Microwave-assisted regioselective synthesis of natural 6-prenylpolyhydroxyisoflavones and their hydrates with hypervalent iodine reagents

Article abstract of DOI:10.1016/j.tet.2006.06.066

Microwave-assisted oxidative rearrangement of 3′-iodotetraalkoxychalcones with hypervalent iodine such as [hydroxy(tosyloxy)iodo]benzene or [bis(trifluoroacetoxy)iodo]benzene, followed by microwave-mediated hydrolysis and in situ cyclization of the resultant acetals gave 6-iodotrialkoxyisoflavones. Pd(0)-catalyzed coupling reaction of the 6-iodoisoflavones with 2-methyl-3-butyn-2-ol under microwave irradiation gave 6-alkynylisoflavones, whose hydrogenation gave the respective hydrates of wighteone, lupisoflavone and derrubone. Wighteone (1a), lupisoflavone (1b) and derrubone (1c) were obtained by dehydration of their respective hydrates under microwave irradiation.

Full text of DOI:10.1016/j.tet.2006.06.066

Tetrahedron 62 (2006) 8625–8635
Microwave-assisted regioselective synthesis of natural
6-prenylpolyhydroxyisoflavones and their hydrates
with hypervalent iodine reagents
*
Mohammad M. Hossain, Yasuhiko Kawamura, Kazuyo Yamashita and Masao Tsukayama
Department of Chemical Science and Technology, Faculty of Engineering, The University of Tokushima,
Minamijosanjima-cho, Tokushima 770-8506, Japan
Received 29 March 2006; accepted 5 June 2006
Available online 10 July 2006
Abstract—Microwave-assisted oxidative rearrangement of 30-iodotetraalkoxychalcones with hypervalent iodine such as [hydroxy(tosyloxy)-
iodo]benzene or [bis(trifluoroacetoxy)iodo]benzene, followed by microwave-mediated hydrolysis and in situ cyclization of the resultant
acetals gave 6-iodotrialkoxyisoflavones. Pd(0)-catalyzed coupling reaction of the 6-iodoisoflavones with 2-methyl-3-butyn-2-ol under micro-
wave irradiation gave 6-alkynylisoflavones, whose hydrogenation gave the respective hydrates of wighteone, lupisoflavone and derrubone.
Wighteone (1a), lupisoflavone (1b) and derrubone (1c) were obtained by dehydration of their respective hydrates under microwave irradiation.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
preventive medicine, food supplements, agrochemicals and
cosmetics in recent years. Soy isoflavones show oxidative
metabolism properties in humans invitro and invivo.13 How-
ever, very recent studies14 have also indicated that some soy
isoflavones such as genistein and/or daidzein induced can-
cers of reproductive organs of female rodents. Despite these
findings, there is growing research interest in isoflavonoids
due to their health-related properties.
In the 10 years since the appearance of the first paper on or-
ganic synthesis under microwave dielectric heating, the field
has expanded dramatically.1–4 Chemistry in the 21st century
is increasingly being called upon to develop green chemistry
methods as it attempts to deal with the scientific challenges
of protecting the human health and the environment from
the hazards posed by chemical processes. Considerable re-
search efforts to use microwave for organic synthesis have
been expended over the last two decades. This is because mi-
crowave minimizes the formation of unwanted by-products,
and it reduces the need for organic solvents to a minimum or
can even be used under solvent-free conditions.5,6 Our pres-
ent study will report on the total synthesis of some physio-
logically important prenylisoflavones under microwave
dielectric heating with environmentally-friendly hypervalent
iodine reagents and minimal use of solvents. Isoflavone de-
rivatives are widely distributed in nature and are very impor-
tant as precursors of prenylisoflavones and pterocarpans.7,8
In addition, they exhibit phytoalexin, antifungal, anti-inflam-
matory and anticancer properties.9–11 Recent studies have
shown that some isoflavones have excellent health-
promoting effects.12 Hence, isoflavones and their derivatives
have been receiving considerable attention in the fields of
Wighteone, which has a strong antifungal property, was first
isolated from healthy leaves of Lupinus albus together with
luteone in 1976, but its structure was not fully identified at
the time.15 The following year (1977), wighteone was iso-
lated from fungus-inoculated stems of Glycine wightii as
a phytoalexin and the structure was assigned to be 5,7,40-tri-
hydroxy-6-(3-methyl-2-butenyl)isoflavone (1a) on the basis
of spectroscopic method.9 Wighteone was also isolated as
erythrinin B from the bark of Erythrina variegata16 and, to-
gether with luteone, from the roots of white lupin.17,18 More-
over, wighteone was metabolized in a culture of Aspergillus
flavus to be transformed into wighteone hydrate as a major
metabolite, whose structure was determined as 5,7,40-tri-
hydroxy-6-(3-hydroxy-3-methylbutyl)isoflavone (2a) by
spectroscopic analysis.19 Synthesis of 1a and 2a by classical
heating method has been reported earlier.20 The isomer
[lupiwighteone¼5,7,40-trihydroxy-8-(3-methyl-2-butenyl)-
isoflavone] of wighteone has also been synthesized by con-
ventional method.21,22 But, we report here the first total
synthesis of wighteone (1a) and wighteone hydrate (2a)
under microwave irradiation (MWI). Lupisoflavone, a new
Keywords: MW-synthesis; Regioselectivity; 6-Prenylisoflavones; 30-Iodo-
chalcones; Hypervalent iodine; Wighteone; Lupisoflavone; Derrubone.
* Corresponding author. Tel.: +81 88 656 7405; fax: +81 88 655 7025;
e-mail: tukayama@chem.tokushima-u.ac.jp
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.06.066

8626
M. M. Hossain et al. / Tetrahedron 62 (2006) 8625–8635
R1
4
2 3
5'
R2
R1O
R2
OMOM
Ac
OR
BnO 4'
6'
1
MW
R2
+
1'
3'
I
EtOH, KOH
reflux (88 °C)
5-7 min
R1
OHC
6
5
2'
OBn O
OR1
6a R1 = H, R2 = OBn
6b R1 = OMe, R2 = OBn
7a R = MOM, R1 = H, R2 = OBn
7b R = MOM, R1 = OMe, R2 = OBn
3 R1 = R2 = H
MW
I2/H5IO6
2 min
4 R1 = H, R2 = I
5 R1 = Bn, R2 = I
O
O
O
O
6c R1 = R2
=
7c R = MOM, R1 = R2
8a R = R1 = H, R2 = OBn
=
8b R = H, R1 = OMe, R2 = OBn
O
O
8c R = H, R1 = R2
=
R1
OMe
OBz
OBz
BnO
BnO
I
R2
MW
OMe
MW
MW
R1 MeOH, NaOH
50 °C, 3-5 min
R2
HTIB/BTIB
BzCl, Pyridine
reflux (125 °C)
5-6 min
I
MeOH, CHCl3
OBn O
OBn
O
60 °C, 12 min
9a R1 = H, R2 = OBn
10a R1 = H, R2 = OBn
9b R1 = OMe, R2 = OBn
10b R1 = OMe, R2 = OBn
O
O
O
O
10c R1 = R2
=
9c R1 = R2
=
8
1
BnO
I
7
O
BnO
O
2
MW
2'
1
6
R1
R2
1'
3'
R
H2, Pd/C
3
5
4
OH
4'
R2
OBn O
MeOH, Dioxane
rt, 1 h
OBn O
6'
Pd (0)
Et3N, DMF
HO
5'
80 °C, 8-10 min
11a R1 = H, R2 = OBn
12a R1 = H, R2 = OBn
12b R1 = OMe, R2 = OBn
11b R1 = OMe, R2 = OBn
O
O
12c R1 = R2
=
11c R1 = R2
=
O
O
HO
O
O
BzO
O
O
BzCl
R1
R1
R2
Acetone
HO
HO
OH
OR
45 °C, 25 min
R2
2a R1 = H, R2 = OH
2b R1 = OMe, R2 = OH
13a R = R1 = H, R2 = OBz
14a R = Ts, R1 = H, R2 = OBz
13b R = H, R1 = OMe, R2 = OBz
MW, TsCl
8 min
O
O
2c R1 = R2
=
MW, TsCl
30 min
14b R = Ts, R1 = OMe, R2 = OBz
O
O
13c R = H, R1 = R2
=
MW, TsCl
O
O
11 min
14c R = Ts, R1 = R2
=
Scheme 1.
prenylated isoflavone, was isolated as a minor constituent
from the leaf extract of white lupin (L. albus L.) and the
structure was deduced as 5,7,40-trihydroxy-6-(3-methyl-
2-butenyl)-30-methoxyisoflavone (1b) with the help of spec-
troscopic analyses.17,18 Lupisoflavone shows moderate
antifungal activity.17 Furthermore, lupisoflavone induces the
conversion of both the C1 and C2 cell wall isoperoxidases to
the C5 isoperoxidases, which possess scopoletin-peroxidase
activity.23 This is a unique characteristic of lupisoflavone to
bring about the conformational change of these cell wall
enzymes. Neither partial nor total synthesis of lupisoflavone
has yet been reported by either conventional or MWI
methods. Derrubone was isolated from the root of the Indian
tree Derris Robosta.24 Structural investigation of derrubone
and its analogues (especially robustic acid, robustone and
derrustone) was carried out by chemical and spectroscopic
methods.24–27 From degradative and spectroscopic analyses,
the structure of derrubone was found to be 5,7-dihydroxy-6-
(3-methyl-2-butenyl)-30,40-methylenedioxyisoflavone (1c).
Synthesis of derrubone has been reported, however, the yield
obtained was very low.28 Moreover, the report lacked spec-
troscopic data to establish the structure of derrubone except
for the melting point. Therefore, we report here the first total
synthesis of 1b and 1c under MWI.
