Solid-phase synthesis of 2-iodomethyl-2, 3-dihydrobenzofurans using recyclable polymer-supported selenium bromide

Article abstract of DOI:10.2174/157017809788489837

Reaction of polymer-supported selenium bromide with ortho allylated phenols and subsequent cleavage from the polymer by treatment of methyl iodide efficiently afforded 2-iodomethyl-2, 3-dihydrobenzofurans in good yields and high purities. The polymeric re

Full text of DOI:10.2174/157017809788489837

Letters in Organic Chemistry, 2009, 6, 345-348
345
Solid-Phase Synthesis of 2-Iodomethyl-2,3-dihydrobenzofurans Using
Recyclable Polymer-Supported Selenium Bromide
Shouri Sheng*, Minggang Hu, Dan Wu, Mingzhong Cai, and Xian Huang
Institutes of Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang, 330022, P. R. China
Received July 10, 2008: Revised December 08, 2008: Accepted December 24, 2008
Abstract: Reaction of polymer-supported selenium bromide with ortho allylated phenols and subsequent cleavage from
the polymer by treatment of methyl iodide efficiently afforded 2-iodomethyl-2,3-dihydrobenzofurans in good yields and
high purities. The polymeric reagent can be regenerated and reused as environmentally friendly reagent.
Keywords: Solid-phase organic synthesis, Polymer-supported selenium bromide, Recyclable, Selenium mediated intramolecu-
lar cyclization, 2-Iodomethyl-2,3-dihydrobenzofuran, Traceless cleavage.
1. INTRODUCTION
furans have now attracted considerable attention [12],
however, to our knowledge, there are few reports about the
synthesis of 2-iodomethyl-2,3-dihydrobenzofurans [13].
Since the first organoselenium resin [14] used in SPOS with
a combined advantage of decrease volatility and simplifica-
tion of product work-up was reported in 1976, several
research groups [15] and our group [16] have developed
selenium-based approaches for SPOS. More recently, we
have reported 5-iodoisoxazolines, iodomethyl-substituted
dihydrofurans and isoxazolines based on polystyrene-
supported selenium reagent [17]. In continuation of our
interest in solid-phase organoselenium chemistry, we here
Polymer-supported reagents have attracted growing
interest because they can provide attractive and practical
methods for combinatorial chemistry and solid-phase organic
synthesis (SPOS) in recent years [1]. Synthesis on a polymer
support shows a number of advantages as compared to solu-
tion chemistry. The most important one is the possibility to
apply excesses of reagents and remove them without involv-
ing time-consuming separation techniques. Now, the synthe-
sis of highly diverse organic molecule libraries using SPOS
methodology is recognized as a valuable tool for acceleration
R
CH3I, NaI
I
OH
Se
SeBr
R
SeCH3
R
+
DMF, 75 oC
O
O
THF, rt, 1h
2
3
1
4
Scheme 1.
of drug discovery. 2,3-Dihydrobenzofuran derivatives are
common in natural products and have attracted considerable
attention as a result of their biological activity [2]. In
addition, 2,3-dihydrobenzofurans have been developed for
the treatment of traumatic and ischemic central nervous
system (CNS) injury [3], and are reported to be useful in the
treatment of arteriosclerosis, hepatopathy, and cerebrovascu-
lar diseases [4]. Consequently, many methods have been
developed for the synthesis of 2,3-dihydrobenzofuran ring
systems, which involve biomimetic couplings of quinines
and phenylpropenyl moieties [5], anionic [6], benzyne [7],
dehydrative [8], electrocyclic [9], radical [10], and transition
metalmediated [11] cyclizations.ꢀ Among the 2,3-dihydro-
benzofuran derivatives, functionalized 2,3-dihydrobenzo-
wish to describe a simple and efficient waste-free solid-
phase synthetic approach to 2-iodomethyl-2,3-dihydroben-
zofurans (Scheme 1).
2. EXPERIMENTAL
2.1. General
Melting points were uncorrected. 1H NMR (400 MHz)
and 13C NMR (100 MHz) spectra were recorded on a Bruker
Avance (400 MHz) spectrometer, using CDCl3 as the solvent
and TMS as internal standard. Mass spectra (EI, 70eV) were
recorded on a HP5989B mass spectrometer. FT-IR spectra
were taken on a Perkin-Elmer SP One FT-IR spectropho-
tometer. Microanalyses were performed with a Carlo Erba
1106 elemental analyzer. HPLC was performed on an
Agilernt 1100 high performance liquid chromatograph. The
ortho allylated phenols were prepared according to the
*Address correspondence to this author at the Institutes of Chemistry and
Chemical Engineering, Jiangxi Normal University, Nanchang, 330022, P. R.
China; E-mail: shengsr@jxnu.edu.cn
1570-1786/09 $55.00+.00
© 2009 Bentham Science Publishers Ltd.

