Synthesis of 2,3-disubstituted benzofurans from ortho-acylphenols

Article abstract of DOI:10.1055/s-2004-834951

2,3-Disubstituted benzofuran derivatives were synthesized from ortho-acylphenols in two steps. The β-aryloxyacrylates prepared from the ortho-acylphenols were treated with n-Bu₃SnH/ AIBN and then with 5% HCl-EtOH to afford 2,3-disubstituted benzofurans. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2004-834951

PAPER
387
Synthesis of 2,3-Disubstituted Benzofurans from ortho-Acylphenols
S
ynthesis of 2,3-D
w
isubstituted Benzo
a
furans from
n
ortho-Acyl
g
phenols -Ok Kim, Jinsung Tae*
Center for Bioactive Molecular Hybrids (CBMH) and Department of Chemistry, Yonsei University, Seoul 120-749, South Korea
Fax +82(2)3647050; E-mail: jstae@yonsei.ac.kr
Received 13 September 2004; revised 27 September 2004
ficient and mild two-step synthetic method of 2,3-disub-
stituted benzofuran derivatives from readily available
ortho-acylphenols.
Abstract: 2,3-Disubstituted benzofuran derivatives were synthe-
sized from ortho-acylphenols in two steps. The b-aryloxyacrylates
prepared from the ortho-acylphenols were treated with n-Bu3SnH/
AIBN and then with 5% HCl–EtOH to afford 2,3-disubstituted ben-
zofurans.
The b-aryloxyacrylates 4a–i were prepared from ortho-
acylphenols 2a–i8 and ethyl propiolate (3) according to
the literature procedure. The yields for the synthesis of b-
aryloxyacrylates 4a–i were uniformly good (90–97%) as
shown in Table 1. Sterically less hindered aldehydes 2a
and 2g (R3 = H) proved to be slightly better substrates in
the O-conjugate addition reactions (entries 1 and 7,
Table 1).
Key words: benzofurans, cyclizations, dehydrations, phenols, rad-
ical reactions
Molecules containing the benzofuran scaffold show a
wide range of biological activities.1 Many synthetic ef-
forts have been devoted to the synthesis of this privileged
structure and recently combinatorial approaches to this
class of compounds have also been an active research ar-
ea.2 General synthetic strategies of this structure include
the condensation reactions between ketones (or alde-
hydes) and several different forms of nucleophiles under
acidic or basic conditions.3 Alternatively, the palladium
catalyzed heteroannulation reactions of ortho-alky-
nylphenols under mild conditions have been utilized a
lot.4 Although these methods are commonly employed in
the synthesis of benzofuran derivatives, they either re-
quire strongly acidic or basic conditions or have difficul-
ties in the introduction of diverse substituent patterns
starting from the readily available materials.
We then investigated one-pot radical cyclization/dehydra-
tion sequence. Treatment of 4a with tributyltin hydride
(1.2 equiv n-Bu3SnH) under standard conditions (cat.
AIBN, benzene, 80 °C) produced two products 5a and 6a
as a mixture (Scheme 2).5 The direct dehydration of these
products into 1a under the reaction conditions was not ob-
served. Therefore, upon completion of the radical cycliza-
tion reaction, the reaction solution was condensed under
vacuum to remove benzene and then treated with an acidic
ethanol solution. Dehydration reaction was completed
with 5% HCl–EtOH in less than 10 minutes and led to the
benzofuran 1a in 98% overall yield.
O
CO2Et
O
CO2Et
OH
CHO
CO2Et
O
1a
4a
O
n-Bu3SnH
98% 5% HCl
in EtOH
AIBN, benzene, reflux
R
2
R
1
CO2Et
O
O
H
CO2Et
– H2O
3
+
O
O
O
CO2Et
OH
H
CO2Et
O
n-Bu3Sn
5a
6a
O
R
HO
Scheme 2
R
5
4
Synthesis of 2,3-disubstituted benzofurans were then ex-
amined. The results of the synthesis of benzofurans 1a–i
are summarized in Table 1. The one-pot radical cycliza-
tion and dehydration reactions proved to be efficient for
various substrates (93–99%). Substitutions on the aromat-
ic ring (R1 and R2) were generally tolerated. Sterically
bulky substituents at C-3 position (R3 = i-Bu, Ph) were
also successfully introduced in excellent yields (entries 4,
5, 8, and 9). The overall two-step sequence (2 → 4 → 1)
is a highly efficient synthetic method in terms of overall
yields (84–94%) and facile introduction of diverse substit-
uents.
