Microwave-assisted preparation of benzo[b]furans under solventless phase-transfer catalytic conditions

Article abstract of DOI:10.1016/S0040-4020(00)00818-8

Condensation of salicylaldehyde and its derivatives with various esters of chloroacetic acids in the presence of tetrabutylammonium bromide (TBAB) leads to the synthesis of benzo[b]furans by a solventless phase-transfer catalytic (PTC) reaction under microwave irradiation. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00818-8

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 8769±8773
Microwave-Assisted Preparation of Benzo[b]furans under
Solventless Phase-Transfer Catalytic Conditions
*
Dariusz Bogdal and Marek Warzala
Department of Chemistry, Politechnika Krakowska, ul. Warszawska 24, 31-155 Krakow, Poland
Received 21 February 2000; revised 24 August 2000; accepted 7 September 2000
AbstractÐCondensation of salicylaldehyde and its derivatives with various esters of chloroacetic acids in the presence of tetrabutyl-
ammonium bromide (TBAB) leads to the synthesis of benzo[b]furans by a solventless phase-transfer catalytic (PTC) reaction under
microwave irradiation. q 2000 Elsevier Science Ltd. All rights reserved.
Benzofuran derivatives are nowadays an important class of
organic compounds that occur in a great number of natural
products, are used in cosmetics and are used as synthetic
to remove in the case of aprotic solvents with high boiling
points. Moreover, the absence of solvent reduces the risk of
an explosion when the reaction takes place in a microwave
oven, and liquid±liquid extraction can be avoided in the
isolation of reaction products. At present, the reactions
under solid±liquid phase-transfer catalytic (PTC) condi-
tions which are specially useful for anionic activation
1
2
3
pharmaceuticals. Moreover, benzo[b]furans are building
blocks for optical brighteners and are applied, for example,
in combination with benzimidazoles as biphenyl end
groups. Many of the natural benzo[b]furans have physio-
4
11
logical, pharmacological and toxic properties, and as a
result there is continuing interest in their chemical
synthesis.
processes are numbered among the `dry' reactions.
5
Recently, it has been shown that under microwave irradia-
tion in dry media a number of alcohols and phenols could be
easily O-alkylated, and aromatic aldehydes could undergo
12
Cyclization reactions of various types have been used to
produce substituted benzo[b]furans.
6
,7
13
14
In the present
condensation and cyclocondensation reactions. Since,
more recently, Varma et al. have reported the preparation
of 2-aroylbenzo[b]furans using microwave irradiation to
drive the condensation of a-tosyloxyketones with salicyl-
aldehyde1 derivatives on potassium ¯uoride doped
paper, we report on the modi®cation of one of the most
popular routes to substituted benzo[b]furans, i.e. O-alkyl-
ation of o-hydroxylated aromatic carbonyl compounds with
a-halogenated carbonyl compounds, followed by intra-
molecular cyclization. The reactions are usually catalysed
by potassium carbonate in acetone or by potassium
5
alumina, we have been prompted to present our results
on the synthesis of benzo[b]furans under solid±liquid
phase-transfer catalytic (PTC) conditions (Scheme 1).
8
hydroxide in ethanol.
In a typical experiment, the reactions were carried out by
simply mixing a salicylaldehyde derivative with a two fold
excess of a chloroacetic acid ester and a catalytic amount of
tetrabutylammonium bromide (TBAB). The mixtures were
adsorbed on potassium carbonate, then irradiated in an open
vessel in a domestic microwave oven for 8±10 min. The
results and conditions of the reactions are summarised in
Table 1.
Result and Discussion
The use of inorganic solid materials for the support of
organic reactants and catalysts has been broadly exempli®ed
and well established as an environmental benign tech-
nology. In recent years, it has been shown that microwave
irradiation is of particular bene®t for such reactions, par-
ticularly for these reactions carried out in the absence of
9
1
0
We found that the shape and size of the reaction vessel are
important factors for microwave heating, the preferred reac-
tion vessel was a conical ¯ask of much larger capacity than
the volume of the reaction mixture, bearing a loose cotton
cover. Due to dif®culties with adjusting temperature in a
domestic microwave oven, one of the best solutions is to
repeat an experiment a couple of times increasing the power
solvents. The solventless reactions offer a number of
advantages: solvents are often expensive, toxic, and dif®cult
Keywords: microwave; benzofurans; condensation; phase-transfer cataly-
sis.