346 Letters in Organic Chemistry, 2009, Vol. 6, No. 4
Sheng et al.
reported method [18]. Polystyrene (H 1000, 100-200 mesh,
cross-linked with 1% divinylbenzene) for the preparation of
polystyrene-supported selenium bromide and other starting
materials were purchased from commercial suppliers and
used without further purification. THF and benzene were
distilled from sodium-benzophenone immediately prior to
use.
36.4, 19.3, 15.8, 9.0. IR (neat): ꢃ = 1589, 1380 cm-1. EIMS:
m/z (%) = 311 (M + Na) . Anal. Calcd for C11H13IO: C,
45.85; H, 4.55. Found: C, 45.92; H, 4.64.
+
5-Chloro-2-iodomethyl-2,3-dihydrobenzofuran (3e)
1
Colorless solid; Mp: 44-45 °C. H NMR: ꢂ = 7.09-7.049
(m, 2 H), 6.65 (s, 1 H), 4.92-4.83 (m, 1 H), 3.45-3.26 (m, 3
H), 2.95 (dd, J= 6.5 Hz, 1 H). 13C NMR: ꢂ = 158.1, 128.4,
127.8, 126.0, 125.5, 110.7, 82.3, 36.5, 8.8. IR (KBr): ꢃ =
2040, 1857, 1742, 1595 cm-1. EIMS: m/z (%) = 317 (M +
Na)+. Anal. Calcd for C9H8ClIO: C, 36.70; H, 2.74. Found:
C, 36.77; H, 2.82.
2.2. General Procedure for the Preparation of 2-
Iodomethyl-2,3-dihydrobenzofurans (3)
Under a positive pressure of nitrogen, to polystyrene-
supported selenium bromide 1 (1.0 g, 1.18 mmol Br/g) swol-
len in THF (15 mL) for 30 min was added ꢀ-allyl phenol (3
mmol). The suspension was stirred at rt for 1 h. The mixture
was filtered and the resin was washed with THF (10 mLꢁ3)
and CH2Cl2 (10 mLꢁ3) and dried under vacuum to afford dry
2-selenomethyl 2,3-dihydrobenzofuran resin 2. To a suspen-
sion of the swollen resin 2 (1.0 g) in dry DMF (15 mL), NaI
(1.5 g) and CH3I (1.5 mL) were added under nitrogen. The
suspension was stirred at 75 °C for 20 h. The mixture was
filtered and the resin was washed with CH2Cl2 (10 mLꢁ3),
the filtrate was washed with saturated Na2S2O3 and H2O
respectively and extracted with ethyl acetate (10 mLꢁ3),
dried over anhydrous Na2SO4, and evaporated to furnish
crude products 3a-3i with 93-97 % purity determined by
HPLC, which were further purified by column chromatogra-
phy [hexane–EtOAc, 20:1 (v/v)] over silica gel to provide
5,7-Dichloro-2-iodomethyl-2,3-dihydrobenzofuran (3f)
Colourless oil. 1H NMR: ꢂ = 7.14 (s, 1 H), 7.02 (s, 1 H),
5.01-4.95 (m, 1 H), 3.52-3.30 (m, 3 H), 3.13 (dd, J = 6.7 Hz,
1 H). 13C NMR: ꢂ = 154.7, 129.1, 128.7, 126.3, 123.8, 116.1,
83.0, 37.0, 8.3.
IR (neat): ꢃ = 1585, 1460 cm-1. EIMS: m/z (%) = 329
(M+). Anal. Calcd for C9H7Cl2IO: C, 32.86; H, 2.14. Found:
C, 32.93; H, 2.23.
5-Chloro-7-methyl-2-iodomethyl-2,3-dihydrobenzofuran
(3g)
1
Colorless oil. H NMR: ꢂ = 7.06 (d, J = 8.3 Hz, 1 H),
6.51 (d, J = 8.3 Hz, 1 H), 4.94-4.83 (m, 1 H), 3.47-3.25 (m, 3
H), 2.92 (dd, J = 6.2 Hz, 1 H), 2.24 (s, 3 H). 13C NMR: ꢂ =
157.5, 128.7, 126.9, 125.2, 112.2, 108.6, 82.4, 36.5, 17.3,
9.0. IR (neat): ꢃ = 1592, 1454, 1375 cm-1. EIMS: m/z (%) =
309 (M+). Anal. Calcd for C10H10ClIO: C, 38.93; H, 3.27.
Found: C, 38.99; H, 3.35.
1
pure 2-iodomethyl-2,3-dihydrobenzofurans (3a-3i) for their
HNMR, 13C NMR, MS and elemental analyses.