Scheme 1
2,3-Disubstututed benzofurans 1 could be readily synthe-
sized from the ortho-acylphenols 2 utilizing the enol
ethers 4 as shown in Scheme 1. b-Aryloxyacrylates 4
could be prepared from the reaction between 2 and ethyl
propiolate (3).5,6 Radical cyclization of 4 under tin hydride
conditions would generate 5 which could be subsequently
dehydrated to give benzofurans 1.7 Here we report an ef-
SYNTHESIS 2005, No. 3, pp 0387–0390
Advanced online publication: 03.12.2004
x
x
.
x
x
.2
0
0
5
DOI: 10.1055/s-2004-834951; Art ID: F13104SS
© Georg Thieme Verlag Stuttgart · New York

388
K.-O. Kim, J. Tae
PAPER
1H NMR (250 MHz, CDCl3): d = 7.48–7.40 (m, 2 H), 7.26–7.21 (m,
2 H), 4.19 (q, J = 7.1 Hz, 2 H), 3.78 (s, 2 H), 2.21 (s, 3 H), 1.27 (t,
J = 7.1 Hz, 3 H).
13C NMR (63 MHz, CDCl3): d = 169.27, 154.24, 146.21, 130.01,
124.03, 122.34, 119.24, 112.93, 111.06, 61.47, 32.94, 14.30, 8.10.
HRMS: m/z [M + H]+ calcd for C13H15O3: 219.1021; found:
219.1018.
Table 1 Synthesis of Benzofurans from ortho-Acylphenolsa
R1
R1
OH
CO2Et
O
a, b
O
R2
R2
R3
R3
1
2
Entry
2
R1
H
H
H
H
H
H
R2
H
H
H
H
H
R3
H
4 (% yield) 1 (% yield)
1c
Rf 0.71 (CH2Cl2).
1
2
3
4
5
6
7
8
9
2a
2b
2c
2d
2e
2f
4a (96)
4b (92)
1a (98)
1b (97)
1c (96)
1d (99)
1e (93)
1f (99)
1g (96)
1h (99)
1i (93)
IR (film): 2960, 2930, 2863, 1737, 1634, 1460, 1240, 1184, 1163,
1030, 748 cm–1.
1H NMR (250 MHz, CDCl3): d = 7.52–7.40 (m, 2 H), 7.28–7.16 (m,
2 H), 4.18 (q, J = 7.1 Hz, 2 H), 3.77 (s, 2 H), 2.64 (t, J = 7.6 Hz, 2
H), 1.79–1.58 (m, 2 H), 1.45–1.30 (m, 2 H), 1.26 (t, J = 7.1 Hz, 3
H), 0.93 (t, J = 7.2 Hz, 3 H).
13C NMR (63 MHz, CDCl3): d = 169.28, 154.42, 146.22, 129.39,
123.91, 122.28, 119.57, 117.67, 111.19, 61.45, 33.04, 31.91, 23.48,
22.68, 14.27, 14.07.
Me
n-Bu 4c (92)
Ph
4d (90)
4e (91)
4f (90)
4g (97)
4h (92)
4i (91)
i-Bu
Me
H
t-Bu
H
2g
2h
2i
OMe
OMe
OMe
HRMS: m/z [M + H]+ calcd for C16H21O3: 261.1491; found:
261.1494.
H
Ph
1d
H
i-Bu
Rf 0.74 (CH2Cl2).
a Reagents and conditions: a) 1.2 equiv ethyl propiolate (3), 1.2 equiv
N-methylmorpholine, CH2Cl2, 25 °C; b) 1.2 equiv n-Bu3SnH, cat.
AIBN, benzene, 80 °C; 5% HCl in EtOH.
IR (film): 3042, 2981, 2935, 1732, 1624, 1455, 1194, 1030, 748,
702 cm–1.
1H NMR (250 MHz, CDCl3): d = 7.26–7.25 (m, 9 H), 4.22 (q, J =
7.1 Hz, 2 H), 3.87 (s, 2 H), 2.77 (t, J = 7.1 Hz, 3 H).
13C NMR (63 MHz, CDCl3): d = 169.35, 154.50, 146.83, 132.03,
129.12, 129.03, 128.40, 127.68, 124.55, 122.99, 120.07, 119.94,
111.38, 61.62, 33.55, 14.29.
