Regioselective Halogenation and Dimerization of Alkoxynaphathalenes with Alumina- or Kieselguhr-supported Copper(II) Halides

Article abstract of DOI:10.1039/a704445c

The reaction of 1-alkoxynaphathalenes 1 with alumina-supported copper(II) bromide or copper(II) chloride gave dimers, 4,4'-dialkoxy-1,1'-binaphthyls 3, as major products, and with Kieselguhr-supported copper(II) bromide afforded 1-bromo-4-alkoxynaphthalenes 2, while the reaction of 2-alkoxynaphathalenes 4 with alumina- or Kieselguhr-supported copper(II) bromide gave preferentially 1-bromo-2-alkoxynaphthalenes 5.

Full text of DOI:10.1039/a704445c

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426 J. CHEM. RESEARCH (S), 1997
J. Chem. Research (S),
1997, 426–427†
Regioselective Halogenation and Dimerization of
Alkoxynaphthalenes with Alumina- or Kieselguhr-
supported Copper(II) Halides†
Yoshitada Suzuki, Kiyoshi Takeuchi and Mitsuo Kodomari*
Department of Industrial Chemistry, Faculty of Engineering, Shibaura Institute of Technology,
Shibaura, Minato-ku, Tokyo 108, Japan
The reaction of 1-alkoxynaphthalenes 1 with alumina-supported copper(II) bromide or copper(II) chloride gave dimers,
4,4؅-dialkoxy-1,1؅-binaphthyls 3, as major products, and with Kieselguhr-supported copper(II) bromide afforded 1-bromo-
4-alkoxynaphthalenes 2, while the reaction of 2-alkoxynaphthalenes 4 with alumina- or Kieselguhr-supported copper(II
)
bromide gave preferentially 1-bromo-2-alkoxynaphthalenes 5.
Copper(II) bromide and chloride have been used as halogen-
OR
OR
Br
ating agents under homogeneous conditions for compounds
containing active hydrogen atoms such as ketones,1 and
under heterogeneous conditions in non-polar solvents for
aromatic hydrocarbons.2 In the latter case, the reaction is
carried out by heating the reagents in a high-boiling solvent
under drastic conditions, when rather complex mixtures of
halogenated compounds, are obtained. We have reported
that copper(II) halides can be activated remarkably by sup-
porting onto neutral alumina, and that polymethylbenzenes
are brominated selectively to give the nuclear-brominated
products by use of alumina-supported copper(II) bromide.3
Alkoxybenzenes are regioselectively chlorinated by alumina-
supported copper(II) chloride to give 4-chloro-1-alkoxyben-
zenes in high yield.4 In this paper, we describe the halogena-
tion and the dimerization of alkoxynaphthalenes with
inorganic-supported copper(II) halides.
CuBr2–Kieselguhr
benzene
30 °C, 3 h
1
2
benzene
30 °C, 3 h
CuBr2–Al2O3
OR
a
b
c
d
R = Me
R = Et
R = Bun
R = C6H13
OR
3
Table 1 Reaction of 1-methoxynaphthalene (1a) with
CuBr2–supporta
The reaction of 1 with copper(II) bromide in refluxing
benzene afforded a mixture of 2 and 3. In contrast, similar
reaction using Kieselguhr-supported copper(II) bromide pro-
ceeded smoothly at 30 °C to give 2 in high yields, and the
