Rhenium-catalyzed regioselective synthesis of 1,2-disubstituted naphthalenes

Article abstract of DOI:10.1016/j.tetlet.2012.10.123

Rhenium-catalyzed coupling reaction of alkynes with phenylacetaldehyde dimethylacetal in the presence of H₂O regioselectively afforded the corresponding 1,2-disubstituted naphthalenes.

Full text of DOI:10.1016/j.tetlet.2012.10.123

Tetrahedron Letters 54 (2013) 179–182
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Rhenium-catalyzed regioselective synthesis of 1,2-disubstituted naphthalenes
⇑
Rui Umeda, Satoru Nishi, Aya Kojima, Kenta Kaiba, Yutaka Nishiyama
Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials and Bioengineering, Kansai University, Yamate-cho, Suita, Osaka 564-8680, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Rhenium-catalyzed coupling reaction of alkynes with phenylacetaldehyde dimethylacetal in the presence
of H2O regioselectively afforded the corresponding 1,2-disubstituted naphthalenes.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 25 September 2012
Revised 22 October 2012
Accepted 29 October 2012
Available online 9 November 2012
Keywords:
Phenylacetaldehyde dimethylacetal
Alkyne
Naphthalenes
Rhenium
The polysubstituted naphthalene compounds constitute an
attractive class of compounds from the view points of chemical,
biologically active molecules, and materials science. Numerous
synthetic procedures have been developed for the preparation of
polysubstituted naphthalenes.1 The traditional regioselective
construction methods of polysubstituted naphthalenes are the
stepwise introduction of a substituent through an electrophilic
substituent reaction2 or transition metal-catalyzed coupling
reaction to naphthalene framework.3 Recently, new and efficient
synthetic methods of polysubstituted naphthalenes have been
accomplished, that is, (i) the annulations via Fischer carbene com-
plexes, called the Dötz reaction,4 (ii) the transition metal-catalyzed
reaction of alkynes with benzynes generated in situ,5 (iii) the ring
expansion reaction of cyclopropane and cyclobutanes,6 (iv) transi-
tion metal-catalyzed intramolecular cyclization of o-substituted
arenes,7 (v) Au- and Cu-catalyzed [4+2] benzannulation between
o-alkynylbenzaldehydes and alkynes,8 (vi) X+ (X = I, Br, or PhSe)-as-
sisted intermolecular electrophilic cyclization of alkynes,9 and (vii)
Lewis acid-, such as gallium trichloride10 and gold trichloride/
AgSbF6,11 catalyzed or titanium tetrachloride12-assisted reaction
of alkynes and phenylacetaldehyde or styrene oxide.
including (i) the coordination of a nitrogen atom of the imines to
the rhenium center, (ii) C–H bond activation, (iii) insertion of car-
bon–carbon or carbon–heteroatom unsaturated bonds into the
rhenium–carbon bond of the arylrhenium intermediate, (iv) intra-
molecular nucleophilic attack of the formed alkyl- and alkenylrhe-
nium moiety on a carbon atom of the imine, and (v) reductive
elimination and 1,3-rearrangement of the hydrogen atom.
This report describes the first rhenium-catalyzed regioselective
synthesis of 1,2-disubstituted naphthalenes by the reaction of phe-
nylacetaldehyde dimethylacetal with alkynes. For the reaction, it
was suggested that the reaction pathway might involve the elec-
trophilic substituted reaction of the vinyl cation intermediate,
which was formed by the addition of an aldehyde generated
in situ by the hydrolysis of the acetal to the carbon–carbon triple
bond of alkynes in the presence of the rhenium complex, on the
aromatic ring.15
When phenylacetaldehyde dimethyl acetal (1a) was allowed to
react with 1-phenyl-1-butyne (2a) in the presence of a catalytic
amount of rhenium bromopentacarbonyl, ReBr(CO)5, (5 mol %) in
1,2-dichloroethane solvent at 80 °C for 20 h, 2-ethyl-1-phenyl-
naphthalene (3a) was formed in 31% yield without the formation
of the regioisomer, 1-ethyl-2-phenylnaphthalene (Table 1, entry
1). During the reaction, the formation of phenylacetaldehyde,
which was a hydrolysis product of 1a, was observed by GC and
GC–MS analyses during the initial stage of the reaction. Based
on this, it was suggested that the formation of phenylacetalde-
hyde is the one of the key steps of the reaction. In order to
smoothly form the phenylacetaldehyde in situ, two equivalent
amounts of H2O were added to the reaction. The yield of 3a
was significantly improved without affecting the selectivity and
3a was obtained in 73% yield (entry 2). Decreasing the amount
of 1a led to the decreasing yield of 3a (entries 3 and 4). The yield
The catalytic use of rhenium complexes in organic synthesis has
shown a tremendous potential in the past few decades.13 Recently,
a novel and efficient synthetic method of aromatic cyclic com-
pounds by the rhenium-catalyzed coupling reaction of aldimine
with various organic compounds bearing carbon–carbon or car-
bon–heteroatom unsaturated bonds has been reported.13a,14 In
these reports, these authors have proposed a reaction mechanism
⇑
Corresponding author. Tel.: +81 6 6368 0902; fax: +81 6 6339 4026.
E-mail address: nishiya@kansai-u.ac.jp (Y. Nishiyama).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.10.123

