Sulfonic acid-functionalized LUS-1: an efficient catalyst for tetrahydropyranylation/depyranylation of alcohols

Article abstract of DOI:10.1007/s11164-016-2465-3

Efficient acidic functionalization of mesoporous silica LUS-1 (Laval University Silica) and its application as a recyclable heterogeneous catalyst for DHP (3,4-dihydro-2H-pyran) protection of alcohols and the subsequent removal of the corresponding protecting group have been reported. This green method offers a number of advantages such as short reaction time, good yields of protection and deprotection, simple work-up procedure, recyclable catalyst, and environmentally friendly conditions.

Full text of DOI:10.1007/s11164-016-2465-3

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Res Chem Intermed
DOI 10.1007/s11164-016-2465-3
Sulfonic acid-functionalized LUS-1: an efficient catalyst
for tetrahydropyranylation/depyranylation of alcohols
Mahshid Rahimifard1 Ghodsi Mohammadi Ziarani1
•
•
Alireza Badiei2
Received: 27 October 2015 / Accepted: 30 January 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract Efficient acidic functionalization of mesoporous silica LUS-1 (Laval
University Silica) and its application as a recyclable heterogeneous catalyst for DHP
(3,4-dihydro-2H-pyran) protection of alcohols and the subsequent removal of the
corresponding protecting group have been reported. This green method offers a
number of advantages such as short reaction time, good yields of protection and
deprotection, simple work-up procedure, recyclable catalyst, and environmentally
friendly conditions.
Keywords Sulfonic acid functionalized LUS-1 Á Tetrahydropyranylation Á DHP Á
Protection Á Deprotection Á Nanoporous acid catalyst
Introduction
Mesoporous silica materials have received significant attention because of their
potential applications as supports. Grafting organo-acidic groups (e.g., propyl
sulfonic acid) to the pore walls of the mesoporous silica materials create
heterogeneous acid catalysts [1–6]. Ordered mesoporous silica LUS-1 has a high
surface area (800 cm2/g), long range ordered pores, and hydrothermal stability [7],
which can be used as a support for heterogeneous catalysts. In comparison to other
ordered mesoporous silica, LUS-1 has more available silanol groups on the silica
surface, which can react with more surface modifying groups [8].
&
Ghodsi Mohammadi Ziarani
gmziarani@hotmail.com; gmohammadi@alzahra.ac.ir
Alireza Badiei
abadiei@khayam.ut.ac.ir
1
2
Department of Chemistry, Alzahra University,
PO Box number: 19938939973, Vanak Square, Tehran, Iran
School of Chemistry, College of Science, University of Tehran, Tehran, Iran
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M. Rahimifard et al.
Tetrahydropyranylation is one of the most useful methods for the protection of
hydroxyl groups, because the resulting tetrahydropyranyl ether is stable under a
variety of reaction conditions such as basic media, acylating agents, and metal
hydrides [9]. There are several methods reported in the literature for tetrahydropy-
ranylation of alcohols in the presence of different catalysts such as ionic liquids [10],
Brønsted acidic ionic liquid [morH]HSO4 [11], silica chloride [12], modified zeolites
[13], silica sulfonic acid [14], LiOTf [15], Al(OTf)3 [16], and SnIV(TPP)(OTf)2 [17].
As mentioned, alcohols are frequently protected as tetrahydropyranyl ethers, and a
number of techniques for deprotection of tetrahydropyranyl ethers to the parent
alcohols are reported in the literature by different catalysts such as Bi(OTf)3Á4H2O
[18], sulfonic acid- bearing polymer brushes [19], dialkylimidazolium tetrachloroa-
luminates [20], and LiBr [21]. In some cases both transformations (tetrahydropy-
ranylation and depyranylation) can be catalyze by one catalyst such as p-
toluenesulfonic acid (PTSA) [22], pyridinium p-toluenesulfonate (PPTS) [23], NH4Cl
[24], ZrCl4 [25], and LiBr [21]. However, many of the reported methods have some
disadvantages, such as long reaction times, low yields, harsh reaction conditions, using
organic solvents, and large amounts of toxic, expensive or unrecyclable catalysts. In
continuation of our previous works on the application of heterogeneous solid catalysts
in organic synthesis [26, 27], herein, we would like to report LUS-Pr-SO3H as a highly
efficient catalyst for tetrahydropyranylation of alcohols and depyranylation of
corresponding ethers in solvent-free conditions.
