N-Methylimidazole-mediated synthesis of aryl alkyl ethers under microwave irradiation and solvent free conditions

Article abstract of DOI:10.2298/JSC131223027D

A microwave-assisted three-component reaction was established for the synthesis of aryl alkyl ethers. The reaction was performed under solvent-free conditions in the presence of N-methylimidazole and dialkyl acetylene-dicarboxylate to furnish a novel approach to O-alkylation of phenol derivatives in high yield.

Full text of DOI:10.2298/JSC131223027D

J. Serb. Chem. Soc. 80 (4) 459–464 (2015)
JSCS–4729
UDC 547.78+54–732+537.5+547.53.024+
547.37+66.095.253
Short communication
SHORT COMMUNICATION
N-Methylimidazole-mediated synthesis of aryl alkyl ethers under
microwave irradiation and solvent free conditions
1
2
3
HOORIEH DJAHANIANI *, LAILA AGHADADASHI-ABHARI and BITA MOHTAT
1Department of Chemistry, Islamic Azad University, East Tehran Branch, Tehran, Iran,
2
Department of Chemistry, East Tehran Branch, Payame Noor University, Tehran, Iran
and Department of Chemistry, Islamic Azad University, Karaj Branch, Karaj, Iran
3
(
Received 23 December 2013, revised and accepted 16 March 2014)
Abstract: A microwave-assisted three-component reaction was established for
the synthesis of aryl alkyl ethers. The reaction was performed under solvent-
-
free conditions in the presence of N-methylimidazole and dialkyl acetylene-
dicarboxylate to furnish a novel approach to O-alkylation of phenol derivatives
in high yield.
Keywords: microwave-assisted; three-component reaction; N-methylimidazole;
O-alkylation; dialkyl acetylenedicarboxylate.
INTRODUCTION
Aryl ethers are used as raw materials for the manufacture of a variety of
durable surface coatings, paints, varnishes, printing inks, wire enamels, surface-
active agents, rubber chemicals, antioxidants, fungicides, heat carriers, foaming
1
–4
agents, synthetic resins and perfumes.
different approaches.
These compounds can be prepared by
It was found that alkylation of phenol could be performed with homogenous
5
catalytic systems, such as imidazolium salts ionic liquids, use of bases such as
NaOH and K CO in the presence of dimethyl sulfate (DMSA) catalyzed by
2
3
6
7
solid base zeolites, Cs-loaded zeolites, dimethyl carbonate under solid/liquid
phase transfer systems and KNO /NaY. Though high catalytic performances
8
9
3
were achieved in homogenous systems, the drawbacks were poor catalyst rec-
overy and product separation. Hence, some heterogeneous catalysts for the sel-
1
0
ective synthesis of aryl alkyl ether were investigated. Basic zeolites, alumina or
alumina–silica were usually used as catalysts for the vapor phase alkylation of
*
Corresponding author. E-mail: jahanbani.ho@gmail.com
doi: 10.2298/JSC131223027D
4
59
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60
DJAHANIANI, AGHADADASHI-ABHARI and MOHTAT
phenol,11 but considerable amounts of by-products (C-alkylation) were always
present.
Thus, the development of an efficient, safe, and environmentally friendly
method for O-alkylation constitutes an important challenge; moreover, synthesis
without solvents under microwave irradiation offers several advantages. The
absence of solvent may reduce the risk of hazardous explosions when the reac-
1
2,13
tion occurs in a closed vessel in an oven.
The addition of phenol derivatives
to tert-butyl propiolate in the presence of triphenylphosphine, which led to alkyl
3
aryloxypropenoates, in CH Cl at room temperature was previously described.
2
2
In connection with ongoing work on the development of new synthetic methods
1
4,15
to heterocyclic compounds using phenol derivatives,
realize O-alkylation of some OH acids by nucleophilic substitution reactions
Scheme 1) is reported.
herein, a method to
(
Scheme 1. Typical procedure for the preparation of compounds 4a–k.
RESULTS AND DISCUSSION
Our studies were initiated by the reaction of 4-hydroxycoumarin (1a) with
dimethyl acetylenedicarboxylate (DMAD) (2a) or diethyl acetylenedicarboxylate
DEAD) (2b) in the presence of N-methylimidazole (3) without solvent under
microwave irradiation (green chemistry), which afforded the 4-alkoxy coumarins
(
4
a and b, respectively, in high yields after 4–7 min.