180
R. Umeda et al. / Tetrahedron Letters 54 (2013) 179–182
Table 1
Table 2
Reaction of phenylacetaldehyde dimethylacetal (1a) with 1-phenyl-1-butyne (2a)a
Reaction of phenylacetaldehyde dimethylacetal (1a) with various aryl substituted
alkynes 2a
cat.Re
H2O
cat.ReBr(CO)5
OMe
OMe
H2O
R
+
+
OMe
ClCH2CH2Cl
OMe
R
Ar
ClCH2CH2Cl
Ar
1a
2
3
1a
2a
3a
Entry
Ar
R
Yieldb (%)
Entry
1a (mmol)
Catalyst
T (°C)
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
C6H5
C6H5
C6H5
C6H5
1-C10H7
2-C10H7
2-CH3C6H4
3-CH3C6H4
4-CH3C6H4
4-CH3C6H4
2-FC6H4
H
CH3
C2H5
3b, 14
3c, 50
3a, 70
3d, 62
3e, 75
3f, 53
3g, 69
3h, 63
3i, 59
3j, 66
3k, 43
3l, 58
3m, 30
3n, 54
3o, 15
3p, 43
3q, 26
1c
2
3
4
5
1.0
1.0
0.50
0.75
1.0
1.0
1.0
1.0
1.0
1.0
1.0
ReBr(CO)5
ReBr(CO)5
ReBr(CO)5
ReBr(CO)5
ReBr(CO)5
ReBr(CO)5
ReCl(CO)5
Re2(CO)10
Re2O7
80
80
80
80
40
60
80
80
80
80
80
40
73 (70)
42
61
Trace
54
n-C3H7
n-C3H7
n-C3H7
n-C3H7
n-C3H7
n-C3H7
n-C3H7
n-C3H7
n-C3H7
n-C3H7
n-C3H7
C6H5
6
7
72
23
12
19
8d
9d
10
11
ReCl5
None
0
4-FC6H4
a
4-BrC6H4
2-Thienyl
C6H5
4-CH3C6H4
2-C10H7
Reaction conditions: 1a, 2a (0.50 mmol), Re catalyst (5 mol %), H2O (1.0 mmol),
ClCH2CH2Cl (2.0 mL), 80 °C, 20 h.
GC yield based on 2a. The number in parenthesis shows the isolated yield based
on 2a.
b
4-CH3C6H4
2-C10H7
c
H2O was not added.
Rhenium complex (2.5 mol %) was used.
d
a
Reaction conditions: 1a (1.0 mmol), 2 (0.50 mmol), ReBr(CO)5 (5 mol %), H2O
(1.0 mmol), ClCH2CH2Cl (2.0 mL), 80 °C, 20 h.
b
Isolated yield based on 2.
of 3a was also diminished at lower reaction temperatures (40 and
60 °C) (entries 5 and 6). For the reaction, other rhenium com-
plexes, such as ReCl(CO)5, Re2(CO)10, Re2O7, and ReCl5, are effec-
tive (entries 7–10). A better yield of 3a was obtained using the
rhenium halo pentacarbonyl complexes, ReBr(CO)5 and ReCl(CO)5
(entries 4 and 7). In the absence of the rhenium complex, 3a was
not formed and the starting materials 1a and 2a were recovered
(entry 11).
presence of H2O, some experiments were carried out. When phe-
nylacetaldehyde was allowed to react with 1-phenyl-1-butyne
(2a), 2-ethyl-1-phenylnaphthalene (3a) was formed in 31% yield
without the formation of a regioisomer. Next, in order to clarify
the selectivity of the reaction, we carried out the reaction of 1a
with unsymmetrical diaryl acetylenes (Scheme 1). When phenyl-
acetaldehyde dimethyl acetal (1a) was treated with 1-(4-methyl-
phenyl)- and 1-(4-tert-butylphenyl)-2-phenyl acetylenes, 2r and
2s, the 1,2-diaryl substituted naphthalenes 3r,s were predomi-
nantly formed together with a small amount of the regioisomers,
3r0,s0. For the 1-(4-methoxyphenyl)-2-phenyl acetylene (2t) having
methoxy group as the strong electron donating group, it is interest-
ing to note that the reaction proceeded with a regioselectivity to
give the 1-(4-methoxyphenyl)-2-phenylnaphthalenes (3t) as a sin-
gle isomer in 78% yield.
Based on the above observations, one of the possible reaction
pathways is shown in Scheme 2. First, the decarbonylation of Re-
Br(CO)5 to form ReBr(CO)4, which is the coordinative unsaturated
16-electron complex, is the first step of the catalytic reaction.16
The coordination on the phenylacetaldehyde, which is generated
in situ by the hydrolysis of acetal 1a with H2O, followed by the
regioselective electrophilic addition of the Re-aldehyde complex
I to C2 of the alkynes 2 forms the alkenyl cation II. Intramolecular
electrophilic attack of II on the aromatic ring followed by elimina-
tion of a proton generates the cyclization product III, which aro-
matizes to form the naphthalene derivatives 3 and regenerate
the catalytic active species. For the reaction of unsymmetrical dia-
ryl acetylenes, it was suggested that the stability of the alkenyl
cation intermediate II played an important role in the selectivity
of the products.
The results of the reaction of phenylacetaldehyde dimethyl ace-
tal (1a) with various alkynes are shown in Table 2. For the terminal
acetylene, the yield of 1-phenylnaphthalene (3b) decreased due to
the formation of various by-products (entry 1). When 1a was al-
lowed to react with 1-phenyl-1-propyne, 1-phenyl-1-butyne, and
1-pheny-1-pentyne in the presence of H2O and a catalytic amount
of ReBr(CO)5 at 80 °C for 20 h, the 2-methyl-, 2-ethyl-, and 2-pro-
pyl-1-phenylnaphthalenes 3a,c,d were obtained in 50%, 70%, and
62% yields, respectively (entries 2–4). Similarly, the reaction of
1a with the 1-(1-naphthyl)- and 1-(2-naphthyl)-1-pentyne effi-
ciently proceeded to give 1-(1-naphthyl)- and 1-(2-naphthyl)-2-
propylnaphthalenes 3e,f in 75% and 53% yields, respectively (en-
tries 5 and 6). Also, the reaction of 1a with the 1-aryl-1-propyne
substituted electron donating groups, such as methyl and methoxy
groups, bromo, and fluoro groups on the aromatic ring gave the
corresponding 1-aryl-2-propyl naphthalenes 3g–m in moderate
to good yields (entries 7–13). In the case of 1-(4-nitrophenyl)-1-
butyne, only uncharacterized products were observed. The
1-(2-thienyl)-2-propylnaphthalene (3n) was prepared by the
rhenium-catalyzed reaction of 1a with 1-(2-thienyl)-1-propyne
(entry 14). For all alkyl aryl acetylenes, other regioisomers were
not detected by the 1H NMR and GC analyses of the crude reaction
mixtures (entries 1–14). One-pot synthesis of the 1,2-diaryl substi-
tuted naphthalenes 3o–q was achieved by the reaction of 1a with
the 1,2-diaryl alkynes (entries 15–17). However, when the
aliphatic alkynes were used, no formation of the corresponding
naphthalenes was observed.
In conclusion, we have developed a rhenium complex-catalyzed
reaction of phenylacetaldehyde dimethylacetal (1a) with alkynes 2
in the presence of H2O, giving the corresponding 1,2-disubstituted
naphthalenes in moderate to good yields. The application of the
reaction and the investigation of the reaction mechanism are
now in progress.
To elucidate the reaction pathways for the regioselective
synthesis of the 1,2-disubstituted naphthalenes by the reaction
of alkynes and phenylacetaldehyde dimethylacetal (1a) in the