* Corresponding author. Tel./fax: 148-12-628-20-38;
e-mail: pcbogdal@cyf-kr.edu.pl
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00818-8

8
770
D. Bogdal, M. Warzala / Tetrahedron 56 (2000) 8769±8773
Scheme 1.
slowly so that vapours do not escape the ¯ask. Furthermore,
at the end of such an experiment, temperature can be
measured with a thermocouple.
are recorded as s (single), d (doublet), t (triplet), q (quartet),
dt (doublet of triplet), and m (multiplet). IR spectra were
obtained on a Bio-Rad FT-IR spectrophotometer FTS 165,
and the wave numbers were given with a precision of
2
1
2
cm . Silica gel column chromatography was performed
Conclusion
with Fluka Kieselgel 60, using mixtures of cyclohexane and
methylene chloride as eluants.
In conclusion, we have described a highly ef®cient micro-
wave-induced procedure for the preparation of various
benzo[b]furan derivatives, that occurs remarkably fast,
under mild conditions, using inexpensive reagents and a
household microwave oven as the irradiation source. The
advantages of this environmentally benign and safe protocol
include a simple reaction set-up, application of commer-
cially available reagents and catalysts, high product yields,
short reaction times as well as the elimination of solvents.
Starting materials
Allyl and cyclohexyl chloroacetates were prepared by the
standard esteri®cation method from chloroacetic acid and
allyl alcohol and cyclohexanol, respectively. All other
reagents were purchased from Aldrich and used as received.
Standard procedure for the preparation of benzo[b]-
furan derivatives
Experimental
General methods
Potassium carbonate (2.70 g, 20 mmol), TBAB (0.16 g,
0
.50 mmol), and a salicylaldehyde derivative (5.0 mmol)
were thoroughly mixed and placed in an open conical,
glass ¯ask. Then a chloroacetate ester (10 mmol) was
added dropwise, the mixture was thoroughly stirred with a
spatula for a few seconds, placed in a domestic microwave
oven, and irradiated for 8±10 min (Table 1). The ®nal
temperature of the reaction mixture was measured with a
thermocouple at the end of the reaction. Upon completion of
the reaction, monitored by GC/MS, the mixture was
extracted with methylene chloride, and the solvent was
then removed. A crude product was puri®ed by column
chromatography.
Elemental analyses were performed on a Perkin±Elmer
2400 microanalyzer. Melting points, measured on a
Boetius-PHMK 05 microscope plates, are uncorrected.
The progress of reactions was monitored by a gas chromato-
graphy (GC) 5890 Hewlett±Packard coupled with a mass
1
detection (MS) 5971 Hewlett±Packard. H NMR spectra
were recorded with a TESLA 487 C spectrometer, TMS
being used as a internal standard; the chemical shifts are
expressed in d values down®eld from TMS. Multiplicities

D. Bogdal, M. Warzala / Tetrahedron 56 (2000) 8769±8773
8771
Table 1. Results and conditions of the synthesis of benzo[b]furans derivatives 3a±i and 5a±c (in all the reactions under microwave irradiation, full conversions
of aromatic aldehydes were achieved; under conventional conditions (oil bath) full conversion of an aldehyde was usually observed after 3 h)
a
Power (W)
b
Temp. (8C)
c
Yield (%)
Product
Number
Time (min)
8
3
a
175
250
175
145
65
68
3
b
8
3
c
8
250
160
138
120
82
85
3
d
10
3
e
10
10
10
160
160
250
245
245
175
91
72
96
3
f
3
g
3
h
8
300
160
175
148
78
88
3
i
10
5
5
a
8
250
191
69
b
10
8
160
300
140
162
79
94
5
c
a
The reactions were carried out in a Philips household microwave oven with maximum power 900 W which was reduced to the range 160±300 W.