yield of 3 was negligible. For instance, when 1a was treated
with Kieselguhr-supported copper(II) bromide in benzene at
30 °C for 3 h, 2a was obtained in 92% yield. Non-polar sol-
vents such as benzene were better than polar solvents. In
polar solvents such as chloroform and tetrahydrofuran, the
yield was decreased. The reaction in ethanol did not proceed
because of the elution of copper(II) bromide from the Kiesel-
guhr into the solution. These results suggest that the reaction
occurs on the surface of the supported reagent and not in
solution.5 When alumina-supported copper(II) bromide was
employed, bromination did not proceed but dimerization of
alkoxynaphthalenes occurred. The reaction of 1a with alu-
mina-supported copper(II) bromide was performed in ben-
zene at 30 °C for 1 h to give 3a in 87% yield and the bromi-
nated compounds were formed only in trace quantities. Silica
gel and graphite were also effective as supports to give the
binaphthyl as a main product along with brominated
products. Alumina was most effective and showed the highest
selectivity among the supports tested (Table 1).
In the reaction of 1 with copper(II) chloride, both Kiesel-
guhr and alumina gave 3 preferentially, and chlorinated
products were formed in low yield (Table 2). The yield of 3 in
the reaction using the reagent supported on alumina was
slightly higher than that in the reaction using the same
reagent supported on Kieselguhr. The reaction of 1a with
copper(II) chloride in refluxing benzene gives a mixture of 3a
and 4-chloro- and 8-chloro-1-methoxynaphthalene,6 whereas
a similar reaction with alumina- or Kieselguhr-supported
copper(II) chloride proceeded smoothly, even at 30 °C, to
Yield (%)
CuBr2/1a
Time
Support
Molar ratio
(t/h)
2ab
3ac
Noned
Kieselguhr
2.0
1.5
3.0
1.5
1.5
1.5
4
1
3
1
1
1
47
40
92
tr
18
17
45
tre
tr
87
69
76
Alumina
Silica gel
Graphite
aAll reactions were carried out at 30 °C in benzene. bBy GLC.
cIsolated yield. dReflux. etr indicates a yield of less than 1%.
Table 2 Reaction of 1-alkoxynaphthalenes (1) with
CuX2–supporta
Yield (%)
Time
(t/h)
1
CuX2
Support
2b
3c
1b
1c
1d
1b
1b
1b
1d
CuBr2
CuBr2
CuBr2
CuCl2
CuBr2
CuCl2
CuCl2
Kieselguhr
Kieselguhr
Kieselguhr
Kieselguhr
alumina
alumina
alumina
3
3
3
1
3
1
1
93
93
95
15
15
13
10
trd
tr
tr
73
80
80
85
aAll reactions were carried out at 30 °C in benzene. bBy GLC.
cIsolated yield. dtr indicates a yield of less than 1%.
give selectively 3a in high yield, no 8-chloro-1-methoxy-
naphthalene being formed. For instance, the reaction fo 1a
with alumina-supported copper(II) chloride in benzene at
30 °C for 1 h afforded 3a in 85% yield and 4-chloro-
1-methoxynaphthalene in 8% yield.
*To receive any correspondence.
†This is a Short Paper as defined in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).
CuCl2–Al2O3 or Kieselguhr
1
3
benzene, 30 °C, 1 h

