Ferrocene tagged functional polymer: A robust solid-phase reagent for O-demethylation

Article abstract of DOI:10.1016/j.tetlet.2012.09.021

Ferrocene tagged functional polymer was synthesized by exploiting the propensity of the Merrifield resin to undergo quaternization with N-ferrocenylmethyl benzimidazole followed by subsequent anion metathesis reaction. The synthesized polymer when employed as a solid-phase reagent for O-demethylation of aryl methyl ethers, showed TON in the range of 7373-8930 and TOF in the range of 279-494 h^-1.

Full text of DOI:10.1016/j.tetlet.2012.09.021

Tetrahedron Letters 53 (2012) 6361–6366
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Ferrocene tagged functional polymer: a robust solid-phase reagent for
O-demethylation
Rajanikant Kurane a, Vipul Gaikwad a, Jagannath Jadhav a, Rajashri Salunkhe a, Gajanan Rashinkar a,
a Department of Chemistry, Shivaji University, Kolhapur 416004, Maharashtra, India
⇑
a r t i c l e i n f o
a b s t r a c t
Article history:
Ferrocene tagged functional polymer was synthesized by exploiting the propensity of the Merrifield resin
to undergo quaternization with N-ferrocenylmethyl benzimidazole followed by subsequent anion
metathesis reaction. The synthesized polymer when employed as a solid-phase reagent for O-demethyl-
Received 2 August 2012
Revised 5 September 2012
Accepted 6 September 2012
Available online 21 September 2012
ation of aryl methyl ethers, showed TON in the range of 7373–8930 and TOF in the range of 279–494 hÀ1
.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Functional polymer
Ferrocene
O-demethylation
Merrifield resin
Reusability
Development of new solid-phase reagents is a subject of im-
mense interest in the context of generating libraries of molecules
for the discovery of biologically active leads and also for the opti-
mization of drug candidates.1 A number of tangible benefits arise
from the use of solid-phase reagents, chief of which are the ease
of purification process after the reaction as well as facilitating sig-
nificant advances in selectivity, recycling reproducibility, and
activity.2 At the same time, they can add economic value via more
efficient consumption of energy, through the use of milder condi-
tions and achieving greater atom-economy containing fewer
steps.3 As a consequence of the need for robust solid-phase re-
agents, the development of functional polymers based on Merri-
field resin has gained considerable momentum in recent years
since they provide significant stability to mechanical, chemical,
and thermal demands under diverse operating conditions.4 Since
the turn of the century, there has been a constant drive to develop
new and improved strategies for organic synthesis using functional
polymers based on Merrifield resin backbone.5
aryl methyl ethers are used as protected phenols.8 The methoxy
unit, being stable to a vast array of reaction conditions, is particu-
larly well utilized for protection of phenols which makes O-demeth-
ylation difficult under normal milder conditions.9 A variety of
reagents such as aluminum chloride,10 boron tribromide,11 cerium
chloride,12 alkaline thiolate,13 -selectride,14 iodocyclohexane,15
L
[Bmim]Br,16 pyridine hydrochloride,17 protic acids in ionic liquids,18
2-(diethylamino)ethanethiol,19 sodium bis(trimethylsilyl)amide
and lithium diisopropylamide,20 chloroaluminate ionic liquids,8
SiCl4/LiI/BF3,211-decanethiol,22 lithium thioethoxide,23 etc have
been developed for O-demethylation. However, despite numerous
and significant methods available to perform this transformation,
a mild protocol for O-demethylation using a highly robust heteroge-
neous catalyst still represents a considerable synthetic challenge.
As a continuation of our on-going investigations related to het-
erogeneous catalysis,24 we report herein a solid-phase O-demeth-
ylation of aryl methyl ethers using ferrocene tagged functional
polymer.