HRMS: m/z [M + H]+ calcd for C18H17O3: 281.1178; found:
281.1179.
In conclusion, we have developed an efficient two-step
synthetic method of 2,3-disubstituted benzofuran deriva-
tives starting from readily available ortho-acylphenols.
Applications of this reaction sequence for the synthesis of
complex benzoforan skeletons are under investigation.
1e
Rf 0.69 (CH2Cl2).
Radical Cyclization/Dehydration Reaction; General Procedure
An anhyd benzene (5 mL) solution of 4a (722 mg, 3.28 mmol), n-
Bu3SnH (1.06 mL, 3.94 mmol), and catalytic amount of AIBN (10
mg) was refluxed at 80 °C for 10 h under N2 atmosphere. The sol-
vent was removed under reduced pressure and the residue was dis-
solved in 5% HCl in EtOH (3 mL). After 10 min at r.t., the solvent
was removed under reduced pressure and purified by column chro-
matography over silica gel (elution with 10% EtOAc in hexane) to
give 1a (659 mg, 98%) as an oil.
IR (film): 3068, 2960, 2935, 2873, 1742, 1455, 1245, 1184, 1035,
753 cm–1.
1H NMR (250 MHz, CDCl3): d = 7.50–7.41 (m, 2 H), 7.27–7.16 (m,
2 H), 4.18 (q, J = 7.1 Hz, 2 H), 3.77 (s, 2 H), 2.51 (d, J = 7.2 Hz, 2
H), 2.10–1.93 (m, 1 H), 1.25 (t, J = 7.1 Hz, 3 H), 0.94 (d, J = 6.6 Hz,
6 H).
13C NMR (63 MHz, CDCl3): d = 169.24, 154.41, 146.84, 129.60,
123.89, 122.27, 119.75, 116.76, 111.15, 61.43, 33.06, 33.00, 28.96,
22.78, 14.26.
HRMS: m/z [M + H]+ calcd for C16H21O3: 261.1491; found:
261.1493.
1a
Rf 0.52 (hexane–EtOAc, 3:1).
IR (film): 2960, 2935, 2873, 1747, 1460, 1250, 1194, 1035, 753
cm–1.
1H NMR (250 MHz, CDCl3): d = 7.53–7.51 (m, 1 H), 7.45–7.43 (m,
1 H), 7.26–7.18 (m, 2 H), 6.63 (s, 1 H), 4.22 (q, J = 7.1 Hz, 2 H),
3.82 (s, 2 H), 1.28 (t, J = 7.1 Hz, 3 H).
1f
Rf 0.74 (CH2Cl2).
IR (film): 2965, 2865, 2357, 1749, 1475, 1362, 1262, 1202, 1161,
1028, 814, 654 cm–1.
1H NMR (500 MHz, CDCl3): d = 7.44 (s, 1 H), 7.35–7.31 (m, 2 H),
4.18 (q, J = 7.1 Hz, 2 H), 3.76 (s, 2 H), 2.21 (s, 3 H), 1.38 (s, 9 H),
1.26 (t, J = 7.1 Hz, 3 H).
13C NMR (126 MHz, CDCl3): d = 169.34, 152.43, 146.28, 145.43,
129.54, 121.93, 115.36, 113.02, 110.37, 61.45, 34.85, 33.02, 32.04,
14.32, 8.16.
13C NMR (63 MHz, CDCl3): d = 169.02, 155.05, 150.92, 128.67,
124.04, 122.84, 120.87, 111.19, 105.19, 61.55, 34.86, 14.29.
HRMS: m/z [M + H]+ calcd for C12H13O3: 205.0865; found:
205.0865.
1b
HRMS: m/z [M + H]+ calcd for C17H23O3: 275.1647; found:
275.1649.
Rf 0.51 (CH2Cl2).
IR (film): 2960, 2873, 1765, 1475, 1265, 1199, 1168, 1030 cm–1.
Synthesis 2005, No. 3, 387–390 © Thieme Stuttgart · New York

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Synthesis of 2,3-Disubstituted Benzofurans from ortho-Acylphenols
389
1g
4c
Rf 0.56 (CH2Cl2).
Rf = 0.33 (CH2Cl2).