The regioselective and direct introduction of an alkenyl or
alkyl group at the 6-position of the isoflavone skeleton is
relatively difficult, as it consists of many protections and con-
sequent deprotections, and the easy isomerization of 6-alkyl-
polyhydroxyisoflavones into 8-alkylpolyhydroxyisoflavones

M. M. Hossain et al. / Tetrahedron 62 (2006) 8625–8635
8627
by bases.29,30 Generally, isoflavones are synthesized by oxi-
dative rearrangement of chalcones with thallium(III) nitrate
trihydrate, Tl(III)(NO3)3$3H2O (TTN).31,32 Compound 2a
was also synthesized by oxidative rearrangement of the cor-
responding 30-iodochalcone with TTN under conventional
heating in low yield.33 These results show the limit and scope
of TTN as an oxidizing reagent of chalcones. Moreover, TTN
is toxic, expensive and adversely affects the environment.
Recently, it has been reported that hypervalent iodine re-
agents such as [hydroxy(tosyloxy)iodo]benzene (HTIB)34
and [bis(trifluoroacetoxy)iodo]benzene (BTIB)35 have be-
come more useful for the oxidative rearrangement of chal-
cones. We were able to achieve far better results by using
hypervalent iodine reagents as oxidizing agents for the con-
versions of chalcones to acetals and isoflavones.20,36 Unlike
TTN, hypervalent iodine reagents are environmentally-
friendly and have the added benefits of being easier to
prepare and handle.37 The use of MW-technique with hyper-
valent iodine reagents was not only accelerated reaction
pathways but also very advantageous from both the economi-
cal and the environmental standpoints. We do report here on
the first total syntheses of 1a, 2a, 1b, 5,7,40-trihydroxy-6-(3-
hydroxy-3-methylbutyl)-30-methoxyisoflavone (2b), 1c and
5,7-dihydroxy-6-(3-hydroxy-3-methylbutyl)-30,40-methyl-
enedioxyisoflavone (2c) from their corresponding 30-iodo-
chalcones using hypervalent iodine reagents under MWI, a
better syntheticroute consideringgreenchemistry (Scheme 1).
2. Results and discussion
Microwave-assisted regioselective introduction of iodine
at the 30-position of 60-methoxymethoxyacetophenone 3,
obtained by the catalytic hydrogenolysis (5% Pd/C) of 20,40-
bis(benzyloxy)-60-methoxymethoxyacetophenone, was car-
ried out with iodine and periodic acid33,38 under temperature
controlled MWI for 2 min to give the desired 30-iodoaceto-
phenone 4 in 96% yield. The benzylation of compound 4
with benzyl chloride in the presence of K2CO3 in dimethyl-
formamide (DMF) gave 20,40-bis(benzyloxy)-30-iodoaceto-
phenone 5 in 82% yield. Microwave-mediated cross aldol
condensations of 5 with different aromatic aldehydes such
as 4-benzyloxybenzaldehyde (6a), 4-benzyloxy-3-methoxy-
benzaldehyde (6b) and 3,4-methylenedioxybenzaldehyde
(6c) in the presence of alcoholic KOH solution from 5 to
7 min gave the 60-methoxymethoxychalcones 7a–c as crude
semisolids, respectively. 60-Hydroxychalcones 8a–c were
obtained from their respective crude compounds 7a–c by
concd HCl-mediated hydrolysis in a mixture of methanol
and chloroform in more than 85% yields (via two steps
from 5). The separate treatment of 8a–c with benzoyl
chloride in pyridine under MWI from 5 to 6 min afforded
60-benzoyloxychalcones 9a–c in 91, 98 and 89% yields,
respectively. The separate oxidative rearrangement of 9a–c
with HTIB in methanol under MWI for 12 min gave the
respective crude acetals 10a–c, which were liable to be un-
stable through silica gel column chromatography (decompo-
sition takes place). The structures of 10a–c were confirmed
by 1H NMR [d: 3.0 and 3.22, CH(OCH3)2]. The subsequent
hydrolysis of 10a–c with 20% NaOH and in situ ring closure
under MWI from 3 to 5 min afforded the desired 6-iodoiso-
flavones 11a–c in 74, 59 and 46% yields (via two steps
from their corresponding 60-benzoyloxychalcones 9a–c),

8628
M. M. Hossain et al. / Tetrahedron 62 (2006) 8625–8635
BzO
O
O
BzO
O
R1
R2
R1
R2
OR
MW
HO
OR
O
.
TsOH H2O
15a' R = Ts, R1 = H, R2 = OBz
15b' R = Ts, R1 = OMe, R2 = OBz
Toluene
14a R = Ts, R1 = H, R2 = OBz
117 °C, 15 min
O
O
15c' R = Ts, R1 = R2
=
14b R = Ts, R1 = OMe, R2 = OBz
O
O
14c R = Ts, R1 = R2
=
+
BzO
O
O
BzO
O
1M BCl3
R1
R2
R1
R2
CH2Cl2
< 20 °C, 1-2 h
OR
OH
O
15a R = Ts, R1 = H, R2 = OBz
16a R1 = H, R2 = OBz
15b R = Ts, R1 = OMe, R2 = OBz
16b R1 = OMe, R2 = OBz
O
O
O
O
16c R1 = R2
=
15c R = Ts, R1 = R2
=
10% NaOH
MeOH, Dioxane
rt, 20 min
HO
O
R
O
O
R1
R2
R1
R2
Ac2O, Pyridine
OH
O
115 °C, 1-2 h
R
17a R = R2 = OAc, R1 = H
1a R1 = H, R2 = OH
1b R1 = OMe, R2 = OH
17b R = R2 = OAc, R1 = OMe
O
O
1c R1 = R2
=
O
O
17c R = OAc, R1 = R2
=
Scheme 2.
respectively. In a similar manner, the oxidative rearrange-
ment of 9a–c was also carried out with BTIB under MWI
for 12 min and the resultant acetals 10a–c were cyclized
with 20% NaOH to give 11a–c in 69, 25 and 32% yields, re-
spectively. Microwave-assisted coupling reaction of 11a–c
with 2-methyl-3-butyn-2-ol in the presence of Pd(0)39,40 in
a mixture of triethylamine and DMF from 8 to 10 min
gave 6-(3-hydroxy-3-methylbutynyl)isoflavones 12a–c in
78, 64 and 68% yields, respectively. The quantitative cata-
lytic hydrogenation and hydrogenolysis of 12a–c with 5%
Pd/C in a mixture of methanol and 1,4-dioxane at room tem-
perature afforded 6-(3-hydroxy-3-methylbuyl)isoflavones
2a–c in 88, 93 and 87% yields, respectively. It has been men-
tioned earlier that compound 2a (wighteone hydrate) is a
natural product although the other two compounds 2b and 2c
are not yet obtained as natural products. The spectral data
and other physical properties of 2a were identical with those
of the natural sample of wighteone hydrate19 (see Table 1,
Section 4). Exhaustive benzoylation of 2a with benzoyl
chloride under MWI gave a mixture (about 1:1) of 40,7-
bis(benzoyloxy)isoflavone 13a and 40,5,7-tris(benzoyloxy)-
6-(3-hydroxy-3-methylbutyl)isoflavone. On the other hand,
the exhaustive benzoylation of 6-alkylpolyhydroxyiso-
flavones with bases in prolonged reaction time causes
their isomerization to 8-alkylpolyhydroxyisoflavones by
conventional heating method.29,30,33 Therefore, the partial
benzoylation of 2a–c was achieved in acetone at 45 ꢀC for
25 min to give the 5-hydroxyisoflavones 13a–c in 85, 86
and 91% yields, respectively. The failure of exhaustive
benzoylation of compounds 2a–c is presumably due to the
non-bonding interaction of 5-OH with C-4 carbonyl oxygen.
Tosylation of the 5-hydroxyisoflavones 13a–c with TsCl
under MWI from 8 to 30 min in acetone gave 5-tosyloxy-
isoflavones 14a–c in 89, 93 and 94% yields, respectively
Scheme 2.
Compound 14a was dehydrated with TsOH$H2O in a solu-
tion of acetic acid and dry toluene under MWI for 15 miny
to give a mixture of the desired 6-prenylisoflavone 15a and
the regioisomer, 6-(3-methyl-3-butenyl)isoflavone 15a0.
The dehydration of the other compounds 14b and 14c was
also carried out in a similar manner to give the respective
6-prenylisoflavones 15b and 15c with a slight amount of
1
their corresponding regioisomers 15b0 and 15c0. The H
NMR spectra of each of the isomeric alkenyl mixtures
(15a and 15a0, 15b and 15b0, 15c and 15c0) showed that
the unwanted regioisomers (15a0–c0) were less than 5% in
y
The total reaction time was observed to be 30 min. But, it took 15 min for
the reaction mixture to get reflux.

M. M. Hossain et al. / Tetrahedron 62 (2006) 8625–8635
8629
every case. The formation of the 6-alkenylisoflavones 15a–c
3. Conclusion
as major products can easily be understood by their 1H NMR
spectra [peaks due to CH2CH]C(CH3)2 at d: 3.37 (2H, d)
and CH2CH2C(CH3)]CH2 at d: 4.51 and 4.62 (each 1H,
s)]. The same dehydration under classical heating condi-
tions, which was reported in our previous papers,20,33 led
to the formation of the unwanted regioisomer in about
28% yield. It is difficult to remove the regioisomer from
the mixture by the usual physical methods. But, in the case
of the microwave method, the unwanted regioisomer, which
is less than 5%, is very easy to remove by usual physical
methods such as recrystallization. It is clear from our data
that microwave heating has advantages over the classical
heating in that it reduces reaction time and solvent quantity
and also on account of its very high regioselectivity, which is
explained below.
For the total synthesis of biologically important 6-prenyliso-
flavones 1a–c, MWI technique was employed successfully.