2-Iodomethyl-2,3-dihydrobenzofuran (3a)
Colorless oil. 1H NMR: ꢂ = 7.37-7.34 (m, 2 H), 7.28-7.24
(m, 2 H), 4.91-4.82 (m, 1 H), 3.44-3.27 (m, 3 H), 2.93 (dd, J
= 6.5 Hz, 1 H). 13C NMR: ꢂ = 157.6, 127.8, 124.5, 123.3,
121.7, 111.1, 82.3, 36.6, 8.5. IR (neat): ꢃ = 1595, 1455 cm-1.
EIMS: m/z (%) = 260 (M+). Anal. Calcd for C9H9IO: C,
41.56; H, 3.49. Found: C, 41.63; H, 3.57.
5-Cyano-2-iodomethyl-2,3-dihydrobenzofuran (3h)
1
Colorless solid; Mp: 84-85 °C. H NMR: ꢂ = 7.48-7.44
(m, 2 H), 6.81 (d, J = 8.7 Hz, 1 H), 5.01-4.95 (m, 1 H), 3.51-
3.33 (m, 3 H), 3.02 (dd, J = 6.0 Hz, 1 H). 13C NMR: ꢂ =
163.1, 134.2, 129.4, 127.8, 119.5, 110.9, 104.6, 82.8, 35.9,
8.3. IR (KBr): ꢃ = 2225, 1716, 1609, 1483 cm-1.
EIMS: m/z (%) = 286 (M+H)+. Anal. Calcd for
C10H8INO: C, 42.13; H, 2.83; N, 4.91. Found: C, 42.20; H,
2.90; N, 4.97.
7-Methyl-2-iodomethyl-2,3-dihydrobenzofuran (3b)
1
Pale brown oil. H NMR: ꢂ = 7.05-6.69 (m, 3 H), 4.93-
4.85 (m, 1 H), 3.49-3.28 (m, 3 H), 2.99 (dd, J = 6.6 Hz, 1 H),
2.23 (s, 3 H). 13C NMR: ꢂ = 158.0, 128.1, 137.8, 125.6,
124.6, 110.5, 82.1, 36.8, 12.1, 9.2. IR (neat): ꢃ = 1596, 1459,
1377 cm-1. EIMS: m/z (%) = 274 (M)+
2-Iodomethyl-2,3-dihdro-benzofuran-5-carbaldehyde (3i)
1
Pale brown oil. H NMR: ꢂ = 9.85 (s, 1 H), 7.65 (d, J =
8.4 Hz, 2 H), 6.85 (d, J = 8.1 Hz, 1 H), 5.03-4.96 (m, 1 H),
3.52-3.32 (m, 3 H), 3.03 (dd, J = 6.4 Hz, 1 H). 13C NMR: ꢂ =
190.1, 164.4, 133.2, 130.8, 127.1, 125.8, 109.9, 82.8, 35.4,
8.1. IR (neat): ꢃ = 1684 cm-1. EIMS: m/z (%) = 289 (M+H)+.
Anal. Calcd for C10H9IO2: C, 41.69; H, 3.15. Found: C,
41.77; H, 3.23.
Anal. Calcd for C10H11IO: C, 43.82; H, 4.05. Found: C,
43.88; H, 4.12.
6,7-Dimethyl-2-iodomethyl-2,3-dihydrobenzofuran (3c)
Brown solid; Mp: 49-50 °C. 1H NMR: ꢂ = 6.86 (d, J = 7.5
Hz, 1 H), 6.65 (d, J= 7.5 Hz, 1 H), 4.94-4.85 (m, 1 H), 3.28-
3.50 (m, 3 H), 3.02 (dd, J = 6.5 Hz, 1 H), 2.25 (s, 3 H), 2.20
(s, 3 H). 13C NMR: ꢂ = 158.2, 137.2, 123.7, 121.7, 118.8,
110.3, 81.8, 36.8, 17.8, 12.3, 9.2. IR (KBr): ꢃ = 1593, 1456
cm-1. EIMS: m/z (%) = 289 (M + H)+. Anal. Calcd for
C11H13IO: C, 45.85; H, 4.55. Found: C, 45.93; H, 4.62.
3. RESULTS AND DISCUSSION
As previously reported [15a], selenenyl bromide resin (1)
was conveniently prepared from commercial polystyrene by
lithiation followed by treatment with dimethyl diselenide to
give methyl selenide resin through oxidation with bromine to
give (1) as a dark red polymer. Simply stirring the resin (1)
in THF at room temperature with 3.0 equiv of the ortho
allylated phenols resulted in a rapid decolorization of the
resin (<5 min). After stirred for 1 h, the ring-closure reaction
4,6-Dimethyl-2-iodomethyl-2,3-dihydrobenzofuran (3d)
1
Colorless oil. H NMR: ꢂ = 6.79 (d, J = 7.5 Hz, 1 H),
6.53 (d, J= 7.5 Hz, 1 H), 4.48-4.52 (m, 1 H), 3.34-3.22 (m, 3
H), 3.01 (dd, J = 6.2 Hz, 1 H), 2.25 (s, 3 H), 2.14 (s, 3 H).