IR (film): 2991, 2960, 2930, 2878, 2242, 1737, 1460, 1382, 1281,
1189, 1153, 1096, 1030 cm–1.
IR (film): 3078, 2960, 2935, 2878, 1716, 1685, 1649, 1603, 1578,
1475, 1445, 1281, 1219, 1163, 1133, 1112, 764 cm–1.
1H NMR (250 MHz, CDCl3): d = 7.13–7.12 (m, 2 H), 6.78–6.76 (m,
1 H), 6.64 (s, 1 H), 4.21 (q, J = 7.1 Hz, 2 H), 4.00 (s, 3 H), 3.84 (s,
2 H), 1.28 (t, J = 7.1 Hz, 3 H).
13C NMR (63 MHz, CDCl3): d = 169.18, 151.37, 145.50, 144.49,
130.62, 123.79, 113.57, 106.49, 105.82, 61.75, 56.38, 34.94, 14.55.
HRMS: m/z [M + H]+ calcd for C13H15O4: 235.0970; found:
235.0978.
1H NMR (500 MHz, CDCl3): d = 7.76 (d, J = 12.2 Hz, 1 H), 7.72–
7.71 (m, 1 H), 7.53–7.50 (m, 1 H), 7.28–7.25 (m, 1 H), 7.11–7.09
(m, 1 H), 5.59 (d, J = 12.2 Hz, 1 H), 4.21 (q, J = 7.1 Hz, 2 H), 2.90
(t, J = 7.2 Hz, 2 H), 1.69–1.61 (m, 2 H), 1.39–1.33 (m, 2 H), 1.29 (t,
J = 7.1 Hz, 3 H), 0.92 (t, J = 7.2 Hz, 3 H).
13C NMR (126 MHz, CDCl3): d = 201.37, 166.85, 158.49, 154.14,
133.43, 130.84, 130.51, 125.48, 118.93, 103.59, 60.42, 43.31,
26.45, 22.53, 14.42, 14.02.
1h
4d
Rf 0.66 (CH2Cl2).
Rf 0.44 (n-hexane–EtOAc, 5:1).
IR (film): 2925, 2851, 1742, 1496, 1276 cm–1.
IR (film): 3063, 2976, 2925, 2858, 1711, 1670, 1650, 1481, 1450,
1224, 1117, 927, 769, 702 cm–1.
1H NMR (250 MHz, CDCl3): d = 7.79–7.76 (m, 2 H), 7.65–7.42 (m,
6 H), 7.35–7.29 (m, 1 H), 7.18–7.15 (m, 1 H), 5.30 (d, J = 12.2 Hz,
1 H), 4.41 (q, J = 7.1 Hz, 2 H), 1.24 (t, J = 7.1 Hz, 3 H).
13C NMR (63 MHz, CDCl3): d = 194.75, 166.92, 158.47, 153.34,
137.38, 133.54, 132.47, 130.93, 130.39, 129.89, 128.58, 125.24,
118.62, 103.12, 60.24, 14.39.
1H NMR (500 MHz, CDCl3): d = 7.54–7.53 (m, 2 H), 7.49–7.37 (m,
3 H), 7.20–7.16 (m, 2 H), 6.84–6.83 (m, 1 H), 4.20 (q, J = 7.1 Hz, 2
H), 4.03 (s, 3 H), 3.88 (s, 2 H), 1.26 (t, J = 7.1 Hz, 3 H).
13C NMR (126 MHz, CDCl3): d = 169.27, 147.08, 145.40, 132.10,
130.16, 129.13, 129.01, 127.71, 123.69, 120.44, 112.49, 106.75,
61.56, 56.24, 33.48, 14.29.
HRMS: m/z [M + H]+ calcd for C19H19O4: 311.1283; found:
311.1281.
4e
1i
Rf 0.36 (n-hexane–EtOAc, 5:1).
Rf 0.74 (CH2Cl2).
IR (film): 3088, 2960, 2930, 2868, 1716, 1685, 1649, 1603, 1480,
1450, 1296, 1276, 1224, 1158, 1112, 764 cm–1.
IR (film): 3053, 2955, 2873, 2848, 1737, 1496, 1276, 1214, 1184,
1066, 1035 cm–1.