MW-synthesis was much more advantageous over the con-
ventional method with regard to reaction time, solvent quan-
tity and product yield. By using the MWI method in our
synthesis, moreover, we were able to achieve very high re-
gioselectivity compared to the results obtained under con-
ventional heating. And though wighteone was obtained in
a slight mixture with its regioisomer (5%), the other two
compounds (lupisoflavone and derrubone) were obtained
with a very small amount of regioisomers under microwave
dehydration. This high regioselective synthesis of prenyliso-
flavones under microwave conditions is very important as it
gave clean product and avoided the need for arduous regio-
isomeric separation.
2.1. High regioselectivity of MW dehydration—
formation of 6-prenylisoflavone as major product
4. Experimental
4.1. General
It has been reported that microwave dielectric heating and
non-thermal effects play an important role in the regio-,
chemo- and stereoselectivity, however, it is worth noting
that there is no concrete clarification of these observations.4
Without exception, we were able to achieve very high regio-
selectivity of the MW dehydration of compounds 14a–c.
Each of the dehydrations led to the formation of the required
6-prenylisoflavones 15a–c as major products (in some cases,
one product exclusively) and far less or almost no regio-
isomers 15a0–c0. This increased selectivity is the most
important factor in MW-synthesis, because the desired
product was obtained, rather than the unwanted regioisomer.
The possible explanation for the formation of 6-prenylisofla-
vones as major products lies in the fact that, due to its
powers, MW provides elevated heating rates and accelerated
reaction times. We used toluene as solvent for the dehydra-
tion and the reflux temperature was observed to be 117 ꢀC,
which was higher than its conventional boiling point
(110 ꢀC). Under such elevated heating conditions, the ther-
modynamically-controlled products, 6-prenylisoflavones,
predominated over the kinetically-controlled regioisomers.
The unwanted regioisomer, thermally labile, is converted
into the more stable 6-prenylisoflavone due to such elevated
heating rates.
All the melting points were taken on a Yanaco MP-J3 micro
melting-point apparatus and were uncorrected. The 1H NMR
spectra were recorded with a JEOL EX-400 spectrophoto-
meter (400 MHz) using tetramethylsilane (TMS) as the
internal standard. The IR spectra were obtained on an FT/
IR-460 Plus (JASCO) spectrophotometer using KBr pellets.
The UV spectra were obtained on a Hitachi U-2000 spectro-
photometer. Elemental analyses were obtained on a Yanaco
CHN corder model MT-5. A microwave oven (650 W and
2.45 GHz, modified properly by fitting a condenser and
a thermo-sensor through the holes made in the roof; Shikoku
Instrumentation Co., Ltd, Japan) was used as a reaction
apparatus. Column chromatography and thin-layer chroma-
tography (TLC) were carried out with Kieselgel 60 (70–230
mesh) and Kieselgel 60 F254 (Merck).
4.1.1. 20,40-Dihydroxy-60-methoxymethoxyacetophenone
(3). The palladium/carbon catalyzed hydrogenolysis of
20,40-bis(benzyloxy)-60-methoxymethoxyacetophenone30
(4.80 g, 12.2 mmol), which was synthesized by methoxy-
methylation of 20,40-bis(benzyloxy)-60-hydroxyacetophe-
none, in a mixture of MeOH (100 ml) and AcOEt (100 ml)
was carried out at 20 ꢀC until the uptake of hydrogen ceased.
The solvent was removed under reduced pressure and the
resulting compound was recrystallized from a mixture of
AcOEt and hexane to give 3 (2.48 g, 95%) as colourless
crystals, mp 117–119 ꢀC. 1H NMR (CDCl3) d: 2.65 (3H, s,
COCH3), 3.52 (3H, s, OCH3), 5.25 (2H, s, OCH2O), 6.04
(1H, d, J¼2.4 Hz, Ar–H), 6.14 (1H, d, J¼2.4 Hz, Ar–H),
The detosylation of 15a–c with 1 M BCl3 solution in
dichloromethane at room temperature gave the respective
5-hydroxyisoflavones 16a–c in 91, 94 and 79% yields,
respectively. The hydrolysis of 16a–c with 10% NaOH
in a mixture of methanol and 1,4-dioxane at room tempera-
ture gave 5,7,40-trihydroxy-6-(3-methyl-2-butenyl)isoflavone
(wighteone) (1a) in 72%, 5,7,40-trihydroxy-6-(3-methyl-2-
butenyl)-30-methoxyisoflavone (lupisoflavone) (1b) in 62%
and 5,7-dihydroxy-6-(3-methyl-2-butenyl)-30,40-methylene-
dioxyisoflavone (derrubone) (1c) in 79% yields, respectively.
The spectral data and other physical properties of 1a, 1b and
1c were identical with those of the natural samples of wight-
eone,19 lupisoflavone17 and derrubone,24 respectively (see
Table 1, Section 4). On the basis of these results, the struc-
tures of wighteone, lupisoflavone and derrubone were con-
firmed for the first time by the MW-synthesis of 1a, 1b and
1c, respectively. 6-Prenylisoflavones 1a–c were converted
into their respective acetate derivatives 17a–c.
0
13.79 (1H, s, C2 –OH); Anal. Calcd for C10H12O5: C,
56.60; H, 5.70. Found: C, 56.61; H, 5.60.
4.1.2. MW-synthesis of 20,40-dihydroxy-30-iodo-60-
methoxymethoxyacetophenone (4). Compound 3 (2.50 g,
11.8 mmol) was dissolved in ethanol (40 ml), followed by
the successive addition of iodine (1.49 g, 5.87 mmol) and
periodic acid (542 mg, 2.37 mmol in water, 5 ml). The reac-
tion mixture was irradiated under MW for 2 min at 45 ꢀC.
Cooling and diluting the reaction mixture with water gave
a crystalline solid, which was recrystallized from a mixture

8630
M. M. Hossain et al. / Tetrahedron 62 (2006) 8625–8635
of AcOEt and hexane to give 4 (3.85 g, 96%) as a pale yellow
]CH); Anal. Calcd for C43H33IO6: C, 66.85; H, 4.31.
Found: C, 66.68; H, 4.45.
1
solid, mp 162–164 ꢀC. H NMR (CDCl3) d: 2.68 (3H, s,
COCH3), 3.51 (3H, s, OCH3), 5.27 (2H, s, OCH2O), 6.0
0
(1H, s, C4 –OH), 6.43 (1H, s, C5 –H), 14.95 (1H, s,
0
C2 –OH); Anal. Calcd for C10H11IO5: C, 35.52; H, 3.28.
Found: C, 35.32; H, 3.17.
0
4.1.6. MW-synthesis of 1-[6-benzoyloxy-2,4-bis(benz-
yloxy)-3-iodophenyl]-2-(4-benzyloxyphenyl)-3,3-di-
methoxypropan-1-one (10a) and 5,7,40-tris(benzyloxy)-
6-iodoisoflavone (11a). Compound 9a (5.50 g, 7.12 mmol)
was dissolved in a mixture of MeOH (50 ml) and CHCl3
(20 ml), followed by the addition of HTIB (4.12 g,
10.5 mmol). The reaction mixture was irradiated under
MW for 12 min (2 minꢁ6 times irradiation, 1–2 min inter-
val/irradiation) at 60 ꢀC. The excess HTIB was decomposed
with 5% Na2SO3 solution (1.5 ml) and then the reaction mix-
ture was extracted with CHCl3, washed with water and dried
(Na2SO4). Removal of the solvent under reduced pressure
gave crude acetal 10a (6.50 g) as a semisolid mass. This
crude mass was dissolved in a mixture of MeOH (40 ml)
and CHCl3 (10 ml), followed by the addition of 20%
NaOH (32 ml) and irradiated under MW at 50 ꢀC for
5 min. The reaction mixture was neutralized with 10%
HCl, extracted with CHCl3, washed with water and dried
(Na2SO4). The solvent was removed under reduced pressure
to give a yellow solid. The crude solid was purified by
column chromatography (CH2Cl2/hexane; 3:1) and further
recrystallized from a mixture of AcOEt and MeOH (1:1)
to give 6-iodoisoflavone 11a (3.51 g, 74%, two steps yield
4.1.3. 20,40-Bis(benzyloxy)-30-iodo-60-methoxymethoxy-
acetophenone (5). A solution of benzyl chloride (4.10 g,
32.4 mmol) in DMF (5 ml) was added slowly to a mixture
of 4 (5.0 g, 14 mmol) and K2CO3 (10.0 g, 72.3 mmol) in
DMF (50 ml) under nitrogen. The reaction mixture was
heated at 70 ꢀC for 1 h, and then cooled to room temperature,
and extracted with CHCl3. The extract was washed with 5%
HCl and water and dried (Na2SO4) after which the solvent
was removed. The residue was recrystallized from a mixture
of AcOEt and MeOH to give 5 (6.30 g, 82%) as colourless
1
needles, mp 98–99 ꢀC. H NMR (CDCl3) d: 2.47 (3H, s,
COCH3), 3.46 (3H, s, OCH3), 4.97 (2H, s, PhCH2), 5.15
0
(2H, s, OCH2O), 5.18 (2H, s, PhCH2), 6.65 (1H, s, C5 –H),
7.32–7.61 (10H, m, Ar–Hꢁ10); Anal. Calcd for
C24H23IO5: C, 55.61; H, 4.47. Found: C, 55.66; H, 4.48.