Experimental section
Melting points were measured using the capillary tube method with an electro
thermal 9200 apparatus. IR spectra were recorded from a KBr disk using a FT-IR
Bruker Tensor 27 instrument. The 1H NMR was run on a Bruker, 250 MHz. The 13
C
NMR was run on a Bruker, 62.9 MHz. Mass spectrometry (MS) analysis was
performed on a model 5973 mass-selective detector (Agilent). The N2 adsorption/
desorption measurements were conducted at liquid nitrogen temperature (77 K)
using BELSORP-mini II. Scanning electron microscopy (SEM) carried out on a
LEO 1445 V microscope.
Synthesis and functionalization of LUS-1
The mesoporous compound LUS-1 was synthesized and functionalized according to
our previous report [28]. Colloidal silica Ludox (15.5 g, 0.26 mol) was added to
sodium hydroxide (2 g, 5 9 10-2 mol) in distilled water (50 mL), and the mixture
was stirred at 70 °C until a clear solution was obtained. A second solution of
Cetyltrimethylammonium p-toluene sulfonate (2.5 g, 5.5 9 10-3 mol) in distilled
water (90 mL) was stirred at 40 °C for 1 h. The first solution was added drop wise
to the second one, and then the mixture was stirred at 40 °C for 2 h. The resulting
sol–gel was heated in an autoclave at 130 °C for 20 h. The surfactant was removed
by treatment with HCl 0.1 M in ethanol for 2 h. After filtration and washing with
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Sulfonic acid-functionalized LUS-1: An efficient catalyst…
distilled water, the synthesized solid (LUS-1) was dried under vacuum at 100 °C.
To a mixture of LUS-1 (10 g) in dry toluene, (3-Mercaptopropyl)trimethoxysilane
(12 mL) was added and the mixture was refluxed for 24 h. The obtained LUS-Pr-SH
was filtered, washed with acetone, and dried. Then, LUS-Pr-SH (10 g) was oxidized
with H2O2 (50 mL) and one drop of H2SO4 in methanol (10 mL) for 24 h at room
temperature, then the mixture was filtered, and washed with H2O and then acetone
to obtain pure LUS-Pr-SO3H as catalyst.
General procedure for tetrahydropyranylation
The sulfonic acid functionalized LUS-1 (0.02 g) was activated in vacuum at 100 °C,
and then, after cooling to room temperature, alcohol 1 (1 mmol) and 3,4-dihydro-
2H-pyran (DHP) 2 (1.2 mmol) were added to it. The mixture was stirred in solvent
free conditions for an appropriate time as shown in Table 2, and the completion of
the reaction was monitored by TLC and/or GC. The mixture was dissolved in
dichloromethane and filtered to remove heterogeneous catalyst. The solvent was
dried in vacuum, and the residue was subjected to column chromatography on silica
to provide the pure product. The catalyst was washed with diluted acid solution,
water, and then acetone, dried under vacuum, and reused for several times without
loss of significant activity.
General procedure for depyranylation
To a solution of THP-protected alcohols (1 mmol) in MeOH (1.0 mL), activated
LUS-Pr-SO3H (0.02 g) was added, and the mixture was stirred at room temperature
for an appropriate time as shown in Table 3. After the completion of the reaction,
the mixture was dissolved in methanol and filtered to remove heterogeneous
catalyst. The solvent was dried in vacuum, and the residue was subjected to column
chromatography on silica to provide the pure product.
The spectral data (1H NMR, 13C NMR, MS, and IR) for selected compounds are
given below.
2-(4-methoxybenzyloxy)tetrahydro-2H-pyran 1H-NMR (250 MHz, CDCl3):
d = 1.55–1.84 (m, 6H, 3CH2), 3.52–3.56 (m, 1H, 1OCH2), 3.78 (s, 3H, 1OCH3),
3.88–3.95 (m, 1H, 1OCH2), 4.43 (d, 2J = 11.5 Hz, 1H, OCH2), 4.72 (d,
2J = 11.5 Hz, 2H, OCHO and OCH2), 6.87 (d, J = 7.7 Hz, 2H, 2CH arom.),
7.30 (d, J = 7.7 Hz, 2H, 2CH arom.); 13C-NMR (62.9 MHz, CDCl3): d = 19.41,
25.51, 30.59, 55.19, 62.09, 68.46, 97.42, 113.73, 129.49, 130.29, 159.12; EIMS m/z
(rel. Int.) 222 (10) (M?), 137 (5), 121 (100), 91 (5), 85 (8); IR (KBr): tmax = 3031,
3026, 2943, 2871, 1613, 1586, 1514, 1461, 1387, 1351, 1300, 1248, 1205, 1177,
1121, 1072, 1031, 974, 904, 870, 817, 758, 524 cm-1
.