Surprisingly, when this reaction was performed with di-tert-butyl acetylene-
1
dicarboxylate (DTAD, 2c), TLC and the H-NMR spectrum of the product
showed that the obtained product was 4-methoxycoumarin (4a). Then the sub-
strate scope of this reaction was investigated by using hydroxyquinoline deri-
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N-METHYLIMIDAZOLE MEDIATED MICROWAVE SYNTHESIS OF ARYL ALKYL ETHERS
461
vatives and naphthols under the same conditions. As expected, using DMAD and
DEAD, the products were methoxy and ethoxy derivatives, respectively. When
the reaction occurred with DTAD, the isolated products were methoxy deri-
vatives. The structures, yields and melting points of the products are summarized
in Table I.
TABLE I. O-Alkylation of hydroxycoumarins, hydroxyquinolines and 2-naphthol
Entry
1
Ar
R
Me
Product
Time, min
6
Yield, %
95
OMe
4-Hydroxycoumarin
O
OEt
O
O
2
3
4-Hydroxycoumarin
4-Hydroxycoumarin
Et
7
5
90
80
O
OMe
t-Bu
O
O
O
O
4
5
7-Hydroxycoumarin
7-Hydroxycoumarin
Me
Et
4
4
98
95
MeO
O
O
EtO
6
7
7-Hydroxycoumarin
4-Hydroxyquinoline
t-Bu
5
7
70
85
MeO
O
OMe
O
Me
N
MeO
8
9
6-Hydroxyquinoline
8-Hydroxyquinoline
Me
Me
6
7
85
95
N
N
N
OMe
OMe
1
1
0
1
8-Hydroxyquinoline
2-Naphthol
t-Bu
7
7
85
90
OMe
Me
To illustrate the role of N-methylimidazole (3), the reaction of 2-naphthol
with DMAD was studied in the absence of N-methylimidazole. The formation of
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4
62
DJAHANIANI, AGHADADASHI-ABHARI and MOHTAT
the O-methylated product was not observed in the absence of N-methylimidazole.
1
The TLC and H-NMR spectra of the reaction mixture confirmed only 2-naph-
thol.
It is reasonable to assume that the products 4a, b, d, e, g–i and k result from
initial addition of N-methylimidazole to the dialkyl acetylenedicarboxylates 2a
1
6
and b and subsequent protonation of the zwitterions 5 by OH acids. Then the
reactions proceed via a protonated intermediate that activates the electrophile for
attack by the conjugate base of phenol onto the carbon atom group of the acetyl-
enic ester, which provides the stable products (Scheme 2). The fact that DMAD
and DEAD reacted showed that the displacement step could have S 2 char-
N
1
7
acter.
Scheme 2. A possible mechanism for the preparation of 4a, b, d, e, g–i and k.
Formation of the product 4c, 4f and 4j using DTAD suggests that steric
effects are important and hence, the conjugate base of phenol attacks into the
methyl group of N-methylimidazole instead of the alkyl group of the acetylenic
ester, which again suggests that the displacement step could have S 2 character
N
(
Scheme 3).
Scheme 3. A possible mechanism for reactions of DTAD.
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N-METHYLIMIDAZOLE MEDIATED MICROWAVE SYNTHESIS OF ARYL ALKYL ETHERS
463
EXPERIMENTAL
Microwave irradiation was performed with a Milestone ETHOS 1600 microwave oven.
The chemicals were purchased from Fluka and used without further purification. The melting
points were measured on an Electrothermal 9100 apparatus. The IR spectra were recorded on
1
13
a Shimadzu IR-460 spectrometer. The H- and C-NMR spectra were obtained on a Bruker
Avance DRX-400 spectrometer using CDCl as the applied solvent and TMS as an internal
3
standard.
Physical, analytical and spectral data for the compounds 4a–k are given in the Sup-
plementary material to this paper.
Typical procedure for the synthesis of alkoxycoumarin (4)
In a 10-mL reaction vial, a mixture of N-methylimidazole (3, 0.26 g, 2.0 mmol) and
dimethyl acetylenedicarboxylate (2a, 0.24 mL, 2.0 mmol) under solvent-free condition was
stirred for 1 min. Subsequently, 4-hydroxycoumarin (1a, 0.32 g, 2.0 mmol) was added to the
reaction mixture, and the reaction vial was capped and pre-stirred for 20 s. The mixture was
subjected to microwave irradiation at a power of 600 W for 6 min at 100 °C. Upon com-
pletion, monitored by TLC, the reaction mixture was cooled to room temperature. The result-
ing precipitate was separated by filtration and recrystallized from diethyl ether (Et O) to
2
afford the pure compound 4a.
