Environmentally benign contemporary Friedel-Crafts acylation of 1-halo-2-methoxynaphthalenes and its related compounds under conventional and nonconventional conditions

Article abstract of DOI:10.1016/j.tetlet.2013.04.075

Environmentally benign simple and practical method has been developed in cationic micellar media for the selective acylations of 1-halo-2- methoxynaphthalenes, 2-methoxynaphthalene, anisole, 2-methoxypyridine, and 2-methoxypyrimidine. Developed protocols

Full text of DOI:10.1016/j.tetlet.2013.04.075

Tetrahedron Letters xxx (2013) xxx–xxx
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Environmentally benign contemporary Friedel–Crafts acylation
of 1-halo-2-methoxynaphthalenes and its related compounds under
conventional and nonconventional conditions
⇑
K. Rajendar Reddy, K. C. Rajanna , K. Uppalaiah
Department of Chemistry, Osmania University (O.U), Hyderabad 500 007, AP, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Environmentally benign simple and practical method has been developed in cationic micellar media for
the selective acylations of 1-halo-2-methoxynaphthalenes, 2-methoxynaphthalene, anisole, 2-methoxy-
pyridine, and 2-methoxypyrimidine. Developed protocols afforded good to excellent yields of products in
the presence of a catalytic amount of cationic micelles (CTAB and CTAC) under conventional and noncon-
ventional (ultrasonic and microwave) conditions.
Received 21 February 2013
Revised 17 April 2013
Accepted 19 April 2013
Available online xxxx
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Friedel–Crafts acylation
1-Halo-2-methoxynaphthalenes
Cationic micelles
Microwave and Ultrasonically assisted
reactions
Friedel–Crafts (FC) acylation is an electrophilic aromatic substi-
tution between arenes and acyl chlorides or anhydrides, which al-
lows the synthesis of monoacylated products.1 This reaction
normally requires a stoichiometric amount of the Lewis acid as
catalyst. Even though Lewis acids are efficient catalysts,2 their
use has a number of disadvantages such as regeneration of catalyst,
hazardous corrosive waste products such as acidic and salty waste
waters produced by the hydrolysis of intermediate Lewis acid
complexes. However, recent literature reports indicate certain
versatile modified protocols on FC acylations.3 In order to over-
come the adverse effects arising from conventional catalysts and
reagents there has been an up surge in the use of eco-friendly
‘green and sustainable’ materials such as micelle forming
surfactants as catalysts.4 Formation of micelles can provide a more
favorable environment to the desired reaction, without the
addition of an organic solvent.4
inflammatory drug (S)-naproxen, when the acyl group is the acetyl
or propionyl group (Fig. 1).
Das and Cheng6 used H-mordenite, H-beta, and H-Y zeolite as
catalysts in the Friedel–Crafts acylation of 2-methoxynaphthalene
in a liquid-phase batch reactor. These reactions indicated 35–40%
conversion of the reactant to 1-acyl-2-methoxynaphthalene as
the primary product in the temperature range of 100–150 °C.
When acetyl chloride was used as the acylating agent, a higher
yield of 6-acyl-2-methoxynaphthalene was obtained through rear-
rangement of the sterically hindered 1-acyl isomer to the 6-acyl
isomer. In the Friedel–Crafts acylation of 2-methoxynaphthalene,
the presence of the electron donating group (OMe) must be taken
into account in order to figure out the reaction mechanism. The
presence of this OMe group activates the 1, 6, and 8 positions of
the naphthalene ring (Fig. 2).
The 1-position is more active than the other two positions and
the 6-position is more stable than the other two positions, so acyl-
ation of 2-methoxynaphthalene generally occurs at this kinetically
favored 1-position at low temperatures and at the thermodynam-
ically favored 6-position at high temperatures. At high tempera-
In recent past quite some attention has been paid toward the
selective acylation of 2-methoxynaphthalene because the reaction
afforded useful intermediates for the synthesis of medicinally
5a
important drugs.5 The findings of Davis
and, Harrington and
Lodewijk5b revealed that the acylation of 2-methoxynaphthalene
in the presence of conventional Lewis-acids gives two major
products 6-acyl-2-methoxynaphthalene and 1-acyl-2-methoxy-
naphthalene. Interestingly, 6-acyl-2-methoxynaphthalene is recog-
nized as an important intermediate for the production of an anti-
O
O
H
O
COOH
(S)-Naproxen
R
6-Acyl-2-methoxynaphthalene
⇑
Corresponding author. Tel.: +91 9030545323.