1H NMR (250 MHz, CDCl3): d = 7.14–7.08 (m, 2 H), 6.78–6.76 (m,
1 H), 4.17 (q, J = 7.1 Hz, 2 H), 4.00 (s, 3 H), 3.79 (s, 2 H), 2.49 (d,
J = 7.2 Hz, 2 H), 2.03–1.98 (m, 1 H), 1.24 (t, J = 7.1 Hz, 3 H), 0.94
(d, J = 6.6 Hz, 6 H).
1H NMR (250 MHz, CDCl3): d = 7.77 (d, J = 12.3 Hz, 1 H), 7.71–
7.68 (m, 1 H), 7.56–7.49 (m, 1 H), 7.30–7.24 (m, 1 H), 7.12–7.08
(m, 1 H), 5.60 (d, J = 12.2 Hz, 1 H), 4.21 (q, J = 7.1 Hz, 2 H), 2.78
(d, J = 6.9 Hz, 2 H), 2.27–2.16 (m, 1 H), 1.29 (t, J = 7.1 Hz, 3 H),
0.95 (d, J = 6.6 Hz, 6 H).
13C NMR (63 MHz, CDCl3): d = 169.15, 147.08, 145.26, 131.37,
122.98, 117.28, 112.28, 106.23, 61.39, 56.13, 33.14, 33.97, 28.95,
22.77, 14.28.
HRMS: m/z [M + H]+ calcd for C17H22O4: 290.1518; found:
290.1517.
13C NMR (63 MHz, CDCl3): d = 201.11, 166.77, 158.38, 153.91,
133.34, 130.94, 130.33, 125.41, 118.74, 103.47, 60.34, 52.44,
24.97, 22.66, 14.35.
4f
Rf 0.56 (n-hexane–EtOAc, 5: 1).
4a
IR (NaCl): 2966, 2914, 2868, 1716, 1685, 1650, 1496, 1368, 1235,
1153, 1102, 1045, 953, 835 cm–1.
Rf 0.39 (n-hexane–EtOAc, 3:1).
1H NMR (500 MHz, CDCl3): d = 7.81 (s, 1 H), 7.77 (d, J = 12.2 Hz,
1 H), 7.57–7.55 (m, 1 H), 7.05–7.03 (m, 1 H), 5.58 (d, J = 12.2 Hz,
1 H), 4.20 (q, J = 7.1 Hz, 2 H), 2.59 (s, 3 H), 1.3 (s, 9 H), 1.29 (t,
J = 7.1 Hz, 3 H).
13C NMR (126 MHz, CDCl3): d = 198.22, 166.86, 158.80, 152.55,
148.62, 131.15, 129.49, 127.43, 118.80, 103.22, 60.35, 34.72,
31.56, 31.34, 14.39.
IR (film): 3089, 2991, 2934, 2899, 2873, 1731, 1711, 1650, 1603,
1219, 1194, 1168, 1117, 1035, 759 cm–1.
1H NMR (250 MHz, CDCl3): d = 10.37 (s, 1 H), 7.94–7.90 (m, 1 H),
7.85 (d, J = 12.2 Hz, 1 H), 7.69–7.62 (m, 1 H), 7.35–7.29 (m, 1 H),
7.18–7.15 (m, 1 H), 5.64 (d, J = 12. Hz, 1 H), 4.21 (q, J = 7.1 Hz, 2
H), 1.30 (t, J = 7.1 Hz, 3 H).
13C NMR (63 MHz, CDCl3): d = 188.15, 166.57, 158.03, 157.59,
136.09, 128.97, 126.54, 125.42, 118.33, 104.22, 60.42, 14.33.
4g
Rf 0.31 (n-hexane–EtOAc, 3:1).
4b
Rf 0.35 (n-hexane–EtOAc, 3:1).
IR (film): 2986, 2950, 2909, 2873, 2838, 1706, 1650, 1634, 1583,
1486, 1322, 1276, 1204, 1178, 1117, 794 cm–1.
1H NMR (250 MHz, CDCl3): d = 10.23 (s, 1 H), 7.80 (d, J = 12.3
Hz, 1 H), 7.51–7.47 (m, 1 H), 7.35–7.23 (m, 2 H), 5.29 (d, J = 12.3
Hz, 1 H), 4.17 (q, J = 7.1 Hz, 2 H), 3.90 (s, 3 H), 1.27 (t, J = 7.1 Hz,
3 H).
IR (film): 2981, 2966, 1716, 1685, 1650, 1486, 1450, 1286, 1224,
1132, 1102, 770 cm–1.