The protection of functional groups and their regeneration is an
important area of research in organic synthesis.6 In this context, O-
demethylation constitutes an important method in the light of its
importance for protection of hydroxyl groups from phenols and its
involvement in the manufacture of a number of pharmaceuticals,
drugs, and other fine chemicals.7 It is a nearly ubiquitous process
in the synthesis of multifunctional heterocyclic compounds where
In the synthesis of ferrocene tagged functional polymer (Scheme
1),25 Merrifield resin was quaternized with 1-N-ferrocenylmethyl
benzimidazole (1) to give [FemMerBenz]Cl (2). The resulting
compound when treated with excess of AlCl3 underwent anion
metathesis reaction to afford the desired ferrocene tagged func-
tional polymer, acronymed as [FemMerBenz]Al2Cl7 (3). The FT-IR
and FT-Raman spectroscopy were performed to monitor the pro-
gress of the reactions involved in the synthesis of 3. The reaction
of 1 with Merrifield resin was supervised by using FT-Raman spec-
troscopy. The negative going bands at 640 cmÀ1 (C–Cl stretching
band) and 1267 cmÀ1 (wagging bands of CH2–Cl) almost
⇑
Corresponding author. Tel.: +91 231 260 9169; fax: +91 231 2692333.
E-mail addresses:
gsrchemsuk@yahoo.co.in,
gsr_chem@unishivaji.ac.in
(G. Rashinkar).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.09.021

6362
R. Kurane et al. / Tetrahedron Letters 53 (2012) 6361–6366
Appearance of peaks at 308 cmÀ1, 333 cmÀ1, 384 cmÀ1À, 437 cmÀ1
,
and 543 cmÀ1 which are characteristic peaks of Al2Cl7 confirmed
the formation of 3.26 The Al loading of the ferrocene tagged func-
tional polymer as determined by EDAX was found to be 0.048 mmol
x
y
z
N
N
Ph
+
Fe
of aluminum gÀ1
.
Cl
Scanning electron micrographs (SEM) at various stages of prep-
aration of 3 were recorded to understand the morphological
changes occurring on the surface of Merrifield resin. Scanning
was done across the length of polymer beads. Comparison of
images taken at a magnification of ꢀ5 Â 102 indicates that the
spherical beads of Merrifield resin with smooth surface (Fig. 1a)
were altered upon functionalization. The resin beads in 3 were
not spherical like the original Merrifield resin beads (Fig. 1). In fact
the bead degradation observed (Fig. 1b) was plausibly due to the
stress generated during the surface confinement of the Merrifield
resin with 1 and the subsequent anion metathesis reaction.27
Thermogravimetric analysis revealed that the Merrifield resin
as well as 3 degraded in two stages (Fig 2). The former began to
decompose at 258 °C and lost almost all of its mass at 757 °C while
the latter which contained about 15% evaporable moieties such as
physisorbed water and volatile solvents occluded during handling,
started to decompose at 239 °C and lost most of its mass at 615 °C.
The profiles of thermogram manifested that 3 was comparatively
less stable than the Merrifield resin.
x
1-N-Ferrocenylmethyl benzimidazole (1)
Merrifield resin
DMF
60 0
C
Cl
Cl
Fe
Fe
Cl
N
N
+
Cl
+
Fe
Fe
N
N
N
+
N
N
+
N
Fe
Cl
Cl
N
+
N
Fe
N
N
+
N
PS
+
N
N
+
N
Fe
Fe
Cl
Cl
N
+
N
+
N
N
Our next task was to assess the catalytic activity of 3 in the O-
demethylation reactions.28 Initial studies started with the reaction
of p-methoxy acetophenone (1a) using 200 mg of catalyst
(0.96 mol %) in DMF under reflux condition (Table 1, entry 8).
The reaction was completed in 24 h as confirmed by TLC. The reac-
tion mixture was poured into water and extracted with ethyl ace-
tate. The corresponding O-demethylation product was obtained in
78% yield. A parallel experiment was also carried out to confirm
that no product was obtained in the absence of 3.
Fe
Fe
Cl
N
+
N
Cl
+
N
N
N
+
N
N
Fe
+
N
Fe
Fe
Cl
Cl
Fe
Cl
Cl
[FemMerBenz]Cl (2)
We also investigated the influence of solvent on the outcome of
the aforementioned O-demethylation reaction catalyzed by ferro-
cene tagged functional polymer (Table 1). DMF was found to be
the most effective solvent. Employing THF as the solvent signifi-
cantly decreased the yield of product. On the other hand, when
dichloromethane, methanol, ethanol, and DMSO were used as a
solvent, no reaction occurred even after prolonged reaction time.