4.1.4. MW-synthesis of 4,20,40-tris(benzyloxy)-30-iodo-60-
methoxymethoxychalcone (7a) and 4,20,40-tris(benzyl-
oxy)-60-hydroxy-30-iodochalcone (8a). A mixture of 5
(5.0 g, 9.6 mmol) and 6a (2.66 g, 12.5 mmol) was dissolved
in alc. KOH (5.40 g, 96.2 mmol in 100 ml EtOH). The reac-
tion mixture was irradiated under MW for 6 min (1 minꢁ6
times irradiation, 1–2 min interval/irradiation), and moni-
tored by TLC to establish completion. The reaction mixture
was neutralized with 10% HCl and extracted with CHCl3,
and then the solvent was removed under reduced pressure
to give a yellow semisolid mass of 7a, which was hydrolyzed
with concd HCl in a mixture of MeOH (60 ml) and CHCl3
(60 ml) at 40 ꢀC for 1 h. The hydrolyzed mixture was al-
lowed to cool to room temperature, extracted with CHCl3,
washed with water and dried (Na2SO4). The solvent was re-
moved under reduced pressure to give a solid mass, which
was recrystallized from a mixture of CHCl3 and AcOEt to
afford 8a (5.99 g, 93%, two steps yield from 5) as a yellow
solid, mp 138–140 ꢀC. 1H NMR (CDCl3) d: 4.85, 5.10
1
from 8a), mp 154–156 ꢀC. H NMR (CDCl3) d: 5.07, 5.10
and 5.26 (each 2H, s, PhCH2), 6.74 (1H, s, C8–H), 7.02
0
0
(2H, d, J¼8.3 Hz, C3 – and C5 –H), 7.31–7.49 (15H, m,
0
0
Ar–Hꢁ15), 7.76 (2H, d, J¼8.3 Hz, C2 – and C6 –H), 7.81
(1H, s, C2–H); Anal. Calcd for C36H27IO5: C, 64.87; H,
4.08. Found: C, 64.65; H, 4.22.
1
Acetal 10a: H NMR (CDCl3) d: 3.0 and 3.22 (each 3H, s,
OCH3), 4.92, 5.02 and 5.11 (each 2H, s, PhCH2), 4.78 and
4.95 (each 1H, d, J¼10.2 Hz, CH), 6.59 (1H, s, Ar–H),
7.05 (2H, d, J¼8.7 Hz, Ar–Hꢁ2), 7.11 (2H, d, J¼8.6 Hz,
Ar–Hꢁ2), 7.13–7.71 (24H, m, Ar–Hꢁ24).
The similar treatment of compound 9a (2.11 g, 2.97 mmol)
with BTIB (1.91 g, 4.44 mmol) under MWI for 12 min
(2 minꢁ6 times irradiation, 1–2 min interval/irradiation) at
60 ꢀC gave crude acetal 10a, which was cyclized with
20% NaOH under MWI for 5 min to give 11a (1.25 g, 69%).
0
and 5.21 (each 2H, s, PhCH2), 6.42 (1H, s, C5 –H), 6.82
(2H, d, J¼8.7 Hz, C3– and C5–H), 7.18–7.52 (17H, m,
Ar–Hꢁ17), 7.83 and 7.88 (each 1H, d, J¼15.4 Hz, ]CH),
4.1.7. MW-synthesis of 5,7,40-tris(benzyloxy)-6-(3-
hydroxy-3-methyl-1-butynyl)isoflavone (12a). Compound
11a (3.50 g, 5.25 mmol) was dissolved in DMF (15 ml), fol-
lowed by the successive addition of Et3N (60 ml), PdCl2
(46 mg, 0.25 mmol), PPh3 (120 mg, 0.457 mmol) and CuI
(44 mg, 0.23 mmol) and finally 2-methyl-3-butyn-2-ol
(1.53 ml, 15.7 mmol). The reaction mixture was irradiated
under MWat 80 ꢀC under nitrogen for 8 min (1 minꢁ8 times
irradiation, 1–2 min interval/irradiation), and then cooled to
room temperature. The cool mixture was filtered through
a sintered glass using Celite and the filtrate was extracted
with AcOEt. The AcOEt extract was washed with 5% HCl
and water and dried (Na2SO4). The solvent was removed
under reduced pressure and the resulting solid was chro-
matographed on silica gel column (CH2Cl2/AcOEt; 9:1)
and further recrystallized from a mixture of AcOEt and
Me2CO (2:1) to give 12a as a colourless crystalline solid
0
13.77 (1H, s, C6 –OH); Anal. Calcd for C36H29IO5: C,
64.68; H, 4.37. Found: C, 64.81; H, 4.53.
4.1.5. MW-synthesis of 4,20,40-tris(benzyloxy)-60-benzoyl-
oxy-30-iodochalcone (9a). Benzoyl chloride (1.73 g,
12.3 mmol) was slowly added to a mixture of 8a (5.50 g,
8.23 mmol) in pyridine (45 ml). The reaction mixture was
irradiated incessantly under MW at 125 ꢀC for 5 min. After
cooling, it was extracted with CHCl3, washed with 5%
HCl and water and dried (Na2SO4). After removal of the
solvent, a pale yellow crude mass was obtained. The crude
was purified on silica gel column chromatography (CHCl3/
hexane; 3:2) to give 9a as a fluffy crystalline solid (5.75 g,
1
91%), mp 47–48 ꢀC. H NMR (CDCl3) d: 4.99, 5.07 and
0
5.21 (each 2H, s, PhCH2), 6.76 (1H, s, C5 –H), 6.88 (1H,
d, J¼15.8 Hz, ]CH), 6.89 (2H, d, J¼8.7 Hz, C2– and
C6–H), 7.27–7.63 (20H, m, Ar–Hꢁ20), 8.04 (2H, d,
J¼8.7 Hz, C3– and C5–H), 8.08 (1H, d, J¼15.8 Hz,
1
(2.55 g, 78%), mp 170–171 ꢀC. H NMR (CDCl3) d: 1.50

M. M. Hossain et al. / Tetrahedron 62 (2006) 8625–8635
8631
(6H, s, CH3ꢁ2), 5.10 (2H, s, PhCH2), 5.20 (4H, s,
PhCH2ꢁ2), 6.71 (1H, s, C8–H), 7.02 (2H, d, J¼8.7 Hz,
at 117 ꢀC for 15 min. After cooling, the reaction mixture was
extracted with ether, washed with 5% NaHCO3 and water
and dried (Na2SO4). After removal of the solvent, the
obtained crude mass was chromatographed on silica gel
column (CHCl3 as a solvent) to give 6-alkenylisoflavone
0
0
0
0
C3 – and C5 –H), 7.66 (2H, d, J¼8.7 Hz, C2 – and C6 –H),
7.29–7.52 (15H, m, Ar–Hꢁ15), 7.79 (1H, s, C2–H); Anal.
Calcd for C41H34O6: C, 79.08; H, 5.50. Found: C, 79.11;
H, 5.68.
1
as a crystalline solid. The H NMR spectrum showed that
it was a mixture of 6-(3-methyl-2-butenyl)isoflavone 15a
and the regioisomer, 6-(3-methyl-3-butenyl)isoflavone 15a0
(15/15a0¼95:5). The isomeric mixture was recrystallized
twice from a mixture of CHCl3 and Me2CO (5:1) to give
15a (720 mg, 74% from 14a) as a crystalline solid, mp
4.1.8. 5,7,40-Trihydroxy-6-(3-hydroxy-3-methylbutyl)iso-
flavone (wighteone hydrate) (2a). Compound 12a (1.0 g,
1.6 mmol) was hydrogenolyzed over 5% Pd/C (120 mg) in
a mixture of methanol (35 ml) and dioxane (35 ml) until
the uptake of hydrogen ceased. The resulting compound
was recrystallized from a mixture of MeOH and Me2CO to
give 2a (504 mg, 88%) as a colourless solid, mp 230–
232 ꢀC (lit.19 225–228 ꢀC). 1H NMR (see Table 1); IR
(KBr) nmax 3340, 3300, 2920, 1620, 1500, 1450, 1220,
1058 cmꢂ1; UV lmax nm (log 3) (MeOH): 265sh (4.41),
214 (4.29), (+AlCl3) 269 (4.37), (+NaOAc) 335.5 (4.1),
274.5sh (4.39), 231sh (4.45); Anal. Calcd for C20H20O6: C,
67.41; H, 5.66. Found: C, 67.61; H, 5.80.
1
202–204 ꢀC. H NMR (CDCl3) d: 1.41 and 1.46 (each 3H,
s, CH3), 2.40 (3H, s, Ar–CH3), 3.36 (2H, d, J¼6.5 Hz,
CH2), 4.96 (1H, t, J¼6.5 Hz, ]CH), 7.25–7.70 (13H,
m, Ar–Hꢁ13), 7.89 (1H, s, C2–H), 7.92–8.25 (6H, m,
Ar–Hꢁ6); Anal. Calcd for C41H32O9S: C, 70.27; H, 4.60.
Found: C, 70.05; H, 4.72.
4.1.12. 7,40-Bis(benzoyloxy)-5-hydroxy-6-(3-methyl-2-
butenyl)isoflavone (16a). Compound 15a (400 mg,
0.571 mmol) was dissolved in dry CH2Cl2 (10 ml), followed
by the addition of BCl3 (0.60 ml, 1 M solution in CH2Cl2)
in an ice bath. The reaction mixture was stirred below
20 ꢀC under nitrogen for 2.5 h. The resulting mixture was
quenched with saturated NH4Cl solution and extracted with
CH2Cl2, washed with water and dried (Na2SO4). The solvent
was removed under reduced pressure and the obtained
compound was purified on silica gel column chromatography
(CHCl3 as a solvent) and further recrystallized from AcOEt
to give 16a (285 mg, 91%) as a colourless crystalline solid,
4.1.9. 7,40-Bis(benzoyloxy)-5-hydroxy-6-(3-hydroxy-3-
methylbutyl)isoflavone (13a). A mixture of 2a (650 mg,
1.82 mmol), benzoyl chloride (0.48 ml, 4.1 mmol) and
K2CO3 (1.40 g, 10.1 mmol) in acetone (25 ml) was heated
at 45 ꢀC under nitrogen for 25 min. Filtered off K2CO3,
andremovalofthesolventunderreducedpressuregavearesi-
due, which was extracted with AcOEt, washed with 5% HCl
and water and dried (Na2SO4). The solvent was removed un-
der reduced pressure and the resulting compound was recrys-
tallized from a mixture of CH2Cl2 and Me2CO to give 13a
1
mp 192–194 ꢀC. H NMR (CDCl3) d: 1.58 and 1.60 (each
1
(880 mg, 85%) as a colourless solid, mp 160–161 ꢀC. H
3H, s, CH3), 3.39 (2H, d, J¼6.8 Hz, CH2), 5.17 (1H, t,
J¼6.8 Hz, ]CH), 6.87 (1H, s, C8–H), 7.32–7.67 (10H,
m, Ar–Hꢁ10), 8.00 (1H, s, C2–H), 8.20–8.24 (4H, m,
Ar–Hꢁ4), 13.10 (1H, s, C5–OH); Anal. Calcd for
C34H26O7: C, 74.71; H, 4.79. Found: C, 74.57; H, 4.91.