The ®nal temperature of the reaction mixture measured with a thermocouple after the completion.
The ®nal yield after product separation.
b
c
Ethyl 2-benzo[b]furancarboxylate (3a). The crude
product was puri®ed by column chromatography (cyclo-
hexane/methyl chloride 8:2) yielding 3a as a colourless
Ethyl 7-methoxy-2-benzo[b]furancarboxylate (3b). The
crude product was puri®ed by column chromatography
(cyclohexane/methyl chloride 8:3) yielding 3b as a white
2
0
oil, n ˆ21.5503; [Found: C, 69.24; H, 5.08 C H O
solid, mp 73±758C; [Found: C, 65.31; H, 5.51 C H O4
12 12
D
11 10
3
requires C, 69.46; H, 5.29%]; nmax(liquid ®lm) 2983(m),
requires C, 65.49; H, 5.49%]; nmax(KBr) 1711(s),
1621(m), 1578(m), 1494(m), 1370(m), 1327(m), 1272(m),
1227(m), 1195(m), 1091(m), 1057(m), 1027(m), 974(s),
942(s), 857(s), 781(s), 761(s), 733(s), 703(m), 624(m),
1
1
9
731(s), 1614(w), 1447(m), 1370(m), 1329 (w), 1297(s),
259(m), 1225(m), 1210(m), 1181(s), 1146(m), 1020(m),
46(w), 888(w), 840(w), 750(s) cm ; d (80 MHz
2
1
H
2
1
CDCl ) 7.66±6.91 (5H, m aromatic protons), 4.37 (2H, q,
3
574(w), 537(s) cm ; d (80 MHz CDCl ) 7.51±6.91 (4H,
H 3
Jˆ7.1 Hz, CH ±Me), 1.35 (3H, t, Jˆ7.1 Hz, CH ±Me); m/z
m aromatic protons), 4.43 (2H, q, Jˆ7.0 Hz, CH ±Me), 4.02
2
2
2
1
70 eV) 191 ((M11) , 11), 190 (M , 82), 162 (83), 145
1
(
(3H, s, OMe) 1.42 (3H, t, Jˆ7.1 Hz, CH ±Me); m/z (70 eV)
2
(
100), 118 (27), 89 (34), 63 (14%).

8
772
D. Bogdal, M. Warzala / Tetrahedron 56 (2000) 8769±8773
1
21 ((M11) , 13), 220 (M , 100), 193 (7.5), 192 (66), 175
1
2
Cyclohexyl 2-benzo[b]furancarboxylate (3g). The crude
(
33), 149 (11%).
product was puri®ed by column chromatography (cyclo-
hexane/methyl chloride 8:3) yielding 3g as a white solid,
mp 70±718C; [Found: C, 73.72; H, 6.70 C H O requires
Ethyl 6-diethylamino-2-benzo[b]furancarboxylate (3c).
The crude product was puri®ed by column chromatography
(
15
16
3
2
1
C, 73.75; H, 6.60%]; nmax(KBr) cm ; 2949(m), 2859(m),
1929(s), 1818(s), 1714(s), 1614(m), 1561(s), 1477(m),
1453(s), 1376(s), 1327(s), 1297(s), 1261(s), 1216(s),
1185(s), 1148(m), 1096(s), 1009(s), 954(m), 885(m),
cyclohexane/methyl chloride 8:2) yielding 3c as a red oil,
20
n ˆ21.6163; [Found: C, 68.69; H, 7.29; N, 5.38
D
C H NO requires C, 68.95; H, 7.33; N, 5.36%];
3
15
19
2
1
nmax(liquid ®lm) 2973(s), 2931(m), 2899(m), 2872(w),
834(m), 760(s) cm ; d (80 MHz CDCl ) 7.73±7.26 (5H,
H 3
1
1
1
716(s), 1626(s), 1578(m), 1556(m), 1509(s), 1398(m),
372(s), 1357(m), 1303(m), 1270(s),1241(s), 1180(s),
120(s), 1095(m), 1017(m), 844(w), 795(m), 759(m)
m, aromatic protons), 5.25±4.84 (1H, m, OCH), 2.20±0.95
(10H, m, (CH ) -cyclohexyl); m/z (70 eV) 245 [(M11) ,
1
2
5
1
1.8%], 244 (M , 9.7), 163 (19), 162 (100), 89 (14%).