Next, we investigated the effect of catalyst loading on the O-
demethylation of 1a (Table 1). The use of 100 mg catalyst
(0.48 mol %) afforded the anticipated product in 51% after 24 h.
When increased to 200 mg (0.96 mol %), the product yield was im-
proved to 78% after 24 h under same reaction conditions. We then
used 300 mg of catalyst (1.44 mol %), to catalyze the reaction, but
no significant change in the yield and reaction time was observed.
Thus, 200 mg of catalyst (0.96 mol %) loading was selected as the
optimum concentration for further studies.
DMF
AlCl3,
RT
Al2Cl7
Al2Cl7
Fe
Fe
N
Al2Cl7
N
+
Al2Cl7
Fe
Fe
+
N
N
N
+
N
N
+
N
Fe
Al2Cl7
+
Al2Cl7
N
N
Fe
N
N
+
N
PS
+
N
+
N
N
Fe
Al2Cl7
Fe
Al2Cl7
N
+
N
+
N
N
Fe
Al2Cl7
Fe
With optimization conditions in hand, we evaluated the scope
of O-demethylation of structurally diverse aryl methyl ethers in
the presence of 3 (Scheme 2) and the results are summarized in
Table 2. A variety of aryl methyl ethers bearing electron-withdraw-
ing as well as electron-donating substituents reacted efficiently
affording products with high TON and TOF.29 The protocol fur-
nished excellent results with both heteroaromatic methyl ethers
and methyl ethers of tetralones. It is worthy of note that com-
pounds with relatively acidic protons could be O-demethylated
in better yields. Surprisingly, selective O-demethylation was ob-
served when 3,4,5-trimethoxy benzaldehyde was reacted with
functional polymer giving 4-hydroxy-3,5-dimethoxy benzalde-
hyde. This selectivity can be rationalized on the fact that once
the first deprotection has taken place, the ring becomes more elec-
tron-rich and additional demethylation is disfavored.19
N
+
N
Al2Cl7
+
N
N
N
N
+
Fe
+
N
N
Fe
Al2Cl7
Al2Cl7
Fe
Fe
Al2Cl7
Al2Cl7
(3)
[FemMerBenz]Al2Cl7
Scheme 1. Synthesis of ferrocene tagged functional polymer, [FemMerBenz]Al2Cl7.
disappeared while the peaks at 455 cmÀ1 (Fe–Cp stretching band),
1258 cmÀ1, 1335 cmÀ1, 1408 cmÀ1, and 1460 cmÀ1 (ring stretching
modes of benzimidazolium ring), 3135 cmÀ1 and 3186 cmÀ1 (C–H
stretching of Cp rings) increased in intensity after 72 h reflecting
the substantial grafting of 1 in the matrix of Merrifield resin. Anion
metathesis reaction was monitored using FT-IR spectroscopy.
When a functional polymer that mimics 3 but without ferro-
cene tag ([MeMerBenz]Al2Cl7)30 was used as
a catalyst, the

R. Kurane et al. / Tetrahedron Letters 53 (2012) 6361–6366
6363
Figure 1. Scanning electron micrographs of (A) Merrifield resin and (B) [FemMerBenz]Al2Cl7.
120
100
80
60
40
20
0
[FemMerBenz] Al2Cl7
DMF, Reflux
Ar OMe
Ar OH
Meriifild Resin
[FemMerBenz]Al2Cl7
Scheme 2. O-demethylation using [FemMerBenz]Al2Cl7.
sonable to assume that the significantly improved catalytic activity
of 3 may stem from ferrocene tag that enhances micropolarity; a
key factor that ascertains the catalytic properties of heterogeneous
catalysts.31 The presence of ferrocene results in unsymmetrical
charge distribution on the benzimidazole ring resulting in the sig-
nificant enhancement of overall polarity of 3.
0
200
400
600
800
1000
Temperature °C
A tentative mechanistic rationale for the O-demethylation using
functional polymer is presented in Scheme 3. Initially, aluminum
coordinates to oxygen atom of methoxy functionality. This phe-
nomenon activates the C–O bond between oxygen and methyl
group. This process is followed by an attack of chloride anion to
methyl carbon atom with a subsequent loss of methyl chloride.