13C NMR: ꢂ = 158.2, 128.3, 127.8, 125.9, 125.4, 110.6, 82.3,

Solid-Phase Synthesis of 2-Iodomethyl-2,3-dihydrobenzofurans
Letters in Organic Chemistry, 2009, Vol. 6, No. 4
347
Table 1. The Yields and Purities of 2-Iodomethyl-2,3-dihydrobenzofurans (3)
Entry
R
Product
Yield (%)a
Purity (%)b
1
2
H
H
3a
3ac
3ad
3b
3c
3d
3e
3f
92
90
88
90
86
88
86
83
84
85
84
97
95
94
95
96
95
94
93
95
95
94
3
H
4
2-CH3
5
2,3-Di-CH3
3,5-Di-CH3
4-Cl
6
7
8
2,4-Di-Cl
2-CH3-4-Cl
4-CN
9
3g
3h
3i
10
11
4-CHO
aOverall yields based on polymer-supported selenium bromide 1 (1.18 mmol Br/g).
bDetermined by HPLC of crude cleavage product.
cWith the third regenerated resin 1.
dWith the fourth regenerated resin 1.
on the solid-phase completed, which was determined by the
elemental analysis of 2-selenomethyl 2,3-dihydrobenzofuran
resin (2) (Br was undetectable). The reaction was also moni-
tored by FT-IR, which showed a strong peak of cyclic ether
absorptions at 1020-1032, 1084–1096 cm-1. According to our
published method [17], treatment of resin (2) with CH3I-NaI
in DMF afforded 2-iodomethyl-2,3-dihydrobenzofurans (3)
in good yields (83-92%) and with excellent purities greater
than 93 % (Table 1). As seen from Table 1, the method ex-
hibited broad tolerance toward the substrates ortho allylated
phenols containing substituents such as halogens (entries 7–
9), cyano (entry 10) and aldehyde (entry 11) group. In addi-
tion, it should be noted that the polystyrene-supported sele-
nium bromide (1) is easily regenerated form the recovered
methyl selenide resin (4) (Scheme 2) and can be reused for
the conversion of o-allylphenol to 2-iodomentyl-2,3-
dihydrobenzofurans (3). After the fourth regeneration and
use, the yield and purity of 3a (Table 1, entries 2-3) was
about the same as those obtained in the first reaction (entry
1).
Se
n-Bu3SnH/AIBN
C6H6, 80 oC, 2h
CH3
O
O
2a
4a
Scheme 3.
4. CONCLUSIONS
In summary, we have developed here an efficient and
convenient protocol for the traceless solid-phase synthesis of
2-iodomethyl-2,3-dihydrobenzofurans with good yields and
purities employing a selenium-based traceless linker strat-
egy. Simple workup procedure replaces the time-consuming
isolation and purification steps in the corresponding
solution-phase synthesis. Moreover, the polymeric reagent
can be recycled without further transformation and reused as
environmentally benign reagent.
ACKNOWLEDGEMENTS
Br2
SeCH3
SeBr
We gratefully acknowledge financial support from the
National Natural Science Foundation of China (No.
20562005), NSF of Jiangxi Province (No. 2008GZH0029
and No. 2007GZW0185) and the Research Program of Ji-
angxi Province Department of Education (No. GJJ08165).
4
1
Scheme 2.
On the other hand, the other two common cleavage
strategies of selenium linkers have been reported: selenoxide
syn-elimination and agilent hydride transfer [19]. Although
REFERENCES AND NOTES
a
ꢀ-H exists in the above molecules, selenoxide
syn-elimination did not occur when we treated resin 2 with
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(Scheme 3) in 90 % overall yields, based on the selenenyl
bromide resin 1. However, we did not apply this reductive
cleavage to the other 2,3-dihydro-2-methylbenzofurans be-
cause n-Bu3SnH is a toxic reagent.
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Colorless oil. H NMR: ꢂ = 7.16 (d, J = 7.3 Hz, 1H), 7.11 (t, J =
7.8 Hz, 1H), 6.82 (t, J = 7.3 Hz, 1H), 6.76 (d, J = 7.8 Hz, 1H),
4.87–4.96 (m, 1H), 3.30 (dd, J = 15.4, 8.8 Hz, 1H), 2.81 (dd, J =
15.4, 7.7 Hz, 1H), 1.46 (d, J = 6.2 Hz, 3H). 13C NMR: ꢂ = 159.7,
128.2, 127.2, 125.2, 120.4, 109.5, 79.7, 37.4, 22.0. IR (neat): ꢃ =
1479, 1463, 1228, 746 cm-1. Anal. Calcd for C9H10O: C, 80.56; H,
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