2
1
cm ; d (80 MHz CDCl ) 7.49±7.26 (2H, m, aromatic
H
3
protons), 6.77±6.40 (2H, m aromatic protons), 4.40 (2H,
q, Jˆ7.0 Hz, CH ±Me), 3.40 (4H, q, Jˆ7.1 Hz, CH Me)
Cyclohexyl 7-methoxy-2-benzo[b]furancarboxylate (3h).
The crude product was puri®ed by column chromatography
(cyclohexane/methyl chloride 8:2) yielding 3h as a colour-
2
2
1
.40 (3H, t, Jˆ7.2 Hz, CH ±Me), 1.19 (6H, t, Jˆ7.0 Hz,
2
1
NCH Me); m/z (70 eV) 261 (M , 42), 247 (16), 246 (100),
20
less oil, n ˆ21.5551; [Found: C, 69.68; H, 6.58 C H O
requires C, 70.06; H, 6.61%]; n (KBr) 2938(s), 2860(s),
max
2
D
16 18
4
218 (23), 190 (10), 116 (6.7%).
1727(s), 1622(w), 1595(m), 1578(m), 1492(s), 1453(m),
1325(m), 1299(s), 1272(m), 1229(w), 1190(s), 1095(s),
Allyl 2-benzo[b]furancarboxylate (3d). The crude product
was puri®ed by column chromatography (cyclohexane/
methyl chloride 8:3) yielding 3d as a white solid, mp 82±
2
1
1013(m), 977(w), 956(m), 842(w), 780(m), 731(m) cm ;
d (80 MHz CDCl ) 7.49±6.84 (4H, m, aromatic protons),
H
3
838C; [Found: C, 71.05; H, 4.92 C H O requires C, 71.28;
H, 4.98%]; nmax (KBr) 3086(w), 2943(w), 1731(s),
5.20±4.45 (1H, m, OCH), 4.02 (3H, s, OMe), 2.20±0.95
(10H, m, (CH ) -cyclohexyl); m/z (70 eV) 275 ((M11) ,
1
2
10
3
1
2 5
1
5.5), 274 (M , 28), 193 (11), 192 (100), 177 (12), 175
(9.5%).
1
1
8
7
564(m), 1447(m), 1368(m), 1297(s), 1259(w), 1222(m),
210(w), 1178(s), 1145(m), 1096(m), 977(m), 936(m),
85(w), 835(w), 750(s) cm ; d (80 MHz CDCl3)
2
1
H
.74±7.26 (5H, m, aromatic protons), 6.35±5.85 (1H, m,
Cyclohexyl 6-diethylamino-2-benzo[b]furancarboxylate
(3i). The crude product was puri®ed by column chromato-
graphy (cyclohexane/methyl chloride 8:2) yielding 3i as a
CH ±CHvCH ), 5.65±5.26 (2H, m, CH ±CHvCH ),
2
2
2
2
4
.88 (2H, dt, Jˆ7.0, 1.2 Hz, CH ±CHvCH ); m/z
2
2
1
1
20
(70 eV) 203 ((M11) , 4.5), 202 (M , 33), 158 (8.7), 157
(9.4), 146(11), 145 (100), 131 (7.4), 118 (17.8), 89 (32), 63
(16%).