The successful recovery and reuse of catalyst is an essential as-
pect of green chemistry and is one of the important factors in
determining its potential value for large-scale operation and indus-
trial point of view. To check the possibility of the catalyst recycling,
Figure 2. TGA curves of Merrifield resin and [FemMerBenz]Al2Cl7.
efficiency of O-demethylation was low and the isolated yield of the
product was only 51%. We have also synthesized and studied the
catalytic activity of the corresponding functional polymer possess-
ing bulky benzyl group instead of ferrocene tag which is acrony-
med as [BnMerBenz]Al2Cl7.30 Although [BnMerBenz]Al2Cl7
showed an increase in catalytic activity as compared to [MeMer-
Benz]Al2Cl7 (ca. 59%), it was still lower as compared to 3. It is rea-
Table 1
Optimization studies of O-demethylation reactiona,b
COMe
COMe
[FemMerBenz]Al2Cl7
solvent, reflux
OH
OMe
1a
2a
Entry
Amount of catalyst (mg)
Solvent
Yieldc (%)
TONd
TOFe (h-1
)
1
2
3
4
5
6
7
8
9
10
200
200
200
200
200
50
100
200
300
Nil
Dichloromethane
MeOH
EtOH
DMSO
THF
DMF
DMF
DMF
DMF
NR
NR
NR
NR
61
24
51
78
79
NR
—
—
—
—
6334
2492
5296
8100
8203
—
—
—
—
—
263
103
220
337
341
—
DMF
a
b
c
All products were characterized by IR, 1H NMR, 13C NMR, and mass spectrometry.
Reaction time of 24 h.
Isolated yields after chromatography.
% Conversion per mol of catalyst.
d
e
TON per hour.

6364
R. Kurane et al. / Tetrahedron Letters 53 (2012) 6361–6366
Table 2
a
O-demethylation of aryl methyl ethers using [FemMerBenz]Al2Cl7
Entry
Aryl methyl ether 1
Product 2
Yieldb (%)
TON
TOF (hÀ1
)
COMe
COMe
a
78
8100
337
OMe
CHO
OH
CHO
b
c
86
76
73
8930
7892
7580
425
438
291
OMe
COMe
OH
COMe
OMe
OH
COOH
COOH
d
OMe
OH
CH2OH
CH2OH
e
79
81
80
78
8203
8411
8307
8100
292
336
361
279
OMe
CHO
OH
CHO
f
OH
OMe
OMe
OH
OH
OH
g
h
Me
Me
CHO
Cl
Cl
CHO
MeO
OMe
MeO
OMe
OMe
CHO
OH
CHO
i
73
71
82
7580
7373
8515
344
320
437
O2N
OMe
N
O2N
HO
OH
N
OH
O
OH
O
MeO
j
k
OMe
OH
O
O
l
79
8203
410
MeO
HO

R. Kurane et al. / Tetrahedron Letters 53 (2012) 6361–6366
6365
Table 2 (continued)
Entry
Aryl methyl ether 1
Product 2
Yieldb (%)
TON
TOF (hÀ1
)
O
O
MeO
HO
m
81
8411
494
a
All products were characterized by IR, 1H NMR, 13C NMR, and mass spectrometry.
Isolated yields after chromatography.
b
Me
+
Al2Cl6
Al2Cl6
+
OMe
O
OH
O
Cl
MeCl
Al2Cl7
+
+
+
Al2Cl7
+
R
R
R
R
Scheme 3. A plausible mechanism for O-demethylation using [FemMerBenz]Al2Cl7.
Angew. Chem., Int. Ed. Engl. 1996, 35, 17–42; (e) Hermkens, P. H. H.; Ottenheijm,
H. C. J.; Rees, D. Tetrahedron 1996, 52, 4527–4554; (f) Terrett, N. K.; Gardner,
M.; Gordon, D. W.; Kobylecki, R. J.; Steele, J. Tetrahedron 1995, 51, 8135–8173;
(g) Thompson, L.; Ellman, J. A Chem. Rev. 1996, 96, 555–600.