NMR (CDCl3) d: 1.20 (6H, s, CH3ꢁ2), 1.74 and 2.77 (each
2H, m, CH2), 6.90 (1H, s, C8–H), 7.34 (2H, d, J¼8.5 Hz,
0
0
C3 – and C5 –H), 7.25–7.68 (10H, m, Ar–Hꢁ10), 8.01 (1H,
0
0
s, C2–H), 8.24 (2H, d, J¼8.5 Hz, C2 – and C6 –H), 13.13
0
(1H, s, C5 –OH); Anal. Calcd for C34H28O8: C, 72.33; H,
5.00. Found: C, 72.45; H, 5.10.
4.1.13. 5,7,40-Trihydroxy-6-(3-methyl-2-butenyl)iso-
flavone (wighteone) (1a). Compound 16a (180 mg,
0.329 mmol) was dissolved in a mixture of methanol
(3 ml) and dioxane (3 ml), followed by the addition of 10%
NaOH (2 ml). The reaction mixture was stirred at 25 ꢀC for
20 min. The resulting mixture was neutralized with 2%
HCl and the organic layer was evaporated under reduced
pressure. The obtained residue was extracted with AcOEt,
washed with water and dried (Na2SO4). The solvent was re-
moved under reduced pressure to give a solid mass, which
was chromatographed on silica gel column (AcOEt/CHCl3;
1:6) and the resulting compound was recrystallized from
a mixture of CHCl3 and AcOEt to give the 6-prenylisofla-
vone 1a (80 mg, 72%) as a pale yellow crystalline solid,
4.1.10. MW-synthesis of 7,40-bis(benzoyloxy)-6-(3-hy-
droxy-3-methylbutyl)-5-tosyloxyisoflavone (14a). A mix-
ture of 13a (500 mg, 0.885 mmol), tosyl chloride (290 mg,
1.52 mmol) and K2CO3 (1.29 g, 9.33 mmol) in acetone
(35 ml) was irradiated under MW for 8 min (2 minꢁ4 times
irradiation, 1–2 min interval/irradiation). The reaction mix-
ture was cooled to room temperature, and neutralized with
5% HCl and then extracted with AcOEt, washed with water
and dried (Na2SO4). After removal of the solvent, the ob-
tained crude solid was recrystallized from a mixture of
CHCl3 and Me2CO (10:3) to give 14a (566 mg, 89%) as col-
ourless needles, mp 178–181 ꢀC. 1H NMR (CDCl3) d: 1.14
(6H, s, CH3ꢁ2), 1.33 (1H, br s, OH), 1.74 and 2.82 (each
2H, m, CH2), 2.42 (3H, s, Ar–CH3), 7.25–7.74 (15H, m,
Ar–Hꢁ15), 7.90 (1H, s, C2–H), 7.96 (2H, d, J¼8.5 Hz,
1
mp 205–207 ꢀC (lit.19 206–208 ꢀC). H NMR (see Table
1); IR (KBr) nmax 3365, 3240, 2930, 1650, 1615, 1510,
1215, 1065, 818 cmꢂ1; UV lmax nm (log 3) (MeOH): 266sh
(4.45), 214 (4.38), (+AlCl3) 268.5sh (4.41), (+NaOAc) 341
(3.93), 275.5 (4.43), 229sh (4.70); Anal. Calcd for
C20H18O5: C, 70.99; H, 5.36. Found: C, 70.88; H, 5.52.
0
0
0
0
C3 – and C5 –H), 8.23 (2H, d, J¼8.5 Hz, C2 – and C6 –H);
Anal. Calcd for C41H34O10S: C, 68.51; H, 4.77. Found: C,
68.75; H, 4.81.
4.1.11. MW-synthesis of 7,40-bis(benzoyloxy)-6-(3-
methyl-2-butenyl)-5-tosyloxyisoflavone (15a). To a solu-
tion of 14a (1.0 g, 1.4 mmol) in dry toluene (15 ml) was
added TsOH$H2O (2.38 ml of a 5.24ꢁ10ꢂ1 M solution in
acetic acid). The reaction mixture was refluxed under MWI
4.1.14. 5,7,40-Triacetoxy-6-(3-methyl-2-butenyl)isofla-
vone (17a). Acetylation of 1a (40 mg, 0.11 mmol) was
achieved by acetic anhydride/pyridine method at 115 ꢀC
for 2 h. The obtained gummy mass was chromatographed
on silica gel column (CHCl3/hexane; 5:1) and further

8632
M. M. Hossain et al. / Tetrahedron 62 (2006) 8625–8635
recrystallized from a mixture of CHCl3 and hexane to give
17a (38 mg, 71%) as a colourless crystalline solid, mp
(15H, m, Ar–Hꢁ15), 7.81 (1H, s, C2–H); Anal. Calcd
for C37H29IO6: C, 63.80; H, 4.22. Found: C, 63.63; H,
4.26.
1
173–175 ꢀC. H NMR (CDCl3) d: 1.67 and 1.75 (each 3H,
s, CH3), 2.31, 2.35 and 2.43 (each 3H, s, COCH3), 3.25
1
(2H, br d, CH2), 5.01 (1H, br t, ]CH), 7.13 (2H, d,
0
Acetal 10b: H NMR (CDCl3) d: 3.0 and 3.22 (each 3H, s,
0
J¼8.6 Hz, C3 – and C5 –H), 7.21 (1H, s, C8–H), 7.49 (2H,
OCH3), 4.68 and 4.78 (each 1H, d, J¼10.2 Hz, CH), 5.10
(2H, s, PhCH2), 5.16 and 5.20 (each 2H, s, PhCH2), 6.56
(1H, d, J¼8.3 Hz, Ar–H), 6.60 (1H, dd, J¼8.3 and 1.7 Hz,
Ar–H), 6.65 (1H, d, J¼1.7 Hz, Ar–H), 6.71–7.70 (21H, m,
Ar–Hꢁ21).
0
0
d, J¼8.6 Hz, C2 – and C6 –H), 7.86 (1H, s, C2–H). Anal.
Calcd for C26H24O8: C, 67.23; H, 5.21. Found: C, 67.35; H,
5.32.
4.1.15. MW-synthesis of 4,20,40-tris(benzyloxy)-30-iodo-3-
methoxy-60-methoxymethoxychalcone (7b) and 4,20,40-
tris(benzyloxy)-60-hydroxy-30-iodo-3-methoxychalcone
(8b). A mixture of 5 (4.40 g, 8.48 mmol) and 6b (2.46 g,
10.2 mmol) was dissolved in alc. KOH (3.30 g, 58.8 mmol
in 60 ml EtOH). The reaction mixture was irradiated under
MW for 7 min (1 minꢁ7 times irradiation, 1–2 min inter-
val/irradiation), and monitored by TLC to establish comple-
tion. A similar treatment of the reaction mixture (as in the
case of compound 8a) gave 8b (5.65 g, 95%, two steps yield
from 5) as a yellow solid, mp 133–134 ꢀC. 1H NMR (CDCl3)
d: 3.66 (3H, s, OCH3), 4.82 (2H, s, PhCH2), 5.20 (4H, s,
The similar treatment of compound 9b (180 mg,
0.224 mmol) with BTIB (145 mg, 0.337 mmol) under
MWI for 12 min (2 minꢁ6 times irradiation, 1–2 min inter-
val/irradiation) at 60 ꢀC gave crude acetal 10b, which was
cyclized with 20% NaOH under MWI for 5 min to give
11b (39 mg, 25%).
4.1.18. MW-synthesis of 5,7,40-tris(benzyloxy)-6-(3-hy-
droxy-3-methyl-1-butynyl)-30-methoxyisoflavone (12b).
Compound 11b (1.50 g, 2.15 mmol) was dissolved in
DMF (12 ml), followed by the successive addition of
Et3N (40 ml), PdCl2 (30 mg, 0.16 mmol), PPh3 (70 mg,
0.26 mmol) and CuI (44 mg, 0.23 mmol) and finally
2-methyl-3-butyn-2-ol (0.85 ml, 8.7 mmol). The similar
treatment of the reaction mixture under MWI for 10 min
(2 minꢁ5 times irradiation, 1–2 min interval/irradiation)
(as in the case of compound 12a) gave 12b as a colourless
0
PhCH2ꢁ2), 6.42 (1H, s, C5 –H), 6.76 (1H, d, J¼8.3 Hz,
C5–H), 6.82 (1H, d, J¼1.7 Hz, C2–H), 6.91 (1H, dd, J¼8.3
and 1.7 Hz, C6–H), 7.15–7.52 (15H, m, Ar–Hꢁ15), 7.81
and 7.86 (each 1H, d, J¼15.3 Hz, ]CH), 13.77 (1H, s,
0
C6 –OH); Anal. Calcd for C37H31IO6: C, 63.62; H, 4.47.
Found: C, 63.47; H, 4.63.