E-mail address: kcrajannaou@yahoo.com (K.C. Rajanna).
Figure 1. Structures of anti-inflammatory drug, (S)-naproxen and its intermediate
(6-acyl-2-methoxy-naphthalene).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.04.075
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2
K. Rajendar Reddy et al. / Tetrahedron Letters xxx (2013) xxx–xxx
8
5
1
Delightfully acetylation occurred to give 6-acyl-1-bromo-
2-methoxynaphthalene (3a) as a predominant product along with
minor product, 8-acyl-1-bromo-2-methoxynaphthalene (4a)
O
7
6
2
3
a
4
(92:08) in excellent yield. Since 6-acyl-1-bromo-2-methoxynaph-
thalene (3a) is thermodynamically favored product at high temper-
atures, we improved the selectivity of this reaction under same
reactants and catalysts by increasing the temperature (40–70 °C)
(Table 2). In case of 2-methoxynaphthalene (1f) with phenyl acetyl
chloride (2g) were obtained the selectively 1-acyl-2-methoxy-
naphthalenes as major products (3r) along with 2-acyl-2-meth-
oxynaphthalenes as minor products (4r) in excellent yields. In
order to attain further clarity, the reaction was carried out under
the similar conditions with 1-bromo-2-methoxynaphthalene (1a)
and 1-chloro-2-methoxynaphthalene (1b) with various acid chlo-
rides and obtained the selectively 6-acyl-1-bromo-2-methoxy-
naphthalenes as major products 3b–3n along with 8-acyl-
1-bromo-2-methoxynaphthalenes as minor products 4b–4n in
excellent yield (Table 2). To demonstrate the wider applicability
of this method, we carried out the acetylation reactions on anisole
(2c), 2-methoxypyridine (2d), and 2-methoxypyrimidine (2e),
which afforded the acetylated products 3o, 3p, and 3q with excel-
lent yield (entries 15–17 in Table 2).
Figure 2. Structure of 2-methoxynaphthalene.
tures resulting product is thermodynamically favored which is 6-
acyl-2-methoxynaphthalene.6 As part of our ongoing study on
the exploration of micelle forming surfactants as catalysts7 we
have undertaken selective acylation of 1-halo-2-methoxynaphtha-
lenes, anisole, 2-methoxypyridine, and 2-methoxypyrimidine with
acyl chlorides in the presence of aqueous cationic micelles such as
CTAB and/or CTAC. In addition to the use of micelles as catalysts,
we have also focused our attention on the use of nonconventional
energy sources such as ultrasonics8 and microwaves9 to trigger and
enhance the reactions.
In order to know the catalytic effect of CTAB or CTAC and
optimize the conditions in micelle mediated reactions, typical acyl-
ation reactions have been carried out with 1-halo-2-methoxynaph-
thalene and 2-methoxynaphthalene in the presence and absence of
CTAB or CTAC.10
Earlier literature reports11 on surfactants such as CTAB or CTAC
revealed that surfactants form spherical shape micellar aggregates
in water with hydrophobic interior containing alkyl chains and
hydrophilic polar head groups on the exterior of the sphere (Stern
layer). In aqueous micellar medium, organic substrates are pushed
away from water molecules toward the hydrophobic core of mi-
celle droplets thus inducing effective collisions between organic
substrates which eventually enhance the reaction rate and result
in rapid reactions in water. Most of the organic substrates are con-
centrated in these spherical aggregates, which act as hydrophobic
reaction sites and result in an increase in the effective concentra-
tion of the organic reactants, which might increase the reaction
rate via a concentration effect. On the other hand acylium ion is
formed due to the interaction of acyl chloride and polar head group
in the Stern layer of the micelle which in turn induces effective col-
lisions in the micellar core due to the interaction with arene and
eventually enhances the reaction rate. Thus the hydrophobic inte-
rior of the micelles act as micro reactors during the course of the
reaction, and shift the equilibrium toward the desired product that
ultimately leads to an increase in the reaction yield. The most plau-
sible mechanism of acylation is explained through the reaction be-
tween arene and acylium ion at the interface of micellar core and
Stern layer of the micelle as shown in Figure 3.