2. Smith, K. Solid Supports and Catalysts in Organic Synthesis; PTR Prentice Hall:
New York, 1992.
79
78
77
76
75
74
73
72
71
70
69
3. Barbaro, P.; Liguori, F. Chem. Rev. 2009, 109, 515–529.
4. Merrifield, R. B. J. Am. Chem. Soc. 1963, 85, 2149–2154.
5. For selected examples see: (a) Lu, J.; Toy, P. H. Chem. Rev. 2009, 109, 815–838;
(b) Buchmeiser, M. R. Chem. Rev. 2009, 109, 303–321; (c) Cai, J.; Wathey, B.
Tetrahedron Lett. 2001, 42, 1383–1385; (d) Török, B.; Bucsi, I.; Suryaprakash, G.
K.; Olah, G. A. Chem. Commun. 2002, 2882–2883; (e) Reddy, C. R. V.; Verkade, J.
G. J. Org. Chem. 2007, 72, 3093–3096; (f) Dyer, P. W.; Handa, S.; Reeve, T. B.;
Suhard, S. Tetrahedron Lett. 2005, 46, 4753–4756; (g) Yang, J.; Li, P.; Wang, L.
Tetrahedron 2011, 67, 5543–5549; (h) Schweizer, S.; Becht, J.-M.; Drian, C. L.
Tetrahedron 2010, 66, 765–772.
0
1
2
3
4
5
Regeneration
6. (a) Ley, S. V.; Baeschlin, D. K.; Dixon, D. J.; Foster, A. C.; Ince, S. J.; Priepke, H. W.
M.; Reynolds, D. J. Chem. Rev. 2001, 101, 53–80; (b) Sureshan, K. M.; Shashidhar,
M. S.; Praveen, T.; Das, T. Chem. Rev. 2003, 103, 4477–4504; (c) Sartori, G.; Bigi,
F.; Bosica, G.; Maggi, R.; Righi, P. Chem. Rev. 2004, 104, 199–250; (d) Isidro-
Llobet, A.; Alvarez, M.; Albericio, F. Chem. Rev. 2009, 109, 2455–2504; (e)
Ramesh, R.; Chandrasekaran, S. Organic Lett. 2005, 7, 4947–4950.
7. (a) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, 3rd ed.;
Wiley: New York, 1999. pp. 246–276; (b) Fang, Z.; Zhou, G.-C.; Zheng, S. L.; He,
G. L.; Li, J.-L.; He, L.; Bei, D. J. Mol. Catal. A: Chem. 2007, 274, 16–23.
8. Kemperman, G. J.; Roeters, T. A.; Hilberink, P. W. Eur. J. Org. Chem. 2003, 1681–
1686.
9. Li, G.; Patel, D.; Hruby, H. J. Tetrahedron Lett. 1993, 34, 5393–5396.
10. Parker, K. A.; Petraitis, J. J. Tetrahedron Lett. 1981, 22, 397–400.
11. Miller, J. M.; So, K. H.; Clark, J. H. Can. J. Chem. 1979, 57, 1887–1889.
12. Yadav, J. S.; Reddy, B. V. S.; Madan, C.; Hashim, S. R. Chem. Lett. 2000, 29, 738–
739.
13. Dodge, J. A.; Stocksdale, M. G.; Fahey, K. J.; Jones, C. D. J. Org. Chem. 1995, 60,
739–741.
14. Coop, A.; Janetka, J. W.; Lewis, J. W.; Rice, K. C. J. Org. Chem. 1998, 63, 4392–
4396.
15. Zuo, L.; Yao, S.; Wang, W.; Duan, W. Tetrahedron Lett. 2008, 49, 4054–4056.
16. Park, J.; Chae, J. Synlett 2010, 1651–1656.
17. Kulkarni, P. P.; Kadam, A. J.; Mane, R. B.; Desai, U. V.; Wadgaonkar, P. P. J. Chem.
Res. (S) 1999, 394–395.