1
crystalline solid (0.89 g, 64%), mp 151–153 ꢀC. H NMR
4.1.16. MW-synthesis of 4,20,40-tris(benzyloxy)-60-benz-
oyloxy-30-iodo-3-methoxychalcone (9b). Benzoyl chloride
(1.56 g, 11.2 mmol) was slowly added to a mixture of
8b (6.0 g, 8.6 mmol) in pyridine (55 ml). The reaction mix-
ture was irradiated incessantly under MW at 125 ꢀC for
5 min. The reaction mixture was worked up in a similar man-
ner (as in the case of compound 9a) to give 9b (6.79 g, 98%)
as a fluffy crystalline solid, mp 65–68 ꢀC. 1H NMR (CDCl3)
d: 3.83 (3H, s, OCH3), 4.98, 5.17 and 5.20 (each 2H, s,
(CDCl3) d: 1.51 (6H, s, CH3ꢁ2), 3.92 (3H, s, OCH3), 5.20
(6H, s, PhCH2ꢁ3), 6.72 (1H, s, C8–H), 6.90 (1H, d,
0
0
J¼8.3 Hz, C5 –H), 6.94 (1H, dd, J¼8.3 and 1.7 Hz, C6 –
0
H), 7.16 (H, d, J¼1.9 Hz, C2 –H), 7.26–7.52 (15H, m,
Ar–Hꢁ15), 7.79 (1H, s, C2–H); Anal. Calcd for C42H36O7:
C, 77.28; H, 5.56. Found: C, 77.13; H, 5.49.
4.1.19. 5,7,40-Trihydroxy-6-(3-hydroxy-3-methylbutyl)-
30-methoxyisoflavone (lupisoflavone hydrate) (2b). Com-
pound 12b (1.0 g, 1.5 mmol) was hydrogenolyzed over 5%
Pd/C (150 mg) in a mixture of methanol (45 ml) and dioxane
(45 ml) until the uptake of hydrogen ceased. The resulting
compound was recrystallized from a mixture of MeOH
and Me2CO to give 2b (550 mg, 93%) as a colourless solid,
mp 220–223 ꢀC. 1H NMR (see Table 1); IR (KBr) nmax 3443,
3083, 2966, 1665, 1519, 1464, 1208, 1057 cmꢂ1; UV lmax
nm (log 3) (MeOH): 269 (4.34), 219 (4.3), (+AlCl3) 267sh
(4.36), 219 (4.31), (+NaOAc) 334 (3.93), 277 (4.36),
234sh (4.24); Anal. Calcd for C21H22O7: C, 65.28; H,
5.74. Found: C, 65.22; H, 5.61.
0
PhCH2), 6.76 (1H, s, C5 –H), 6.79 (1H, d, J¼8.3 Hz, C5–
H), 6.91 (1H, dd, J¼8.3 and 1.7 Hz, C6–H), 6.89 (1H, d,
J¼15.8 Hz, ]CH), 6.94 (1H, d, J¼1.7 Hz, C2–H), 6.96
(1H, d, J¼15.8 Hz, ]CH), 7.25–7.59 (20H, m, Ar–Hꢁ20);
Anal. Calcd for C44H35IO7: C, 65.84; H, 4.58. Found: C,
65.84; H, 4.43.
4.1.17. MW-synthesis of 1-[6-benzoyloxy-2,4-bis(benzyl-
oxy)-3-iodophenyl]-2-(4-benzyloxy-3-methoxyphenyl)-
3,3-dimethoxypropan-1-one (10b) and 5,7,40-tris(benzyl-
oxy)-6-iodo-30-methoxyisoflavone (11b). Compound 9b
(7.0 g, 8.7 mmol) was dissolved in a mixture of MeOH
(50 ml) and CHCl3 (10 ml), followed by the addition of
HTIB (5.46 g, 13.9 mmol). The reaction mixture was irra-
diated under MW for 12 min (2 minꢁ6 times irradiation,
1–2 min interval/irradiation) at 60 ꢀC. The reaction mix-
ture was worked up in a similar manner (as in the case
of compound 10a) to give crude acetal 10b. This crude
mass was hydrolyzed and cyclized in a similar manner
(as in the case of compound 11a) to give isoflavone 11b
(3.53 g, 59%, two steps yield from 8b), mp 198–200 ꢀC.
1H NMR (CDCl3) d: 3.92 (3H, s, OCH3), 5.06, 5.20 and
5.26 (each 2H, s, PhCH2), 6.75 (1H, s, C8–H), 6.92 (1H,
4.1.20. 7,40-Bis(benzoyloxy)-5-hydroxy-6-(3-hydroxy-3-
methylbutyl)-30-methoxyisoflavone (13b). A mixture of
2b (480 mg, 1.24 mmol), benzoyl chloride (0.52 ml,
4.5 mmol) and K2CO3 (1.71 g, 12.4 mmol) in acetone
(30 ml) was heated at 45 ꢀC under nitrogen for 25 min.
The reaction mixture was worked up in a similar manner
(as in the case of compound 13a) to give 13b (642 mg,
86%) as colourless needles, mp 182–183 ꢀC. 1H NMR
(CDCl3) d: 1.21 (6H, s, CH3ꢁ2), 1.74 and 2.77 (each 2H,
m, CH2), 3.86 (3H, s, OCH3), 6.90 (1H, s, C8–H), 7.10–
7.71 (13H, m, Ar–Hꢁ13), 8.03 (1H, s, C2–H), 13.16 (1H,
s, C5–OH); Anal. Calcd for C35H30O9: C, 70.70; H, 5.09.
Found: C, 70.57; H, 5.17.
0
d, J¼7.8 Hz, C5 –H), 6.94 (1H, dd, J¼7.8 and 1.9 Hz,
0
0
C6 –H), 7.16 (1H, d, J¼1.9 Hz, C2 –H), 7.26–7.53

M. M. Hossain et al. / Tetrahedron 62 (2006) 8625–8635
8633
4.1.21. MW-synthesis of 7,40-bis(benzoyloxy)-6-(3-hy-
droxy-3-methylbutyl)-30-methoxy-5-tosyloxyisoflavone
(14b). A mixture of 13b (500 mg, 0.840 mmol), tosyl chlo-
ride (257 mg, 1.34 mmol) and K2CO3 (1.16 g, 8.32 mmol) in
acetone (20 ml) was irradiated under MW for 30 min
(3 minꢁ10 times irradiation, 1–2 min interval/irradiation).
The reaction mixture was worked up in a similar manner
(as in the case of compound 14a) to give compound 14b
as a colourless crystalline solid (585 mg, 93%), mp 170–
4.1.25. 5,7,40-Triacetoxy-6-(3-methyl-2-butenyl)-30-
methoxyisoflavone (17b). Acetylation of 1b (50 mg,
0.13 mmol) was achieved in a similar manner (as in the
case of compound 17a) to give 17b (54 mg, 80%) as a colour-
less crystalline solid, mp 154–156 ꢀC. 1H NMR (CDCl3) d:
1.67 and 1.75 (each 3H, s, CH3), 2.33, 2.35 and 2.43 (each
3H, s, COCH3), 3.30 (2H, br d, CH2), 3.86 (3H, s, OCH3),
5.01 (1H, br t, ]CH), 6.97 (1H, dd, J¼8.3 and 1.7 Hz,
0
0
C6 –H), 7.06 (1H, d, J¼8.3 Hz, C5 –H), 7.12 (1H, d,
1
171 ꢀC. H NMR (CDCl3) d: 1.13 (6H, s, CH3ꢁ2), 1.71
J¼1.7 Hz, C2 –H), 7.22 (1H, s, C8–H), 7.87 (1H, s, C2–H).
0
and 2.79 (each 2H, m, CH2), 2.42 (3H, s, CH3–Ar), 3.86
(3H, s, OCH3), 7.02–7.82 (18H, m, Ar–Hꢁ18), 7.92 (1H,
s, C2–H); Anal. Calcd for C42H36O11S: C, 67.37; H, 4.85.
Found: C, 67.19; H, 4.96.
Anal. Calcd for C27H26O9: C, 65.68; H, 5.25. Found: C,
65.93; H, 4.95.
4.1.26. MW-synthesis of 20,40-bis(benzyloxy)-30-iodo-3,4-
methylenedioxy-60-methoxymethoxychalcone (7c) and
20,40-bis(benzyloxy)-60-hydroxy-30-iodo-3,4-methylene-
dioxychalcone (8c). A mixture of 5 (4.0 g, 7.7 mmol) and 6c
(1.60 g, 10.6 mmol) was dissolved in alc. KOH (3.0 g,
53 mmol in 50 ml EtOH). The reaction mixture was irradi-
ated under MW for 6 min (2 minꢁ3 times irradiation,
1–2 min interval/irradiation), and monitored by TLC to
establish completion. A similar treatment of the reaction
mixture (as in the case of compound 8a) gave 8c (4.15 g,
89%, two steps yield from 5) as a yellow solid, mp 161–
4.1.22. MW-synthesisof7,40-bis(benzoyloxy)-6-(3-methyl-
2-butenyl)-30-methoxy-5-tosyloxyisoflavone (15b). To a
solution of 14b (430 mg, 0.574 mmol) in dry toluene
(20 ml) was added TsOH$H2O (1.40 ml of a 5.24ꢁ10ꢂ1 M
solution in acetic acid). The reaction mixture was irradiated
incessantly under MW at 117 ꢀC for 15–20 min. The similar
work up of the reaction mixture (as in the case of compound
1
15a) gave the 6-alkenylisoflavone. The H NMR spectrum
showed that it was a mixture of 6-(3-methyl-2-butenyl)iso-
flavone 15b and the regioisomer, 6-(3-methyl-3-butenyl)iso-
flavone 15b0 (15b/15b0¼99:1). The isomeric mixture was
recrystallized from a mixture of CHCl3 and AcOEt to give
15b (359 mg, 86% from 14b) as a crystalline solid,
1
163 ꢀC. H NMR (CDCl3) d: 4.86 and 5.21 (each 2H, s,
0
PhCH2), 5.99 (2H, s, O–CH2–O), 6.42 (1H, s, C5 –H), 6.69
(1H, d, J¼1.7 Hz, C2–H), 6.71 (1H, d, J¼7.8 Hz, C5–H),
6.89 (1H, dd, J¼8.05 and 1.7 Hz, C6–H), 7.24–7.52 (10H,
m, Ar–Hꢁ10), 7.76 and 7.81 (each 1H, d, J¼15.3 Hz,
1
mp 170–172 ꢀC. H NMR (CDCl3) d: 1.39 and 1.46 (each
0
3H, s, CH3), 2.39 (3H, s, CH3–Ar), 3.35 (2H, d, J¼6.3 Hz,
CH2), 3.86 (3H, s, OCH3), 4.95 (1H, br t, ]CH), 7.02–
7.70 (18H, m, Ar–Hꢁ18), 7.91 (1H, s, C2–H); Anal. Calcd
for C42H34O10S: C, 69.03; H, 4.69. Found: C, 68.80; H, 4.77.