In order to have an insight into the effect of solvent in micelle
mediated synthesis, we have conducted the reactions in dichloro-
ethane (DCE) medium. In a nonpolar solvent such as DCE, architec-
ture of the micelle is inverted with hydrophobic exterior
surrounding interior (hydrophilic) polar head groups. These in-
verse micelles are proportionally less likely to form on increasing
head – group charge, since hydrophilic sequestration would create
highly unfavorable electrostatic interactions. This confirms the
importance of hydrophobic interactions and relatively higher
reaction rates in DCE medium. This explanation is schematically
Data presented in Table 1, clearly show the rate of accelerations
due to the variation of cationic micelle. Rates enhanced with an in-
crease in [CTAB] or [CTAC]. It is worth to note that in the absence of
surfactant reaction did not occur even under drastic conditions, but
underwent smoothly in the presence of 0.001 moles of CTAB or
CTAC as shown in Table 1 . Further increase in micellar concentra-
tion beyond 0.001 mol did not have significant effect on the reac-
tion rates. Therefore, all the micelle mediated reactions are
conducted in 0.001 mol of CTAB or CTAC. To explore the generality
we carried out acylation reactions on 1-bromo-2-methoxynaph-
thalene (1a) with acetyl chloride (2a) and 2-methoxynaphthalene
(1f) with phenyl acetyl chloride (2g), in the presence of catalytic
amount (0.001 mmol, 5 mol %) of cetyltrimethyl ammonium bro-
mide (CTAB) and/or cetyltrimethyl ammonium chloride (CTAC),
in dichloroethane at 40 °C for 2 h (Scheme 1).
Table 1
Effects of catalyst system on the reaction and activity of acylation reactions with 1-
halo-2-methoxynaphthalene and 2-methoxynaphthalene in 2 h
Substrate
Sub./Acylchloride/
CTAB/CTAC
Conversion
(%)
1-Halo-2-
1:1:0.00
0
methoxynaphthalene
1:1:0.0001
1:1:0.00025
1:1:0.0005
1:1:0.001
1:1:0.005
84
88
93
99
99
2-Methoxynaphthalene
1:1:0.00
0
1:1:0.0001
1:1:0.00025
1:1:0.0005
1:1:0.001
1:1:0.005
81
83
91
99
99
R
O
X
X
X
O
O
O
CTAB/CTAC
+
+
RCOCl
R
1a-b
2a-g
3a-n
Major
4a-n
Minor
O
R = Various alkyl groups; X = Br, Cl
Scheme 1. Acylation of 1-halo-2-methoxynaphthalenes in the presence of micellar media (CTAB/CTAC).
Please cite this article in press as: Rajendar Reddy, K.; et al. Tetrahedron Lett. (2013), http://dx.doi.org/10.1016/j.tetlet.2013.04.075

Table 2
Reaction of 1-halo-2-methoxynaphthalenes 1(a and b), anisole (1c), 2-methoxypyridine (1d), and 2-methoxypyrimidine (1e) with acyl chlorides 2(a–g) in the presence of CTAB/CTAC (0.001 mol) micellar media
Entry
Substrates
Products
Products ratio (3:4)a,c
Total (%) yield
Aqueous medium
DCE medium
Br
R
O
Br
OMe
OMe
R
R
3a-3g
O
4a-g
Br
O
92:08 (40 °C)
98:02 (70 °C)
81
82
93
96
OMe
Cl
2a
1
CH3
3a
4a
1a
O
92:08 (40 °C)
98:02 (70 °C)
80
79
90
94
2
3
4
1a
3b
3c
3d
4b
4c
4d
Cl
O
2b
92:08 (40 °C)
98:02 (70 °C)
78
81
89
93
1a
1a
1a
1a
Cl
2c
O
92:08 (40 °C)
98:02 (70 °C)
78
89
92
95
Cl
O
2d
92:08 (40 °C)
98:02 (70 °C)
78
80
90
95
5
6
3e
3f
4e
4f
Cl
2e
O
90:10 (40 °C)
98:02 (70 °C)
79
78
93
96
Cl
O
2f
90:10 (40 °C)
98:02 (70 °C)
81
81
94
97
7
1a
3g
4g
Cl
2g
Cl
R
O
Cl
OMe
OMe
R
R
3h-3n
O
4h-4n
Cl
91:09 (40 °C)
98:02 (70 °C)
77
78
93
96
OMe
8
2a
CH3
3h
4h
1b
92:08 (40 °C) 98:02 (70 °C)
80 81
90 94
9
1b
2b
2c
3i
3j
4i
4j
92:08 (40 °C)
98:02 (70 °C)
79
82
89
93
10
1b
(continued on next page)

Table 2 (continued)
Entry Substrates
Products
Products ratio (3:4)a,c
Total (%) yield
Aqueous medium
DCE medium
Br
R
O
Br
OMe
OMe
R
R
3a-3g
O
4a-g
92:08 (40 °C)
98:02 (70 °C)
79
78
92
95
11
1b
2d
3k
3l
4k
92:08 (40 °C)
98:02 (70 °C)
80
81
90
95
12
13
1b
1b
2e
2f
4l
92:08 (40 °C)
98:02 (70 °C)
92:08 (40 °C)
98:02 (70 °C)
83
84
93
96
3m
3n
4m
81
82
94
97
14
15
1b
2g
2a
4n
––
OMe
MeO
CH3
CH3
(70 °C)
(70 °C)
84
82
94
92
O
3o
1c
N
MeO
N
16
17
2a
2a
––
––
R
N
OMe
OMe
1d
O
3p
N
OMe
O
N
CH3
(70 °C)
80
95
N
3q
1e
OMe
R
O
OMe
90:10 (40 °C)
98:02 (70 °C)
81
81
94
97
OMe
18
2g
1f
4r
O
3r
a
Products ratio was determined by HPLC.
