90 ,s, 3H), 4.19 ,d, 1H,
4.2.4. 2-'3,4-Dihydroxyphenyl)benzo[b]furan 5e. Brown-
grey powder; mpˆ179±1818C; dH ,200 MHz, acetone-d6;
Me4Si): 6.96 ,d, 1H, 3Jˆ8.1 Hz), 7.00 ,d, 1H, 5Jˆ1.15 Hz),
3
3Jˆ1.9 Hz), 6.83±6.97 ,m, 5H), 7.09 ,t, 1H, Jˆ7.95 Hz).
3
4
7.13±7.28 ,m, 2H), 7.31 ,dd, 1H, Jˆ8.1 Hz, Jˆ2.0 Hz),
4
4.1.11. 2-'3-Chlorobenzoyloxy)-1-'2,5-dimethoxyphenyl)-
2-'3,4-dimethoxyphenyl)ethan-1-ol 3g. Orange oil: dH
,200 MHz, CDCl3; Me4Si): 3.66 ,s, 3H), 3.72 ,s, 3H), 3.76
7.44 ,d, 1H, Jˆ2.0 Hz), 7.46±7.58 ,m, 2H), 8.44 ,s, 1H),
8.55 ,s, 1H); dC,50 MHz, acetone-d6; Me4Si): 100.2 ,d),
111.5 ,d), 112.8 ,d), 116.5 ,d), 118.0 ,d), 121.4 ,d), 123.3
,s), 123.7 ,d), 124.5 ,d), 130.5 ,s), 146.4 ,s), 147.2 ,s), 155.4
,s), 157.3 ,s); MS ,EI) m/z ,%): 226 ,100), 152 ,14), 139
,13), 113 ,29), 84 ,74), 49 ,100); elemental analysis calcd
for C14H10O3: C, 74.33; H, 4.46; found: C, 74.28; H, 4.57.
3
,s, 3H), 3.82 ,s, 3H), 5.17 ,d, 1H, Jˆ7.0 Hz), 6.24 ,d, 1H,
3
3Jˆ7.0 Hz), 6.70±6.76 ,m, 6H), 7.39 ,dd, 1H, Jˆ7.95 Hz,
3Jˆ7.65 Hz), 7.51 ,ddd, 1H, 3Jˆ7.95 Hz, 4Jˆ2.20 Hz,
4Jˆ1.3 Hz), 7.97 ,ddd, 1H, 3Jˆ7.65 Hz, 4Jˆ1.6 Hz,
4
4
4Jˆ1.3 Hz), 8.08 ,dd, 1H, Jˆ1.9 Hz, Jˆ1.6 Hz).
4.2.5. 2-'3,4-Dihydroxyphenyl)-7-hydroxybenzo[b]furan
5f. Dark powder; mpˆ99±1018C; dH ,200 MHz, metha-
nol-d4; Me4Si): 6.58 ,dd, 1H, 3Jˆ6.1 Hz, 4Jˆ2.8 Hz),
4.2. Reaction of 1a, 2 or 3 with boron tribromide: general
procedure
3
6.741 ,d, 1H, Jˆ8.2 Hz), 6.743 ,s, 1H), 6.86 ,dd, 1H,
3Jˆ7.8 Hz, 3Jˆ6.1 Hz), 6.91 ,dd, 1H, 3Jˆ7.8 Hz, 4Jˆ
BBr3 ,1 M in CH2Cl2, 15 mL, 15 mmol for 1a, 2a and 3a,
20 mL, 20 mmol for 2b, 2c and 2e or 25 mL, 25 mmol for
3d, 2f and 3g) was added dropwise to a solution of 1a, 2 or 3
,5 mmol) in CH2Cl2 ,20 mL) at room temperature. The
mixture was stirred for 1 h, then water ,40 mL) was added
dropwise. The solid was ®ltered off, dried and crystallized
from acetone ,5d, 5f and 5g). In the other cases, no solid was
obtained and the aqueous layer was extracted twice with
ethyl acetate ,20 mL). The organic layer was dried
,MgSO4), the solvent evaporated and the residue was
puri®ed by column chromatography ,eluent: hexane/ethyl
acetate 1:1).