R. Umeda et al. / Tetrahedron Letters 54 (2013) 179–182
181
Me
cat.ReBr(CO)5 (5mol%)
H2O (1.0 mmol)
1a
1a
+
+
+
ClCH2CH2Cl (2.0 mL)
Me
Me
2r
3r, 27%
3r', 8 %
C(CH3)3
cat.ReBr(CO)5 (5mol%)
H2O (1.0 mmol)
+
ClCH2CH2Cl (2.0 mL)
C(CH3)3
C(CH3)3
2s
3s, 40%
3s', 9 %
OMe
cat.ReBr(CO)5 (5mol%)
H2O (1.0 mmol)
1a
+
+
ClCH2CH2Cl (2.0 mL)
OMe
OMe
not detected
3t, 78%
2t
Scheme 1. Reaction of 1a with unsymmetrical diaryl acetylenes 2r-t.
ReBr(CO)5
OMe
OMe
H2O
Δ
H
H
R
R
-CO
Ar
-H+
O
O
3
H2O
ReBr(CO)4
1a
H+
H
H
ReBr(CO)4
Ar
I
Ar
R
H
O
2
ReBr(CO)4
O
R
ReBr(CO)4
Ar
R
H+
Ar
II
O
R
ReBr(CO)4
O
R
ReBr(CO)4
Ar
III
H
Ar
Scheme 2. A possible reaction pathway of 1a with alkyne 2.
Acknowledgments
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