Convenient synthesis of 2-arylbenzoxazoles mediated by solid-supported phenyliodine diacetate

Article abstract of DOI:10.1081/SCC-120005426

2-Arylbenzoxazoles were prepared in good yields through the intramolecular cyclization of phenolic Schiff's base in conjunction with poly[styrene(iodoso diacetate)], and the regenerated reagent kept the same activity in the reaction.

Full text of DOI:10.1081/SCC-120005426

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CONVENIENT SYNTHESIS OF 2-ARYLBENZOXAZOLES
MEDIATED BY SOLID-SUPPORTED PHENYLIODINE
DIACETATE
a
a
a
Ji-Zheng Zhang , Qing Zhu & Xian Huang
a
Department of Chemistry, Zhejiang University, Xixi Campus, Hangzhou, 310028, P.R. China
Department of Chemistry, Yanbian University, Jilin Province, 133002, P.R. China
b
Version of record first published: 18 Oct 2011
To cite this article: Ji-Zheng Zhang, Qing Zhu & Xian Huang (2002): CONVENIENT SYNTHESIS OF 2-ARYLBENZOXAZOLES
MEDIATED BY SOLID-SUPPORTED PHENYLIODINE DIACETATE, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 32:14, 2175-2179
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 14, pp. 2175–2179, 2002
CONVENIENT SYNTHESIS OF
-ARYLBENZOXAZOLES MEDIATED
BY SOLID-SUPPORTED
2
PHENYLIODINE DIACETATE
y
Ji-Zheng Zhang,* Qing Zhu, and Xian Huang
Department of Chemistry, Zhejiang University,
Xixi Campus, Hangzhou, 310028, P.R. China
ABSTRACT
2-Arylbenzoxazoles were prepared in good yields through
the intramolecular cyclization of phenolic Schiff’s base in
conjunction with poly[styrene(iodoso diacetate)], and the
regenerated reagent kept the same activity in the reaction.
Recently Togo reported that the polymer supported phenyliodine
diacetate could be used for the oxidative 1,2-aryl migration of alkyl aryl
[1]
ketone. For the benefits of the reagent, such as ease in handling and
1,2]
[
efficient regeneration without loss of activity,
poly[styrene(iodoso
[
2]
diacetate)] has attracted considerable attentions in recent years. Ley and
his cooperator applied this polymer supported reagent to synthesize
quinones from quinols, prepare spirodienones by oxidative reactions of
*
Current address. Department of Chemistry, Yanbian University, Jilin Province
33002, P.R. China.
Corresponding author.
1
y
2
175
DOI: 10.1081/SCC-120005426
Copyright & 2002 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

2
176
ZHANG, ZHU, AND HUANG
[
3]
tyrosine derivatives. Togo et al. later also reported that the ꢀ-hydroxyla-
tion of ketones, oxidation of sulfides and iodination of aromatic
compounds. In view of our ongoing program on the application of
cross-linked poly- [styrene(iodoso diacetate)][CPSID] in the formation
[
4]
of heterocyclic compounds, we explored the intramolecular cyclization
of phenolic Schiff’s bases with CPSID.
The oxazole derivatives have been found wide application in agricul-
[5]
[6]
ture and medicine. It was also reported that the benzoxazole ring is key
part of the antitumor metabolite UK-1. Among the known methods for the
synthesis of 2-arylbenzoxazoles, the general approach involved the oxidative
cyclization of phenolic Schiff’s base by oxidants such as barium
[
7]
[8]
[9]
[10]
manganate, lead tetraacetate, nickle peroxide. Prakash
reported
phenyliodine diacetate could be used to synthesize 2-arylbenzoxazoles via
the oxidative intramolecular cyclization of phenolic Schiff’s base. Here the
cross-linked poly[styrene(iodoso diacetate)] could be applied into this reac-
tion, and gage 2-arylbenzoxazoles in good yields. Additionally, CPSID has
two advantages over phenyliodine diacetate: the poly(iodostyrene) as bypro-
duct could be removed from the product just by filtration and the regener-
ated CPSID had the same activity in the reaction.
The 2% cross-linked poly[styrene(iodoso diacetate)] was prepared
[
4]
according to our previous work. Commercially available 2% cross-
linked polystyrene (200–400 mesh) reacted with iodine and iodine pentoxide
to give iodinated polystyrene. Then poly(iodostyrene) was treated with per-
ꢀ
acetic acid at 40 C for one day to give cross-linked poly[styrene(iodoso
diacetate)]. The loading of the polymer was determined to be 1.99 mmol/g.
To a stirred solution of Schiff’s base (1) in acetonitrile, cross-linked
poly[styrene(iodoso diacetate)] was added at room temperature. After
several hours, the reaction was completed (monitored by TLC), and filtered
to separate the resin. The solvent was removed under reduced pressure,
and the residue was neutralized with aqueous sodium bicarbonate solution
to give 2-arylbenzoxazoles (Scheme 1) in good yields (Table 1).
We also investigated the activity of the recycled cross-linked poly-
styrene(iodoso diacetate)] which could be reused for more than 4 times.
[
Scheme 1.