2.8 Hz), 7.17 ,dd, 1H, 3Jˆ8.2 Hz, 4Jˆ2.0 Hz), 7.23 ,d,
4
1H, Jˆ2.0 Hz); dC,50 MHz, methanol-d4; Me4Si): 100.5
,d), 111.0 ,d), 112.8 ,d), 113.1 ,d), 116.6 ,d), 118.2 ,d),
124.0 ,s), 124.5 ,d), 132.8 ,s), 143.3 ,s), 144.6 ,s), 146.6
,s), 147.3 ,s), 157.6 ,s); MS ,EI) m/z ,%): 242 ,100), 139
,24), 121 ,20), 57 ,22); elemental analysis calcd for
C14H10O4: C, 69.42; H, 4.16; found: C, 69.48; H, 4.08.
4.2.6. 2-'3,4-Dihydroxyphenyl)-6-hydroxybenzo[b]furan
5g. Grey powder; mp.2308C; dH ,200 MHz, acetone-d4;
3
4
Me4Si): 6.76 ,dd, 1H, Jˆ9.0 Hz, Jˆ2.3 Hz), 6.89 ,d, 1H,
3
4
5Jˆ1.1 Hz), 6.91 ,d, 1H, Jˆ8.1 Hz), 6.96 ,d, 1H, Jˆ
3
4
2.3 Hz), 7.26 ,dd, 1H, Jˆ8.1 Hz, Jˆ2.0 Hz), 7.29 ,bd,
1H, 3Jˆ9.0 Hz), 7.35 ,d, 1H, 4Jˆ2.0 Hz); dC,50 MHz,
acetone-d4; Me4Si): 105.9 ,d), 110.6 ,d), 111.6 ,d), 112.6
,d), 113.0 ,d), 116.4 ,d), 127.8 ,s), 123.6 ,d), 131.2 ,s),
146.0 ,s), 146.7 ,s), 149.8 ,s), 150.0 ,s), 154.2 ,s); MS
,EI) m/z ,%): 242 ,100), 139 ,32), 121 ,27); elemental
analysis calcd for C14H10O4: C, 69.42; H, 4.16; found: C,
69.57; H, 4.29.
4.2.1. 7-Hydroxy-2-'4-hydroxyphenyl)benzo[b]furan 5b.
Beige powder; mpˆ176±1788C; dH ,200 MHz, acetone-d6;
Me4Si): 6.75 ,dd, 1H, 3Jˆ6.5 Hz, 4Jˆ2.45 Hz), 6.94 ,d, 2H,
3
3Jˆ8.8 Hz), 6.97±7.08 ,m, 3H), 7.78 ,d, 2H, Jˆ8.8 Hz),
8.91 ,s, 1H), 9.00 ,s, 1H); dC,50 MHz, acetone-d6; Me4Si):
100.4 ,d), 111.1 ,d), 112.5 ,d), 116.6 ,d), 123.0 ,s), 124.5
,d), 127.2 ,d), 132.3 ,s), 143.2 ,s), 144.1 ,s), 157.0 ,s), 159.0
,s); MS ,EI) m/z ,%): 226 ,100), 197 ,12), 113 ,19), 110
,13); elemental analysis calcd for C14H10O3: C, 74.33; H,
4.46; found: C, 74.17; H, 4.53.
Acknowledgements
4.2.2. 5-Hydroxy-2-'4-hydroxyphenyl)benzo[b]furan 5c.
Beige powder; mpˆ2578C; dH ,200 MHz, acetone-d6;
This work was supported by grants from the Centre National
Â
de la Recherche Scienti®que ,CNRS) and the Region Nord-
Pas-de-Calais.
3
4
Me4Si): 6.78 ,dd, 1H, Jˆ8.7 Hz, Jˆ2.6 Hz), 6.92 ,d, 1H,
5Jˆ0.85 Hz), 6.94 ,d, 2H, 3Jˆ8.7 Hz), 6.99 ,dd, 1H,
4Jˆ2.6 Hz, 5Jˆ0.6 Hz), 7.32 ,dt, 1H, 3Jˆ8.7 Hz, 5Jˆ
0.85 Hz, 5Jˆ0.6 Hz), 7.74 ,d, 2H, 3Jˆ8.7 Hz), 8.13 ,s,
1H), 8.75 ,s, 1H); dC,50 MHz, acetone-d6; Me4Si): 100.1
,d), 106.1 ,d), 111.7 ,d), 113.2 ,d), 116.6 ,d), 123.1 ,s),
127.2 ,d), 131.3 ,s), 149.9 ,s), 154.4 ,s), 157.8 ,s), 158.9
,s); MS ,EI) m/z ,%):226 ,100), 197 ,7), 115 ,11), 113 ,24),
110 ,10); elemental analysis calcd for C14H10O3: C, 74.33;
H, 4.46; found: C, 74.52; H, 4.41.
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