View Article Online
J. CHEM. RESEARCH (S), 1997 427
Table 4 Halogenation of methylsulfanylnaphthalenes (7) with
2-Alkoxynaphthalenes 4 were easily brominated under
mild conditions by use of Kieselguhr- or alumina-supported
copper(II) bromide to give 5 (X = Br) in high yields.
CuX2–Al2Oa3
Conditions
Yield (%)b
Although the reaction with alumina-supported copper(II
)
bromide proceeded even at 10 °C, dibrominated compounds
7
CuX2
T/°C
t/h
8a
80
81
8b
7a
7b
7a
7b
CuBr2
CuBr2
Cucl2
CuCl2
50
50
80
80
2
2
1
1
X
92
90
OR
OR
OR
CuX2–Support
RO
benzene
50 °C, 2 h
aSolvent: benzene, CuX2/7 = 5. bBy GLC.
4
5
6
Table 3 Reaction of 2-alkoxynaphthalenes (4) with
CuX2–supporta
Experimental
Yield (%)
5b
Preparation of Supported Copper(II) Halides.sThe reagents were
prepared by a method previously reported.3a Kieselguhr-supported
copper(II) halides were also prepared by similar method. Reagents
having 9% (w/w) copper(II) halide on a support were used.
1-Bromo-4-methoxynaphthalene 2a: General Procedure for Bromi-
nation of 1-Alkoxynaphthalenes.sA mixture of 1a (1.90 g, 12
mmol) and Kieselguhr-supported copper(II) bromide (24 g, 36
mmol) in benzene (150 ml) was stirred at 30 °C for 3 h. The mixture
was filtered, and the spent reagent was washed with benzene. The
combined filtrates were evaporated, and the residue was distilled
under vacuum to give 2.3 g (85%) of 1-bromo-4-methoxynaphtha-
lene 2a bp 155–157 °C at 5 Torr (lit.,6 159–160 °C at 4 Torr).
4,4؅-Dimethoxy-1,1؅-binaphthyl 3a.sA mixture of 1a (0.95 g, 6
mmol) and alumina-supported copper(II) chloride (5.56 g, 12
mmol) in benzene was stirred at 30 °C for 1 h. The mixture was
filtered and the spent reagent was washed several times with hot
benzene. Hexane was added to the combined filtrates, which were
concentrated, to precipitate 4,4؅-dimethoxy-1,1؅-binaphthyl 3a
(0.8 g, 85%) mp 254–255 °C (from hexane–benzene) (lit.,6
252–254 °C). GLC analysis of the filtrate after removal of the
material showed the presence of 1-chloro-4-methoxynaphthalene.
1-Chloro-2-methoxynaphthalene 5a: General Procedure for Chlor-
ination of 2-Alkoxynaphthalenes.sA mixture of 4a (0.95 g, 6 mmol)
and alumina-supported copper(II) chloride (8.34 g, 18 mmol) in
benzene (30 ml) was stirred at 50 °C for 2 h. The mixture was
worked up as above and 2,2؅-dimethoxy-1,1؅-binaphthyl 6a (0.09 g,
10%), mp 193–195 °C (lit.,7 190–195 °C), separated out from the
cold filtrate. The filtrate after removal of 6a was shown by GLC to
contain 4a (3%) and 1-chloro-2-methoxynaphthalene 5a (83%).
This filtrate was evaporated and the residue was chromatographed
on silica gel. Elution with hexane gave 5a (X = Cl), mp 66–67 °C
(lit.,8 68 °C).
4
CuX2
Support
6c
4a
4b
4c
CuBr2
CuBr2
CuBr2
CuBr2
CuBr2
CuCl2
CuCl2
CuCl2
CuCl2
Kieselguhr
Kieselguhr
Kieselguhr
Kieselguhr
alumina
89
90
86
90
72
83
84
85
82
0
0
1
4d
4ad
4a
4b
4c
0
20
10
10
10
15
alumina
alumina
alumina
4d
alumina
aSolvent: benzene, CuX2:4 = 3, 50 °C, 2 h. bBy GLC. cIsolated
yield. d10 °C, 1 h.
and 6 were produced along with 5 (X = Br). In contrast, with
Kieselguhr-supported copper(II) bromide, only 5 (X = Br)
were obtained in high yields (Table 3).
For example, while the reaction of 4c with copper(II
)
bromide in benzene at 50 °C for 2 h produced only a 6% yield
of 5c (X = Br), a similar reaction with Kieselguhr-supported
copper(II) bromide gave an 86% yield of 5c (X = Br). On the
other hand, with alumina-supported copper(II) bromide, the
reaction proceeded completely at 10 °C in 1 h to give, in
addition to 5c (X = Br) (77%), the dibromide (21%) and 6c
(2%). In contrast to the bromination, chlorination of 4 with
alumina-supported copper(II) chloride proceeded at 50 °C to
give 5 (X = Cl) in high yields. When the reagent supported
on Kieselguhr was employed, a mixture of 5 (X = Cl) and 6
was obtained. 4a was chlorinated with alumina-supported
copper(II) chloride in benzene at 50 °C for 2 h to give 5
(C = Cl) in 83% yield, whereas a similar reaction with cop-
per(II) chloride under the same conditions did not take place.
These reactions are postulated to proceed by electron trans-
1-Chloro-2-methylsulfanylnaphthalene 8b.sThe reaction was
carried out as above using 2-methoxysulfanylnaphthalene (0.52 g, 3
mmol) and alumina-supported copper(II) chloride (6.95 g, 15
mmol) in benzene (30 ml) at 80 °C for 1.5 h. The mixture was
filtered and the spent reagent was washed with benzene. The com-
bined filtrates were evaporated and the residue was recrystallized
from ethanol to give 8b (X = Cl) (0.58 g, 93%), mp 77–78 °C.
X
CuX2–Al2O3
Received, 24th June 1997; Accepted, 31st July 1997
Paper E/7/04445C
SMe
SMe
7a 1-MeS-
b 2-MeS-
8a 4-X-1-MeS-
b 1-X-2-MeS-
References
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compounds 8 in high yields, and dimerization of 7 did not
occur. The reaction of 7b with copper(II) bromide in benzene
at 50 °C yielded no detectable products after 5 h. In contrast,
with alumina-supported copper(II) bromide, 8b (X = Br) was
obtained in 92% yield from a reaction run at 50 °C for 1 h.
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less reactive than copper(II) bromide towards 7. Chlorination
required a higher temperature than bromination.
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