Figure 3. Reusability of [FemMerBenz]Al2Cl7 in O-demethylation reaction.
the O-demethylation of p-methoxy acetophenone was carried out
in the presence of 3. After the reaction, the catalyst was separated
by simple filtration, washed with DMF, and dried in vacuum before
being reused in subsequent runs. The catalyst could be reused at
least five times without noticeable decrease in the catalytic activity
(Fig. 3). The FT-IR and FT-Raman spectra of reused catalyst were
indistinguishable from those of the fresh catalyst, which revealed
that the main characteristics of the catalyst were preserved during
recycling and reuse.
In conclusion, we have developed a simple and efficient meth-
odology for the O-demethylation of aryl methyl ethers using ferro-
cene tagged functional polymer, which served as an excellent
recyclable and reusable heterogeneous catalyst. The operational
simplicity, application of stable catalyst, excellent TON, and TOF
are the unique features of the presented protocol.
18. Boovanahalli, S. K.; Kim, D. W.; Chi, D. Y. J. Org. Chem. 2004, 69, 3340–3344.
19. Magano, J.; Chen, M. H.; Clark, J. D.; Nussbaumer, T. J. Org. Chem. 2006, 71,
7103–7105.
Acknowledgments
20. Hwu, J. R.; Wong, F. F.; Huang, J. J.; Tsay, S. C. J. Org. Chem. 1997, 62, 4097–4104.
21. Zewge, D.; King, A.; Weissman, S.; Tschaen, D. Tetrahedron Lett. 2004, 19, 3729–
3732.
22. Kale, B.; Shinde, A.; Sonar, S.; Shingate, B.; Kumar, S.; Ghosh, S.; Venugopal, S.;
Shingare, M. Tetrahedron Lett. 2010, 51, 3075–3078.
23. Cvengroš, J.; Neufeind, S.; Becker, A.; Schmalz, H.-G. Synlett 2008, 1993–1998.
24. (a) Rashinkar, G.; Salunkhe, R. J. Mol. Catal. A: Chem. 2010, 316, 146–152; (b)
Rashinkar, G.; Kamble, S.; Kumbhar, A.; Salunkhe, R. Catal. Commun. 2011, 11,
1442–1447.
Authors G.S.R., R.S.S., and R.M.K. thank UGC, New Delhi for
financial assistance [F. No. 40-96/2011 (SR)] and for the research
fellowship, respectively.
References and notes
1. (a) Crowley, J. I.; Rapoport, H. Acc. Chem. Res. 1976, 9, 135–144; (b) Ley, S. V.;
Baxendale, I. R.; Bream, R. N.; Jackson, P. S.; Leach, A. G.; Longbottom, D. A.;
Nesi, M.; Scott, J. S.; Storer, R. I.; Taylor, S. J. Chem. Soc., Perkin Trans. 2000, 1,
3815–4195; (c) Gordon, E. M.; Dower, W. J.; Barrett, R. W.; Fodor, S. P. A.;
Gallop, M. A. J. Med. Chem. 1994, 37, 1233–1251; (d) Fruchtel, J. S.; Jung, G.