]CH), 13.69 (1H, s, C6 –OH); Anal. Calcd for
C30H23IO6: C, 59.42; H, 3.82. Found: C, 59.29; H, 3.97.
4.1.27. MW-synthesis of 20,40-bis(benzyloxy)-60-benzoyl-
oxy-30-iodo-3,4-methylenedioxychalcone (9c). Benzoyl
chloride (1.21 g, 8.52 mmol) was slowly added to a mixture
of 8c (4.0 g, 6.6 mmol) in pyridine (40 ml). The reaction
mixture was irradiated incessantly under MW at 125 ꢀC
for 6 min. The reaction mixture was worked up in a similar
manner (as in the case of compound 9a) to give 9c (4.10 g,
89%) as a fluffy crystalline solid. 1H NMR (CDCl3) d:
4.99 and 5.21 (each 2H, s, PhCH2), 5.98 (2H, s, O–CH2–
4.1.23. Synthesis of 7,40-bis(benzoyloxy)-5-hydroxy-6-(3-
methyl-2-butenyl)-30-methoxyisoflavone (16b). Com-
pound 15b (200 mg, 0.273 mmol) was dissolved in dry
CH2Cl2 (10 ml), followed by the addition of BCl3
(0.25 ml, 1 M solution in CH2Cl2) in an ice bath. The similar
treatment and work up of the reaction mixture (as in the case
of compound 16a) gave the 6-alkenylisoflavone 16b
(148 mg, 94%) as a colourless crystalline solid, mp 153–
0
O), 6.73 (1H, s, C5 –H), 6.75–6.94 (3H, m, Ar–Hꢁ3),
1
155 ꢀC. H NMR (CDCl3) d: 1.58 and 1.60 (each 3H, s,
7.24–7.52 (15H, m, Ar–Hꢁ15), 7.53 and 7.56 (each 1H, d,
J¼17.5 Hz, ]CH); Anal. Calcd for C37H27IO7: C, 62.55;
H, 3.83. Found: C, 62.56; H, 3.97.
CH3), 3.39 (2H, d, J¼6.6 Hz, CH2), 3.88 (3H, s, OCH3),
5.16 (1H, br t, ]CH), 6.87 (1H, s, C8–H), 7.10–7.70
(13H, m, Ar–Hꢁ13), 8.02 (1H, s, C2–H), 13.13 (1H, s,
C5–OH); Anal. Calcd for C35H28O8: C, 72.91; H, 4.89.
Found: C, 72.97; H, 5.12.
4.1.28. MW-synthesis of 1-[6-benzoyloxy-2,4-bis(benzyl-
oxy)-3-iodophenyl]-2-(3,4-methylenedioxyphenyl)-3,3-
dimethoxypropan-1-one (10c) and 5,7-bis(benzyloxy)-6-
iodo-30,40-methylenedioxyisoflavone (11c). Compound 9c
(2.0 g, 2.8 mmol) was dissolved in a mixture of MeOH
(25 ml) and CHCl3 (6 ml), followed by the addition of
HTIB (1.76 g, 4.48 mmol). The reaction mixture was irradi-
ated under MW for 12 min (2 minꢁ6 times irradiation,
1–2 min interval/irradiation) at 60 ꢀC. The reaction mixture
was worked up in a similar manner (as in the case of com-
pound 10a) to give crude acetal 10c as a semisolid mass.
This crude mass was hydrolyzed and cyclized under MWI
for 5 min in a similar way (as in the case of compound
11a) to give iodoisoflavone 11c (0.78 g, 46%, two steps yield
4.1.24. Synthesis of 5,7,40-trihydroxy-6-(3-methyl-2-
butenyl)-30-methoxyisoflavone (lupisoflavone) (1b). Com-
pound 16b (130 mg, 0.225 mmol) was dissolved in a
mixture of methanol (3 ml) and dioxane (3 ml), followed
by the addition of 10% NaOH (1 ml, 2.5 mmol). The simi-
lar work up of the reaction mixture (as in the case of com-
pound 1a) gave 6-prenylisoflavone 1b (52 mg, 62%) as
1
a pale yellow crystalline solid, mp 161–163 ꢀC. H NMR
(see Table 1); IR (KBr) nmax 3435, 3085, 2949, 1649,
1517, 1459, 1205, 1068 cmꢂ1; UV lmax nm (log 3)
(MeOH): 267sh (4.39), 220 (4.36), (+AlCl3) 341 (3.97),
274sh (4.39), (+NaOAc) 338 (4.02), 276sh (4.45); Anal.
Calcd for C21H20O6: C, 68.47; H, 5.47. Found: C, 68.39;
H, 5.31.
1
from 8c), mp 205–206 ꢀC. H NMR (CDCl3) d: 5.07 and
5.26 (each 2H, s, PhCH2), 5.99 (2H, s, O–CH2–O), 6.75
0
(1H, s, C8–H), 6.85 (1H, d, J¼7.8 Hz, C5 –H), 6.92 (1H,

8634
M. M. Hossain et al. / Tetrahedron 62 (2006) 8625–8635
0
0
dd, J¼8.05 and 1.7 Hz, C6 –H), 7.08 (1H, d, J¼1.7 Hz, C2 –
H), 7.26–7.57 (10H, m, Ar–Hꢁ10), 7.80 (1H, s, C2–H);
Anal. Calcd for C30H21IO6: C, 59.62; H, 3.49. Found: C,
59.36; H, 3.62.
C5–OH); Anal. Calcd for C28H24O8: C, 68.85; H, 4.95.
Found: C, 68.77; H, 4.85.
4.1.32. MW-synthesis of 7-benzoyloxy-6-(3-hydroxy-3-
methylbutyl)-30,40-methylenedioxy-5-tosyloxyisoflavone
(14c). A mixture of 13c (800 mg, 1.63 mmol), tosyl chloride
(468 mg, 2.45 mmol) and K2CO3 (2.50 g, 18.1 mmol) in
acetone (25 ml) was irradiated incessantly under MW for
11 min. The reaction mixture was worked up in a similar
manner (as in the case of compound 14a) to give compound
14c as a colourless crystalline solid (990 mg, 94%), mp 183–
184 ꢀC. 1H NMR (CDCl3) d: 1.13 (6H, s, CH3ꢁ2), 1.71 and
2.74 (each 2H, m, CH2), 2.43 (3H, s, Ar–CH3), 6.0 (2H, s,
O–CH2–O), 6.85 (1H, s, C8–H), 6.84 (1H, d, J¼8.0 Hz,
Acetal 10c: 1H NMR (CDCl3) d: 3.03 and 3.22 (each 3H, s,
OCH3), 4.70 and 4.79 (each 1H, d, J¼10.2 Hz, CH), 4.98
and 5.11 (each 2H, s, PhCH2), 5.84 (2H, s, O–CH2–O),
6.48 (1H, s, Ar–H), 6.50 (1H, d, J¼7.8 Hz, Ar–H), 6.57
(1H, dd, J¼7.8 and 1.7 Hz, Ar–H), 6.67 (1H, d, J¼1.7 Hz,
Ar–H), 7.25–7.65 (15H, m, Ar–Hꢁ15).
The similar treatment of compound 9c (2.01 g, 2.82 mmol)
with BTIB (1.89 g, 4.39 mmol) under MWI (2 minꢁ6 times
irradiation, 1–2 min interval/irradiation) at 60 ꢀC gave crude
acetal 10c, which was cyclized under MWI for 6 min to give
11c (547 g, 32%).
0
0
C5 –H), 6.87 (1H, dd, J¼8.0 and 1.7 Hz, C6 –H), 6.97 (1H,
0
d, J¼1.7 Hz, C2 –H), 7.26–7.71 (9H, m, Ar–Hꢁ9), 7.83
(1H, s, C2–H); Anal. Calcd for C35H30O10S: C, 65.41; H,
4.71. Found: C, 65.29; H, 4.67.
4.1.29. MW-synthesis of 5,7-bis(benzyloxy)-6-(3-hy-
droxy-3-methyl-1-butynyl)-30,40-methylenedioxyisofla-
vone (12c). Compound 11c (2.0 g, 3.3 mmol) was dissolved
in DMF (12 ml), followed by the successive addition of Et3N
(55 ml), PdCl2 (30 mg, 0.16 mmol), PPh3 (82 mg,
0.31 mmol) and CuI (32 mg, 0.16 mmol) and finally 2-meth-
yl-3-butyn-2-ol (1.2 ml, 16 mmol). The similar treatment of
the reaction mixture under MWI (2 minꢁ4 times irradiation,
1–2 min interval/irradiation) (as in the case of compound
12a) gave 12c as a colourless crystalline solid (1.26 g,
4.1.33. MW-synthesis of 7-benzoyloxy-6-(3-methyl-2-bu-
tenyl)-30,40-methylenedioxy-5-tosyloxyisoflavone (15c).
To a solution of 14c (400 g, 0.622 mmol) in dry toluene
(20 ml) was added TsOH$H2O (1.16 ml of a 5.24ꢁ10ꢂ1 M
solution in acetic acid). The reaction mixture was irradiated
incessantly under MW at 117 ꢀC (refluxing) for 20 min.