2-(2-chlorobenzyloxy)tetrahydro-2H-pyran 1H-NMR (250 MHz, CDCl3):
d = 1.56–1.90 (m, 6H, 3CH2), 3.53–3.58 (m, 1H, 1OCH2), 3.87–3.95 (m, 1H,
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M. Rahimifard et al.
1OCH2), 4.60 (d, 2J = 13.2 Hz, 1H, OCH2), 4.77–4.96 (m, 2H, OCHO and OCH2),
7.16–7.28 (m, 2H, 2CH arom.), 7.33 (d, J = 7.2 Hz, 1H, 1CH arom.), 7.52 (d,
J = 7.0 Hz, 1H, 1CH arom.); 13C-NMR (62.9 MHz, CDCl3): d = 19.31, 25.46,
30.51, 62.03, 66.22. 98.31, 126.69, 128.46, 128.91, 129.25, 132.86, 136.22; EIMS
m/z (rel. Int.) 226 (2) (M?), 180 (5), 145 (20), 138 (10), 125 (100), 101 (12), 85 (15);
IR (KBr): tmax = 3066, 2941, 2870, 1573, 1445, 1390, 1349, 1267, 1201, 1128,
1070, 1032, 973, 905, 871, 814, 752 cm-1
.
2-(9H-fluoren-9-yloxy)tetrahydro-2H-pyran 1H-NMR (250 MHz, CDCl3):
d = 1.68–1.91 (m, 6H, 3CH2), 3.63–3.67 (m, 1H, 1CH), 4.10–4.19 (m, 1H, 1CH),
5.19 (t, J = 3.1 Hz, 1H, 1CH), 5.71 (s, 1H, 1CH), 7.26–7.71 (m, 8H, 8CH arom.);
13C-NMR (62.9 MHz, CDCl3): d = 19.53, 25.52, 31.13, 62.79, 79.03. 98.87,
119.76, 119.95, 125.52, 126.13, 127.37, 127.64, 128.83, 128.88, 140.54, 140.65,
143.92, 144.08; EIMS m/z (rel. Int.) 266 (12) (M?), 220 (8), 182 (25), 165 (100),
152 (8), 85 (20); IR (KBr): tmax = 3039, 2943, 2869, 2846, 2640, 1580, 1468, 1449,
1390, 1352, 1323, 1304, 1274, 1210, 1179, 1151, 1125, 1076, 1037, 1013, 974, 951,
934, 906, 888, 840, 812, 766, 742, 664, 620, 596 cm-1
.
Results and discussion
In our first attempts at direct tetrahydropyranylation, we treated benzyl alcohol with
3,4-dihydro-2H-pyran (DHP) in the presence of LUS-Pr-SO3H (0.02 g) as a
heterogeneous acid catalyst in dichloromethane. As shown in Table 1, entry 1, the
reaction was completed in 5 min at 95 % yield. We also studied the reaction of
benzhydrol (Table 1, entry 2) in the same condition, but the reaction was not carried
out successfully, it seems the steric effect of the second phenyl group decreased the
yield and increased the reaction time. So we tried solvent free conditions for both
reactions. As shown in Table 1, entries 3 and 4, the reactions were completed in 3
and 15 min for benzyl alcohol and benzhydrol with 98 and 85 % yields,
respectively. Therefore, among the tested conditions, the best result was obtained
in solvent-free and room temperature conditions (Scheme 1).
After optimizing the reaction conditions for tetrahydropyranylation, we next
developed the best condition for depyranylation of THP-protected alcohols
(Scheme 2). We first treated 2-(benzyloxy)tetrahydro-2H-pyran (1 mmol) with
methanol (3 mL) in the presence of LUS-Pr-SO3H (0.02 g) as a heterogeneous acid
catalyst in reflux condition. As shown in Table 2, the reaction was completed in
10 min at 98 % yield. We also tried the room temperature condition for this
Table 1 The optimization of
Entry
Alcohol
Solvent
Time (min)
Yield (%)
reaction conditions for
protection of alcohols using
LUS-Pr-SO3H
1
2
3
4
Benzyl alcohol
Benzhydrol
CH2Cl2
5
40
3
95
30
98
85
CH2Cl2
Benzyl alcohol
Benzhydrol
–
–
15
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