CONCLUSIONS
In the present investigation, a simple and economical one-step procedure for
ethers of coumarin, quinoline and naphthol under microwave irradiation was
developed. This method offers marked improvements concerning high isolated
yields of the products, avoidance of hazardous organic solvents and toxic cat-
alysts and a simple protocol of the alkylation of different phenols.
SUPPLEMENTARY MATERIAL
Physical, analytical and spectral data for the compounds 4a–k are available electro-
nically from http://www.shd.org.rs/JSCS/, or from the corresponding author on request.
И З В О Д
СИНТЕЗА АЛКИЛ-АРИЛ-ЕТАРА У ПРИСУСТВУ N-МЕТИЛИМИДАЗОЛА ПОД
УТИЦАЈЕМ МИКРОТАЛАСА И У ОДСУСТВУ РАСТВАРАЧА
1
2
3
HOORIEH DJAHANIANI , LAILA AGHADADASHI-ABHARI и BITA MOHTAT
1
2
Chemistry Department, Islamic Azad University, East Tehran Branch, Tehran, Iran, Chemistry
3
Department, East Tehran Branch, Payame Noor University, Tehran, Iran и Chemistry Department,
Islamic Azad University, Karaj Branch, Karaj, Iran
Развијен је поступак за трокомпонентну реакцију за синтезу арил-алкил-етара под
утицајем микроталаса. Реакције су вршене у присуству N-метилимидазола и диалкил
ацетилендикарбоксилата без растварача. Овим поступком је остварена синтеза О-алки-
лованих фенола у високом приносу.
(
Примљено 23. децембра 2013, ревидирано и прихваћено 16. марта 2014)
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DJAHANIANI, AGHADADASHI-ABHARI and MOHTAT
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. J. Gui, H. Ban, X. Cong, X. Zhang, Z. Hu, Z. Sun, J. Mol. Catal. A: Chem. 225 (2005) 27
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4
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661
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8
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2
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10. L. Ronchin, A. Vavasori, L. Toniolo, J. Mol. Catal. A: Chem. 355 (2012) 134
11. R. Bal, K. Chaudhari, S. Sivasanker, Catal. Lett. 70 (2000) 75
12. A. B. Tapase, V. S. Suryawanshi, N. D. Shinde, B. D. Shinde, Bull. Environ. Pharmacol.
Life Sci. 1 (2012) 30
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3. D. H. More, D. G. Hundiwale, U. R. Kapadi, P. P. Mahulikar, J. Sci. Ind. Res. 65 (2006)
8
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4. B. Mohtat, H. Djahaniani, R. Khorrami, S. Mashayekhi, I. Yavari, Synth. Commun. 41
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(
5. B. Mohtat, S. Rezazadeh, M. Matinfar, V. Arabzadeh, H. Djahaniani, Z. Hossaini, Lett.
Org. Chem. 9 (2012) 150
1
1
6. R. Ghahremanzadeh, S. Ahadi, M. Sayyafi, A. Bazgir, Tetrahedron Lett. 49 (2008) 4479
7. G. Lamoureux, C. Agüero, Arkivoc i (2009) 251
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________________________________________________________________________________________________________________________
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J. Serb. Chem. Soc. 80 (4) S122–S124 (2015)
Supplementary material
SUPPLEMENTARY MATERIAL TO
N-Methylimidazole-mediated synthesis of aryl alkyl ethers under
microwave irradiation and solvent free conditions
1
2
3
HOORIEH DJAHANIANI *, LAILA AGHADADASHI-ABHARI and BITA MOHTAT
1Chemistry Department, Islamic Azad University, East Tehran Branch, Tehran, Iran,
2
Chemistry Department, East Tehran Branch, Payame Noor University, Tehran, Iran and
3
Chemistry Department, Islamic Azad University, Karaj Branch, Karaj, Iran
J. Serb. Chem. Soc. 80 (4) (2015) 459–464
PHYSICAL, ANALYTICAL AND SPECTRAL DATA FOR THE COMPOUNDS 4a–k
4
-Methoxy-2H-chromen-2-one (4-methoxycoumarin, 4a). [20280-81-3]
1
Yield: 0.33 g (95 %); pale yellow crystals; m.p.: 121–123 °C [lit.: 123–125 °C ];
IR (KBr, cm ): 1705 (–C=O stretching of –COOR group), 1238 and 1030 (–C–O
stretching of –C–O group); H-NMR (400 MHz, CDCl , δ / ppm): 4.02 (3H, s,
–
1
1
3
CH ), 5.72 (1H, s, vinyl), 7.28–7.35 (2H, m, aromatic), 7.57 (1H, dt, J = 7.2 Hz,
3
1
3
J = 1.6 Hz, aromatic), 7.84 (1H, dd, J =6.4 Hz, J =1.6 Hz, aromatic); C-NMR
(
(
(
100.6 MHz, CDCl , δ / ppm): 56.4 (OCH ), 90.1 (CH=), 115.6 (CH=), 116.8
CH=), 123.0 (CH=), 123.9 (CH=), 132.4 (C), 153.3 (C–O), 162.9 (C=O), 166.5
C–O).