1H NMR (250 MHz, CDCl3): d = 7.82–7.74 (m, 2 H), 7.57–7.50 (m,
1 H), 7.29–7.23 (m, 1 H), 7.12–7.08 (m, 1 H), 5.60 (d, J = 12.2 Hz,
1 H), 4.19 (q, J = 7.1 Hz, 2 H), 2.58 (s, 3 H), 1.28 (t, J = 7.1 Hz, 2 H).
13C NMR (63 MHz, CDCl3): d = 188.33, 166.85, 161.34, 151.36,
145.88, 128.97, 126.80, 119.67, 118.45, 101.09, 60.23, 56.38,
14.31.
13C NMR (63 MHz, CDCl3): d = 197.82, 166.76, 158.31, 154.67,
134.02, 130.74, 130.12, 125.42, 118.99, 103.69, 60.41, 31.48.
14.38.
Synthesis 2005, No. 3, 387–390 © Thieme Stuttgart · New York

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4h
K.-O. Kim, J. Tae
PAPER
References
Rf 0.20 (n-hexane–EtOAc, 5:1).
(1) Hou, X.-L.; Yang, Z.; Wong, H. N. C. Furans and
IR (film): 2925, 2853, 1716, 1675, 1650, 1460, 1322, 1276, 1112,
968, 707 cm–1.
1H NMR (250 MHz, CDCl3): d = 7.79–7.01 (m, 9 H), 5.11 (d, J =
12.2 Hz, 1 H), 4.10 (q, J = 7.1 Hz, 2 H), 3.89 (s, 3 H), 1.22 (t, J =
7.1 Hz, 3 H).
Benzofurans, In Progress in Heterocyclic Chemistry, Vol.
14; Gribble, G. W.; Gilchrist, T. L., Eds.; Pergamon: Oxford,
2002, 139–179.
(2) Horton, D. A.; Bourne, G. T.; Smythe, M. L. Chem. Rev.
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13C NMR (63 MHz, CDCl3): d = 194.34, 167.12, 161.22, 151.34,
141.39, 137.09, 133.54, 129.93, 128.50, 126.56, 121.01, 114.93,
100.42, 59.95, 56.28, 14.33.
4i
Rf 0.25 (n-hexane–EtOAc, 5:1).
IR (film): 3083, 2960, 2930, 2873, 1711, 1655, 1578, 1470, 1373,
1312, 1271, 1184, 1112, 1020, 953, 789, 748 cm–1.
1H NMR (250 MHz, CDCl3): d = 7.65 (d, J = 12.3 Hz, 1 H), 7.28–
7.09 (m, 3 H), 5.31 (d, J = 12.3 Hz, 1 H), 4.17 (q, J = 7.1 Hz, 2 H),
3.87 (s, 3 H), 2.73 (d, J = 6.9 Hz, 2 H), 2.22–2.18 (m, 1 H), 1.27 (t,
J = 7.1 Hz, 3 H), 0.94 (d, J = 6.6 Hz, 6 H).
13C NMR (63 MHz, CDCl3): d = 201.43, 167.22, 161.44, 151.41,
142.04, 133.90, 126.67, 120.90, 115.78, 100.68, 60.20, 56.43,
52.39, 25.01, 22.69, 14.41.
(5) Lee, E.; Tae, J. S.; Chong, Y. H.; Park, Y. C.; Yun, M.; Kim,
S. Tetrahedron Lett. 1994, 35, 129.
(6) (a) Kerr, M. S.; de Alaniz, J. R.; Rovis, T. J. Am. Chem. Soc.
2001, 124, 10298. (b) Ciganek, E. Synthesis 1995, 1311.
(7) Tae, J.; Kim, K.-O. Tetrahedron Lett. 2003, 44, 2125.
(8) (a) Substrates 2a, 2b, and 2g were purchased from Aldrich.
Substrate 2f was prepared from 4-tert-butylphenol according
to the known literature procedure: Bensari, A.; Zaveri, N. T.
Synthesis 2003, 267. (b) Other substrates were prepared
from salicyl aldehyde and ortho-vanillin in two steps [1)
RMgBr, THF; 2) MnO2, benzene].
Acknowledgment
This work was supported by the Center for Bioactive Molecular Hy-
brids (CBMH).
Synthesis 2005, No. 3, 387–390 © Thieme Stuttgart · New York