Reaction temperature in parentheses.
b

K. Rajendar Reddy et al. / Tetrahedron Letters xxx (2013) xxx–xxx
5
Table 3
X-
Reaction of 1-halo-2-methoxynaphthalenes 1(a and b), anisole (1c), 2-methoxypyr-
idine (1d) and 2-methoxypyrimidine (1e) with acyl chlorides 2(a–g) in presence of
CTAB/CTAC (0.001 mol) micellar media under ultrasonic sonication and microwave
irradiation
N+
X-
X
X
O
O
N+
Entry Substrates Products Sonication
Microwave
(5 min)b,c
CTAX
a,c
(45 min)
Total yield (%)
Total yield (%)
X-
N+
Aqueous
medium
DCE
Aqueous
DCE
medium medium
medium
X-
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1a
1a
1a
1b
1b
1b
1b
1b
1b
1b
1c
1d
1e
1f
2a
2b
2c
2d
2e
2f
2g
2a
2b
2c
2d
2e
2f
3a:4a
3b:4b
3c:4c
3d:4d
3e:4e
3f:4f
3g:4g
3h:4h
3i:4i
3j:4j
3k:4k
3l:4l
3m:4m
3n:4n
3o
81
82
83
83
82
83
84
82
81
81
83
81
80
82
81
80
81
82
94
91
93
92
93
93
94
93
90
91
92
92
91
94
92
90
93
85
83
84
85
86
85
85
85
83
83
83
84
83
85
85
85
82
84
82
95
94
94
95
95
96
97
94
94
93
95
95
96
97
96
94
97
89
RCOCl
X-
N+
X
R
O
X-
Cl
X
X
O
9
O
O
O
10
11
12
13
14
15
16
17
18
N+
R
R
Major
Minor
O
X-
N+
2g
2a
2a
2a
2r
R = Various alkyl groups; X = Cl or Br
3p
3q
3r:4r
X-
Figure 3. Reaction scheme representing the role of CTAX in aqueous medium.
a
b
c
Products ratio 95:05 (3:4).
Products ratio 97:03 (3:4).
Products ratio was determined by HPLC.
represented in Figure 4. Further, the study on the acylation of
naphthalene has suggested that the structure of the intermediate
sigma-complexes between naphthalene and acyl chloride coordi-
nated by CTAB or CTAC is also significant in determining the sub-
stitution regio-chemistry, which is mainly determined by steric
effects in the intermediate 4a–4n.
mention here that under nonconventional methods (ultrasound
(45 min) and microwave (5 min) the rate and efficiency of the reac-
tion are greater than those of the conventional method.