red oil, n ˆ21.6022 [Found: C, 72.12; H, 7.65; N, 4.08
D
C H NO requires C, 72.35; H, 7.99; N, 4.44%];
25
19
3
nmax(KBr) 3086(w), 2970(m), 2937(s), 2861(m), 1715(s),
627(s), 1577(m), 1556(m), 1510(s), 1450(m), 1356(m),
1
Allyl 7-methoxy-2-benzo[b]furancarboxylate (3e). The
crude product was puri®ed by column chromatography
1324(m), 1301(m), 1270(s), 1240(s), 1179(s), 1120(s),
1093(w), 1013(m), 963(m), 842(w), 801(m), 793(m),
759(m) cm ; d (80 MHz CDCl ) 7.48±7.38 (2H, m
H 3
2
1
(
cyclohexane/methyl chloride 8:2) yielding 3e as a colour-
2
0
less oil, n ˆ21.5107; [Found: C, 67.48; H, 5.29 C H O
aromatic protons), 6.76±6.67 (2H, m aromatic protons),
5.25±4.77 (1H, m, OCH), 3.40 (4H, k, Jˆ7.0 Hz, 2£N-
CH ±CH ), 2.15±0.85 (10H, m, (CH ) -cyclohexyl),
D
13 12
4
requires C, 67.24; H, 5.21%]; nmax (KBr) 2942(w), 1731(s),
1
1
7
622(w), 1594(m), 1577(m), 1492(s), 1325(w), 1302(m),
272(m), 1227(w), 1185(s), 1094(s), 974(m), 779(m),
31(m) cm ; d (80 MHz CDCl ) 7.57±6.97 (4H, m,
2
3
2 5
1.28±1.19 (6H, t, Jˆ7.0 Hz, ±CH ±Me); m/z (70 eV) 316
2
2
1
1
((M11) , 5.6), 315 (M , 26), 300 (7.5), 233 (16), 219 (13),
1
H
3
aromatic protons), 6.40±5.77 (1H, m, CH ±CHvCH ),
2
218 (100), 190 (7.7%).
2
5
1
2
1
.52±5.15(2H, m, CH±CHvCH ), 4.88 (2H, dt, Jˆ5.4,
1
33 ((M11) , 12), 232 (M , 85), 175 (100), 148 (18),
2
.2 Hz, CH ±CHvCH ), 4.02(3H, s, OMe); m/z (70 eV)
2
Ethyl naphtho[2,1-b]furan-2-carboxylate (5a). The crude
product was puri®ed by column chromatography (cyclo-
hexane/methyl chloride 8:3) yielding 5a as a white solid,
mp 85±888C; [Found: C, 74.71; H, 5.24 C H O requires
2
1
19 (12), 89(11%).
15
12
3
Allyl 6-diethylamino-2-benzo[b]furancarboxylate (3f).
The crude product was puri®ed by column chromatography
C, 74.99; H, 5.03%;]; nmax(KBr) 3086(w), 3060(w),
2987(m), 1728(s), 1586(m), 1552(s), 1367(m), 1326(s),
1281(m), 1224(m), 1172(s), 1124(m), 1020(s), 823(s),
(
cyclohexane/methyl chloride 8:2) yielding 3f as a red oil;
20
21
n ˆ21.6228; [Found: C, 70.21; H, 7.02; N, 5.14
803(m), 761(s), 743(m) cm ; d (80 MHz CDCl ) 8.23±
H
D
3
C H NO requires C, 70.31; H, 7.01; N, 5.12%];
19
7.59 (7H, m, aromatic protons), 4.62±4.35 (2H, q,
Jˆ7.1 Hz, CH ±Me), 1.55±1.37 (3H, t, Jˆ7.1 Hz, ±CH ±
16
3
nmax(KBr) 3086(w), 2973(m), 1719(s), 1626(s), 1577(w),
2
2
1
Me); m/z (70 eV) 241 ((M11) , 16), 240 (M , 100), 213
1
1
1
554(m), 1510(s), 1356(m), 1304(m), 1270(s), 1240(s),
175(s), 1121(s), 978(m), 793(m), 758(m) cm ; d
2
1
(12), 212 (79), 196 (6.6), 195 (27), 168 (24), 139(52).