SYNTHESIS OF 2-ARYLBENZOXAZOLES
2177
Table 1. Formation of 2-Arylbenzoxazoles (2) from Schiff’s Base (1)
by Using CPSID
a
Compound
(1)
Product
(2)
Time
(h)
Yield
(%)
1
2
Entry
R
R
1
2
3
4
5
6
7
1a
1b
1c
1d
1e
1f
1g
Me
1i
H
H
H
H
H
H
2a
2b
2c
2d
2e
2f
2g
3
2i
1.5
1
3
3
2
2
2
70
3
2
71
62
60
75
78
80
67
Me
MeO
Cl
NO
H
Me
2h
Cl
2
Me
Me
8
9
0
1
2
1h
MeO
Me
Me
H
8
3
1
1
1
1j
1b
1a
NO2
Me
H
2j
2b
2a
80
61
83
b
c
1
0.5
H
a
Isolated yield.
b
By applying regenerated CPSID for 4 times.
By applying phenyliodine diacetate.
c
The result (Table 1) showed the reagent could be regenerated and reused for
the reaction without loss of the activity.
EXPERIMENTAL
Two percent cross-linked polystyrene was purchased from Aldrich.
H-NMR spectra were recorded at 60 MHz on a Varian EM-300
1
spectrometer of solutions in CDCl or CCl . Infrared spectra were recorded
3
4
on a Perkin Elmer 683 spectrophotometer in KBr. Phenolic Schiff’s base
12]
was prepared by the literature method.
[
Typical Procedure for the Preparation of 2-Arylbenzoxazoles (2)
Two percent cross-linked poly[styrene(iodoso diacetate)](1.4 mmol),
which has been soaked in CH CN over night, was added to the solution
3
of phenolic Schiff’s base (1) in 8–20 mL CH CN at room temperature. After
3
the reaction was completed (monitored by TLC), the resin was filtrated and
washed with CHCl (2 ꢁ 5 mL). The solvent was removed in vacuo and the
3