3 3
4
-Ethoxy-2H-chromen-2-one (4-ethoxycoumarin, 4b). Yield: 0.34 g (90 %);
–
1
yellow crystals; m.p.: 135–137 °C; IR (KBr, cm ): 1721 (–C=O stretching of
COOR group), 1238 and 1027 (–C–O stretching of –C–O group); H-NMR
1
–
(
400 MHz, CDCl , δ / ppm): 1.57 (3H, t, J = 7.2 Hz, CH ), 4.23 (2H, q, J = 7.2
3 3
Hz, OCH ), 5.69 (1H, s, vinyl), 7.29–7.35 (2H, m, aromatic), 7.57 (1H, dt, J =
2
=
7.2 Hz, J = 1.6 Hz, aromatic), 7.86 (1H, dd, J = 6.4 Hz, J = 1.6 Hz, aromatic);
1
3
C-NMR (100.6 MHz, CDCl , δ / ppm): 14.1 (CH ), 65.2 (OCH ), 90.4 (CH=),
3
3
2
1
1
15.8 (CH=), 116.9 (CH=), 123.1 (CH=), 123.8 (CH=), 132.3 (C), 153.4 (C–O),
63.1 (C = O), 165.7 (C–O).
7
-Methoxy-2H-chromen-2-one (7-methoxycoumarin,4d). [531-59-9] Yield:
1
0
.34 g (98 %), pale yellow crystals; m.p.: 119–121 [lit. 117–121 °C ]; IR (KBr,
–
1
cm ): 1702 (–C=O stretching of –COOR group), 1230 (–C–O stretching of –C–O
1
group); H-NMR (400 MHz, CDCl , δ / ppm): 3.91 (3H, s, OCH ), 6.29 (1H, d,
3
3
J = 9.5 Hz, aromatic), 6.85–6.89 (1H, m, aromatic), 7.40 (1H, d, J = 8.5 Hz,
*
Corresponding author. E-mail: jahanbani.ho@gmail.com
S122
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SUPPLEMENTARY MATERIAL
S123
aromatic), 7.67 (1H, d, J = 9.5 Hz, aromatic); 13C-NMR (100.6 MHz, CDCl3,
δ / ppm): 55.8 (OCH ), 101.0 (CH=), 112.6 (C), 112.7 (CH=), 113.2 (CH=),
3
1
28.8 (CH=), 143.8 (CH=), 156.0 (C–O), 161.3 (C=O), 163.0 (C–O).
7
-Ethoxy-2H-chromen-2-one (7-ethoxycoumarin, 4e). [31005-02-4] Yield:
1
0
.36 g (95 %); golden yellow crystals; m.p.: 84–86 °C [lit. 89–90 °C ]. IR (KBr,
–
1
cm ): 1734 (–C=O stretching of –COOR group), 1231 and 1044 (–C–O,
1
stretching of –C–O group); H-NMR (400 MHz, CDCl , δ / ppm): 1.46 (3H, t,
3
J = 6.8 Hz, CH ), 4.08 (2H, q, J = 6.8 Hz, OCH ), 6.24 (1H, d, J = 9.2 Hz,
3
2
aromatic), 6.79–6.85 (2H, m, aromatic), 7.37 (1H, d, J = 8.8 Hz, aromatic), 7.64
1
3
(
(
(
1H, d, J = 9.6 Hz, aromatic); C-NMR (100.6 MHz, CDCl , δ / ppm): 14.6
3
CH ), 64.2 (OCH ), 101.3 (CH=), 112.4 (C), 112.9 (CH=), 112.9 (CH=), 128.7
CH=), 143.5 (CH=), 155.9 (C–O), 161.3 (C=O), 162.2 (C–O).