H
(
80 MHz CDCl ) 7.50±7.02 (2H, m, aromatic protons),
3
6.78±6.69 (2H, m, aromatic protons), 6.40±5.84 (1H, m,
CH ±CHvCH ), 5.54±5.32 (2H, m, CHvCH ), 4.84
Allyl naphtho[2,1-b]furan-2-carboxylate (5b). The crude
product was puri®ed by column chromatography (cyclo-
hexane/methyl chloride 8:3) yielding 5b as a white solid,
mp 72±748C; [Found: C, 75.95; H, 4.88 C H O requires
C, 76.18; H, 4.79%;]; nmax(KBr) 3084(w), 3051(w),
2932(w), 1731(s), 1646(w), 1585(m), 1554(w), 14529w),
2
2
2
(
2H, dt, Jˆ5.4, 1.3 Hz, CH ±CHvCH ), 3.41 (4H, q,
2
2
Jˆ7.0 Hz, CH ±CH ), 1.20 (6H, t, Jˆ7.0 Hz, CH ±Me);
2 3 2
16 12
3
1
1
m/z (70 eV) 274 ((M11) , 6.6), 273 (M , 37), 259 (17),
58 (100), 230 (7.7%).
2

D. Bogdal, M. Warzala / Tetrahedron 56 (2000) 8769±8773
8773
1
9
378(m), 1331(m), 1283(m), 1224(m), 1175(s), 1123(m),
14(s), 873(m), 830(s), 759(s), 751(s), 562(m) cm ; d
(d) Zawadowski, T.; Suski, S.; Rajchman, J.; Bogdal, M.;
Szafranski, B. Acta Pol. Pharm. 1993, 50, 457±460. (e) Yang,
Z.; Liu, H. B.; Lee, C. M.; Chang, H. M.; Wong, H. N. C. J. Org.
Chem. 1992, 57, 7248±7257.
2
1
H
(
80 MHz CDCl ) 8.23±7.55 (7H, m, aromatic protons),
3
6.28±5.88 (1H, m, CH ±CHvCH ), 5.60±5.29 (2H, m,
CH ±CHvCH ), 4.97±4.42(2H, m, CH ±CHvCH ); m/z
2 2
2
2
2
2
4. Schmidt, E., In Ullmann's Ecyclopedia, VI ed.; Optical Bright-
eners; Electronic Release, 1999.
1
1
(70 eV) 253 ((M11) , 18), 252 (M , 100), 212 (9.8), 208
(8.8), 207 (9.0), 196 (13), 195 (86), 181(8.8), 168 (68), 139
(82%).
5. (a) Gilchrist, T. Heterocyclic Chemistry, 3rd ed.; Longman:
Singapore 1997. (b) Katrizky, A. R.; Fali, C. N.; Li, J. J. Org.
Chem. 1997, 62, 8205±8209. (c) Kappe, C.; Murphree, S.;
Padwa, A. Tetrahedron 1997, 53, 14179±14233.
Cyclohexyl naphtho[2,1-b]furan-2-carboxylate (5c). The
crude product was puri®ed by column chromatography
(cyclohexane/methyl chloride 8:3) yielding 5c as a white
solid, mp 134±1368C; [Found: C, 77.50; H, 6.16 C H O
6
. Cagniant, P.; Cagniat, D. Adv. Heterocycl. Chem. 1975, 18, 337.
. Mustafa, A. Benzofurans; Wiley: New York, 1974.
7
1
9
18
3
8. Comprehensive Heterocyclic Chemistry, Vol. 4; Katrizky, A.
requires C, 77.53; H, 6.16%;]; nmax(KBr) 3106(m),
R., Rees, C. W., Eds.; Pergamon: Oxford, 1984; Vol. 4.
3
1
1
9
050(w), 2933(s), 2857(s), 1713(s), 1627(w), 1589(m),
562(w), 1450(m), 1354(m), 1307(m), 1320(m), 1283(s),
237(s), 1170(s), 1116(s), 1014(s), 990(m), 960(m),
9
4
4
. (a) McKillop, A.; Young, D. W. Synthesis 1979, 401±422 and
81±500. (b) Posner, G. H. Angew. Chem., Int. Ed. Engl. 1978, 17,
87±511. (c) Balogh, M.; Laszlo, P. Organic Chemistry Using
2
1
30(m), 881(m), 827(w), 807(s), 762(m), 741(m) cm ;
Clays; Springer: Berlin, 1993. (d) Clark, J. H. Catalysis of Organic
Reactions by Supported Inorganic Reagents; VCH: New York,
d (80 MHz CDCl ) 8.02±7.54 (7H, m, aromatic protons),
H
5.25±4.95 (1H, m, OCH), 2.15±1.10 (10H, m, (CH ) -
cyclohexyl); m/z (70eV) 295 ((M11) , 4.7), 294 (M ,
3
2 5
1
1
994. (e) Smith, K., Ed. Solid Supports and Catalyst in Organic
Synthesis; Ellis Horwood, PTR Prentice Hall: Chichester, 1992.