Rate accelerations in ultrasonically assisted reactions are based
upon the effects resulting from the collapse of acoustic cavitation
bubbles that generate regions of extremely high local temperature
and pressure. This can cause homogeneous ruptures of covalent
bonds and result in the formation of radicals that can enter into
a great variety of reactions.8,14 Rate enhancements in microwave-
assisted organic synthesis (MAOS) could be attributed to the ability
of microwaves to rapidly heat reactions significantly above the
boiling point of the solvent, which ultimately resulted in bulk acti-
vation of molecules followed by a dramatic decrease in reaction
times and increases in reaction yields.9,15
In summary, we developed an environmentally benign simple
and practical method for the selective acylation of 1-halo-2-meth-
oxynaphthalenes, 2-methoxynaphthalenes, anisole, 2-methoxy-
pyridine, and 2-methoxypyrimidine in excellent yields in the
presence of cationic micelles (CTAB and CTAC) under conventional
Encouraged by the above conventional method’s results (Ta-
ble 2), we focused on non-conventional methods12,13 (ultrasonic
and microwave-assisted reactions) to enhance the rate of reaction
and productivity. We carried out reactions on 1-bromo-2-
methoxynaphthalene (1a) and 1-chloro-2-methoxynaphthalene
(1b) with various acid chlorides under ultrasonic and microwave
conditions in the presence of micellar media (CTAB/CTAC), which
provided the desired 6-acyl-1-bromo-2-methoxynaphthalenes,
3a–3n as major products along with 8-acyl-1-bromo-2-methoxy-
naphthalenes, 4a–4n as minor products in a shorter reaction time
(5–45 min) with excellent yield (Scheme 1 and Table 2). To in-
crease the significance of our methodology under nonconventional
conditions, we carried out the acetylation reactions on anisole (2c),
2-methoxypyridine (2d), and 2-methoxypyrimidine (2e), which
afforded the acetylated products 3o, 3p, and 3q, respectively, with
excellent yield (entries 15–17 in Table 3). It is noteworthy to
R
O
OH
X
X
O
O
O
+
+
R
RCOCl
Major
Minor
O
Hydrophilic Interior
Hydrophobic Exterior
Figure 4. Reaction scheme representing the role of CTAB as reverse-micelle in nonaqueous DCE medium, nonconventional (ultrasonic- and microwave) method.
Please cite this article in press as: Rajendar Reddy, K.; et al. Tetrahedron Lett. (2013), http://dx.doi.org/10.1016/j.tetlet.2013.04.075

6
K. Rajendar Reddy et al. / Tetrahedron Letters xxx (2013) xxx–xxx
8. (a) Mason, T. J. Chemistry with Ultrasound; Elsevier Science Publishers Ltd:
England, 1990; (b) Mason, T. J.; Peters, D. Practical Sonochemistry: Power
Ultrasound Uses and Applications, 2nd ed; Hoorwood Publishing, 2003; (c)
Suslick, K. S. Ultrasound, its Chemical, Physical and Biological Effects; VCH
Publishers, Inc, 1988; (d) Margulis, M. A. Advances in Sonochemistry In Mason,
T. J., Ed.; ; Greenweich Connection J.A.: London, 1990; 1, p 49.
9. (a) Chaouchi, M.; Loupy, A.; Marque, S.; Petit, A. Eur. J. Org. Chem. 2002, 1278;
(b) Gedye, R. N.; Smith, F. E.; Westaway, K. C. Can. J. Chem. 1988, 66, 17; (c)
Loupy, A.; Perreux, L.; Liagre, M.; Burle, K.; Moneuse, M. Pure Appl. Chem. 2001,
73, 161.
and nonconventional (ultrasound and microwave) conditions for
the first time. This new method overcomes the disadvantages asso-
ciated with the previous (conventional) methods such as pro-
longed reaction time, harsh reaction conditions (reflux
temperature), metal triflates, mineral acids, and stoichiometric
amount of metal halides, which lead to the formation of interme-
diate complexes that upon hydrolysis produce hazardous corrosive
waste products such as acidic and salty waste waters. From the
green or sustainable chemistry point of view this method is novel,
economical, eco-friendly. This methodology can be extended to
other aromatics.