-Methoxyquinoline (4g). [607-31-8] Yield: 0.27 g (85 %); dark yellow oil;
IR (KBr, cm ): 1273 and 1073 (–C–O, stretching of –C–O group), 1618–1506
C=C, stretching of –C=C aromatic group); H-NMR (400 MHz, CDCl , δ / ppm):
3
2
4
–
1
1
(
3
4
.09 (3H, s, OCH ), 6.79 (1H, d, J = 5.6 Hz, aromatic), 7.55 (1H, dt, J = 6.8 Hz,
3
J = 0.8 Hz, aromatic), 7.74 (1H, dd, J = 7.2 Hz, J = 1.6 Hz, aromatic). 8.1 (1H, d,
J = 8.4 Hz, aromatic), 8.24 (1H, dd, J = 8.4 Hz, J = 1.2 Hz, aromatic), 8.80 (1H,
1
3
d, J = 5.2 Hz, aromatic); C-NMR (100.6 MHz, CDCl , δ / ppm): 55.8 (OCH ),
3
3
1
1
00.1 (CH=), 121.4 (CH=), 121.9 (CH=), 125.9 (CH=), 128.4 (C), 130.1 (CH=),
48.5 (C), 151.0 (CN), 162.7 (C–O).
6
-Methoxyquinoline (4h). [5263-87-6] Yield: 0.27 g (85 %); brown oil; m.p.:
1
–1
[
lit. 18–20 °C ]; IR (KBr, cm ): 1247 and 1037 (–C–O, stretching of –C–O
group), 1600–1500 (C=C, stretching of –C=C aromatic group); H-NMR (400
1
MHz, CDCl , δ / ppm): 3.92 (3H, s, OCH ), 7.12 (1H, d, J = 2.8 Hz, aromatic),
3
3
7
.41–7.44 (2H, m, aromatic), 8.08–8.15 (2H, m, aromatic), 8.8 (1H, d, J = 3.2 Hz,
1
3
aromatic); C-NMR (100.6 MHz, CDCl , δ / ppm): 55.6 (OCH ), 105.1 (CH=),
3
3
1
1
21.4 (CH=), 121.7 (CH=), 122.8 (CH=), 129.5 (C), 130.3 (CH=), 135.5 (CH=),
47.3 (C–N), 158.0 (C–O).
8
-Methoxyquinoline (4i). [938-33-0] Yield: 0.3 g (95 %); dark brown oil; IR
–
1
(
(
KBr, cm ): 1258 and 1076 (–C–O, stretching of –C–O group), 1600–1500
C=C, stretching of –C=C aromatic group); H-NMR (400 MHz, CDCl , δ / ppm):
1
3
4
.1 (3H, s, OCH ), 7.04 (1H, d, J = 7.6 Hz, aromatic), 7.30–7.46 (3H, m,
3
aromatic), 8.11 (1H, dd, J = 8.3 Hz, J = 1.6 Hz, aromatic), 8.92 (1H, dd, J = 4.2
1
3
Hz, J = 1.6 Hz, aromatic); C-NMR (100.6 MHz, CDCl , δ / ppm): 56.1
3
(
OCH ), 108.0 (CH=), 119.9 (CH=), 122.1 (CH=), 127.1 (C), 129.7 (CH=),
3
1
36.4 (CH=), 140.4 (C), 149.5 (N–C), 155.7 (C–O).
-Methoxynaphthalene (4k). [93-04-9] Yield: 0.28 g (90 %); gray solid;
2
1
–1
m.p.: 70–72 °C [lit. 70–73 °C ]; IR (KBr, cm ): 1256 and 1027 (–C–O,
stretching of –C–O group), 1593–1506 (C=C, stretching of –C=C aromatic
1
group); H-NMR (400 MHz, CDCl , δ / ppm): 3.96 (3H, s, OCH ), 7.17 (1H, s,
3
3
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S124
DJAHANIANI, AGHADADASHI-ABHARI and MOHTAT
aromatic), 7.19 (1H, d, J = 2.4 Hz, aromatic), 7.38–7.47 (2H, m, aromatic), 7.76–
1
3
–
1
7.81 (3H, m, aromatic); C-NMR (100.6 MHz, CDCl , δ / ppm): 55.3 (OCH ),
3 3
05.7 (CH=), 118.7 (CH=), 123.6 (CH=), 126.4 (CH=), 126.7 (CH=), 127.7
(
CH=), 129.0 (C), 129.4 (CH=), 134.5 (C), 157.6 (C–O).
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1
. LookChem , Look for Chemicals, www.lookchem.com and www.chemicalbook.com
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