The reaction mixture was worked up in a similar manner
(as in the case of compound 15a) to give the 6-alkenylisofla-
1
vone 15c as a crystalline solid. The H NMR spectrum
1
68%), mp 188–190 ꢀC. H NMR (CDCl3) d: 1.50 (6H, s,
showed that it was a mixture of 6-(3-methyl-2-butenyl)isofla-
vone 15c and the regioisomer, 6-(3-methyl-3-butenyl)isofla-
vone 15c0 (15c/15c0¼99:1). The isomeric mixture was
recrystallized from a mixture of CHCl3 and Me2CO (5:1)
to give 15c (328 mg, 85% from 14c) as a crystalline solid,
CH3ꢁ2), 5.20 and 5.21 (each 2H, s, PhCH2), 5.98 (2H, s,
O–CH2–O), 6.71 (1H, s, C8–H), 6.85 (1H, d, J¼8.0 Hz,
0
0
C5 –H), 6.92 (1H, dd, J¼8.0 and 1.7 Hz, C6 –H), 7.08 (1H,
0
d, J¼1.7 Hz, C2 –H), 7.25–7.52 (10H, m, Ar–Hꢁ10), 7.78
1
(1H, s, C2–H); Anal. Calcd for C35H28O7: C, 74.99; H,
5.03. Found: C, 74.75; H, 4.97.
mp 157–158 ꢀC. H NMR (CDCl3) d: 1.40 and 1.45 (each
3H, s, CH3), 2.41 (3H, s, Ar–CH3), 3.34 (2H, d, J¼6.5 Hz,
CH2), 4.94 (1H, t, J¼6.5 Hz, ]CH), 6.0 (2H, s, O–CH2–
O), 6.83–7.96 (13H, m, Ar–Hꢁ13), 7.81 (1H, s, C2–H);
Anal. Calcd for C35H28O9S: C, 67.63; H, 4.52. Found: C,
67.59; H, 4.41.
4.1.30. 5,7-Dihydroxy-6-(3-hydroxy-3-methylbutyl)-30,40-
methylenedioxyisoflavone (derrubone hydrate) (2c).
Compound 12c (500 mg, 0.895 mmol) was hydrogenolyzed
over 5% Pd/C (80 mg) in a mixture of methanol (25 ml)
and dioxane (25 ml) until the uptake of hydrogen ceased.
The similar treatment of the reaction mixture (as in the
case of compound 2a)gave 2c as a colourless crystalline solid
(300 mg, 87%), mp 186–187 ꢀC. 1H NMR (see Table 1); IR
(KBr) nmax 3429, 3090, 2972, 2892, 1654, 1572, 1490,
1253, 1061 cmꢂ1; UV lmax nm (log 3) (MeOH): 338 (3.87),
272sh (4.35), 219 (4.31), (+AlCl3) 381 (3.0), 267sh (4.33),
(+NaOAc) 292 (3.27), 233sh (4.45); Anal. Calcd for
C21H20O7: C, 65.62; H, 5.24. Found: C, 65.40; H, 5.29.
4.1.34. 7-Benzoyloxy-5-hydroxy-6-(3-methyl-2-butenyl)-
30,40-methylenedioxyisoflavone (16c). Compound 15c
(400 mg, 0.640 mmol) was dissolved in dry CH2Cl2
(10 ml), followed by the addition of BCl3 (0.37 ml, 1 M so-
lution in CH2Cl2) in an ice bath. The similar treatment and
work up of the reaction mixture (as in the case of compound
16a) gave the 6-alkenylisoflavone 16c (240 mg, 79%) as
1
a colourless crystalline solid, mp 115–117 ꢀC. H NMR
(CDCl3) d: 1.57 and 1.59 (each 3H, s, CH3), 3.38 (2H, d,
J¼6.8 Hz, CH2), 5.15 (1H, t, J¼6.8 Hz, ]CH), 6.01 (2H,
s, O–CH2–O), 6.84 (1H, s, C8–H), 6.88 (1H, d, J¼8.0 Hz,
4.1.31. Synthesis of 7-benzoyloxy-5-hydroxy-6-(3-hy-
droxy-3-methylbutyl)-30,40-methylenedioxyisoflavone
(13c). A mixture of 2c (700 mg, 1.82 mmol), benzoyl chlo-
ride (0.25 ml, 2.2 mmol) and K2CO3 (2.51 g, 18.2 mmol) in
acetone (25 ml) was heated at 45 ꢀC under nitrogen for
25 min. The similar treatment of the reaction mixture (as
in the case of compound 13a) gave 13c as a colourless crys-
talline solid (809 mg, 91%), mp 156–158 ꢀC. 1H NMR
(CDCl3) d: 1.20 (6H, s, CH3ꢁ2), 1.71 and 2.74 (each 2H,
m, CH2), 6.01 (2H, s, O–CH2–O), 6.84 (1H, d, J¼8.0 Hz,
0
0
C5 –H), 6.95 (1H, dd, J¼8.0 and 1.7 Hz, C6 –H), 7.05 (1H,
0
d, J¼1.7 Hz, C2 –H), 7.25–7.69 (5H, m, Ar–Hꢁ5), 7.93
(1H, s, C2–H), 13.13 (1H, s, C5–OH); Anal. Calcd for
C28H22O7: C, 71.48; H, 4.71. Found: C, 71.62; H, 4.81.
4.1.35. Synthesis of 5,7-dihydroxy-6-(3-methyl-2-butenyl)-
30,40-methylenedioxyisoflavone (derrubone) (1c). Com-
pound 16c (150 mg, 0.318 mmol) was dissolved in a mixture
of methanol (3 ml) and dioxane (3 ml), followed by the
addition of 10% NaOH (1.1 ml). The similar treatment and
work up of the reaction mixture (as in the case of compound
1a) gave 6-prenylisoflavone 1c (92 mg, 79%) as a pale
0
C5 –H), 6.90 (1H, s, C8–H), 6.94 (1H, dd, J¼8.0 and
0
0
1.7 Hz, C6 –H), 7.05 (1H, d, J¼1.7 Hz, C2 –H), 7.26–7.70
(5H, m, Ar–Hꢁ5), 7.94 (1H, s, C2–H), 13.15 (1H, s,

M. M. Hossain et al. / Tetrahedron 62 (2006) 8625–8635
8635
yellow crystalline solid, mp 210–211 ꢀC (lit.24 210–212 ꢀC).
1H NMR (see Table 1); IR (KBr) nmax 3443, 3083, 2925,
2858, 1647, 1506, 1436, 1245, 1056 cmꢂ1; UV lmax nm
(log 3) (MeOH): 341 (4.03), 274sh (4.39), 223 (4.40),
(+AlCl3) 266sh (4.41), 222 (4.37), (+NaOAc) 341 (4.07),
276 (4.41), 234sh (4.45); Anal. Calcd for C21H18O6: C,
68.85; H, 4.95. Found: C, 68.63; H, 4.98.
14. Murata, M.; Midorikawa, K.; Koh, M.; Umezawa, K.;
Kawanishi, S. Biochemistry 2004, 43, 2569–2577.
15. Harborne, J. B.; Ingham, J. L.; King, L.; Payne, M.
Phytochemistry 1976, 15, 1485–1487.
16. Deshpande, V. H.; Pendse, A. D.; Pendse, R. Indian J. Chem.,
Sect. B 1977, 15, 205–207.
17. Ingham, J. L.; Tahara, S.; Harborne, J. B. Z. Naturforsch., C:
Biosci. 1983, 38, 194–200.
4.1.36. 5,7-Diacetoxy-6-(3-methyl-2-butenyl)-30,40-
methylenedioxyisoflavone (17c). Acetylation of 1c (60 mg,
0.16 mmol) was achieved in a similar manner (as in the case
of compound 17a) to give 17c (65 mg, 88%) as a colourless
crystalline solid, mp 204–205 ꢀC. 1H NMR (CDCl3) d: 1.67
and 1.75 (each 3H, s, CH3), 2.34 and 2.43 (each 3H, s,
COCH3), 3.25 (2H, br d, CH2), 5.01 (1H, br t, ]CH),
18. Tahara, S.; Ingham, J. L.; Nakahara, S.; Mizutani, J.; Harborne,
J. B. Phytochemistry 1984, 23, 1889–1900.
19. Tahara, S.; Nakahara, S.; Ingham, J. L.; Mizutani, J. Nippon
No^geik. Kaishi 1985, 59, 1039–1044.
20. Hossain, M. M.; Tokuoka, T.; Yamashita, K.; Kawamura, Y.;
Tsukayama, M. Synth. Commun. 2006, 36, 1201–1211.
21. Tsukayama, M.; Li, H.; Nishiuchi, M.; Takahashi, M.;
Kawamura, Y. J. Chem. Res., Synop. 1998, 238–239;
J. Chem. Res., Miniprint 1998, 1181–1196.
22. Al-Maharik, N.; Botting, N. P. Tetrahedron 2003, 59, 4177–
4181.
23. Barcelo, A. R.; Munoz, R. Phytochemistry 1989, 28, 1331–
1333.
0
5.98 (2H, s, O–CH2–O), 6.83 (1H, d, J¼8.0 Hz, C5 –H),
0
6.86 (1H, dd, J¼8.0 and 1.7 Hz, C6 –H), 6.99 (1H, d,
0
J¼1.7 Hz, C2 –H), 7.20 (1H, s, C8–H), 7.83 (1H, s, C2–H).
Anal. Calcd for C25H22O8: C, 66.66; H, 4.92. Found: C,
66.49; H, 4.87.
24. East, A. J.; Ollis, W. D.; Wheeler, R. E. J. Chem. Soc. C 1969,
365–374.
References and notes
25. Johnson, A. P.;Pelter, A. TetrahedronLett. 1964, 20, 1267–1274.
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