0. For relevant papers and reviews on microwave assisted chemi-
cal reactions see: (a) Abramovitch, R. A. Org. Prep. Proced. Int.
991, 23, 683±714. (b) Majetich, G.; Hicks, R. Radiat. Phys.
1
21), 212 (100), 213 (15), 195 (9.0), 139 (21%).
1
1
Acknowledgements
Chem. 1995, 45, 567±579. (c) Caddick, S. Tetrahedron 1995, 51,
10403±10432. (d) Strauss, C. R.; Trainor, R. W. Aust. J. Chem.
1995, 48, 1665±1692. (e) Varma, R. S. Green Chemistry 1999, 1,
43±55. (f) Loupy, A.; Petit, A.; Hamelin, J.; Texier-Boullet, F.;
Jacquault, P.; Mathe, D. Synthesis 1998, 1213±1224. (g) Bogdal,
D. Wiad. Chem. 1999, 53, 66±99.
This work was undertaken as part of the EU sponsored D10
COST Program (Innovative Methods and Techniques for
Chemical Transformations).
References
11. (a) Bram, G.; Loupy, A.; Sansoulet, J. Isr. J. Chem. 1985, 25,
291. (b) Deshayes, S.; Liagre, M.; Loupy, A.; Luche, J. L.; Petit, A.
1
. Simpson, T. J. Aromatic Compounds. In The Chemistry of
Natural Products; Thomson, R. H., Ed.; Blackie: London, 1985.
. Leung, A. Y.; Foster, S. Encyclopedia of Common Natural
Tetrahedron 1999, 55, 10851±10870.
2. (a) Bogdal, D.; Pielichowski, J.; Jaskot, K. Org. Prep. Proced.
1
2
Int. 1998, 30, 427±432. (b) Bogdal, D.; Pielichowski, J.; Boron, A.
Synth. Commun. 1998, 28, 3029±3039.
Ingredients Used in Food, Drugs, and Cosmetics; Wiley: New
York, 1996.
1
3. (a) Ayoubi, S. A.; Texier-Boullet, F.; Hamelin, D. Synthesis
994, 258±260. (b) Kim, S. Y.; Kwon, P. S.; Kwon, T. W. Synth.
3
. (a) Nagahara, T.; Yokoyama, Y.; Inamura, K.; Katakura, S.;
1
Komoriya, S.; Yamaguchi, H.; Hara, T.; Iwamoto, M. J. Med.
Chem. 1994, 37, 1200±1207. (b) Ohemeng, K. A.; Appollina,
M. A.; Nguyen, V. N.; Schwender, C. F.; Singer, M.; Steber, M.;
Ansell, J.; Argentieri, D.; Hageman, W. J. Med. Chem. 1994, 37,
Commun. 1997, 27, 533±541.
4. (a) Petit, A.; Loupy, A.; Maillard, P.; Momenteau, M. Synth.
Commun. 1992, 22, 1137. (b) Bogdal, D. J. Chem. Res., Synopsis
1
1
998, 468±469.
5. Varma, R. S.; Kumar, D.; Liesen, P. J. J. Chem. Soc., Perkin
3663±3667. (c) Gubin, J.; Vogelaer, H.; Inion, H.; Houben, C.;
Lucchetti, J.; Mahaux, J.; Rosseels, G.; Peiren, M.; Clinet, M.;
Polster, P.; Chatelain, P. J. Med. Chem. 1993, 36, 1425±1433.
1
Trans. 1 1998, 4093±4096.