2
178
ZHANG, ZHU, AND HUANG
residue was neutralized with NaHCO solution (5 mL). The crude product
3
was extracted with CH Cl (3 ꢁ 5 mL). The combined organic layer was
2
2
washed with H O (5 mL), dried over MgSO and evaporated. The residue
2
4
was chromatographed on a column (silica gel, acetone : hexane ¼ 1 : 9 as an
eluent) to afford pure 2-arylbenzoxazole (2).
2a: White solid; m.p. 101–102 C (lit
ꢀ
[10]
ꢀ
1
m.p. 102 C); H-NMR
À1
(
CDCl ) ꢁ: 8.1–8.3 (m, 2H), 7.2–7.8 (m, 7H); IR (KBr) ꢂ (cm ): 1625,
3
1
555, 1460, 1450, 1340, 1240, 1050; MS: m/z (relative intensity) 195
þ
(
M 100) 92 (8).
ꢀ
[10]
ꢀ
1
m.p. 113–114 C); H-NMR
2
b: White solid; m.p. 112–113 C (lit
(
CDCl ) ꢁ: 8.07–8.37 (m, 2H), 7.07–7.63 (m, 6H), 2.45 (s, 3H); IR (KBr)
3
À1
ꢂ (cm ): 1630, 1545, 1455, 1240, 1050; MS: m/z (relative intensity) 209
þ
(
M 100) 91 (8).
ꢀ
[10]
1
2
c: White solid; m.p. 99–100 C (lit m.p. 101); H-NMR (CDCl ) ꢁ:
3
À1
8
1
2
.07–8.21 (m, 2H), 7.12–7.81 (m, 6H); 3.78 (s, 3H); IR (KBr) ꢂ (cm ): 1630,
590, 1450, 1350, 1250, 1240, 1055; MS: m/z (relative intensity) 225 (M 100)
10 (41) 182 (34).
d: White solid; m.p. 145–147 C (lit
CDCl ) ꢁ: 8.03–8.20 (m, 2H), 7.10–7.70 (m, 6H); IR (KBr) ꢂ (cm ):
þ
ꢀ
[10]
ꢀ
1
m.p. 147 C); H-NMR
2
À1
(
3
1
620, 1555, 1455, 1345, 1240, 1045; MS: m/z (relative intensity) 231
þ
þ
(
M þ 2, 33) 229 (M 100) 194 (2) 92 (12).
ꢀ
[10]
ꢀ
1
m.p. 266–268 C); H-NMR
2
e: White solid; m.p. 263–266 C (lit
À1
(
CDCl ) ꢁ: 9.05–9.10 (m, 2H), 6.8–8.1 (m, 6H); IR (KBr) ꢂ (cm ): 1630,
3
þ
1
560, 1510, 1465, 1330,1240, 1050; MS: m/z (relative intensity) 240 (M 100)
1
94 (28) 182 (22).
2
ꢀ
[10]
ꢀ
1
f: White solid; m.p. 102–103 C (lit m.p. 103 C); H-NMR (CDCl )
3
À1
ꢁ: 8.21–8.40 (m, 2H), 7.07–7.60 (m, 6H); 2.43 (s, 3H); IR (KBr) ꢂ (cm ):
þ
1640, 1555, 1470, 1330, 1250, 1050; MS: m/z (relative intensity) 209 (M
100) 106 (20).
ꢀ
1
2g: White solid; m.p. 132–133 C; H-NMR (CDCl ) ꢁ: 8.00–8.17 (m,
3
À1
2H), 6.90–7.54 (m, 5H); 2.43 (s, 3H); IR (KBr) ꢂ (cm ): 1620, 1560, 1470,
þ
1255, 1050; MS: m/z (relative intensity) 223 (M 100) 106 (9); Anal.
calcd for C H NO: C, 80.72; H, 5.83; N, 6.28. Found: C, 80.63; H, 5.82;
N, 6.18.
1
5
13
ꢀ
1
2h: White solid; m.p. 106–107 C; H-NMR (CDCl ) ꢁ: 8.03–8.18 (m,
3
À1
2
1
2
5
H), 6.78–7.50 (m, 5H), 3.78 (s, 3H), 2.43 (s, 3H); IR (KBr) ꢂ (cm ): 1615,
530, 1450, 1250, 1240, 1060, 1055; MS: m/z (relative intensity) 239 (M 100)
24 (35) 208(1) 196 (24); Anal. calcd for C 15H NO : C, 75.31; H, 5.44; N,
.86. Found: C, 75.43; H, 5.42; N, 5.68.
ꢀ
þ
13
2
1
2i: White solid; m.p. 144–145 C; H-NMR (CDCl ) ꢁ: 8.00–8.25 (m,
3
À1
2H), 6.90–7.65 (m, 5H), 2.44 (s, 3H); IR (KBr) ꢂ (cm ): 1630, 1550, 1460,
þ
þ
1260, 1050, 1000; MS: m/z (relative intensity) 245 (M þ 2, 33) 243 (M 100)

SYNTHESIS OF 2-ARYLBENZOXAZOLES
2179
208(2) 106 (22). Anal. calcd for C 14H ClNO: C, 68.43; H, 4.07; N, 5.75.
Found: C, 68.27; H, 4.02; N, 5.68.
10
ꢀ
[11]
ꢀ
1
m.p. 211–212 C); H-NMR
2
j: White solid; m.p. 209–211 C (lit
(
CDCl ) ꢁ: 8.37–8.40 (m, 2H), 7.2–7.6 (m, 5H), 2.45 (s, 3H); IR (KBr)
3
À1
ꢂ (cm ): 1640, 1560, 1510, 1465, 1330, 1240, 1050; MS: m/z (relative
intensity) 254 (M 100) 224 (16) 208(31) 196 (15) 106 (11).
þ
ACKNOWLEDGMENT
Project 29932020 was supported by the National Natural Foundation
of China.
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Received in Japan February 24, 2001