25. Preparation of [FemMerBenz]Cl (2): A mixture of Merrifield resin (3.0 g) and 1-
N-ferrocenylmethyl benzimidazole (3.16 g, 10 mmol) in 25 mL of DMF was
heated at 80 °C in an oil bath. After 72 h, the polymer was filtered, washed with
DMF (3 Â 50 mL), MeOH (3 Â 50 mL), CH2Cl2 (3 Â 50 mL), and dried under
vacuum at 50 °C for 24 h to afford [FemMerBenz]Cl (2). IR (neat, thin film):

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R. Kurane et al. / Tetrahedron Letters 53 (2012) 6361–6366
t
t
= 2922, 2849, 1613, 1384, 1248, 1175, 1016, 810, 744, 690, 616 cmÀ1; Raman:
= 3186, 3135, 1460, 1408, 1335, 1258, 770, 620, 459 cmÀ1
Elemental
analysis observed: C, 70.82; H, 5.81; N, 3.97. Loading: 1.41 mmol functional
group gÀ1 resin. Preparation of [FemMerBenz]Al2Cl7 (3):
suspension of
chromatography over silica gel using ethyl acetate/ petroleum ether (1:4 v/v)
afforded pure O-demethylated product, which was characterized by spectral
methods. Spectral data for p-hydroxy acetophenone (Table 1, entry 1): IR (neat,
;
A
thin film):
t = 3303, 1663, 2922, 1436, 1358, 1275, 1161, 1112, 848, 671,
[FemMerBenz]Cl (3.0 g) in DMF (25 mL) was stirred under a stream of nitrogen
gas while being cooled in an ice bath. Aluminum chloride (3.7 g, 0.02 mol) was
added in small portions to the stirred suspension. After all the aluminum
chloride had been added, the system was heated at 70 °C for 72 h. Afterward
the polymer was filtered and washed with DMF, MeOH (3 Â 20 mL),
MeOH:H2O (1:1) (3 Â 20 mL), H2O (3 Â 20 mL), and MeOH (3 Â 20 mL), and
dried under vacuum at 50 °C for 48 h to afford [FemMerBenz]Al2Cl7 (3). IR
567 cmÀ1 1H NMR (300 MHz, CDCl3): d 2.59 (s, 3H), 6.90 (d, J = 8.7 Hz, 2H),
;
7.90 (d, J = 8.4 Hz, 2H); 13C NMR (75 MHz, CDCl3): d 26.1, 115.3, 129.8, 131.0,
160.67, 196.8; MS(EI): m/z 136 (M+).
29. Based on the EDAX analysis of Al, the amount of Al in 3 was found to be 0.26%.
This corresponds to 0.52 mg of Al in 200 mg quantity of 3 which is equivalent
to 0.0096 mmol of Al2Cl7-, which is an active site for catalysis. TON which is
equal to % conversion per mmol of active catalyst was calculated to be 8100 for
the O-demethylation of p-methoxyacetophenone which yielded p-
hydroxyacetophenone in 78% yield.
(neat, thin film):
t = 2922, 1658, 1386, 1252, 1183, 1015, 805, 748, 656, 543,
437, 384, 333, 308 cmÀ1; Raman:
t = 3135, 1478, 1408, 1327, 1251, 778, 625,
468 cmÀ1; Loading: 0.048 mmol of aluminum gÀ1 resin.
30. [MeMerBenz] Al2Cl7 and [BnMerBenz]Al2Cl7 were synthesized by using the
similar procedure depicted in Scheme 1. Data for [MeMerBenz]Al2Cl7. IR (neat,
26. Hvistendahl, J.; Klaeboe, P.; Rytter, E.; Øye, H. A. Inorg. Chem. 1984, 23, 706–
715.
27. Sanclimens, G.; Crespo, L.; Pons, M.; Giralt, E.; Albericio, F.; Royo, M.
Tetrahedron Lett. 2003, 44, 1751–1754.
28. Typical procedure for O-demethylation: A mixture of aryl methyl ether (1 mmol)
and [FemMerBenz]Al2Cl7 (200 mg, 0.96 mol %) in DMF (5 mL) was refluxed in
an oil bath. After completion of the reaction as monitored by the TLC, the
reaction mixture was cooled and filtered. The filtrate was poured into water
(20 mL) and extracted with ethyl acetate (3 Â 20 mL). The combined organic
layers were dried over Na2SO4. Evaporation of the solvent followed by column
thin film):
307 cmÀ1
0.084 mmol of aluminum gÀ1 resin. Data for [BnMerBenz]Al2Cl7: IR (neat, thin
film): = 3023, 2920, 1613, 1558, 1451, 1372, 1276, 1185, 1016, 816, 749, 702,
547, 357, 337, 305 cmÀ1; Raman:
t
= 2927, 1614, 1371, 1183, 1017, 876, 749, 699, 529, 364, 337,
;
Raman: Loading:
t
= 3057, 1450, 1350, 1189, 776, 641 cmÀ1
;
t
t
= 3056, 1613, 1583, 1452, 1431, 1348, 1187,
1032, 1003, 818, 774, 642 cmÀ1; Loading: 0.035 mmol of aluminum gÀ1 resin.
31. Burguete, M. I.; Galindo, F.; García-Verdugo, E.; Karbass, N.; Luis, S. V. Chem.
Commun. 2007, 3086–3088. and references therein.