10. Representative procedure for acylation of 1a in the presence of micellar
media: To
a stirred solution of 1-bromo-2-methoxynaphthalene (1a)
(0.474 mg, 2 mmol) and hexanoylchloride (2b) (0.269 mg, 2 mmol) in
dichloroethane (10 mL) was added CTAB/CTAC (0.001 mol), and the resulting
reaction mixture was heated up to the desired temperature (40 or 70 °C). The
product (3b) and its regioisomer, (4b) were obtained in the ratio 92:08 at 40 °C
and 98:02 at 70 °C, which were confirmed by HPLC analysis of crude
compound. Finally, the resulting crude compound was purified by column
chromatography on silica gel using ethyl acetate–petroleum ether as the
eluent. 1-(5-Bromo-6-methoxynaphthalen-2-yl)hexan-1-one (3b): 1H NMR
(400 MHz, CDCl3) d 0.95 (t, J = 6.6 Hz, 3H), 1.38À1.42 (m, 4H), 1.93 (m, 2H),
3.03 (t, J = 7.7 Hz, 2H), 4.02 (s, 3H), 7.28 (d, J = 8.7 Hz, 1H), 7.98 (d, J = 8.7 Hz,
1H), 8.04 (s, 1H), 8.23 (d, J = 8.7 Hz, 1H), 8.41 (d, J = 8.7 Hz, 1H); IR (KBr) 3430,
3057, 3016, 2957, 2922, 2882, 2126, 1943, 1716, 1672, 1621, 1559, 1492, 1472,
1440, 1408, 1357, 1328, 1272, 1252, 1219, 1177, 1065, 965, 908, 863, 822, 801,
768, 732, 663, 596, 520, 467 cmÀ1; MS (ES) m/z 335 [M+H]+, 337.0 [M+H]+2
HRMS (ESI) calcd for C17H19BrO [M+H]+, 335.0647; found, 335.0646.
Acknowledgments
The authors are indebted to Professor P.K. Saiprakash (Former
Dean, Faculty of Science, O.U), Professor T. Navaneeth Rao (Former
Vice-Chancellor, O.U), Principal, Nizam College and Head, Depart-
ment of Chemistry, O.U) for constant encouragement and facilities.
Supplementary data
11. (a) Wang, L. M.; Jiao, N.; Qiu, J.; Yu, J. J.; Liu, J. Q.; Guo, F. L.; Liu, Y. Tetrahedron
2010, 66, 339; (b) Watanabe, Y.; Sawada, K.; Hayashi, M. Green Chem. 2010, 12,
384; (c) Lidström, P.; Tierney, J.; Wathey, B.; Westman, J. Tetrahedron 2001, 57,
9225; (d) Firouzabadi, H.; Iranpoor, N.; Garzan, A. Adv. Synth. Catal. 1925, 2005,
347; (e) Hayes, B. L. Aldrichim. Acta 2004, 37, 66; (f) Pravin, V. S.; Amol, H. K.;
Bapurao, B. S.; Murlidhar, S. S.; Beilstein, J. Org. Chem. 2011, 7, 53.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.04.075.
References and notes
12. General procedure for ultrasonically-assisted synthesis: To a solution of 1-
chloro-2-methoxynaphthalene (1b) (0.385 mg, 2 mmol) and hexanoylchloride
(2b) (0.269 mg, 2 mmol) in dichloroethane (10 mL) was added CTAB/CTAC
(0.001 mmol, 5 mol %) and the resulting reaction mixture was sonicated at
40 °C in an ultrasonic bath. The ultrasonic bath had a frequency of 33 kHz and
electric power rating of 100 W. The reaction was carried out in a round bottom
flask of 50 mL capacity equipped with a mechanical agitator and the flask was
suspended at the centre of the ultrasonic bath. Progress of the reaction was
monitored by TLC. Finally, the resulting crude compound was purified by
column chromatography on silica gel using ethyl acetate–petroleum ether as
the eluent. 1-(5-Chloro-6-methoxynaphthalen-2-yl)hexan-1-one (3i): 1H NMR
(400 MHz, CDCl3) d 0.95 (t, J = 6.4 Hz, 3H), 1.38À1.42 (m, 4H), 1.93 (m, 2H),
3.03 (t, J = 7.7 Hz, 2H), 4.02 (s, 3H), 7.28 (d, J = 8.2Hz, 1H), 7.98 (d, J = 8.2 Hz,
1H), 8.14 (s, 1H), 8.25 (d, J = 8.6 Hz, 1H), 8.42 (d, J = 8.6 Hz, 1H); IR (KBr) 3429,
3062, 3023, 2943, 2919, 2841, 2539, 2346, 2132, 1794, 1734, 1714, 1672, 1623,
1565, 1497, 1478, 1440, 1408, 1358, 1334, 1317, 1274, 1253, 1220, 1187, 1115,
1067, 989, 974, 908, 896, 877, 823, 802, 770, 733, 665, 609, 526 MS (ES) m/z
290.0 [MÀH]+ HRMS (ESI) calcd for C17H19ClO [M+H]+, 291.1152; found,
291.1154.
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a controlled microwave synthesizer (Biotage
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Please cite this article in press as: Rajendar Reddy, K.; et al. Tetrahedron Lett. (2013), http://dx.doi.org/10.1016/j.tetlet.2013.04.075